TEACHERS 
 
 
John Swett 
 
 
PRACTICAL 
 
 LESSONS IN SCIENCE 
 
 BY 
 
 JOSIAH T. SCOVELL, M.A., M.D., 
 
 FOB TEN YEARS PROFESSOR OF NATURAL SCIENCE IN THE INDIANA STATE 
 NORMAL SCHOOL. 
 
 CHICAGO 
 
 THE WERNER COMPANY 
 1894 ! 
 
COPYBIGHT, 1894, 
 
 THE WERNER COMPANY, 
 
 CHICAGO. 
 
 EDUCATION DEFT. 
 
PEEFAOE. 
 
 THE question before each one of us is how to use all our facul- 
 ties to the highest advantage of ourselves and others. This is 
 the great thing to learn, the great thing to teach. If we would 
 be strong in body and mind we must obey nature's laws. If 
 the farmer would succeed, he must work in accordance with the 
 laws that govern the phenomena of vegetable and animal life. 
 The miner and quarry man must recognize the laws of the min- 
 eral world; the machinist and mechanic the laws of mathematics 
 and physics, and the manufacturer the laws of chemistry ; while 
 the work of the artist, poet and musician must conform to and 
 interpret nature; so that from every economic standpoint the 
 study of science is of the widest importance. Nature is the field 
 of observation, the primary source of our ideas. Here we find 
 objects for comparison, material for the exercise of the memory 
 and data for the formation of judgments. The study of nature 
 promotes respect for law, developing honesty, self-reliance and 
 reverence, so that the careful study of nature's laws is of the 
 highest educational value. 
 
 It is the recognition of these truths that has given science a 
 prominent place in every university , college and high school, and 
 their wider appreciation has given rise to the demand for its 
 introduction into the common schools. 
 
 While admitting the great value of scientific training it did 
 not eeem desirable in this case to write a formal text-book, or an 
 
 (8) 
 
4 PREFACE. 
 
 exhaustive discussion of science, but rather to set forth in a clear 
 and concise manner the general principles of this important 
 branch of study. The plan has been to consider briefly the fun- 
 damental ideas of the different departments of science, illustrat- 
 ing them by examples of their practical application, and also to 
 consider the relation of these branches to each other as constitu- 
 ent parts of one great organic whole the earth, the home of 
 man. The writer has aimed to open up the fascinating field of 
 science in such a manner as to awaken and develop the spirit of 
 scientific inquiry, and the desire for scientific work. Such experi- 
 ments have been suggested as can easily be performed anywhere 
 without costly or complicated apparatus, and lines of work have 
 been mapped out in each division that may be pursued with 
 pleasure and profit in almost any locality. 
 
 It is hoped that the work will stimulate many to study nature 
 for themselves, to observe the phenomena of climate, to notice 
 the surface changes of the earth, to study plants and animals as 
 living things, to observe them in their homes, amid their natural 
 surroundings in fact, to study nature as the great fountain of 
 knowledge. Numbers may thus be encouraged to go beyond the 
 limits of these discussions, into special fields to which they may 
 have served as an introduction; yet if the book only helps to 
 bring our teachers and school children into closer sympathy with 
 nature, the purpose of the author will be well accomplished. 
 
 JOSIAH T. SCOVELL. 
 
 TERRE HAUTE, IXD., January 10, 1894. 
 
CONTENTS. 
 
 CHAPTER I. 
 INTRODUCTION GENERAL PRINCIPLES OP SCIENCE, . : . 9 
 
 CHAPTER II. 
 
 PHYSICS: MATTER AND THE ATTRACTIVE FORCES, . . . 15 
 
 CHAPTER III. 
 HEAT : ITS SOURCES, EFFECTS AND MODE OF TRANSMISSION, . 24 
 
 CHAPTER IV. 
 PROPERTIES OF SOLIDS, LIQUIDS AND GASES, . . . . 32 
 
 CHAPTER V. 
 
 THE COMPOSITION AND RESOLUTION OF FORCES, .... 43 
 
 CHAPTER VI. 
 
 VIBRATIONS OF THE PENDULUM CORDS AND AIR, . " . . 50 
 
 CHAPTER VII. 
 
 FORCE, WORK AND ENERGY KINETIC AND POTENTIAL, ... . 58 
 
 CHAPTER VII Continued. 
 SIMPLE MACHINES, LEVER PULLEY, SCREW AND WHEEL, . . : 68 
 
 CHAPTER VIII. 
 LIGHT : ITS SOURCESINTENSITYREFLECTION AND REFRACTION, 70 
 
 CHAPTER IX. 
 OPTICAL INSTRUMENTS RAINBOW AND COLOR, .... 78 
 
 CHAPTER X. 
 FRICTIONAL ELECTRICITY, LIGHTNING AND MAGNETISM, . . 87 
 
 CHAPTER XI. 
 
 DYKAMICAL ELECTRICITY AND IT APPLICATIONS, . 93 
 
 (v) 
 
Ti CONTENTS. 
 
 CHAPTER XII. PAOK 
 
 CHEMISTRY HISTORICAL, GENERAL AND THEORETICAL, , - r ; 101 
 
 CHAPTER XIII. 
 OXYGEN AND COMBUSTION, HYDROGEN AND WATER, . . . lOti 
 
 CHAPTER XIV. 
 NITROGEN, THE AIR, AMMONIA AND NITRIC ACID, . , . 116 
 
 CHAPTER XV. 
 
 CHLORINE, BROMINE, IODINE AND FLUORINE, . . .''. 120 
 
 CHAPTER XVI. 
 DIFFERENT FORMS OF CARBON, SILICON AND BORON, . . . 127 
 
 CHAPTER XVII. 
 SULPHUR, PHOSPHORUS, ARSENIC AND THEIR COMPOUNDS, . . 137 
 
 CHAPTER XVIII. 
 POTASSIUM, SODIUM, LITHIUM AND THEIR COMPOUNDS, . J . 146 
 
 CHAPTER XIX. 
 CALCIUM, BARIUM, STRONTIUM, MAGNESIUM AND ZINC, . . 156 
 
 CHAPTER XX. 
 COPPER, MERCURY, SILVER AND ALUMINIUM, . ... . 158 
 
 CHAPTER XXI. 
 IRON, NICKEL, COBALT, LEAD, TIN, GOLD AND PLATINUM, . . 168 
 
 CHAPTER XXII. 
 ILLUMINATING GAS, ANILINE DYES, RESINS AND GUMS, . . 169 
 
 CHAPTER XXIII. 
 STARCH, SUGAR, ALCOHOL, OILS AND VEGETABLE ACIDS, ... . 175 
 
 CHAPTER XXIV. 
 BOTANY GENERAL AND STRUCTURAL, . ... . . 182 
 
 CHAPTER XXV. 
 BACTERIA, ALGA, FUNGI, SEAWEEDS AND LICHXVI, . . . 190 
 
CONTENTS. vii 
 
 CHAPTER XXVI. wo 
 
 BRYOPHYTA, Moss PLANTS AND PTERIDOPHYTA, FERN PLANTS, . 200 
 
 CHAPTER XXVII. 
 THE ANTHOPHYTA, LEAVES, REPRODUCTIVE ORGANS AND FBUIT, . 207 
 
 CHAPTER XXVIII. 
 THE GYMNOSPERM^E, AND A STUDY OF THE PINE, . . . . 215 
 
 CHAPTER XXIX. 
 
 THE MONOCOTYLEDONS, AND A STUDY OP THE OAT, .. ....-_.* 220 
 
 CHAPTER XXX. 
 THE DICOTYLEDONS, AS THE OAK, WALNUT AND MAGNOLIA. . . 227 
 
 CHAPTER XXXI. 
 THE DICOTYLEDONS, AS THE VINE, ROSE AND MINT, . . . 236 
 
 CHAPTER XXXII. 
 FORM, COLOR, ODOR AND RELATIONS OF PLANTS, . . . . 244 
 
 CHAPTER XXXIII. 
 ZOOLOGY GENERAL AND STRUCTURAL, . . . . . 251 
 
 CHAPTER XXXIV. 
 PROTOZOA, C<ELBNTBRATA, ECHINODERMATA AND VERMBS, . . 258 
 
 CHAPTER XXXV. 
 ARTHROPOD ACRUSTACEA, ARACHNIDA, AND MYRIAPODA, . . 267 
 
 CHAPTER XXXVI. 
 
 THE INSECTA, WITH A STUDY OF THE GRASSHOPPER, , . . 275 
 
 CHAPTER XXXVII. 
 
 MOLLUSCA, MOLLUSCOIDEA AND TUNICATA, . . _. . . 285 
 
 CHAPTER XXXVIII. 
 THI VERTEBRATA PISCES AND AMPHIBIA, . . . . . 290 
 
 CHAPTER XXXIX. 
 RKPTILIA AND Avis, AS SERPENTS, LIZARDS AND BIRDS, . . 298 
 
riii CONTENTS. 
 
 CHAPTER XL. 
 THE MAMMALIA, AS HOESES, DEER, DOGS AND MONKEYS, . . 805 
 
 CHAPTER XLI. 
 GEOLOGY ASTRONOMICAL, SUN, STARS, PLANETS, ETC., . . 316 
 
 CHAPTER XLII. 
 MINERALS AND ROCKS, AS FELDSPAR AND GRANITE, . . , 320 
 
 CHAPTER XLIII. 
 EARTHQUAKES, VOLCANOES, GEYSERS AND HOT SPRINGS, . . 820 
 
 CHAPTER XLIV. 
 TEMPERATURE, WINDS, WAVES, TIDES AND CURRENTS, . . 331 
 
 CHAPTER XLV. 
 GEOLOGICAL ACTION OP AIR, WATER AND VARYING TEMPERATURE, 337 
 
 CHAPTER XLVI. 
 RIVER AND MARINE EROSION, COMPARED, . . . . 342 
 
 CHAPTER XLVII. 
 GEOLOGY THE ARCHAEAN AND ALGONKIAN ERAS, . . . 848 
 
 CHAPTER XLVIII. 
 GEOLOGY THE PALAEOZOIC ERA, . . . . 852 
 
 CHAPTER XLIX. 
 THE MESOZOIC OR SECONDARY ERA AND THE TERTIARY AGE, . 858 
 
 CHAPTER L. 
 THE QUATERNARY AGE AND THE GLACIAL PERIOD, . . 362 
 
 CHAPTER LI. 
 THE CHAMPLAIN, TERRACE AND RECENT PERIODS, . . . 369 
 
 CHAPTER LII. 
 THE THEORY OP ORGANIC DEVELOPMENT STATED, . . e 877 
 
 CHAPTER LIII. 
 
 SUGGESTIONS AS TO LINES OF STUDY, ... . t 384 
 
PRACTICAL LESSONS IN SCIENCE. 
 
 CHAPTER I. 
 
 INTRODUCTION GENERAL PRINCIPLES OF SCIENCE. 
 
 SCIENCE is scarcely more than a century old. In fact the 
 investigations, discoveries and generalizations, which have 
 given science a standing before the intellectual world, were for 
 the most part made within the present century. The growth 
 and development of that great body of systematic knowledge, 
 which we call science, has been interesting from many points of 
 view. The scientific investigator, penetratiDg the hidden realms 
 of nature, has set forth new ideas. These ideas excited opposi- 
 tion, so that there has been a constant conflict between the new 
 and the old, between the conservative and the progressive. 
 Every advancement in science has been opposed by those who 
 thought its tendencies were atheistic, leading toward the sub- 
 version of religion and the church; by those who considered the 
 reasoning and conclusions of science unphilosophical ; by those 
 who considered the processes and results unpractical, and by 
 those who were willing to leave well enough alone, being hostile 
 to every change. Science has been looked upon with distrust by 
 the learned professions, has been sneered at by practical men, 
 and shunned as something uncanny by the illiterate. 
 
 The wide dissemination of information, the growth of intelli- 
 gence, the continued stability of the essentials of religion, the 
 immense economical value of many of the results of scientific 
 investigation and discovery, have happily dispelled nearly every 
 form of distrust and opposition. And the unanimity of opinion 
 among scientific men, on all the important conclusions and gen- 
 
10 PRACTICAL LESSONS IN SCIENCE. 
 
 eralizations of science, and the wide application and continued 
 stability of these conclusions, is leading even philosophers and 
 metaphysicians to accord science some degree of respect. 
 
 While at the present time there is little active opposition to 
 science, there are still many people who, through lack of infor- 
 mation, think of science as something peculiar and difficult, 
 which only persons of superior ability and intelligence can under- 
 stand and appreciate. There are many people who have no 
 idea that scientific investigations are of any interest or value 
 to them, who have no idea that they suffer less pain, will live 
 longor, are surrounded on every hand by comforts and conven- 
 iences, and means for enjoying life, all as the direct results of 
 scientific work. 
 
 Science is neither strange nor peculiar. It deals in a business 
 way with those common facts and phenomena which are the 
 familiar events of our every-day experience. The earth on which 
 we live, the air we breathe, the water we drink, the food we eat, 
 the clothes we wear, the dwellings which afford us shelter, the 
 tools we use, the soil we cultivate, the sun that rules our day, 
 the moon and stars that cheer the night, and the myriad forms 
 of vegetable and animal life that swarm around us everywhere, 
 constitute the subject matter of science. 
 
 The discovery of facts, the arrangement of these facts in 
 accordance with their relations, and the formation of judgments 
 from these facts, which shall be free from personal feeling or bias, 
 is scientific work. Through this kind of work science attempts 
 to explain in a rational way the facts and phenomena of the 
 world. Such work results in the discovery of important laws 
 and principles, which lead the way to valuable inventions, and to 
 the development of new processes, that enable us more fully to 
 utilize the vast and varied resources of nature. Knowledge 
 gained in this way underlies the success of every industry, has 
 been potent in every wave of progress made by the human race. 
 
 The observations of Sir Isaac Newton on the relation between 
 the motions of a falling apple and the moon, gave the world 
 clearer ideas of the order that pervades the universe. The con- 
 
LESSONS /A 7 PHYSICS. 11 
 
 vulsive movements of a frog's legs when in contact with iron and 
 copper, started in the mind of Galvani a train of thought which 
 grew and developed into the telegraph, telephone, ocean cables, 
 electric motors, electric light, etc. From other ideas, suggested 
 by the bobbing lid of a kettle partly filled with boiling water, 
 have resulted the steam engine and our modern steamship and 
 railway systems, which have revolutionized every form of in- 
 dustry. 
 
 But the chief value of science is not in its practical applica- 
 tions, valuable as they may be, but rather in the development of 
 the scientific method of thought and investigation. That train- 
 ing of the mind, which grows out of the nature of scientific work, 
 is of the highest educational value. The collection of facts, the 
 study of their varied relations, the testing of conclusions by 
 comparison and experiment, result in habits of thought that are 
 valuable in any field of human endeavor. Such work tends to 
 make man a self-reliant, independent thinker. The field of science 
 is the universe of matter. As more and more of this field was 
 opened by investigators, it was gradually divided into depart- 
 ments and sub-departments until there are as many as fifty 
 separate lines of scientific inquiry, either one of which would 
 furnish material enough to employ the life-time of an industrious 
 student. 
 
 The boundaries of these departments are, in many cases, not 
 sharply defined. The different parts of the universe are so inti- 
 mately related that any scheme of classification must be largely 
 artificial. 
 
 Of these departments, physics and chemistry seem to be funda- 
 mental. Physics deals with those phenomena of matter that do 
 not involve a change of substance, but simply change of position, 
 form or condition. Chemistry deals with those phenomena which 
 do involve a change of substance, as the various kinds of com- 
 bustion and decay. But the distinction between these branches 
 of science is not very exact. In fact there is a wide field of com- 
 mon ground between them. 
 
 Every body, whether mineral, vegetable or animal, whatever 
 
12 PRACTICAL LESSONS IN SCIENCE. 
 
 its form, or substance, comes under the domain of physics and 
 chemistry. Some knowledge of these subjects is therefore neces- 
 sary to intelligent work in any other department of science. 
 
 Botany treats of the vegetable kingdom, including trees, flow- 
 ering plants, ferns, mosses, fungi, molds, alga?, etc., considering 
 their form and structure, the conditions of their growth, and 
 their relation on one side to minerals and on the other to ani- 
 mals. Zoology and its sub-departments deals with animal life, 
 including birds, fish, insects, reptiles, mammals, etc., in much the 
 same way that botany deals with vegetation. 
 
 Geology, drawing largely from other branches of science, con- 
 siders the earth as a working organism, giving special attention 
 to climate and those relations between the mineral, vegetable 
 and animal worlds which have so largely determined the past 
 and present conditions of our eartk. Geology covers much of 
 the field usually treated in physical geography, taking a general 
 view of the earth as a whole. 
 
 Yon Humboldt, at the beginning of the century, was able to 
 master the whole domain of science as known at that time. No 
 student of to-day could survey the whole field of science; in fact, 
 few can master the whole work of any one of its departments. 
 The growth of scientific knowledge during the present century 
 has been wonderful, not only as to quantity but as to quality. 
 It is as if workers from all parts of the world, bringing the pro- 
 ducts of their investigations, as bricks and stones, had laid them 
 somewhat haphazard into an edifice; these workers, following 
 the lead of a few master builders, have laid a structure of giant 
 proportions, rugged in form, incomplete in detail, but broad of 
 foundation, showing few lines of weakness and possessing a unity 
 and symmetry surpassing the work done by man in any other 
 field of human endeavor. The strength, unity and symmetry 
 of this body of knowledge depends mainly upon the scientific 
 method. 
 
 The great body of scientific knowledge may well discourage us 
 from attempting to master the whole, but should not turn us 
 aside from this important study. Careful scientific work in any 
 
LESSONS IN PHTSrCS. 18 
 
 department of science, however limited, will be of greater educa- 
 tional value to the individual and will make him more helpful to 
 his fellows, than less careful work over a wider range of the sub- 
 ject. And so intimate are the relations of } the different parts of 
 the scientific field, that a thorough knowledge of one portion gives 
 one a better view of the whole than does the mere superficial 
 knowledge of even several branches. 
 
 Time is an important element in scientific investigations. It 
 takes time, often a long time, to gather sufficient facts, time to 
 arrange these facts according to their relations, time to draw 
 conclusions and form judgments. Many would-be scientific men 
 fail because they are over-anxious to reach conclusions. It was 
 a long time from Galvani's observations of the muscles of a frog 
 to the laying of the Atlantic cable, and yet they were related as 
 cause and effect. While time is necessary to reach scientific con- 
 clusions, some of the best scientific work the world has known 
 was done at odd moments, between the hours of regular employ- 
 ment. 
 
 The term law, as used in scientific discussions, means simply a 
 statement of the observed order, sequence or relation observed 
 among natural phenomena. The law of gravitation merely ex- 
 plains to us how every particle of matter in the universe is, or 
 appears to be, altering its motion with reference to every other 
 particle. It does not tell why the particles move as they do; it 
 does not tell why the moon moves in a certain curve about the 
 earth. It simply gives in a few brief words the relationships 
 observed between a vast range of phenomena. This is the nature 
 of all scientific law. Men gather facts, classify them, analyze 
 them, discover their relationships, and then describe in simple 
 terms the widest possible range of phenomena. A scientific law is 
 always liable to be replaced or reformed as knowledge increases. 
 Newton's law of gravitation has stood the test of human expe- 
 rience for over 200 years without necessity of change. 
 
 An hypothesis or theory is the supposition assumed to account 
 for that which is only partially known. Such suppositions have 
 been baaed on a larger or smaller knowledge of facts. They may 
 
14 PRACTICAL LESSONS IN SCIENCE. 
 
 be more or less in harmony with natural phenomena, and they 
 may more or less fully agree with accepted ideas in science, but 
 they differ from natural laws, in that they attempt to explain 
 how a given order of phenomena might have been produced. 
 They are made by men who are fully acquainted with what is 
 known of the subject and whose gifts are often higher than 
 knowledge. Call it genius, call it intuition, or by whatever name, 
 there is an element which we all recognize in such creative minds 
 that enables them to apprehend truth in a manner and to an 
 extent which ordinary men cannot appreciate or understand. 
 Such theories are inductions and the whole history of science is 
 simply the story of verified inductions. 
 
 Many theories have failed when tested by experiment and ex- 
 perience, others have been verified and are permanent landmarks 
 in the field of science. The theories of Ptolemy and Aristotle 
 dominated the intellectual world for more than a thousand years. 
 Those theories were good working propositions, the best the 
 world then had, and it was hundreds of years before advancing 
 knowledge began to find out their weakness. To us they may 
 seem fanciful and crude, but considering the amount of knowledge 
 possessed by man those theories, for their time, were creditable. 
 If, without telescope, charts, or higher mathematics, one should 
 attempt to formulate some scheme to account for the motions 
 of the sun, moon, planets and stars, his respect for the old 
 Egyptian astronomers would be greatly enhanced. 
 
 At the present time, besides many lesser theories, there are 
 four great systems of science under whose guidance most of the 
 scientific work of to-day is being done. These are the theory of 
 universal gravity, the undulatory theory of light and heat, the 
 molecular theory of matter, and the theory of organic develop- 
 ment. These may or may not stand the test of progressive inves- 
 tigations, but they are good working theories and the best and 
 only ones we have regarding their subject-matter. Their value 
 and bearings will be developed in our treatment of the various 
 branches of science. 
 
CHAPTER II. 
 
 PHYSICS MATTER AND THE ATTRACTIVE FORCES. 
 
 PHYSICS deals with matter and energy. It treats of the prop- 
 erties and phenomena of matter due to the action of the dif- 
 ferent forms of energy. We know many things about how 
 matter appears, and many things about how energy acts, but 
 we know very little about what matter really is and very little 
 about the true nature of energy. 
 
 A rod of iron may be heated, may be melted, may be molded 
 or worked into any form, it may be made a magnet, all without 
 change of substance. But if the rod of iron is exposed to- moist 
 air it soon begins to change into a reddish substance called rust, 
 or if we expose it to the action of strong acids other changes 
 occur and other products are formed. Experiments with other 
 substances show that matter is subject to two groups of changes 
 or phenomena, one resulting in change of substance, the other 
 resulting merely in change of form or structure without change 
 of substance. 
 
 Chemistry treats of those phenomena which result in change 
 of substance or composition, while physics treats of those phe- 
 nomena which do not result in change of substance. While this 
 is the distinction usually made between physics and chemistry it 
 scarcely exists in nature. There is a wide field of common ground 
 between these branches of science called chemical physics, which 
 considers heat, light and electricity in some of their phases, and 
 discusses some of the phenomena of gases and other subjects 
 which seem to involve both groups of changes. 
 
 The earth, air and water, plants and animals, are composed of 
 matter. Matter occupies space, it extends in three directions 
 that is, it has length, breadth and thickness, and as far as known 
 matter is indestructible. 
 
 (15) 
 
16 PRACTICAL LESSONS IN SCIENCE. 
 
 The property of matter, by virtue of which it occupies space, 
 is called extension. Most arithmetics contain tables of the Eng- 
 lish and French systems of linear, square and cubical measures, 
 and they need not be given or discussed here. 
 
 Under ordinary circumstances, matter exists in three forms or 
 conditions : Solids, as wood and stone; liquids, as water and oil ; 
 gases, as air and illuminating gas. 
 
 Impenetrability is a property of matter which depends upon 
 extension, illustrating and emphasizing that property. By im- 
 penetrability is meant that property by which one body of mat- 
 ter occupies space to the exclusion of all other bodies of matter, 
 or that two bodies of matter cannot occupy the same space at 
 the same time. 
 
 The truth of the above statement may be shown by trying to 
 put two solids, as a stone and a block of wood , or two stones or 
 any other two solids, in the same place at the same time. The 
 nail in the board separates the particles of wood ; does not occupy 
 the same place with them. Take a cup or glass partly filled with 
 water, and put into it a piece of lead, a little stone, or thrust 
 into it a piece of wood, and in each case the rising of the water in 
 the glass shows that the solid does not occupy the same place 
 as the liquid water; and again, if we pour more water or some 
 other liquid into the glass, it is manifest that the two liquids 
 do not occupy the same space at the same time. Fill a deep pan, 
 holding four or five quarts, nearly full of water, and put a com- 
 mon tumbler into it; the water will force the air out of the tum- 
 bler and take its place. Invert the tumber and raise it partly 
 out of the water, being careful not to let any air enter it ; then 
 through a straw or some kind of a tube blow a little air under 
 the tumbler; the air rising drives out some of the water, showing 
 that air and water can not occupy the same place at the same 
 time. The diving bell, formerly much used for work under water, 
 illustrates this principle. If another portion of air is forced into 
 the tumbler more water is forced out, showing that two bodies of 
 air can not occupy the same space at the same time. When the 
 glefls is partly filled with air, if a piece of cork or light wood is 
 
LESSONS IN PHYSICS. 17 
 
 pushed under the rim of the glass it rises to the surface of the 
 water inside the glass, pushing out a bubble of air, showing that 
 air and wood or cork can not occupy the same place at the same 
 time. These experiments may be varied in many ways with profit 
 and pleasure, and will fully satisfy the experimenter of the fact 
 that matter occupies space and possesses the properties of exten- 
 sion and impenetrability. 
 
 The property of matter, which allows it to be divided into small 
 particles, is called divisibility. We may crush a piece of common 
 salt to powder, and dissolve the powder in water, when the par- 
 ticles become so small as to escape the sense of sight, even when 
 aided by the most powerful microscope, and only the sense of 
 taste or the chemist's art can detect the salt. Again, take apiece 
 of aniline (magenta) about the size of a pin-head, dissolve in a 
 few drops of alcohol, then stir into a gallon of clear water, and 
 the little particles or divisions of aniline will tinge every drop of 
 the whole mass of water. Experiments with other substances 
 show that matter may be divided into particles that are exceed- 
 ingly small, without changing its composition. 
 
 When we have crushed and dissolved the salt the particles are 
 so small that we can divide them no further without changing 
 their nature. But the chemist can divide the smallest particle of 
 salt into two substances, one a silvery -white metal called sodium, 
 the other a greenish-yellow gas called chlorine, while the aniline 
 may be divided into the gases hydrogen and nitrogen, and 
 the solid, carbon. Those who have experimented with great 
 numbers of substances tell us that most bodies, mineral, vege- 
 table or animal, are compound bodies, like the salt or ani- 
 line, made up of two or more simpler bodies, which are called 
 elements. 
 
 The smallest division that can be made of a compound body, 
 without breaking it up into its component parts, is called a mole- 
 cule, and the particles that unite to form the molecule, whether 
 of the same or different kinds of matter, are called atoms. The 
 atom is the smallest division that we can make of matter. We 
 may in the future learn to divide atoms, but at present they seem 
 
 L. S. 2 
 
18 PRACTICAL LESSONS IN SCIENCE. 
 
 to be indivisible, absolutely hard, inelastic, unchangeable as 
 bright, sharp-angled and perfect as when they left the creative 
 hand . They are the bricks of the material world . They have com- 
 bined with each other to form millions of compounds; these com 
 pounds have been broken up and new combinations formed over 
 and over again, and yet these particles of matter show no marks 
 of abrasion or signs of decay. 
 
 In general the molecules composing bodies are arranged in 
 some definite way, as the crystals so common among minerals, 
 and the various structural forms in plants and animals, leaving 
 many spaces unoccupied, which may be called structural spaces; 
 and it is supposed that the atoms and molecules which make up 
 even the most compact bodies, as the metals, do not touch each 
 other, so that even in a piece of gold there is more vacant than 
 occupied space. These spaces between the particles which make 
 up a body are called pores, and the property of matter depend- 
 ing upon the existence of pores is called porosity. Porosity sug- 
 gests the idea and possibility of the properties of compressibility 
 and expansibility. The porosity of water may be shown by filling 
 a glass with water and then sprinkling into the water fine salt or 
 sugar. The particles of salt seem to be smaller than the parti- 
 cles of water, and to run down among them as wheat may be 
 shaken into a barrel of apples or potatoes. Again, water pene- 
 trates the pores of wood, cloth, paper, some kinds of rock, etc., 
 by a process called absorption, showing the existence of pores in 
 all such bodies. 
 
 Rest is that condition of a body when it is not changing its 
 position in regard to other bodies around it, while motion is that 
 condition of a body when it is changing its position in regard 
 to other bodies around it. 
 
 That which changes the condition of a body as regards rest 
 or motion is called force. 
 
 Bodies have no control over their conditions of rest or mo- 
 tion. They can not move themselves if at rest, and can not stop 
 themselves if in motion. It requires force to put a body, as a 
 wheel, in motion, and it requires force to stop the wheel when in 
 
LESSONS IN PHYSICS. 19 
 
 motion. Inertia is the property of matter which does not allow 
 a body to change its condition of rest or motion. 
 
 Leaves and fruit fall to the earth ; force is necessary to lift a 
 body from the earth ; in short, all our experience seems to indi- 
 t-ate the existence of a force which draws or tends to draw all 
 things together into one mass. This force is called attraction. 
 It is known by different names from its different modes of action. 
 
 Gravitation is that form of attraction which acts on all 
 bodies and throughout all distances. Every body or particle of 
 matter in the universe attracts every other body or particle of 
 matter. The rain, the snow, the dead branch, or loosened rock, 
 falls under the action of gravitation; and it also holds the heav- 
 enly bodies in their accustomed orbits. The action of gravity, as 
 manifested on the earth, is to bring all bodies as near the center 
 of the earth as possible and hold them there. 
 
 The force of gravity is found to vary in accordance with two 
 laws. 
 
 If two bodies, one containing twice as much matter as the 
 other, are attracting a third body, equally distant from the 
 others, the force exerted by the larger one will be twice as great 
 as that exerted by the other. If one contained three times as 
 much matter as the other it would exert three times as muchforce, 
 etc., illustrating the first law of gravity, that the force of gravi- 
 tation varies directly as the quantity of matter exerting it; that 
 is, the greater the quantity of matter the greater the force of 
 attraction. 
 
 Suppose a body to be twice as far from a source of attraction 
 at one time as at another. In the first position the force of 
 attraction will be only one-fourth as strong as in the second. 
 If the distance be three times as great the attraction will be 
 one-ninth as strong, etc., illustrating the second law of gravity, 
 that the force of gravitation varies inversely as the square 
 of the distance through which it acts. In discussing gravity, 
 the center of gravity is considered as the center of the mass 
 of matter exerting the force, and the distances are estimated 
 from the center of gravity in each case. In the case of a sphere 
 
20 PRACTICAL LESSONS IN SCIENCE. 
 
 or cube of uniform density the center of gravity is at the cen- 
 ter of the body, while in a pyramid or cone it is below the 
 center of the body. The lower the center of gravity the more 
 stable the body. A load of hay may be overturned more easily 
 than a load of stone, as the center of gravity is lower in the load 
 of stone. A body will stand up as long as a vertical line from its 
 center of gravity falls within the base of the body. It is easier 
 to stand on our feet than on a pair of stilts, because, in the 
 latter case, the slightest motion will throw the vertical line out- 
 side the supporting base. 
 
 It is difficult to illustrate the second law of gravity, but the 
 intensity of light and heat vary according to the same law, and 
 it can be more easily illustrated when treating of those subjects. 
 
 The weight of a body is the downward pressure which it can 
 exert, and this pressure or weight is due to the action of gravi- 
 tation exerted by the earth. Weight depends upon gravity, 
 measures gravity, and varies according to the laws of gravity. 
 On the surface of the earth the variations of gravity are so 
 slight that weight is usually considered as a good measure of the 
 mass or quantity of matter in a body as well as of the force of 
 gravitation. As the earth is eomewhat flattened at the poles, 
 the distance to the center of gravity of the earth is less at the 
 poles than at the equator, consequently the force of gravity is 
 -greater and a body will weigh more at or near the poles than at 
 or near the equator. Water, dirt or mud is thrown from a rap- 
 idly turning wheel; the earth as a rotating body tends to throw 
 off matter from the equatorial regions; this tendency also less- 
 ens the force of gravity and consequently the weight of bodies 
 at the equator. The combined effect of these two causes is to 
 make gravitation at the equator less by about 1-192 part of 
 its value at the poles. Conversely, the increase of the force of 
 gravity from the equator north and south, as shown by the 
 vibrations of the pendulum, indicates a flattening of the earth 
 toward the poles. 
 
 The quantity of space a body of matter occupies is its volume, 
 and is expressed in cubic inches or feet. The quantity of matter 
 
LESSONS IN PHYSICS. 21 
 
 in a body is its mass, and is expressed in ounces, pounds, etc. If 
 you cut blocks of wood, cheese and lead of the same size you 
 will find their weights to be different; that is, bodies of the same 
 volume may contain unequal quantities of matter. Those bodies 
 which contain more matter in the same volume than others 
 are said to be more dense than the others. Density refers 
 to the quantity of matter in a given volume as compared 
 with some standard. Lead is more dense than iron, because 
 a cubic inch of lead contains more matter than a cubic inch 
 of iron. 
 
 Cohesion is that form of attraction which acts between the 
 molecules of a body, and which resists dividing, breaking, or 
 tearing forces, differing from gravity in that it only acts 
 through small distances and between molecules of the same 
 kind, making the diamond hard, copper tenacious, and iron 
 strong. 
 
 Cohesion varies with the kind of matter, being stronger in some 
 kinds than in others, and it varies on account of what seems to 
 be a different arrangement of molecules in the same kind of 
 matter, as in the case of tempered and untempered steel. In 
 welding iron the pieces must be heated, at least to the plastic 
 state, before the particles can be hammered together so that 
 cohesion will act. 
 
 Adhesion is that form of attraction which holds together 
 molecules of different kinds of matter. It is this form of attrac- 
 tion that makes glue, paint, mucilage and varnish valuable, and 
 is more m.arked between solids and liquids. 
 
 While adhesion is more marked between solids and liquids it 
 does exist between solids and solids, as in the case of dust adher- 
 ing to a wall, and between liquids and gases as well. This may 
 be shown by pouring water from one vessel into another; air 
 adhering to the descending stream is carried with it, as shown 
 by the bubbles of air formed in the water of the receiving vessel. 
 Gases sometimes adhere to solids. If a piece of glass be immersed 
 in water, bubbles will often appear on its surface. Dust, even 
 iron filings, gently spread over the surface of water, will float, 
 
22 PRACTICAL LESSONS IN SCIENCE. 
 
 though much heavier than water. A layer of air adhering to the 
 particles of iron, serves as a boat in which the iron floats. 
 
 If a tumbler be placed on the surface of water and then lifted 
 slowly upward, ifc will draw up the water, forming a little hill. 
 After it has been raised from the water, the film of water on the 
 bottom of the tumbler shows that the force of adhesion between 
 the glass and the water was stronger than the force of cohesion 
 between the molecules of water. This can be measured by letting 
 one pan of a balance rest on the surface of water and then add- 
 ing weights to the other pan till the force of cohesion is overcome. 
 
 Capillary attraction is a kind of adhesion which causes some 
 liquids to rise along the sides of solids partly immersed in them 
 and to rise in narrow tubes, or between plates that are brought 
 near each other. By capillary attraction the blotter absorbs 
 ink, the oil rises in the lamp-wick, and doubtless, in the case of 
 paint and glue, these substances actually penetrate the solid by 
 capillary attraction, and when hardened, mechanical interlocking 
 of the particles aids the force of adhesion in making the union 
 firm. This form of attraction does not act the same in all cases. 
 If a glass tube be partly immersed in mercury, the mercury sinks 
 instead of rising in the tube; in general, those liquids which wet 
 the solid will rise, those that do not will be pushed down, and 
 the smaller the tube the higher the liquid will be raised or the 
 farther it will be pushed down. Experiments with two pieces of 
 glass three or four inches square, separated by different distances, 
 shows that capillary force is manifested between plates in the 
 same manner as within tubes. 
 
 The surface of a solid or liquid, is in a state of tension. It is 
 explained as follows : In the interior of bodies, each molecule is 
 attracted equally in all direction, and no tension exists, while 
 at the surface the molecules a re attracted laterally and inward , 
 but not outward, so that there is strain on the surface molecules. 
 It is through this surface strain that cohesion causes small 
 bodies of liquids to assume a spherical form, as drops of water or 
 mercury. When a soap bubble is formed at the mouth of a pipe, 
 and the stem left open, the bubble soon shrinks and expels the 
 
LESSONS IN PHYSICS. 23 
 
 air, which indicates tension in the surfaces of the bubble. Pure 
 water has the highest surface tension of any ordinary liquid 
 except mercury. It is the surface tension of water that causes oil, 
 dust, or any impurities that may settle on it, to spread out over 
 the whole surface. The interesting phenomena observed when 
 trying to spread a small quantity of water over an oily surface, 
 or when a drop of oil and a drop of alcohol are made to touch 
 each other on a plate of glass, or when small quantities of water 
 and alcohol or water and ether are brought together on a plate 
 or piece of glass, are all explained by the action of surf ace tension. 
 Surface tension explains capillarity. The force of adhesion be- 
 tween glass and water is stronger than the force of cohesion 
 between the molecules of water, and the water rises along the 
 sides of the tube, making the surface of the water inside the tube 
 concave like a cup. The effect of this action is to lessen the press- 
 ure on the water in the tube, and the air pressure on the outside 
 forces the water up in the tube until the weight of the column of 
 water equals the difference between the forces of adhesion and co- 
 hesion. In the case of an oiled tube and water, or a glass tube and 
 mercury, no cohesion is manifested, and surface tension causes 
 an increased pressure inside the tube, and the liquid is depressed. 
 
 Magnetic attraction is that form of attraction which acts 
 between a- lodestone or a magnet and iron, drawing the bodies 
 towards each other and causing them to assume some particular 
 position in reference to each other. The compass, so important 
 in navigation and in surveying, owes its value to this form of 
 attraction. 
 
 Electrical attraction is shown in lightning, and often results 
 from chemical action. Through the action of magnetic and elec- 
 trical forces we have the telegraph, telephone, dynamo, electric 
 motor, etc., which will be more fully discussed under the subjects 
 of magnetism and electricity. 
 
 Chemical attraction or affinity acts between the" atoms or 
 molecules of elementary bodies, binding them together into mole- 
 cules of compound bodies, whose molecules are held together by 
 the force of cohesion. 
 
CHAPTER III. 
 
 HEAT: ITS SOURCES, EFFECTS AND MODES OF TRANS- 
 MISSION. 
 
 HEAT and the different forms of attraction are called physical 
 agents, forces, or forms of energy. They are known to us chiefly 
 by their effects. 
 
 Heat was once called an element ; later it was regarded as a 
 subtile form of matter contained in bodies, and manifesting itself 
 with more or less intensity. Now it is thought to be the vibra- 
 tory motion of the molecules of bodies, which may be increased 
 or diminished in various ways. When this motion is increased 
 the body becomes hot, the molecules are separated and the body 
 expands. When the motion is diminished the body grows cold, 
 the molecules approach each other and the body contracts. 
 Concerning the ultimate source of this motion which affects us as 
 heat, science as yet has no suggestions to make. 
 
 The process by which the blacksmith sets the tire of a wheel 
 shows that heat causes iron to expand and that when the heat 
 is removed or its intensity lessened, the iron contracts. Lay a 
 rod of iron or copper, ten or twelve inches long, on a board, and 
 drive a nail at each end so that the rod just touches the nails ; 
 then place the rod in the fire and when red-hot test its length 
 by the nails. A few experiments with different solids will show 
 that heat causes them to expand and that some expand more 
 than others. Purchase from the druggist an alcohol lamp, 
 some test tubes fitted with corks, and a few pieces of nar- 
 row glass tubing, and have holes cut in some of the corks of 
 such size that the glass tubing will fit them closely. If a lamp 
 seems too costly, one can be made with little trouble. Get a 
 bottle holding from two to four ounces, with a wide mouth, fit it 
 with a cork, bore the cork for a small tube made of tin, or the 
 (24) 
 
LESSONS IN PHYSICS. 25 
 
 ferrule of an old penholder ; then a little candle wicking and an 
 extinguisher, which may be made of cork, completes the lamp. 
 Take a piece of glass tubing, from eight to ten inches long, soften 
 it near the middle in the alcohol flame and bend it to an angle of 
 about 60 degrees, and, when cold, fit it in one of the perforated 
 corks. Fill a test tube with water and force in the cork, carry ing 
 the glass tube so that the water rises in the tube through the 
 cork ; then wipe dry, place the lower end of the test tube in the 
 alcohol flame, and notice the water in the smaller tube; with- 
 draw the heat and again observe the effect. The experiment 
 may be more interesting if colored water is used. If a vessel be 
 filled with cold water and heat applied, the water will expand and 
 overflow before it is hot enough to boil; this is a common oc- 
 currence in the cook room. Empty the water from the test tube, 
 used in showing the expansion of water, and when dry, close it 
 with the cork carrying the delivery tube ; then dip the free end 
 of the tube under water and apply the flame to the test tube. 
 The bubbles formed indicate that the air in the tube is expanding; 
 that some of it has been forced out. Remove the flame, keeping 
 the end of the delivery tube under the water, and soon the water 
 will be seen rising in the carrying tube; showing that the air 
 is contracting. These and other experiments indicate that heat 
 causes solids, liquids and gases to expand, and that when heat is 
 removed they contract, the attractive forces drawing the mole- 
 cules closer together. 
 
 The forces of heat and cohesive attraction, acting upon the 
 molecules of bodies, are called molecular forces, and from the 
 direction of their action are called attractive or repellant forces. 
 They are constantly struggling between the molecules of bodies, 
 and as the one or the other prevails the body is hot or cold, 
 is a solid, a liquid, or a gas. In a solid body the attractive 
 forces prevail, and its molecules are firmly bound together, so 
 that solid bodies tend to retain the form given them by nature 
 or art. In a liquid body the attractive and repellant forces are 
 nearly equal, and the molecules are free to move easily among 
 themselves, so that the form of liquids depends on the form of 
 
26 PRACTICAL LESSONS IN SCIENCE. 
 
 some solid in which they are inclosed. In a gaseous body the 
 repellant forces prevail and the molecules are driven away from 
 each other to the greatest possible distance; consequently gases 
 have no independent form or volume. In the firmest solid the 
 repellant force is still active, and some degree of mobility still 
 exists, even in the hardest body. But in the case of gases the 
 particles seem to have been separated so far as to be beyond the 
 influence of cohesive attraction, so that if they ever become 
 liquids it must be through the action of some other force than 
 cohesion. 
 
 If we apply heat to a solid, as ice, it soon becomes a liquid; 
 and if the heat continues to increase, the liquid expands into a 
 gas. If heat is removed the pressure of the air and the force of 
 gravity bring the molecules together into a liquid form, and 
 finally the cohesive force draws them into the solid form again. 
 In common language, the gas cools and condenses into a liquid 
 and the liquid cools to a solid ; that is, cold is often spoken of as 
 an active force, while it is simply a condition of a body due to 
 the diminished action of heat ; as heat diminishes, the body be- 
 comes cooler, and the attractive forces prevail more and more 
 fully. 
 
 By temperature is meant the warmth or intensity of heat in a 
 body as compared with some standard. Temperature is not the 
 same as quantity of heat ; that is, a pond of water at a tempera- 
 ture of 40 degrees would contain more heat than a pail of water 
 at a temperature of 100 degrees. 
 
 We can tell by touch that one body is warmer than another if 
 the difference is considerable, but the touch does not give us an 
 accurate knowledge of the difference. In some substances there 
 is a definite amount of expansion or contraction for a definite 
 increase or diminution of the intensity of heat! This makes it 
 possible to construct an instrument called a thermometer, or 
 heat measurer, which, by the expansion or contraction of some 
 substance, enables us to get an accurate idea of the relative tem- 
 perature of bodies. In the thermometer for ordinary use the 
 temperature is indicated by the expansion or contraction of 
 
LESSONS IX PHYSICS. 27 
 
 mercury which has been confined in a glass tube. A scale of 
 degrees is attached to the tube, of which the following are the 
 most important points : 212 degrees, which indicates the tem- 
 perature of boiling water; 32 degrees, which indicates the tem- 
 perature of freezing water; and zero, indicating a temperature 
 32 deegrees below that of freezing water. At 39 degrees below 
 zero mercury freezes, and to indicate lower temperatures alcohol 
 thermometers are commonly used. 
 
 The above are the figures on the Fahrenheit scale. On the 
 Centigrade scale, zero marks the freezing point, and 100 the boil- 
 ing point. Other scales are sometimes used. 
 
 To measure higher temperatures, an instrument called a pyrom- 
 eter is used, in which some metal or one of the permanent gases 
 serves to indicate the intensity of the heat. To measure delicate 
 changes in temperature an air thermometer is sometimes used. 
 In our experiments for showing the expansion of water and air 
 by heat, the tubes, with the water in one case and the air in the 
 other, formed a thermometer, needing only a scale for completion. 
 
 The principal sources of heat for the earth are the sun and 
 stars. Chemical action, as combustion, fermentation, and the 
 vital processes, is a source of heat; so is mechanical action, as 
 friction, percussion, etc. Illustrations of heat from these various 
 sources will be familiar to everyone. 
 
 Heat is assumed to be the motion of the molecules of bodies. 
 An imponderable but highly elastic substance, called ether, is 
 supposed to fill the spaces between the molecules of bodies and all 
 spaces throughout the universe not otherwise occupied. The 
 vibrating molecules of the heated body cause vibrations or waves 
 in this ether. These waves spreading out in all directions cause a 
 more rapid movement of the particles of bodies which they meet, 
 thus causing more intense heat. In fact, heat does not pass from 
 point to point as heat, but rather as energy which becomes heat 
 in the bodies acted upon by the waves of ether. This transfer- 
 ence of heat through waves of ether is called radiation. The 
 intensity of heat by radiation varies; first, as the intensity of 
 heat in the source; second, inversely, as the square ofthedistance 
 
28 PRACTICAL LESSONS IN SCIENCE. 
 
 from the source. The first law needs no illustration, and our 
 experience leads us to believe that the other may be true also, 
 but its truth can be better illustrated in the discussion on the 
 subject of light, which varies according to the same law. 
 
 Radiant heat or energy moves in straight lines, as can be 
 shown by arranging screens about the source of heat. A body 
 with a rough surface will radiate heat more readily than a 
 similar body with a smooth surface. The teapot is given a 
 polished surface because such surfaces retain heat better than 
 rough ones do. 
 
 Suppose one end of an iron rod is held in the flame of a lamp, 
 the molecules in contact with the flame are made to vibrate 
 more rapidly. They swing against their neighbors and put them 
 also in more rapid motion ; they in turn give motion to the next, 
 and so on until those at the end of the rod are in more rapid 
 motion, and can put in more rapid motion molecules of other 
 bodies in contact with them, thereby increasing their tempera- 
 ture. This method of transferring heat from molecule to molecule, 
 through a body, is called conduction. The metals are, in general, 
 the best conductors of heat. Liquids and gases are poor con- 
 ductors of heat. If we take a test tube and put a piece of ice in 
 the bottom, weighted by a piece of iron or lead, and then fill the 
 tube with water, the water at the top of the test tube may be 
 boiled without melting the ice, showing that water does not 
 conduct heat as rapidly as some solids do. 
 
 The heat applied to a body is divided by it into two parts, 
 one part is used to increase the temperature of the body, an- 
 other part is used to expand the body. The first can be appre- 
 ciated by the touch, and is called sensible heat; the second 
 can not be appreciated by the touch or by the thermometer, 
 and is called latent heat. The latent heat has not been lost, 
 but it has simply been used up in doing the work of expansion. 
 Different substances do not divide heat in the same proportion. 
 Let equal parts of water and mercury be placed over the same 
 source of heat. Each divides the heat it receives into two parts 
 as above; but the heat devoted to temperature is more in the 
 
LESSONS IN PHYSICS. 29 
 
 mercury thaD in the water, while that devoted to expansion is 
 less. We find that the temperature of mercury rises much faster 
 than that of water. It takes thirty times as long to raise water 
 to a given temperature as it does mercury, which means that 
 there must be thirty times as much heat in the water as in the 
 mercury when the same temperature is reached by both. We see, 
 then, that at the same temperature different substances may 
 have different quantities of heat in them. The relative quanti- 
 ties of heat in different bodies at the same temperature is called 
 specific heat. Water is the standard of specific heat. At a given 
 temperature water contains more heat than any other known 
 substance, its specific heat being 1, when the specific heat of 
 mercury is .03. By this is meant that when equal weights of 
 water and mercury are at the same temperature mercury will 
 contain only .03 as much heat as the water. 
 
 The expansion of a solid body continues nearly uniform until 
 its temperature has reached the melting point; the temperature 
 then stops rising while the expansion increases, and continues 
 until the solid is melted, the liquid resulting having the same 
 temperature as the melting point of the solid; that is, after the 
 body reaches the melting point all the heat applied is used in ex- 
 pansion, and none is used to increase temperature. 
 
 The melting points of different substances is uot the same. 
 Ice melts at 32 F., mercury at -39, iron at about 3,000, plat- 
 inum at about 5,000. Melting ice contracts while most other 
 bodies expand in melting. The expansion of a. liquid continues 
 gradually until the boiling point is reached ; at the boiling point 
 the temperature stops rising, while the expansion increases and 
 continues until the liquid is vaporized or becomes a gas. The 
 temperature at which a liquid begins to boil is called its boiling- 
 point. Liquids change to vapor slowly at all temperatures, the 
 change being called evaporation, but at the boiling point the 
 body changes rapidly into vapor, and the change is called vapor- 
 ization. The temperature of the boiling point depends upon the 
 purity of the liquid ; the presence of some impurities raises the 
 boiling point, while the presence of others lowers it. Salt water, 
 
30 PRACTICAL LESSONS IN SCIENCE. 
 
 for example, boils at a higher temperature than pure water, 
 while that which contains air boils at a much lower temperature 
 than that which contains none. In the salt water the attract- 
 ive force is stronger than in the fresh water, and more heat 
 is necessary to overcome this force, while in the water contain- 
 ing air the attractive force is less, and less heat is necessary to 
 raise it to the boiling point. The temperature of the boiling 
 point also depends upon the nature of the vessel in which the 
 water is boiled. If the adhesion between the water and the vessel 
 is strong it requires more heat to overcome it, and vice versa. 
 Thus, water will boil at a lower temperature in an iron vessel 
 than in a glass vessel, because the force of adhesion is stronger 
 between water and glass than between water and iron. The tem- 
 perature of the boiling point of water also depends upon the 
 pressure. This pressure may be due to the atmosphere, or to 
 some force which may be brought to bear upon it by artificial 
 means. Whatever may be the cause of pressure the effect is to 
 raise the boiling point. Whatever serves to decrease the press- 
 ure lowers the temperature of the boiling point. It is well 
 known that water boils at a lower temperature on the top of a 
 mountain than at its base. It does so because the pressure of 
 the air upon it is less. At some high mountain stations the tem- 
 perature of boiling water is so low that it is of little value for 
 cooking purposes. 
 
 When heat falls upon a body a portion is thrown back, or 
 reflected, from the surface. Dense bodies, as the metals, with 
 smooth surfaces, are the best reflectors of heat as well as light. 
 About midday in summer, when the sun is shining, it is warmer 
 on the south side of a building than in an open field, showing 
 that even rough surfaces will reflect heat. Heat is reflected ac- 
 cording to the same laws observed in the reflection of light, but 
 they can be illustrated more easily in connection with the study 
 of light. 
 
 When heat falls on the surface of a body from any source, one 
 portion is reflected, while another portion penetrates the body, 
 passing from molecule to molecule, as in the case of conduction. 
 
LESSONS IN PHYSICS. 31 
 
 While this process is called absorption, it is practically the same 
 as conduction. 
 
 Con vection is the process by which one body carries heat from 
 its source to another body. Air receives heat from the stove, 
 moves to other parts of the room and gives up the heat to other 
 bodies. Liquids and gases are good conveyers of heat. 
 
 Experiment: Take a test tube and fill it nearly full of dirty 
 water, and, inclining it slightly, apply heat to the bottom and 
 very soon currents will be observed in the tube, and if we test 
 with the finger the temperature of this water, we shall find that 
 there is a warm current on the upper side of the tube and a 
 cooler current on the lower side; now remove the heat and hold 
 the tube in a vertical position and it will be found that the 
 water at the top is warmer than the w r ater at the bottom of the 
 tube. The water has conveyed the heat from the bottom of the 
 tube to the top by the process of convection. 
 
 Heat from the sun will pass through the air and window glass, 
 and warm the window sill or the hand much more than it warms 
 the glass or the air. The property by which some bodies allow 
 heat to pass through them without themselves being much 
 warmed, is called diathermancy. Such bodies are called diather- 
 mic bodies. They are transparent to heat as some bodies are 
 transparent to light. 
 
CHAPTER IV. 
 
 PROPERTIES OF SOLIDS, LIQUIDS AND GASES. 
 
 THE resistance which a substance offers to the separation of its 
 parts by pulling is called tenacity. This property varies greatly 
 in different substances, cast steel being the most tenacious sub- 
 stance known. Tenacity differs from toughness; the cast steel 
 will bear a pulling strain but will not bear much twisting or 
 bending backward and forward, while copper, which is not as 
 tenacious as the steel, will bear twisting and bending many 
 times before breaking, having the property of toughness in a 
 higher degree. Cast steel does not stretch. Other substances, as 
 copper, soft steel and iron, gold, silver, etc., yield to the pull- 
 ing force and may be drawn into wire, thus exhibiting the prop- 
 erty of ductility. This property varies greatly in different sub- 
 stances, and many substances which are but slightly ductile when 
 cold possess that property in a high degree when heated, as glass 
 and iron. The tenacity of a substance is increased by drawing it 
 out into wire. Thus the cables of suspension bridges are made 
 of fine wire twisted together, not only because such form makes 
 them flexible, but because the steel, in that form, possesses more 
 tenacity. Platinum is the most ductile of metals. Gold and 
 silver also possess this property in a high degree, while lead and 
 tin are only slightly ductile. 
 
 Malleability is a property similar to ductility, which allows a 
 body to be rolled or hammered into plates or thin sheets. Gold 
 is the most malleable substance known. Most of the metals 
 possess this group of properties in some degree. 
 
 Hardness is that property of solids which enables them to 
 resist any action which tends to abrade or scratch them. Hard- 
 ness does not mean strength, indeed hard substances usually 
 possess the property of brittleness as well, yielding easily to a 
 (32) 
 
LESSONS IN PHYSICS. 33 
 
 sudden blow, as glass or the diamond. The relative hardness of 
 two bodies is ascertained by trying which will scratch the other. 
 This test shows the diamond to be hardest of all substances and 
 the mineral, talc, to possess the property of hardness in the least 
 degree, or the property of softness in the highest degree. Many 
 substances after having been raised to a high temperature may 
 be tempered to almost any degree of hardness, and other sub- 
 stances, as glass, may be greatly toughened by the process of 
 annealing. 
 
 In many cases when substances pass from the liquid or gase- 
 ous state into the solid form, their molecules arrange themselves 
 in regular geometrical forms called crystals, as ice, common salt, 
 sugar and quartz. The greater portion of the older rocks are of 
 a crystalline structure, and most of the metallic ores and miner- 
 als have distinctive crystalline forms. Metals, by jarring, often 
 become crystalline, losing their ductility and tenacity. From this 
 cause, bells long rung change their tone; cannon, after long use, 
 lose their strength ; and the perpetual jar of bridges, shafts of ma- 
 chinery, car axles, etc., gradually changes the tough, fibrous iron 
 into the weaker crystalline form, which explains many accidents. 
 
 Most substances expand as they are heated, and contract as 
 they cool. In many cases the contraction and expansion is 
 somewhat uniform ; but those substances which crystallize when 
 cooling usually expand slightly as their temperature approaches 
 the point of solidification. Most crystalline structures occupy 
 more space than the same matter in a liquid form. Water con- 
 tracts as its temperature falls from the boiling point to 39 F., 
 and then it expands, so that the volume at 32 F. is the same 
 as it was at 48 F. If water continued to contract to the freez- 
 ing point, it would be denser and heavier than the warmer water 
 below, and would sink. Lakes, rivers and other bodies of water 
 would begin to freeze at the bottom, and would soon become 
 solid ice. But as the surface stratum of water approaches the 
 freezing point, it expands, and, becoming lighter, floats, and thus 
 the cooler water and ice remain at the surface. Similar phe- 
 nomena occur in the cooling of some other substances. In freez- 
 L. s. s 
 
84 PRACTICAL LESSONS IN SCIENCE. 
 
 ing, water expands with such force as to burst the strongest ves- 
 sels, and break up the most tenacious rocks. The molecular force 
 seems irresistible. The cohesive force is also very strong, and 
 is frequently made use of in mechanical operations, as in setting 
 the tires of wheels, in riveting the plates of boilers, etc. In the 
 building of iron bridges and similar structures provision must 
 be made for the expansion and contraction due to ordinary 
 changes of climate, or the structures would soon go to ruin from 
 the constantly recurring strains due to these forces. 
 
 Glass is a poor conductor of heat; so that if hot water is 
 poured into a thick glass bottle the inner part becomes hot and 
 expands before the outer part gets warm, and the glass is liable 
 to break from the sudden strain. Hence, glass vessels which are 
 to be subjected to extremes of temperature should be thin, so 
 that there may be less chance for unequal expansion. 
 
 Most solid bodies may be changed in form by compressing, 
 stretching, bending, or twisting forces, but when the forces cease 
 to act, in most cases, the body tends to resume its original form. 
 If the body has been compressed, the repellant force corrects the 
 form, while if the body has been stretched, it is the attractive 
 force that does the work of correction. After bending and twist- 
 ing, the same forces attempt to restore the original form. This 
 property of matter by which it assumes its original form after 
 distortion is called elasticity. Many bodies are elastic only 
 within certain limits that is, a body may be strained beyond the 
 limit of recovery the particles may be separated so far that 
 cohesion can not assert its power again. Vegetable and animal 
 substances decay, metals become crystalline and the properties 
 of tenacity, elasticity and strength are gradually lost. 
 
 Liquids are elastic and have other properties in common with 
 solids, but the characteristic property of liquids is mobility. 
 The attractive and repellant forces are so nearly balanced in 
 liquids, that the molecules are allowed to move freely among 
 themselves. Liquids under the action of gravity press down- 
 ward, but their mobility allows them to press sidewise as well as 
 downwards, so that water will pass out through holes in the sides 
 
LESSONS IN PHYSICS. 35 
 
 of a pail or barrel filled with water, as well as through holes in 
 the bottom. And the fact that objects float on liquids, shows 
 that they press upward ; hence, it seems clear that liquids press in 
 all directions downward, sidewise and upward. Careful experi- 
 ments show that in a body of water, at rest, pressure is equal in 
 all these directions. The rigid mountain seeks its level as eagerly 
 as a body of water but the mobility of the water enables it to 
 find its level more easily and quickly than the mountain can. 
 Every body of liquid when at rest has a level surface, that is, 
 every part of the surface is equally distant from the center of the 
 earth, arid this is true however irregular the body of water may 
 be. If a tube or pipe, even miles in length, be connected with a 
 pond, lake, or other body of water, it becomes a part of the 
 pond or lake and the water rises to the same level in the pipe as 
 in the pond. This accounts for many springs and artesian wells, 
 and on this principal many cities and towns are supplied with 
 water from ponds or lakes, often miles away among the hills 
 above them, the main pipe being divided and subdivided into 
 thousands of service pipes in each of which the water rises to any 
 level not above the level of the reservoir. In practice it will not 
 rise quite as high as the source, on account of friction in pipes. 
 The liquid water weighs about 62% pounds or 1,000 ounces per 
 cubic foot, or about .577 of an ounce per cubic inch. Water is 
 heavy and when urged down a steep slope by the force of gravity 
 exhibits a terrific power; even when the slope is only moderately 
 steep its destructive power is immense, as shown in the case of 
 the disaster from the breaking of the dam at Johnstown, Penn- 
 sylvania, and as manifested everywhere in the work of torrents 
 and rivers. This force is sometimes utilized in placer mining, by 
 bringing the water down a steep slope in pipes, using it to move 
 soil, gravel and rocks, much as a garden hose is sometimes used 
 for cleaning walks, etc. It is also used for driving various kinds 
 of machinery. 
 
 The fact that liquids press upwards may be shown as follows : 
 Suspend a solid, as a stone, by a wire from one end of a scale 
 beam, so that it hangs near the bottom of a pail or tub. After 
 
36 PRACTICAL LESSONS IN SCIENCE. 
 
 noting the weight, fill the pail with water, so that the stone 
 is covered, and again note the weight. The water seems to have 
 pushed upward against the stone, with a force equal to the 
 difference of weight in the two cases. Experiments show that 
 this difference between the weight of the stone in the air, and its 
 weight in water, is equal to the weight of a volume of water 
 which is equal to the volume of the stone. Now, if we divide the 
 weight of this volume of water by .577, the weight of a cubic inch 
 of water, in ounces, we get the volume of the water in cubic 
 inches, and the volume of the stone as well, however irregular the 
 stone may be. In this way the volume of any substance heavier 
 than water may be found. 
 
 Now, if we divide the weight of the stone, in air, by the weight 
 of an equal volume of water, which is equal to the difference 
 between the weight of the stone, in air, and its weight in water, 
 we find what is called the specific gravity of the stone. 
 
 Suppose a piece of marble weighs in the air 10 ounces ; in 
 water it weighs 6.3 ounces; the difference of weight in air and in 
 water, or the weight of an equal volume of water, is 3.7 ounces; 
 then 10 -r 3.7 = 2.7, the specific gravity of the piece of marble. 
 Now, if the specific gravity of all the more valuable substances be 
 carefully determined, we have at hand an easy method of testing 
 the purity of articles supposed to be made of gold or silver, of 
 jewels supposed to be diamonds or other precious stones, and for 
 determining the identity of many doubtful substances. The pro- 
 cess of finding the specific gravity of solids heavier than water 
 is simple, but in the case of solids lighter than water, the process 
 is more complicated, though not difficult. 
 
 In case we wish to find the specific gravity of a body lighter 
 than water, it will be necessary to attach some heavier substance, 
 as lead, to it, in order to make it sink in the water, and then we 
 need to consider the volume of water displaced by the lead. This 
 may be illustrated by the following experiment: A body lighter 
 than water weighs in air 200 grains. When attached to a piece 
 of lead weighing 1,736 grains, they both weigh in the air 1,936 
 grains; in water they together weighed 1,460, the loss in weight 
 
LESSONS IN PHYSICS. 37 
 
 of the two being 476 grains, which is the weight of a volume of 
 water equal to the volume of both bodies. Then weighing the 
 lead by itself in water, it is found to lose 152 grains, and this 
 subtracted from 476, the loss of both, gives 324 grains as the 
 weight of the water displaced by the lighter body. Then dividing 
 the weight of the lighter body in air (200 gr.) by the weight of 
 an equal bulk of water (324 gr.) gives the specific gravity of the 
 lighter body. From this data the volume of the lighter body 
 may be found as before. 
 
 To do this kind of work accurately, delicate scales and pure 
 water of definite temperature, are necessary ; but with a home- 
 made balance, using bird-shot for weights, results of great accur- 
 acy may be obtained . Water is the standard in finding the specific 
 gravity of liquids as well as solids. We may find the specific 
 gravity of a liquid by weighing a given volume of the liquid and 
 dividing that weight by the weight of an equal volume of water. 
 To facilitate such operations specific gravity bottles are made, 
 holding 1,000 grains of pure water, so that one has only to fill 
 the bottle with the liquid he wishes to test, and weigh it and 
 divide the result by 1,000, to get the specific gravity. In this 
 way we compare the weight of a volume of the liquid to be tested 
 and the weight of an equal volume of the standard that is, 
 we compare weights of equal volumes but the same result 
 may be reached by comparing the volumes of equal weights, 
 which is the principle of the hydrometer, lactometer, alcohol- 
 meter, etc. These instruments are made so as to sink to a 
 given depth in pure water, milk, or alcohol. If the liquid tested 
 is lighter than the standard the instrument sinks deeper if 
 heavier it does not sink as far and the difference is read from 
 the scale. This principle may be illustrated by using a piece of 
 wood about an inch square by 6 or 8 inches long, into one end 
 of which a nail has been driven so that it will stand erect in a 
 liquid. Place the stick in a jar of water and note how far it sinks 
 then put it in a jar of milk, kerosene oil, or any other liquid, 
 and note how far it sinks, and the principle of the hydrometer is 
 easily understood. 
 
38 PRACTICAL LESSONS IN SCIENCE. 
 
 Again, if a heavier body, as glass or iron, of known weight in 
 air, be weighed in water, the loss of weight shows the volume of 
 an equal weight of water. If the same body be weighed in alco- 
 hol or milk, the loss of weight shows the volume of an equal 
 weight of the milk or alcohol, which may be compared with that 
 of water and the specific gravity found. It is said that the prin- 
 ciple on which the whole subject of specific gravity is based was 
 accidentally discovered by Archimedes, an eminent philosopher, 
 who lived in the third century B. C., who used it to test the purity 
 of a crown, supposed to have been made of gold. 
 
 Liquids not only press in all directions, but they transmit 
 pressure in all directions. Fill a bottle with water, fit it with a 
 good cork, so that the cork touches the water in the bottle; 
 now pressure on the cork will be distributed to every part of the 
 bottle. Insert a pipe into the bottom of a cask and bend it so 
 that the free end is about as high as the cask, then fill the cask 
 with water, and the water will be found as high in the pipe as 
 in the cask. If you pour water into the tube, the water level 
 rises in the cask. If we fit a piston in the pipe and press down 
 upon the water, that force is transmitted to the whole mass in 
 the cask, as the whole mass rises to a higher level. The law 
 may be stated as follows : Pressure exerted on any given area 
 of a fluid, inclosed in a vessel, is transmitted without loss to 
 every equal area of the interior of that vessel. This principle 
 has been fully established by experiment and is utilized in the 
 construction of the hydraulic press. Presses have been made 
 that are capable of lifting as much as 3,000 tons. 
 
 Gases have weight and elasticity, and they surpass liquids in 
 mobility, but they are distinguished for their high degree of com- 
 pressibility and expansibility. Take a test tube fitted with a 
 cork and a delivery tube of about twelve inches in length. Insert 
 the free end of the delivery tube in water or some colored liquid, 
 and apply the flame of the lamp to the test tube until some of 
 the air is forced out; then remove the heat, keeping the delivery 
 tube under the liquid till about one-fourth of it is filled with 
 the liquid; then we have an air thermometer, with which can 
 
LESSONS IN PHYSICS. 39 
 
 be illustrated the compressibility and expansibility of air. Blow 
 gently into the end of the delivery tube and the air will be com- 
 pressed ; apply the hand to the test tube and the air will expand 
 as shown by the movement of the fluid in the delivery tube. 
 The elasticity of the air may also be shown when illustrating 
 its compressibility. Experiments with other gases show that 
 they possess these properties in common with air. 
 
 Gases press in all directions. Fill a common tumbler with 
 water and cover it with a piece of paper a little larger than the 
 top of the glass; then, holding the paper in place with the fingers, 
 invert the glass, and the pressure of the air on the paper will 
 hold the water in the glass. It will do the same when the glass 
 is turned sidewiser This experiment shows that air presses up- 
 ward and side wise, and surely it must press downward, must 
 have weight. The specific gravity of gases is usually found by 
 comparing them with the weight of an equal bulk of hydrogen 
 or air. Objects floating in the air, as leaves, feathers, birds, bal- 
 loons, etc., show that air is buoyant, behaving much as liquids 
 do, and the destructive force of winds indicates that it must 
 have weight and other properties like liquids and solids. 
 
 Invert a tumbler under water, as in the experiment for im- 
 penetrability, and raising it partly out of the water, notice that 
 the water is higher inside the glass than on the outside. The air 
 can not press on the water inside the tumbler, but the pressure of 
 the air on the water outside keeps the water up on the inside. 
 This experiment shows the downward pressure of the air and 
 illustrates the principle of the common pump and the barometer. 
 
 Take a glass tube a little more than thirty inches long, closed 
 at one end, and fill it with mercury; then, closing the open end 
 with the finger, invert the tube, and place the end closed by the 
 finger in a cup of mercury; then withdraw the finger. The press- 
 ure of the air on the surface of the mercury in the cup will sus- 
 tain a column of mercury nearly thirty inches high in the tube. 
 Experiments of this kind show that the pressure of the air at the 
 level of the sea is about 15 pounds to the square inch, sustaining 
 a column of mercury about 30 inches high, or a column of water 
 
40 PRACTICAL LESSONS IN SCIENCE. 
 
 about 33 feet high, varying somewhat with the condition of the 
 air, as to temperature, as to the presence of water vapor, etc. 
 At higher elevations some of the air is below the experimenter, 
 so that the pressure is less and the barometer column is shorter. 
 In this way elevations may be measured with considerable ac- 
 curacy. The mercurial barometer consists of a tube filled with 
 mercury inverted in an open cup of mercury, fitted with a scale, 
 an arrangement for making corrections, etc., the whole provided 
 with a case of wood or metal for protection. It is used for meas- 
 uring elevations, but its most important use is in connection 
 with navigation as a weather glass. It shows the varying press- 
 ure of the atmosphere, from which one may gain some idea of 
 what weather to expect. In general, a rising column, or increas- 
 ing pressure, indicates fair weather, while a falling column, or 
 diminishing pressure, indicates foul weather. An instrument 
 called an aneroid barometer is much used because of its porta- 
 bilitya good one need not be much larger than a watch. 
 Atmospheric pressure is indicated by its effect on an elastic box 
 containing slightly rarefied air. The aneroid is not as reliable 
 as the mercurial, and should be adjusted frequently by a stand- 
 ard mercurial, if one expects to get reliable indications. The 
 upward pressure or buoyancy of the air interferes somewhat 
 with the accuracy of weighing operations. 
 
 The molecules of gases are so far apart that one gas does not 
 hinder the expansibility of another. If a number of gases are 
 mixed in a limited space, each will be diffused throughout the 
 whole space, gases acting as vacuums to each other. In this way 
 poisonous gases, the products of respiration, combustion and 
 decay, and of various manufacturing operations, instead of 
 accumulating in one place are continually dissolved away and 
 dispersed in the great atmospheric ocean. 
 
 The siphon is an instrument by which liquids may be trans- 
 ferred from one vessel to another by atmospheric pressure. It 
 consists of a bent tube, one arm of which is longer than the 
 other. Take a piece of glass tubing about twelve inches long 
 and bend it into a U shape at five inches from one end. Fill the 
 
LESSONS IN PHYSICS. 41 
 
 tube with water, then closing the end of the longer arm with the 
 finger, place the end of the short arm in a glass of water and 
 open the end of the long arm, when the water will flow from the 
 glass through the tube. If the water be allowed to run into 
 another glass it will flow until the water is at the same level in 
 the two glasses. If we take a glass in each hand, by changing 
 the level slightly the water may be made to run either way. 
 Almost any substance may be used for a tube. The first siphon 
 the writer ever saw was made of dandelion stems. In studying 
 the barometer we learned that the pressure of the air would sus- 
 tain a column of water that was over thirty feet high, in case the 
 air pressure was removed from the column. In the case of the 
 barometer the air pressure was removed by closing the end of 
 the tube. In the siphon the air pressure is removed by bending 
 the tube, so that both ends are under water. When both arms 
 are of the same length, that is when the water in each glass 
 is at the same level, the air pressure sustains equal columns of 
 water, and there is no motion ; but if we change the level of the 
 two glasses of water the pressure on the water in the lower glass 
 has a longer column of water to sustain than is sustained in the 
 upper glass, and water is pushed over into the lower glass to 
 establish an equilibrium. The long arm and short arm means 
 the perpendicular distance from the arch of the siphon to the 
 surface of the water on either side. 
 
 The common pump depends upon atmospheric pressure for its 
 usefulness. It consists of two barrels separated by a valve open- 
 ing upward. In the upper barrel there is a piston with a valve 
 opening upward. When the piston is raised the pressure of the 
 air is removed from the water in the lower barrel, and the press- 
 ure of the air on the water outside forces it up the barrel 
 through the lower valve. When the piston is pushed down the 
 lower valve closes and the valve in the piston opens so that the 
 water rises above the upper valve; as the piston is raised again 
 it lifts the water above the upper valve and allows water to be 
 forced through the lower, and so on. In the ordinary force pump 
 the piston is solid, and a valve, opening outward in the side of the 
 
42 PRACTICAL LESSONS IN SCIENCE. 
 
 upper barrel, near its lower end, allows the downward stroke of 
 the piston to force the water into an air chamber, compressing 
 the air, and the elasticity of the air forces the water forward in a 
 steady stream. 
 
 The volume of a given weight of air or other gas varies in- 
 versely as the pressure upon it ; that is, the more pressure the 
 less the volume and vice versa. We have already learned that 
 air can be compressed, but careful experiments show that if we 
 double the pressure on a given body of air or other gas its vol- 
 ume will be reduced one-half, and if we lessen the pressure by 
 one-half the volume will be doubled. This is called Boyle's or 
 Mariotte's law, from the names of its discoverers. If the volume 
 of gas is decreased by pressure the density is increased, so that 
 the density of air or other gases varies directly as the pressure. 
 The density of the air is greatest at the sea level, while on high 
 mountains the density is much less. 
 
 We have already learned that gases expand and contract as 
 they are heated or cooled, but careful experiments show that this 
 expansion and contraction is somewhat uniform. If we have 491 
 cubic inches of air at the temperature of 32 F. it will have a 
 volume of 492 cubic inches when heated to a temperature of 33 
 F.; that is, it expands - 4 -i- T of the volume at 32 F. for each addi- 
 tional degree of heat. If the law holds good for lower tempera- 
 tures we should find absolute zero at about 495 F. below the 
 present Fahrenheit zero. 
 
CHAPTER V. 
 
 FORCES AND MOTION. 
 
 THE forces which cause all the variety of motions in nature are 
 but different forms of attraction and repulsion. A constant force 
 is one that acts continually, as the force of gravity, while an 
 impulsive force is one that acts for a time, then ceases, as the 
 blow of a hammer, or the stroke of a bat that drives the ball. 
 
 A unit of time is a measured portion of time, as a second, a 
 minute, or an hour, and velocity is the distance passed over by 
 a body in a unit of time, as the train moves 40 miles an hour. 
 The velocity of a body may be uniform, increasing, decreasing, 
 or variable. 
 
 Space is the whole distance passed over by a body while in 
 motion. It equals velocity multiplied by the units of time, as 
 the velocity of a train is 40 miles an hour, units of time are 10 
 hours, then space equals 400 miles, the distance passed over by 
 the train. Motion will be uniform when the velocity of the body 
 is the same in successive units of time, and will be accelerated 
 when the velocity increases in successive units of time, and re- 
 tarded when the velocity decreases. Accelerated and retarded 
 motions may be uniform or variable. 
 
 The first law of motion is that a body at rest will remain at 
 rest, or if in motion, will continue in motion, unless acted upon 
 by some force to change its condition. This is practically the 
 law of inertia. The second law is that a given force will produce 
 the same amount of motion whether it acts upon a body at rest 
 or upon a body in motion. This law is illustrated by the motion 
 of a boat in crossing a river; the steam drives the boat across 
 the river while the current carries it down the river, and under 
 the action of both forces the boat moves across the stream in a 
 diagonal course. 
 
 (48) 
 
44 
 
 PRACTICAL LESSONS IN SCIENCE. 
 
 The third law is that action and reaction are equal and in op- 
 posite directions. If the hand strikes the wall, the wall reacts on 
 the hand and the hand is bruised ; the bullet that shatters the 
 bone is itself bruised and flattened. The fact of reaction seems 
 evident, but careful experiments are necessary to show that 
 action and reaction are equal. 
 
 A constant force acting alone causes uniformly accelerated 
 motion, in a straight line, as the motion of a body falling by the 
 force of gravity. Experiments show that a falling body passes 
 over a space of about 16^ feet in the first second, over three 
 such spaces in the next second, over five the third, and so on. 
 The distance a body falls in a given number of seconds, equals 
 the square of the number of seconds multiplied by 16 T L feet. 
 The distance a body will fall in four seconds may be shown as 
 follows: 4 X 4 = 16 X 16^ = 257.25 feet. In the case of falling 
 bodies the motion is due to the action of the one force of gravity 
 retarded somewhat by the resistance of the air, but most of the 
 motions met with in nature are the result of the combined action 
 of several forces. 
 
 If we represent the intensity and direction of forces by lines, we 
 can more easily solve some of the problems of motion. Suppose 
 
 a body at A (see Fig. 1) is acted upon 
 by a force, whose intensity and direc- 
 tion is represented by the line AB, 
 sufficient to carry the body to B. At 
 B the body is acted upon by a force, 
 represented by the line BC, sufficient 
 to carry the body to C. The forces 
 AB and BC, acting separately, have 
 carried the body to C over the lines 
 AB and BC. But if the two forces 
 AB and AD, which equals BC, should act together on the body at 
 A, they would carry it to C, as before, but along the line AC, not 
 along the lines AB and BC, as in the former case. This illustrates 
 the truth of the second law of motion, and shows that one force 
 whose intensity and direction is represented by the line AC would 
 
 C 
 
 Fio.l 
 
LESSONS IN PHYSICS. 45 
 
 carry the body to the same point as the two forces AB and BC, 
 acting separately or together. The separate forces, represented 
 by the lines AB and BC or AD, are called components and the 
 single force, represented by the line AC, their equivalent, is called 
 the resultant. The process of finding the resultant of two or 
 more forces is called the composition of forces. A resultant may 
 be made up of, and equivalent to, more than two forces. Suppose 
 that when the body is at C it is acted on by a force represented 
 by CF sufficient to carry the body to F. The forces AB, BC and 
 EF, acting successively, have carried the body to F. In the 
 former case we found that the force represented by AC equaled 
 the forces represented by the lines AB and BC ; now if we com- 
 plete the parallelogram on AC and CF we find that a force 
 represented by AF will carry the body to the same point as the 
 forces represented by AC and CF, acting separately, and conse- 
 quently to the same point as all three forces represented by AB, 
 BC and CF would carry it if acting separately, or as AB, AD, 
 which equals BC, and AE, which equals CF, would carry it if 
 acting together. In this way a resultant may be found for any 
 number of component forces. 
 
 If two or more parallel forces act on a body, at the same time, 
 and in the same direction, their resultant would be a force equal 
 to the sum of the component forces, and the motion would be 
 in the same direction. A span of horses drawing a wagon illus- 
 trates this principle. If two parallel forces act on a body at 
 different points, and in opposite directions, they will produce 
 rotary motion. No single force can replace two such forces. 
 
 If we have a force represented by AF ( Fig. 1 ) , we may find other 
 forces that would produce the same effect. AC and CF together 
 would equal AF. AB and BC would equal AC, and AB and BC 
 and CF together equaling AF, reversing the process of composi- 
 tion offerees. This process of finding two or more forces that 
 are equivalent to one force, is called the resolution of forces. 
 
 The study of motions in straight lines is interesting and im- 
 portant, but most of the motions in nature are along curved 
 lines ; so that the study of motion in curved lines will be as prac- 
 
46 PRACTICAL LESSONS IN SCIENCE. 
 
 tical, and perhaps more interesting than the other. Every ripple 
 and wave, every swaying branch and rustling leaf, each nodding 
 flower, each bird and beast moves in ever varying curves. 
 
 Curved motion is produced by the action of at least two forces, 
 one of which must be a constant force. The motion of a ball, when 
 fastened to a string and whirled around the hand, is an example 
 of curved motion. The string represents a constant force, and 
 the muscles of the arm an impulsive force. An impulsive force, 
 acting alone, or any number of impulsive forces acting together, 
 tend to cause motion in a straight line, but one or more impul- 
 sive forces acting with a constant force, gives motion in a curved 
 line. The forces which cause circular motion are called central 
 forces ; one acts toward the center, from which the curve is de- 
 scribed, while the other acts in the direction of a tangent to the 
 curve. The one is called the centripetal force, and the other the 
 centrifugal force. The grandest examples of the actions of these 
 forces are found in the motions of the heavenly bodies, gravita- 
 tion acting as the centripetal force. 
 
 The centrifugal force varies as the quantity of matter in the 
 moving body ; that is, the more matter there is in the body the 
 greater will be the reaction against the centripetal force. It also 
 varies as the square of the velocity of the body in motion. These 
 laws are illustrated in a general way by the use of a sling ; the 
 heavier the stone the greater the reaction or pull, and the greater 
 the velocity the greater the pull. When a wagon moves slowly 
 along the road no mud is thrown from the wheels, but as the mo- 
 tion is increased the centrifugal force overcomes the force of ad- 
 hesion between the mud and the wheel, and the mud is thrown 
 off. This principle is made use of in the centrifugal machines 
 employed in laundries for drying clothes, in sugar refineries for 
 removing molasses from the sugar, and in apiaries for extract- 
 ing honey from the comb. It accounts for the action of the gov- 
 ernor on a steam engine; for bursting grindstones and balance 
 wheels; and the increased size of the earth at the equator was 
 undoubtedly caused by centrifugal force when the earth was cool- 
 ing from the liquid state. The effect of centrifugal forces may be 
 
LESSONS IN PHYSICS. 47 
 
 illustrated by swinging a pail partly filled with water over the 
 head or in any direction; the centrifugal force so overcomes the 
 force of gravity that not a drop of water falls. Race tracks and 
 railroad tracks are raised on the outside of a curve to prevent 
 overturning from the centrifugal force exerted when -passing the 
 ciirve. 
 
 The ball from the bat, the arrow from the bow, the bullet from 
 the gun, are projectiles, and all move in curved lines. An impul- 
 sive force in each case gives the body motion, which would be in a 
 straight line but for the action of the constant force of gravity. 
 The range of a projectile is the horizontal distance through which 
 it moves. This distance depends upon the energy of the impulsive 
 force, the angle at which the body starts and on the resistance of 
 the air. Theoretically an angle of 45 degrees would give the 
 greatest range ; but in practice an angle of about 30 degrees is 
 found to be best for a bullet, and about 35 degrees for an arrow. 
 
 Motions in liquids may be waves caused by winds; may be 
 tidal waves caused by the attraction of the sun and moon; may 
 be currents caused by gravity, by winds or unequal heating; or 
 they may be vibrations arising from an endless variety of causes. 
 In either case the motions vary greatly, and are useful and in- 
 teresting in various ways. Examples of these motions and their 
 effects are so common and well known that they need only be 
 mentioned here. But wa,ter is often conveyed from reservoirs 
 through pipes for use in various ways, and it is interesting to 
 notice that the results in practice differ so widely from theoret- 
 ical deductions that most calculations are made from arbitrary 
 rules. If we examine a. jet of water flowing from an orifice in a 
 vessel we shall see that it grows rapidly smaller, so that at a 
 little distance its size is only about two-thirds as great as at the 
 orifice. Beyond this point the contraction of the jet is gradual . The 
 rapid contraction near the orifice is due to cross currents, caused 
 by the water flowing toward the orifice from different directions. 
 The effect of these cross currents can be diminished somewhat by 
 the use of short tubes; but when all is done scarcely more than 
 80 per cent, of theoretical flow can be secured. The flow of water 
 
48 PRACTICAL LESSONS IN SCIENCE. 
 
 is greatly retarded by friction in the pipes, so that much larger 
 pipes should be used than might at first seem necessary. 
 
 Motions in the air and other gases are very common, 
 in fact the air is seldom or never at rest. The differences in 
 temperature between day and night, between the sea and 
 land, between forest and plain, all tend to cause inequalities 
 of pressure which result in more or less extensive motions, 
 which vary from gentle, almost imperceptible, breezes of two or 
 three miles per hour, to the fierce and destructive tornado in 
 which the velocity of the air is as great as 50, 75, or even 100 
 miles per hour. The difference of temperature between the equa- 
 torial and polar regions is perhaps the main cause of the general 
 system of winds of the globe, the rotation of the earth influ- 
 encing the direction of the air movement. If a fire is built, the 
 air near it is heated, and expanding becomes less dense than the 
 surrounding air. The heavier air crowding in from all directions 
 forces the lighter air upward, giving rise to currents of air from 
 all directions toward the fire, all of which unite in an upward 
 current from the fire. The great heat of the equatorial regions 
 causes the air of those regions to be less dense than that of regions 
 north or south. This gives rise to a movement of air from both 
 directions toward the equatorial regions, forming there an up- 
 ward current, which, spreading out, flows back toward the polar 
 regions as counter-currents, so that the air of the earth is in con- 
 stant circulation in a general way, besides the thousands of minor 
 movements due to local causes. If the earth did not rotate we 
 might expect these currents to move directly north and south ; 
 but the spherical form and rotary motion of the earth change the 
 directions somewhat. On account of the form and rotation of 
 the earth, those places near the equator move more rapidly than 
 those either north or south of the equator. Places on the equa- 
 tor have a motion of 1,042 miles per hour, while those at 20 N. 
 or S. have a motion of only 975 miles per hour. Air, moving 
 toward the equator, having the slower motion of places north 
 and south, falls behind places at the equator having the same 
 longitude as those from which it started, so that these currents 
 
LESSONS IN PHYSICS. 49 
 
 instead of being north and south winds, are northeast winds 
 north of the equator, and southeast winds south of the equator. 
 Those currents going from the equator, having the more rapid 
 motion of places near the equator, are constantly getting in ad- 
 vance of places having the same longitude as those from which 
 they started, so that north of the equator they are southwest 
 winds instead of south winds, and south of the equator they are 
 northwest winds instead of north winds. Numerous observations 
 show that the winds between 32 N. and 25 S. have the direc- 
 tions given above. 
 
 As the land is a better absorber of heat than the water, in the 
 torrid zones and during summer in the temperate zones, it be- 
 comes hotter than the water during the day, and the air over the 
 land becomes hotter and lighter than that over the water, which 
 gives rise to a wind from the sea toward the land, called the sea 
 breeze. The land is also a better radiator than the water, so 
 that during the night the land becomes cooler than the water, 
 and the air over the land becomes heavier than that over the 
 water, which gives rise to a wind from the land toward the sea, 
 called the land breeze. The land and the sea breeze illustrate 
 how variations in the surface of the earth serve to promote mo- 
 tions in the air. 
 
 L. S. 4 
 
CHAPTER VI. 
 
 VIBRATIONS. 
 
 VIBRATIONS are alternate movements backward and forward. 
 If with the finger we depress one scale-pan of a balance, it will 
 continue to move alternately up and down over the same path 
 for a long time after the finger is removed, or if we pull the scale- 
 pan to one side and then release it, it will swing backward and 
 forward for a time; or suppose a ball, hung by a fine wire, be 
 twirled by the finger so as to'twist the wire; let go of it, and, 
 speedily untwisting the wire, it will go on for a time twisting it 
 up the other way; these alternate motions are vibrations. 
 
 The pendulum is a body hanging from a fixed point upon 
 which it can swing freely. The fixed point is called the point of 
 suspension, and the point in the pendulum which vibrates as if 
 only under the influence of its own gravitation and inertia, is 
 called the center of oscillation, and the length of the pendulum 
 is the distance between the point of suspension and the center of 
 oscillation. The center of oscillation is generally a little below 
 the center of gravity of the pendulum ball. 
 
 The pendulum vibrates under the in- 
 fluence of gravitation and inertia. Sup- 
 pose a ball at M (see Fig. 2) to repre- 
 sent a pendulum hung from the fixed 
 point, C, by a cord MC. Now, if this 
 ball be lifted to the point A and for a 
 moment held there, the force of gravity 
 will act upon it in a vertical direction. 
 FIG. 2 \^ We will represent this force by the line 
 
 AB, and resolve it into two compo- 
 nents, shown by the lines AD and AE. The force, AD, acts length- 
 wise of the string without effect to move the ball ; the other force, 
 (50) 
 
LESSONS IN PHYSICS. 51 
 
 AE, acting at right angles to AD, will pull the ball toward the 
 point M. If the ball is allowed to fall to M, its inertia will carry 
 it beyond that point; but when it passes the point M, gravita- 
 tion begins to pull backward, with just the same power it exerted 
 to pull the ball from A to M. The ball will rise from M to N, a 
 distance just as far beyond M as it has fallen to reach M. It will 
 there stop and gravitation will bring it back to M, while its 
 inertia will carry it up to A again. The resistance of the air and 
 friction of the cord will finally make it stop at M. 
 
 The time of one vibration at any given place varies as the 
 square root of the length of the pendulum, and varies inversely 
 as the square root of the force of gravity. In general, the am- 
 plitude or extent of vibration does not affect the time. The truth 
 of the first law may be shown by experiments with pendulums of 
 different lengths, when it will be found that a pendulum one foot 
 long vibrates twice, while a pendulum four feet long vibrates 
 once. The pendulum is used to measure time. If the wire sus- 
 pending the pendulum ball is of steel or any single substance, it 
 varies in length with the temperature during the year, so that the 
 pendulum will vibrate more rapidly in some seasons of the year 
 than in others; usually the movement will be more rapid in win- 
 ter and slower in summer. Compensation pendulums are some- 
 times made by using different metals, so that the contraction 
 of one balances the expansion of the other. 
 
 The pendulum? is also used to determine the figure of the earth. 
 The rate of the vibrations of the pendulum depends upon the force 
 of gravity. If at any place the pendulum vibrates more rapidly, 
 other conditions being the same, it shows an increase of the 
 force of gravity. If it vibrates more slowly, then the force of 
 gravitation must be less, indicating that in the one case the 
 pendulum was nearer the center of gravity of the earth than in 
 the other, which would indicate variations from a true spherical 
 form. The vibrations of the pendulum are more rapid toward 
 the poles, and vary somewhat in other directions. 
 
 Let a stone be thrown into the water of a lake or pond and 
 the tranquil surface will be carved into a series of circular ridges 
 
52 PRACTICAL LESSONS IN SCIENCE. 
 
 and furrows called waves, which extend onward and onward, 
 finally breaking against the shore. The ridges and furrows 
 move outward from the point of disturbance, but the water only 
 moves upward and downward; that is, it vibrates. Another 
 stone dropped into the water a little distance from the first sets 
 up another series of waves. These waves interfere with the waves 
 caused by the first stone, breaking up the symmetry of each, cut- 
 ting the surface of the water into curious shaped elevations and 
 depressions having no semblance to uniformity. Sometimes the 
 elevation of one group of waves is piled upon the elevation of 
 the other group, making waves nearly twice as high as a single 
 wave of either group ; and sometimes the furrows of one group 
 correspond with the furrows of the other, making a much deeper 
 furrow than a single wave of either group; and again, a ridge of 
 one set will correspond with the furrow of another set, and a 
 level surface will result. 
 
 Waves may be caused in the air as in the water, but they differ 
 in form. The waves of water are circular, while the air waves are 
 like spherical shells, spreading out in every direction. The air 
 particles simply move backward and forward, as the water par- 
 ticles move upward and downward. Sometimes the vibrations of 
 the air are intense enough, so that, acting on the organs of hear- 
 ing, they give rise to sensation of sound. Single intense air 
 waves cause a sound called a report ; a series of such sounds in 
 irregular succession makes a noise, and when the waves succeed 
 each other so rapidly and regularly that there seems to be no in- 
 terval between them, the result is a musical sound or tone. In 
 general, less than from thirty -two to forty vibrations in a second 
 give rise to reports or noises, but vibrations, varying in number 
 from 40 to 40,000 per second, can ordinarily be appreciated as 
 musical tones. 
 
 The tones of the voice and of many musical instruments de- 
 pend upon the vibrations of chords that are subject to more or 
 less tension. Lay a brick or a piece of wood about the size of a 
 brick upon each end of a table. Tie a string to one leg of the 
 table, pass it over the bricks, and tie it to another brick as a 
 
LESSONS IN PHYSICS. 53 
 
 weight; strike the cord near the center and notice the vibra- 
 tions. Add another brick as a weight and strike it again, and 
 compare the vibrations in the two cases. Stretch a heavier cord 
 and compare the vibrations of the two cords when stretched 
 with the same weight. Stretch a light wire and experiment with 
 it, and compare the vibrations of the wire with vibrations of 
 the cords. Shorten the strings, by putting a brick in the middle, 
 and then test the vibrations again; then shift the brick either 
 way, so that one end of the cord is longer than the other, and 
 again test the vibrations. Vary the weights, causing tension in 
 different ways, and notice and compare the vibrations in each 
 case. The result of these experiments will convince one that the 
 shorter the string, the cord or wire, the more rapid the vibra- 
 tions; and second, that the greater the weight or tension the 
 more rapid the vibrations; and that the heavier the cord or wire 
 the slower the vibrations. Experiments with more delicate appa- 
 ratus show that in the second case the vibrations vary as the 
 square root of the weight producing tension ; and in the third 
 case that they vary inversely as the square root of the weight of 
 the cord. 
 
 Musical sounds differ in pitch; the pitch of sounds is that 
 which distinguishes them as being high or low. It depends en- 
 tirely upon the rapidity of vibrations; the more rapid the vibra- 
 tions the higher the sound produced. Two sounds made by the 
 same number of vibrations per second, however they may differ 
 in other respects, will have the same pitch. With pitch as a guide, 
 test the laws of vibrating cords just given. When the num- 
 ber of vibrations which produce one sound is twice as great 
 as that which produces another, we do not say that the sound is 
 twice as high, but rather that it is an octave higher. The term 
 octave is used to designate the tone which is made by twice the 
 number of vibrations needed to produce the lower tone, called the 
 fundamental. The difference in pitch between a fundamental note 
 and its octave is very great. To fill up this interval sounds have 
 been chosen which blend and harmonize most perfectly with the 
 fundamental or with each other. These placed between the fun- 
 
54 PRACTICAL LESSONS IN SCIENCE. 
 
 damental and its octave form a series of eight tones called the 
 natural or diatonic scale. Sounds resulting from the same num- 
 ber of vibrations are said to be in unison. When two notes differ 
 in pitch, but their combination is agreeable to the ear, they are 
 said to be consonant; when disagreeable, dissonant. This scale 
 repeated eleven times includes all sounds within the range of the 
 human ear. The capacity of the ear to appreciate vibrations 
 varies greatly. Some cannot appreciate one-half as many as 
 others can. Only about seven octaves are used in music. By the 
 English standard of pitch the note A of the treble clef is made 
 up of 400 vibrations in a second ; by the French standard the 
 rate for the same note is 435 vibrations per second. The tones 
 in the scale have definite relations to each other. If we represent 
 the number of vibrations for a fundamental note by one, then 
 the several notes of the scale will be made by the following 
 ratios: C 1, D 9-8, E 5-4, F 4-3, G 3-2, A 5-3, B 15-8, C 2. Now, 
 from this scale of fractions, and the fact that A is made up of 
 440 vibrations, the number for the others may be found; as. 
 for example, the number of vibrations to give the fundamental 
 C would be 3-5 of 440, equal to 264. 
 
 The intensity of sound is that which distinguishes it as being 
 loud or soft. It depends entirely upon the amplitude or width of 
 the vibrations which produce it. The greater the amplitude the 
 louder the sound will be. 
 
 Whenever a piano wire, or the cord of any stringed instrument 
 is struck, it vibrates as a whole and in segments at the same 
 time. The vibrations as a whole yield the fundamental note of 
 the cord; the vibrations in segments yield higher tones called 
 overtones or sometimes harmonics. 
 
 By quality we refer to that peculiarity of sound by which we 
 may distinguish notes of the same pitch and intensity made on 
 different instruments. The pitch or intensity of tones made on a 
 violin and on a piano may not differ and yet how easy to tell the 
 sounds apart. We recognize the voices of friends, not by their 
 pitch or intensity but by their quality. The various stringed 
 instruments, as the piano, harp, violin, depend for their value 
 
LESSONS IN PHYSICS. 55 
 
 upon the vibrations of cords, in accordance with the laws already 
 discussed. Vibrations of the air, giving musical sounds, may arise 
 from the vibrations of strips of metal, wood, or other substances, 
 and on this principle the construction of organs, horns, trumpets, 
 and other reed and wind instruments depends. In an organ 
 sounds are made by vibrating columns of air in pipes, sometimes 
 aided by the vibrations of a slender and elastic tongue called a 
 reed. The pitch of sound in pipes depends upon the length of 
 the pipes, or in case of reed pipes on the length and weight of the 
 reed. The air in the pipes of an organ vibrates as a whole and 
 in segments as well, so that there are overtones or harmonics in 
 pipe instruments as well as in stringed instruments. In the case 
 of the horn the sounds are made by vibrating columns of air, the 
 lips aiding the vibrations, as the reed aids the vibrations in the 
 organ pipes. 
 
 The human voice is regarded by the best authorities as being 
 analogous to a reed-pipe, the vocal chords forming the reed, 
 and the cavity of the mouth the pipe; like the reed, it is rich in 
 harmonics, as many as sixteen having been detected in some 
 voices. But their number and relative intensities differ much in 
 different individuals, or even in the same person at different 
 times; and it is on this variety that the peculiarities depend by 
 which any one voice may be unmistakably distinguished from 
 every other. Voices in which overtones abound are sharp, and 
 even rough; those in which they are few or faint, are soft and 
 sweet. 
 
 Sound waves move through all elastic media, as wood, iron, 
 the earth, water, air, etc. The velocity of sound waves varies 
 inversely as the square root of the density of the substance, and 
 directly as the square root of its elasticity. These laws are 
 doubtless true for gases whose structure is uniform throughout, 
 but are not true for the air. Through the air at ordinary tem- 
 perature sound waves move with a velocity of about 1,118 ft. 
 per second, varying somewhat with temperature and with the 
 amounts of water vapor in the air, etc. One great danger to 
 commerce is the difficulty of locating rocks, shoals, and other 
 
56 PRACTICAL LESSONS IN SCIENCE. 
 
 dangerous places during fogs and thick weather, which make the 
 sense of sight of no value. All the maritime nations have been 
 experimenting for years on various kinds of sound signals. These 
 experiments have resulted in some interesting facts about the air 
 and some of its peculiarities in transmitting sound waves. Prof. 
 Tyndall found the capacity of the air to transmit sound waves 
 vary so much that no laws could be discovered. He experimented 
 with guns, fog horns, steam whistles, and a steam syren. He 
 found that frequently, under a clear sky, when the air seemed 
 especially transparent to the sense of sight, it was especially 
 opaque to sound waves. These acoustic clouds so filled the 
 transparent air, that guns, fog horns, whistles and syrens which 
 had been heard from 10 to 13 miles, could not be heard at a dis- 
 tance of three miles. The interrupted sound waves seemed to be 
 wasted by repeated reflections from streams of air differently 
 heated or saturated in different degrees with water vapor. 
 Neither rain, hail, snow, or fog seem to have any power to ob- 
 struct sound waves. In fact, air that is filled with water vapor, 
 in some form, is in a highly favorable state for the transmission 
 of soundwaves. Sometimes the guns could be heard moreclearly, 
 sometiines the whistles, and sometimes the syrens; sometimes 
 low pitched, long-waved sounds could be heard more distinctly, and 
 again the high tones penetrated farthest. Prof. Tyndall thought 
 the steam syren the best instrument, considering it reliable for 
 two miles, and generally for three and three and one-half miles. 
 In general, when it could not be heard at least four miles, the 
 sky would be optically clear so that the sound signal would not 
 be as necessary as in thick weather. Other things being equal, 
 sound waves travel better with the wind than against it. The 
 velocity of sound in water is given by some authorities as about 
 4,700 ft. per second; in caoutchouc, as 197 ft. per second; in 
 lead, as 4,030 ft.; in copper, as 11,666 ft.; in oak timber, along 
 the grain or fiber, 12,622 ft.; in iron, as 16,800 ft. per second. *In 
 wet sand, as 825 ft. ; and in solid granite, as 1,664 ft. in a second. 
 Sound waves are often reflected from plane or curved surfaces, 
 causing echoes. At Woodstock, England, an echo returns 14 
 
LESSONS IN PHYSICS. 57 
 
 syllables, and many other localities furnish interesting echoes. 
 Echoes are sometimes interesting; but sometimes they are 
 annoying, and the usefulness of many large halls or assembly 
 rooms is much diminished by conflicting echoes. Theceilings and 
 walls of such rooms should be so broken up by arches, balconies, 
 beveled angles, etc., that no large areas of plane surface appear; 
 drapery, furniture, etc., tend to break up and disperse the sound 
 waves so as to lessen the effect of reflections. People do not 
 intentionally build whispering galleries, but there are many 
 rooms in which at certain points the slightest noise is conveyed 
 with great intensity to certain other points, while it may not be 
 heard at all at intermediate points. The Mormon Tabernacle, 
 and the dome of St. Paul's Cathedral, London, are illustrations. 
 Sounds or vibrations are not only reflected, but are also re- 
 fracted. The laws of reflection and refraction of vibrations 
 causing sound are similar to those of vibrations causing light, 
 and may be considered in connection with the study of light. 
 
CHAPTER VII. 
 
 FORCE AND ENERGY. 
 
 FORCE is that which causes motion or changes motion. While 
 this definition conveys no idea of what force is, it does give us 
 some idea of what force does. Force may be measured by an in- 
 strument called a dynamometer, of which the common draw 
 scale is an illustration. When a body is moved by the action of 
 force upon it, the force is said to do work on the body. For ex- 
 ample, steam exerts pressure on the piston of a cylinder of an 
 engine, causing it to move. The expansive force of the steam 
 does work on the piston in overcoming resistance and putting it 
 in motion. If there had been no motion of the piston no work 
 would have been done. In merely supporting a body no work is 
 done, since no motion is produced. The force of gravity does no 
 work on the stone resting on the ground, yet it causes a pressure 
 between the stone and the earth. Force and space are essential 
 elements of work. A force acting through a space of one foot in 
 raising a weight does a certain amount of work. The same force 
 acting through a space of two feet would do twice as much work. 
 That is, in general, force multiplied by the space through which 
 it acts equals the work done. Formula : Force, F. X Space, S. 
 work, W. 
 
 Every moving body can impart motion; can do work on any 
 other body, and is said to possess energy. The energy of a body 
 is its capacity to do work. For example, the moving bat in the 
 hands of a ball player imparts motion to the ball ; it does work 
 on the ball. The energy which a body, as the bat, possesses, 
 in consequence of its motion, is called kinetic energy. A stone 
 lying on the ground is devoid of energy. Do work upon the 
 stone by lifting it up to a shelf, or other support, and it seems as 
 devoid of energy as when lying on the earth. Attach one end of 
 (58) 
 
LESSONS IN PHYSICS. 59 
 
 a cord to the stone, pass the cord over a pulley and wind a por- 
 tion of it around a shaft connected with a sewing machine, coffee 
 mill, or other convenient machine. Suddenly withdraw the shelf 
 from beneath the stone, the stone falling communicates motion 
 to the machinery and you may sew, grind coffee, etc., with the 
 energy given to the machinery by the stone. The work done on 
 the stone in raising it was not lost. The stone gives it back 
 while descending to the earth. There is a very important differ- 
 ence between the stone lying on the ground and the stone lying 
 on the shelf. The former is powerless to do work, the latter can 
 do work. Both are alike motionless, and you can see no differ- 
 ence excepting the advantage which the latter has over the 
 former in having a position such that it can move. The work 
 done in raising it to its place on the shelf gave it this ad- 
 vantage. A body thus may possess energy due merely to the 
 advantage of its position derived always from work bestowed 
 upon it. Energy due to advantage of position is called potential 
 energy. We see, therefore, that energy may exist in either of two 
 widely different states. It may exist as actual motion in the 
 case of the bat, or it may exist in a stored-up condition, as in 
 the case of the stone lying on the shelf. The energy which the 
 stone on the shelf possesses is due to the fact that its position is 
 such that it can move, and that there is stress between it and the 
 earth which will cause it to move. The force of gravity is em- 
 ployed to do work as when mills are driven by falling water; but 
 the water must first be raised from the ocean bed to the hill side 
 by the work of the sun's heat. The elastic force of springs is 
 employed as a motive power; but this power is due to the ad- 
 vantage of position, which the molecules of the springs have 
 acquired by work done upon them. We are as much accustomed 
 to storing energy for future use as provisions for winter's con- 
 sumption. We store it when we wind up the spring or weight of 
 a clock to be doled out gradually in the movements of the ma- 
 chinery. We store it when we bend the bow, raise the hammer or 
 any body above the earth's surface. 
 The energy of a body is dependent wholly upon the work which 
 
60 PRACTICAL LESSONS IN SCIENCE. 
 
 has been done upon it, so that both work and energy may be 
 measured by the same unit. The unit usually employed is the 
 work done, or energy imparted, in raising one pound to a ver- 
 tical height of one foot; it is called a foot-pound. With this unit 
 we may measure any species of work, and thereby compare work 
 of any kind with that of any other kind. For instance, let us 
 compare the work done by a man in sawing through a stick of 
 wood, whose saw must move 100 ft. against an average re- 
 sistance of 20 Ibs., with that done by a bullet in penetrating 
 a plank to a depth of two inches (1-6 ft.) against an average 
 resistance of 500 Ibs. Moving a saw 100 ft. against a resist- 
 ance of 20 Ibs. is equivalent to raising 20 Ibs. 100 ft., or doing 
 2,000 ft.-lbs. of work. A bullet moving 1-6 of a foot against 
 500 Ibs. resistance does the same amount of work as is required 
 to raise 500 Ibs. 1-6 of a foot high; that is, about 83 1-3 ft.-lbs. 
 of work ; hence the sawyer does about 24 times as much work as 
 is done by the bullet. The work done, the energy exerted by a 
 moving body, is equal to the weight of the body moved, multi- 
 plied by the number of feet it is raised. With a given velocity a 
 body will rise to a definite elevation, which is determined by 
 dividing the square of the velocity by twice the force of gravity ; 
 formula : -^-, the force of gravity being about 32 1-6. Hence, the 
 energy of a moving body, the work it may do, can be estimated, 
 if we know its weight and its velocity, by the following formula : 
 w * ya . Illustration: The energy of a cannon ball weighing 
 40 Ibs., and moving with the velocity of 800 ft. per second, 
 would be about 398,134 foot-pounds. The kinetic energy of two 
 bodies having the same velocity will vary as the weight of the 
 bodies; that is, if one body weighs 50 Ibs. and the other 100 
 Ibs., the energy in the one case will be twice as great as in 
 the other. The kinetic energy of two bodies having the same 
 weight varies as the square of the velocity; that is, doubling 
 the velocity multiplies the energy by 4, or tripling the velocity 
 multiplies the energy by 9. A railroad train, having a velocity 
 of 20 miles an hour, will, if the steam is shut off, run four 
 times as far as it would if its velocity were only 10 miles an 
 
LESSONS IN PHYSICS. 61 
 
 hour. Thus, light substances, as the air, exhibit great energy 
 when their velocity is great. As a body is raised higher and 
 higher the work accumulates in the form of potential energy. 
 The accumulated work, or the potential energy, does not always 
 equal the work performed. Some of the work done is used in 
 overcoming friction, and is wasted. The work done by the saw- 
 yer and the bullet imparted no energy to the bodies upon which 
 they did work; it was entirely consumed in overcoming resist- 
 ance, disappearing as energy. Of the vast amount of work done 
 in propelling steam cars or vessels none accumulates, all is 
 wasted, and cannot be recovered or made available for doing 
 work. The available energy that a body possesses is the work 
 done upon the body, less the lost or wasted work. We may 
 calculate in foot-pounds the work performed on a body, and from 
 this deduct the number of foot-pounds wasted, and the remain- 
 der is the number of foot-pounds of energy that is imparted to 
 the body. 
 
 In estimating the total amount of work done, the time con- 
 sumed is not considered. The work done by a hod-carrier in 
 carrying 1,000 bricks -to the top of a building is the same 
 whether he does it in one day or a week. But in estimating the 
 power of any agent to do work, or the rate at which it is capable 
 of doing work, time is an important element. The unit in which 
 power or rate of doing work is estimated, is called a horse 
 power. A horse power represents the power to perform 33,000 
 foot-pounds of work in a minute. 
 
 Energy, like matter, is indestructible. It may be transmitted, 
 it may be changed into other forms, but not destroyed. The 
 quantity of energy cannot be increased or diminished. Whenever 
 a body in motion meets an obstacle energy is transmitted to it as 
 in the case of the bat and the ball. 
 
 Let a ball be shot vertically upwards. On starting, its energy 
 is kinetic, and it rises more and more slowly until it stops, and 
 then falls to the ground. At the moment it stops at the top of 
 its path its energy is potential. During its flight upwards kinetic 
 energy has been changing into potential energy, and again, dur- 
 
62 PRACTICAL LESSONS IN SCIENCE. 
 
 ing its fall, potential energy is changed into kinetic energy. There 
 is no loss, but simply a change in the character of the energy. 
 The same thing is true in a swinging pendulum. The mechanical 
 energy of the hammer is not lost when the hammer stops. It 
 has been changed into molecular energy or heat. Whenever 
 energy disappears it has been changed into another form. 
 
 One of the most interesting discoveries of modern science is 
 that all forms of energy are so related to one another that 
 energy of any kind may be changed into energy of any other 
 kind. That a definite quantity of mechanical work when trans- 
 formed without waste will yield a definite quantity of heat ; and 
 that this heat, if there were no waste, could perform the original 
 mechanical work. That when one form of energy disappears an 
 exact equivalent of another form takes its place, so that the sum 
 total of energy is unchanged. This principle is known as the law 
 of conservation of energy. 
 
CHAPTER VII Continued. 
 
 MACHINES. 
 
 A MACHINE is any contrivance which has for its object the 
 transferring or transforming of energy. In an electric-light plant 
 the energy of the steam is communicated to the moving parts of 
 the engine, to be transferred by belts to the armatures of the 
 dynamo, where it is transformed into electric energy. In me- 
 chanics it is customary to restrict the term " machine" to such 
 devices as merely transfer energy. This is clearly the case with 
 those known as simple machines. They are the lever, the wheel 
 and axle, the pully, inclined plane, wedge and screw; all other 
 machines, however complicated, are but combinations of two or 
 more of these simple machines. 
 
 No force is gained by the use of machines; indeed, much of the 
 force applied to the machine is wasted in overcoming friction 
 and other resistances, so that force is lost by the use of ma- 
 chines. But machines enable us to apply force advantageously; 
 enables us to employ the force of wind, water, steam or the 
 strength of animals. By the use of machines a small force mov- 
 ing rapidly may move a great body slowly, or a great force 
 moving slowly may put a small body in rapid motion. The force 
 applied to do work is called power, P. ; the resistance to be over- 
 come is called weight, W. Work consists of overcoming resist- 
 ance, 'and equals the product of the weight by the vertical height 
 to which it has been raised. Two forces, acting in opposite direc- 
 tions upon the same body, will be in equilibrium when they do 
 equal amounts of work. 
 
 With this principle as a test, we may study with interest the 
 simple machines mentioned, considering the parts as without 
 weight and moving without friction. 
 
 The lever is an inflexible bar, turning freely on a point called 
 
 (63) 
 
64 PRACTICAL LESSONS IN SCIENCE. 
 
 the fulcrum. Levers are divided into three classes, on the relative 
 positions of the fulcrum and the points of application of the 
 power and weight. If the fulcrum is between the points of appli- 
 tion it is a lever of the first class, as in Fig. 3. The ordinary 
 
 steelyard and beam balances are illus- 
 p ?\ " trations of levers of this class. If the 
 
 weight is between the power and the 
 
 fulcrum, the lever is of the second class, as in Fig. 4. The 
 ordinary crowbar, when used for prying, is a lever of the first 
 class; when used for lifting, it is a lever of the second class. Two 
 persons carrying a weight hung from a pole are using a lever of 
 the second class, and a wheelbarrow is an illustration of a lever 
 
 of this class. If the power is between P p 
 
 the weight and fulcrum the lever is of Fio^ 
 
 the third class, as in Fig. 5. The common fire tongs, sugar 
 tongs and sheep shears are pairs of levers of this class. When 
 we lift a weight with the hand the forearm is a lever of the third 
 class; the fulcrum is at the elbow and the power is applied 
 through the tendons which are inserted between the fulcrum and 
 
 weight. Levers may be combined in 
 
 p- ~ ~ w various ways. Fig. 6 shows a com- 
 
 bination of a lever of the first class 
 and one of the second class. 
 
 A lever consists of two arms along arm or power arm, which 
 is the distance from the fulcrum to the power, and a short arm 
 or weight arm which is the distance between the fulcrum and the 
 weight. Thus in Fig. 3, PF is the long arm and WF the short 
 arm, which is shorter than the power w * _* 
 arm, while in Fig. 5, the power arm, f""1 JTF 
 
 PT ~~w r 
 
 PF, is shorter than the weight arm A ' ^ 
 
 WF. It may be shown by geometry 
 
 that the distances PF and WF in Fig. 3, have the same relations 
 to each other as the perpendicular distances through which the 
 power and weight, respectively, move, so that work will equal 
 the product of the power by its arm, and the product of the 
 weight by its arm, and the forces will be in equilibrium when 
 
LESSONS IN PHYSICS. 65 
 
 P X PF = W X WF, in which case P : W :: WF : PF. That is the 
 power and weight will be in equilibrium when they are to each 
 other inversely as the lengths of their respective arms. The 
 greater the difference in the length of the arms, the more 
 effective is the lever in transferring power. If the arms of the 
 lever are equal, the power and weight will be equal, and in 
 case of motion the space moved by each will be equal. If the 
 weight arm is shortened by moving the fulcrum toward the right 
 a given power will overcome a greater resistance and do more 
 work. If the power arm is shortened by moving the fulcrum 
 toward the power, the power becomes less effective for overcom- 
 ing resistance, but more effective for producing motion, as in lift- 
 ing a weight with the hand the power acts through two or three 
 inches, while the weight moves through two or three feet. 
 
 In the case of the compound lever the power and weight will 
 be in equilibrium when the product of the power by the long arms 
 equals the product of the weight by the short arms, as in Fig. 6. 
 P X PF' X P'F = W X WF X W'F'. 
 
 The wheel and axle consists of a wheel and cylinder fitted 
 together so as to turn on the same axis. The power is applied to 
 the circumference of the wheel, and the weight, usually by means of 
 a rope is applied to the circumference 
 of the cylinder or axle. The power acts 
 through the circumference of the wheel 
 while the weight acts through the 
 circumference of the axle. And they 
 will be in equilibrium when P X cir. of 
 the wheel = W X cir. of the axle. An 
 end view of the wheel and axle shown 
 in Fig. 7, shows the wheel and axle to 
 be a lever of the first class and the FIG. 7. 
 
 equation may be P X PF the radius of the wheel =W X WF, the 
 radius of the axle. If power is applied to the axle there is gain 
 in velocity, as in the case of a circular saw. The common wind- 
 lass for drawing water from a well or raising weights is a familiar 
 illustration of this machine. The capstan used in moving build- 
 
 L. S. 5 
 
66 PRACTICAL LESSONS IN SCIENCE. 
 
 ings, and on shipboard for raising the anchor or drawing the 
 ship to the dock, is a vertical wheel and axle. 
 
 Sometimes the wheel and axle appears in a modified form as 
 when they are on separate axes and connected by belts, cogs or 
 friction, in which case equilibrium is obtained by using the ratio 
 of the circumferences or the radii as above. In the case of a com- 
 pound wheel and axle there will be equilibrium when the power 
 multiplied by the product of the radii of the wheels equals the 
 weight multiplied by the product of the radii of the axles. 
 
 A pulley is a grooved wheel, turning freely on an axis, over 
 which runs a rope, to which the power and the weight are 
 attached. The frame of the pulley is the block and the pulley 
 may be fixed or movable. It is a lever of the first class having 
 equal arms. No force, or motion is gained by the use of a single 
 pulley, yet it is one of the most useful of the simple machines. By 
 its aid the sails of ships are adjusted, objects may be moved to 
 places otherwise inaccessible, and by the use of a horse or man 
 working on the ground, objects can be raised to the highest 
 elevations. 
 
 In the case of a single pulley or group of pulleys with a single 
 rope, power multiplied into the vertical distance it moves equals 
 the weight into the vertical distance it moves. If the weight 
 is supported by one branch of the rope, power and weight are 
 equal. If the weight is supported by two branches of the rope, 
 as the weight rises both branches shorten and the power moves 
 twice as far as the weight, in which case power would equal 
 weight divided by two, so in a general way power equals weight 
 divided by the number of ropes supporting it. 
 
 In the case of movable pulleys 
 with separate supporting ropes the 
 equation is: power equals weight, 
 divided by the power of two, whose 
 index is the number of pulleys. 
 A Fig. 8. C Any sloping surface may be used 
 
 as a simple machine called an incline plane (See Fig. 8.) AB 
 represents the incline plane; BC the height of the plane; AC the 
 
LESSONS IN PHYSICS. 67 
 
 base of the plane. In case a weight is carried up this plane, 
 it rises only through the distance BC, while the power moves 
 through the distance AB, so that power multiplied by AB 
 equals weight multiplied by BC. That is, power is to weight 
 as the height of the plane is to the length of the plane. Casks, 
 etc., are frequently loaded into wagons by an inclined plane. It 
 was by means of the inclined plane that ancients raised the great 
 blocks of stone which we find in the ruins of the pyramids, tem- 
 ples, and other buildings. Common stairs are examples of an 
 inclined plane. 
 
 A wedge consists of two inclined planes joined by their base. 
 It is mostly used for cleaving timber. It is inserted in a crack, 
 and then driven home by blows from a hammer; but as we can- 
 not measure the energy of these blows, we cannot determine the 
 equilibrium of force in the case of a wedge. 
 
 A screw is a cylinder of wood or metal around which runs a 
 spiral ridge called a thread. This cylinder passes through a 
 block in which there is a corresponding groove to fit the ridge or 
 thread of the cylinder. When the cylinder makes one revolution 
 it rises in the nut to a distance equal to the distance between two 
 consecutive sections of the thread. The arm or bar through the 
 head of a screw increases the length of the power arm. The 
 equation of a screw is : power multiplied by the circumference of 
 the circle through which it moves, equals weight multiplied by 
 the distance between two contiguous threads of the screw. The 
 screw is used for raising buildings and for exerting pressure, as 
 in the pressing of hay or cotton; and when the thread is very 
 fine, it may be used to measure short distances, as in the case of 
 the micrometer screw. 
 
 The toggle joint, used commonly in adjusting the tops of car- 
 riages, is a very useful form of the lever, especially in exerting 
 pressure through a short distance. 
 
 In every class of machinery there is loss of power through 
 friction, rigidity of ropes, resistance of air, etc., so that power 
 must be furnished not only to do the work but to run the ma- 
 chine. Illustrations of the simple machines are common, and it 
 
68 PRACTICAL LESSONS IN SCIENCE. 
 
 is interesting to notice how widespread their application is. 
 Every motion of the body, every tool, and nearly every article 
 we use, involves the action of some form of a simple machine. 
 
 Water wheels are simple machines, something like the wheel 
 and axle, designed for the utilization of the force of gravity 
 through running water. One of the most common forms is the 
 undershot wheel, which is driven by the current flowing under the 
 wheel against the floats. In the case of the breast wheel, the 
 water falls on the wheel near its center and more power is ex- 
 erted. In the case of the overshot wheel the water falls upon the 
 top of the wheel, and more force is exerted than in either of the 
 other cases. The undershot wheel, with plane floats, transmits 
 about 30% of the power of the water. With curved floats it 
 transmits from 50% to 60%. The breast wheel transmits from 
 40% to 50%, and the overshot wheel transmits from 70% to 80%. 
 
 The turbine wheel is the most valuable and economical of the 
 water wheels. While the other wheels are horizontal the axis of 
 the turbine wheel is vertical. In the center of the wheel is a sta- 
 tionary disk of cast-iron, circular in form and horizontal in posi- 
 tion. On the upper surface of this disk are fastened curved 
 guides. The wheel proper revolves outside of this disk. It con- 
 sists of two cast-iron plates, one above the other, the space 
 between them being divided into numerous channels by curved 
 partitions. The partitions in the wheel, and the guides on the 
 disk, curving in opposite directions. To the bottom of this 
 wheel is fastened a cast-iron plate which extends under the cen- 
 tral disk, and to the center of this plate is attached a vertical 
 shaft which comes up through the disk. The revolving part, 
 therefore, consists of an outside wheel, an iron plate underneath, 
 and the vertical shaft. This wheel is placed at the bottom of a 
 column of water. The weight of water upon the disk forces the 
 water between the curved guides on the disk against the curved 
 partitions of the wheel. The energy of these streams turns the 
 wheel and the shaft, and by means of cogs and belts this motion 
 is transferred to machinery. The turbine wheel transmits 80 
 per cent, or more of the computed energy of the falling water. 
 
LESSONS IN PHYSICS. 69 
 
 While experimenting in the line of conservation of energy, Mr. 
 Joule of England discovered that a quantity of heat necessary 
 to raise one pound of water one degree Far. would raise 772 Ibs. 
 one foot high, or would do 772 foot-pounds of work, which is 
 called the mechanical equivalent of heat. A steam boiler and 
 engine constitutes a machine whose purpose is to transform heat 
 into mechanical motion or work. The essential parts are the 
 furnace, the boiler, the steam pipe, the steam chest and slide 
 valves, the cylinder, the piston, the exhaust pipe, piston rod, 
 crank and shaft. The fire in the furnace expands the water in 
 the boiler into steam. The steam pipe conveys this to the steam 
 chest from which it passes through the slide valves into the cylin- 
 der, where expanding now against one, then against the other end 
 of the piston, gives a forward and backward movement, which is 
 conveyed by the piston rod to the crank, where the backward and 
 forward movement is changed into a rotary movement. The 
 steam after expansion in the cylinder passes out through the 
 exhaust pipe. The shaft carries a heavy balance wheel which 
 serves as a reservoir of energy, which is needed to make the rota- 
 tion of the shaft and all machinery connected with it uniform, so 
 that the sudden changes connected with the driving power or 
 resistance are avoided by means of the inertia of this wheel. 
 Motion may be communicated from the shaft to any machinery 
 desirable. While this machine is for the purpose of transforming 
 heat into mechanical work, yet with all modern improvements 
 not more than 20 per cent, of the heat units can be utilized as 
 work. 
 
CHAPTER VIII. 
 
 LIGHT: ITS SOURCES INTENSITY REFLECTION AND 
 REFRACTION. 
 
 IF we place the hand in the sunlight it soon becomes warm. 
 It also becomes illuminated so that it can be seen, and the skin 
 of the hand at length becomes tanned. Some force has been 
 transmitted to us causing the sensations of heat and of light, 
 and causing also chemical action. What we receive from the sun, 
 whether it affects the sense of touch, or the sense of sight, or 
 whether it promotes chemical action, must be energy. 
 
 These forms of energy are transmitted to us from the sun, 
 through waves of an exceedingly rare and tenuous medium, called 
 ether. This method of transmitting energy is called radiation. 
 All the ether waves from the sun, whatever their intensity, cause 
 an increase of heat in terrestrial objects, but only those of a par- 
 ticular intensity give us light. Probably all the ether waves 
 promote chemical action, but particular waves are more active. 
 Bodies hot enough to emit light waves are said to be incandes- 
 cent. The sun, the fixed stars, and other bodies which are 
 sources of light, are incandescent. Most artificial sources of 
 light depend for their light waves on the incandescence of car- 
 bon. There are some substances which, receiving light waves, 
 absorb their energy without becoming hot, and in turn emit 
 light waves in the dark for several hours after exposure to 
 the light. Such bodies are said to be phosphorescent. Some 
 forms of vegetable and animal life emit phosphorescent light, as 
 certain fungi among plants, and the glowworm and firefly among 
 animals. 
 
 Light waves move in straight lines, as may be seen by ar- 
 ranging screens before a source of light, or by examining a ray 
 of light through the dusty air of a room. A single line of light, 
 (70) 
 
LESSONS IN PHYSICS. 71 
 
 or the path of a single point in the light wave, is called a ray of 
 light. The smallest portion of light which can be separated for 
 experiment is called a beam of light; a collection of rays which 
 diverge from a point or converge to a point is called a pencil of 
 light. 
 
 When light waves fall upon the surface of bodies some of them 
 are thrown back or reflected, and some of them are absorbed by 
 the bodies, so that they disappear as light waves, while in the 
 case of some bodies many of the light waves are allowed to pass 
 through them without much loss or change, the bodies being 
 called transparent, translucent, or opaque, as they allow differ- 
 ent quantities of light to pass. Transparent bodies allow so 
 much light to pass that objects can be seen through them dis-" 
 tinctly, as in the case of air, glass, water, etc. Translucent 
 bodies allow light to pass through them, but in such a scattered 
 condition that objects cannot be seen distinctly, as ground glass, 
 oiled paper, etc. Those objects are opaque which apparently ab- 
 sorb or cut off the .light waves so that nothing can be seen 
 through them. Transparent and opaque are relative terms, as 
 no body is wholly transparent or wholly opaque. 
 
 The Velocity of Light. For all distances upon the surface of 
 the earth the passage of light seems to be instantaneous, but in 
 observing the eclipse of one of the moons of Jupiter it was found 
 to occur earlier than the time indicated by calculation. On 
 investigation it was found that when the earth is in that part of 
 its orbit nearest to Jupiter, the eclipse begins 16 minutes 36 sec- 
 onds sooner than it appears to begin when the earth is in the oppo- 
 site part of its orbit. From this it was concluded that light must 
 take 16 minutes 36 seconds to go across the earth's orbit. This 
 distance being known and divided by the number of seconds, 
 the velocity of light is found. The result is about 186,000 
 miles a second. Other investigations have led to the same con- 
 clusions. 
 
 The intensity of light varies as the intensity of light in the 
 source. Again, the intensity of light varies inversely as the square 
 of the distance of the bodies emitting light, which is the same law 
 
72 
 
 PRACTICAL LESSONS IN SCIENCE. 
 
 that applies to the intensity of heat and gravity, and in fact to 
 all forms of radiant energy. This law may be illustrated by the 
 following experiment: Take a piece of stiff cardboard, or tin, 
 about four inches square, and place it at a distance of four feet 
 from a wall or screen. Now, if a candle be placed in front of this 
 card, a shadow will be cast upon the wall which will be larger or 
 smaller as the candle is moved nearer or farther from the card. 
 If the candle is one foot in front of the card the shadow on the 
 wall will be about sixteen inches square, that is the light which is 
 intercepted by the card if allowed to pass on, would be spread out 
 over a surface sixteen times as large upon the wall, but if the 
 same amount of light is spread over sixteen times as much sur- 
 face in one case as in the other it can be only one-sixteenth as in- 
 
 A 
 
 FIG. 7'. 
 
 tense. At four times the distance from the luminous body in this 
 case the intensity of light is one-sixteenth as great; at three times 
 the distance the light would in the same way be found to be one- 
 ninth as intense. In other words, the intensity of light varies 
 inversely as the square of the distance from the luminous body. 
 These experiments may be varied in numerous ways with the 
 result of establishing the truth of this law. 
 
 It is often desirable to compare the illuminating power of dif- 
 ferent flames. The art of doing this is called photometry. The 
 simplest method employed is to place the two flames to be com- 
 pared at such distances from a screen that the intensity of light 
 each throws upon it shall be equal. Suppose, for example, we 
 want to know how many times more light one candle will give 
 than another candle of inferior quality. Let a slender rod be 
 placed just in front of a screen, and then move the flames to 
 
LESSONS IN PHYSICS. 
 
 73 
 
 such a distance that the two shadows of the rod falling side by 
 side upon the screen shall appear to be of equal darkness, then 
 measure the distance from the flames to the screen, and the 
 amounts of light they give will be as squares of their distance; 
 that is, the one twice as far away gives four times as much light. 
 
 The angle formed in the eye by the rays of light coming from 
 the extremities of an object is called the visual angle, and its size 
 varies with the distance of the object. (See Fig.7 / .) The angle 
 ACB is greater than the angle AEB, and the object seen from 
 C appears larger and nearer than when seen from E. The dis- 
 tance and size of objects are so associated in our minds that we 
 judge of the distance of objects know- 
 ing their size, and knowing their dis- 
 tance we judge of their size. 
 
 The different kinds of vibrations, as 
 sound waves, heat waves, light waves, 
 etc., maybe reflected, but the laws of re- 
 flection which are the same in each case, 
 may be more easily illustrated in con- 
 nection with the study of light. More 
 or less light is reflected from bodies; 
 in fact, we see bodies by reflected light, 
 but some of the metals with smooth 
 surfaces throw back nearly all the light M FIG. 8'. 
 waves and are the best reflectors. In the case of ordinary 
 reflectors or mirrors, the reflecting surface is mercury. In fine 
 telescopic reflectors silver is considered the best material for a 
 reflecting surface. Reflecting surfaces may be plane, concave, or 
 convex. When a beam of light falls on a mirror so as to make a 
 right angle with the surface of the mirror, it is thrown back over 
 the incident path ; but when the beam falls upon the surface so as 
 to form an oblique angle with it, the beam is reflected in some other 
 direction. Suppose a beam of light falls upon a mirror MM at 
 the point A from the direction IA ; it will be reflected in the direc- 
 tion AR. (See Fig. 8'.) Now, if we measure the angles made 
 with the line AP perpendicular to the mirror at A, we find that the 
 
74 
 
 PRACTICAL LESSONS IN SCIENCE. 
 
 angle IAP equals the angle PAR, that is the angle of reflection 
 PAR equals the angle of incidence IAP. IA is called the incident 
 beam, AR the reflected beam, and A the point of incidence. 
 
 Rays of light may be parallel, or converging or diverging. 
 They cannot have any other relation. As the angle of reflection 
 equals the angle of incidence in the case of plane mirrors, they do 
 not change the relations of rays of light falling upon them. The 
 reflected rays are parallel, converging or diverging after as 
 before reflection. In the case of concave mirrors the effect on the 
 pays of light is different and more interesting. Let MM in Fig. 
 
 F.c9 
 
 9 represent a concave mirror, C the center of curvature, G the 
 vertex of the mirror, and CG, its principal axis. The lines CA, 
 CB, and CG are radii, and perpendicular to the mirror. Light- 
 waves emanating from the point C would be reflected to their 
 source at C, but rays of light from E, as EA and EB, fall upon 
 the mirror at the points A and B, and as the angle of reflection 
 is equal to the angle of incidence, they would be reflected to 
 H; while if H were a source of light the rays HA and HB would 
 be reflected to E. The diverging rays in each case are by reflec- 
 tion made to converge to a point called a focus. As the light 
 waves which emanate from either of these points are brought 
 
LESSONS IN PHYSICS. 75 
 
 by reflection to a focus at the other, they are nailed conjugate 
 foci. Parallel rays, as I A and KB falling on the mirror at 
 A and B are reflected to F, a point midway between C and G, 
 which is called the principal focus; while rays diverging from 
 the principal focus would be reflected as parallel rays, and the 
 converging rays LA and PB are reflected to S. This shows that 
 the general effect of the concave mirror is to converge the rays of 
 light they reflect, and they converge rays of heat as well, so that 
 a piece of paper or a chip of wood at the principal focus, may be 
 burned in the collected rays of the sun. 
 
 The reflector of a locomotive headlight is a parabolic mirror. 
 The light is placed at the principal focus, so that the reflected 
 rays are... parallel. 
 
 The general effect of convex mirrors is to separate rays of 
 light. 
 
 The image of an object made by a plane mirror appears to be 
 behind the mirror as far as the object is in front of it. It 
 appears to be of the same size as the object and is erect that is, 
 the plane mirror gives a perfect image of the object. 
 
 In the case of the concave mirror, if the object is beyond the 
 center of curvature the image will be between the center of curva- 
 ture and the principal focus, and will be inverted and smaller than 
 the object. If the object is between the center of curvature and 
 the principal focus, the image will be beyond the center of curva- 
 ture, inverted and larger than the object. The image of an object 
 between the principal focus and the mirror will be back of the 
 mirror, erect and larger than the object. 
 
 The images formed by the convex mirror are always erect, 
 behind the mirror and smaller than the object, and are generally 
 curiously distorted. 
 
 Many valuable and interesting experiments may be made with 
 cheap plane and curved mirrors, which will serve to verify these 
 laws. A bright silver spoon may serve both as a concave and a 
 convex mirror ; so of metal cups, bells and other articles of com- 
 mon use. 
 
 Light moves with different velocity, through different trans- 
 
76 
 
 PRACTICAL LESSONS IN SCIENCE. 
 
 parent substances. This is shown by the bending or breaking 
 of a ray of light as it passes from one medium into another of 
 different density, if the ray is oblique to the surface separating 
 the two media. Thrust a pencil into the water so that it is per- 
 pendicular to the surface of the water and there is no apparent 
 change in the shape of the pencil, but if it be made oblique to the 
 surface of the water it appears to be bent or broken at the sur- 
 face, and the immersed portion seems elevated. Again, place a coin 
 on the bottom of an opaque dish as at B (Fig. 10), then standing 
 so that the coin is just hid from sight by the side of thedish,have 
 water poured slowly into the dish and the coin will rise into view 
 
 as the dish fills with 
 water. The difficulty 
 of putting a stick on a 
 given object in a body 
 of water is a familiar 
 illustration of the 
 same principle. Now, if 
 we remember that ob- 
 jects are seen by light 
 reflected from them, 
 we know that a ray of 
 light from the coin or 
 pencil point, is bent at the surface of the water at C toward A, 
 instead of going on to E, so that the ray appears to come from 
 D, and the coin seems to have been lifted from B to D, the pencil 
 appearing to be shorter and the water shallower than it is in 
 reality. If one looks at a pencil so that one part is seen through 
 glass oblique to the surface, and the other part through air, the 
 pencil appears broken at the surface of the glass, on account of 
 refraction of light. 
 
 The laws of refraction are that a ray of light, in passing from 
 a rarer into a denser medium, is bent toward the perpendicular 
 at the point of incidence, while in passing from a denser into a 
 rarer medium it is bent from the perpendicular at the point 
 of incidence. (See Fig. 10.) The angle ACF is the angle of 
 
 FIG 10 
 
LESSONS IN PHYSICS. 
 
 77 
 
 incidence, BCG is the angle of refraction, and DCB is the angle of 
 deviation. The ray AC passing into the water at C is bent to- 
 ward the perpendicular FG, instead of going to D, while the ray 
 BC passing into the air at C, is bent from the perpendicular FG, 
 toward A, not going on to E. 
 
 The cause of refraction. In. the case of ether waves, the parti- 
 cles vibrate transversely to the direction in which the waves 
 move. Now, as the waves pass obliquely from one medium into 
 another that is more dense, the end that first enters the denser 
 medium seems to move more 
 slowly, while the end that is still 
 in the rare medium moving as be- 
 fore gets a little in advance, so 
 that there is a bending of the ray 
 at the surface separating the two 
 media; much as a column of sol- 
 diers changes direction by filing 
 right or left. The reverse is true 
 as the light passes into a rarer 
 medium. (See Fig. 11.) 
 
 
 FIG 1 1 
 
 \ 
 
 From A as a center (see Fig. 10) describe the circumference of a 
 circle and draw the lines ab and df. The line ab is the sine of the 
 angle of incidence ACF, and the line df is the sine of the angle of 
 refraction BCG. Now if we divide the line ab by the line df the 
 quotient will be what is called the index of refraction, which is 
 constant with the same substance but varies with different sub- 
 stances, lead chromate having the highest index of refraction, 
 2.97; the diamond next, 2.5, and flint glass next, 1.61. 
 
CHAPTER IX. 
 
 OPTICAL INSTRUMENTS RAINBOW AND COLOR. 
 
 LENSES are transparent bodies, usually glass, one or both of 
 whose surfaces are curved . The principal forms are the double 
 convex lens A, bounded by two convex surfaces; the piano con- 
 vex lens B, bounded by a plane surface and a convex surface; 
 the concavo convex lens C, in which one surface is convex and 
 the other concave, the concavity being less than the convexity ; 
 
 the double concave lens 
 D, which has two con- 
 cave surfaces ; the piano 
 concave lens E, with one 
 plane surface and the 
 other concave, and the 
 concavo convex lens F, 
 in which there is one 
 concave and one convex 
 surface, the convexity being less than the concavity. The con- 
 vex lenses diminish in width towards the edge, while the concave 
 lenses increase in width towards the edge. (See Fig. 12.) 
 
 The effect of convex lenses on rays of light may be shown by 
 tracing them through a lens according to the law of refraction. 
 Suppose MN, Fig. 13, represents a double convex lens, C and C' 
 representing the centers of curvature, and the line C C' the prin- 
 cipal axis of the lens. Now, if a ray of light from C fall upon the 
 lens at A it will be bent toward the perpendicular C'A at the 
 point A towards the point B, on emerging from the lens the ray 
 will be bent from the perpendicular CB at the point B towards 
 C'; and the ray of light from C' in the same way would be re- 
 fracted to the point C, so that C and C' are called the conjugate- 
 (78) 
 
LESSONS IN PHYSICS. 
 
 79 
 
 foci of the lens, as light diverging from one point is converged 
 to the other. 
 
 Suppose that a ray of light from H parallel with the principal 
 axis, falls upon the lens at the point A, it will be bent toward 
 the perpendicular C' A to the point of G. At G it will be bent 
 from the perpendicular CG to F, which is called the principal 
 focus, while rays diverging from the principal focus become par- 
 allel on the other side of the lens. Thus the general effect of the 
 double convex lens is to collect the rays of light. Diverging rays 
 are made to diverge less, parallel rays are made to converge, and 
 
 1 - ^_ M 
 
 F.G 13 
 
 the converging rays will be made more convergent. Experiments 
 with the other convex lenses show the same effect. The point S 
 in the center of the lens on the principal axis is called the optical 
 center of the lens. Any line, as LSO, through the optical center 
 is called the secondary axis. 
 
 The effect of the concave lenses on rays of light may be shown 
 as follows: (See Fig. 14.) Let MN represent a double concave 
 lens, C and C' being the centers of curvature. Suppose the ray 
 of light S should fall upon the lens at A it will be bent toward 
 the perpendicular CB to D, on emerging from the lens it will be 
 bent from the perpendicular C' D to F, showing that the effect of 
 
80 
 
 PRACTICAL LESSONS IN SCIENCE. 
 
 the double concave lens is to render rays parallel to the principal 
 axis divergent. 
 
 Experiments with diverging and converging rays show that 
 the general effect of the double concave lens is to disperse rays of 
 
 FIG 14 
 
 light. Experiments with the other concave lenses show the same 
 effect. 
 
 The double convex lens, or any of the convex lenses, not only 
 collect rays of light, but rays of heat as well, and are sometimes 
 called burning glasses. These lenses are also used as magnifying 
 glasses, or simple microscopes. The relations of images to ob- 
 jects in different cases are shown in the following figures (see 
 Fig. 15), in which the object is between the focus and the lens. 
 
 Let MN represent the lens whose focus is at C, and let the ob- 
 ject AB be placed between 
 
 s' 
 
 Fic.15. 
 
 point and the lens ; if we 
 trace the rays of light from 
 the object through the lens, 
 they are diverging after re- 
 fraction and cannot meet; 
 
 but if the eye receives these rays at E, they will have the same 
 effect as if they came from A' and B' ; hence the image will be 
 formed at A'B', which will be on the same side of the lens as 
 the object, erect and larger, than the object. In case the object 
 
LESSONS IN PHYSICS. 
 
 81 
 
 be placed beyond the principal focus, and less than twice the dis- 
 tance of the principal focus, the image will be inverted and larger 
 than the object. (See Fig. 16.) Again, if it is twice the distance 
 of the principal focus the image will be inverted, but of the same 
 size. (See Fig. 17.) If the 
 object be placed more than 
 twice the distance of the 
 principal focus the image will 
 be inverted and smaller. 
 
 For the image in the case of the double concave lenses (see Fig. 
 18.) MN represents a double concave lens ; suppose the object at 
 AB, the rays of light are made to diverge in passing through 
 the lens, and if received by the eye at E, they appear to come 
 from a b, and the image is on the same side of the lens as the ob- 
 ject, erect and smaller. 
 
 The compound micro- 
 scope consists of two 
 double convex lenses, the 
 smaller called the object 
 
 glass and the larger the 
 
 ' ' s ' ' 
 
 eye-piece. If the object is placed just beyond the focus of the 
 object glass, an image will be formed on the other side which is 
 inverted and larger than the object; the eye-piece is so placed 
 that the image formed by the object glass falls just within its 
 focus, so that it is again enlarged by the eye-piece, as in Fig. 15. 
 
 The refracting tele- 
 scope consists of two 
 double convex lenses, 
 the larger called the 
 object glass, the 
 smaller the eye-piece. 
 
 Fie. 1 8. 
 
 The object is so far beyond the principal focus of the object glass 
 that the image is inverted and smaller, and the eye-piece is ad- 
 justed so that the image formed by the object glass falls just 
 within its principal focus, and is magnified by the eye-piece. In 
 a microscope an object is magnified both by the object glass and 
 
 L. S. <j 
 
82 PRACTICAL LESSONS IN SCIENCE. 
 
 the eye-piece ; but in the case of the telescope the object is magni- 
 fied only by the eye-piece. . The object glass of the telescope serv- 
 ing as a light gatherer, an object glass of 20, 30 or 35 inches 
 collecting vastly more light than can the unaided eye. 
 
 The Galilean telescope consists of a double convex object 
 glass and a double concave eye-piece ; the object being more than 
 twice the focal distance of the lens, the image would be inverted 
 and smaller than the object; but between the object glass and 
 its focus the concave lens is inserted which separates or disperses 
 the converging rays, and the image is seen erect and enlarged. 
 The ordinary opera glass consists of two Galilean telescopes. 
 
 The terrestrial telescope used in surveying frequently consists 
 of four double convex lenses; the inverted image of the ordinary 
 telescope being confusing, two more lenses are added so as to give 
 an erect image of the object. 
 
 In the reflecting telescope light is gathered by a large concave 
 mirror, and the image formed is enlarged by a double convex 
 lens. 
 
 The magic lantern is an instrument by which the image of a 
 small object greatly magnified may be thrown upon a screen. It 
 consists of a dark box in which there is a strong light ; behind 
 this light there is a concave mirror, and in front of it an opening 
 from which projects a tube. At the entrance of the tube is 
 placed a double convex lens. or two piano convex lenses; inside 
 of this tube slides a smaller tube in which is fixed another 
 double convex lens. The picture or object is placed between the 
 lenses. 
 
 The first lens receiving light from the lamp, and by reflection 
 from the mirror, concentrates it upon the transparent object or 
 picture, strongly illuminating it. Light from the object goes on 
 through the second lens to a distant screen and there forms a 
 large and perfect image. 
 
 The camera consists of a dark box divided by a partition or 
 screen of ground glass. The box has openings in two opposite 
 sides, from one of which projects a tube in which slides a smaller 
 tube carrying a double convex lens. If the lens is properly 
 
LESSONS IN PHYSICS. 
 
 88 
 
 adjusted a distinct image of objects in front of it may be seen 
 upon the screen by looking through the opening in the oppo- 
 site side of the box. When the image is properly focused the 
 photographer replaces the screen by a sensitized plate, and the 
 chemical powers of the sun's rays impress a true picture of the 
 object on this plate. (See Fig. 19.) 
 
 The human eye is a camera which differs from the common 
 form of that instrument only in its wonderful perfection. 
 
 A prism is a triangular transparent body that so refracts the 
 white light of the sun as to separate it into a band of colored 
 light called the solar spectrum. The solar spectrum is made up 
 of seven colors red, yellow, orange, blue, indigo, and violet, and 
 depends upon the fact that the waves of ether which give rise 
 
 to the different colors are bent at different angles by refraction 
 through the prism. This is explained by the fact that the vibra- 
 tions which give rise to red light are longer and less rapid than 
 those which give rise to the yellow light, and are less refrangible; 
 that is, are bent less than those which give rise to yellow light, 
 and so on through the spectrum the waves which give rise to 
 violet light being shorter, more rapid and more refrangible than 
 those which give rise to any other color. Experiments show that 
 there are waves outside those which give rise to the red light, 
 which are less refrangible than the red waves, and which we may 
 recognize as heat waves; and there are other waves, which are 
 more rapid, shorter and more refrangible than the violet rays, 
 which we may recognize by their chemical effects. 
 
 To the naked eye the colors of the spectrum seem continuous, 
 but when examined through a telescope the spectrum is found to 
 
84 PRACTICAL LESSONS IN SCIENCE. 
 
 be crossed by great numbers of fine black lines, which for a long 
 time could not be explained. 
 
 Each of the elements which make up our earth gives its own 
 peculiar spectrum ; as sodium gives two yellow lines, potassium 
 two red lines and one purple line, nitrogen many lines of different 
 colors, hydrogen two lines, etc. The colors are as variable as 
 those of the solar spectrum, and vary in number through an im- 
 mense range. For instance: Iron shows as many as 450 lines, 
 while sodium shows only two. On comparing the spectrum 
 of iron with the solar spectrum, the bright lines of iron were 
 found to correspond with certain black lines in the solar spec- 
 trum, and similar results were obtained by experimenting with 
 other substances. This coincidence called for explanation. Ex- 
 perimenting with sodium vapor it was found that light passing 
 through sodium vapor gave a spectrum that was perfect, except- 
 ing that the place of the yellow light was occupied by a dark band. 
 Similar results were obtained from experimenting with the vapor 
 of other substances. These facts led to the conclusion that vapors 
 absorb the kind of light which they emit, letting the other kinds 
 pass through. And these facts led to the further conclusion that 
 the sun consists of a molten mass surrounded by an atmosphere 
 of metallic vapors, which absorb the light from the molten metals 
 within, thus giving rise to the dark lines in the solar spectrum. 
 
 An examination of the light of the fixed stars shows that 
 they are bodies like our sun, while the nebulae seem to be com- 
 posed entirely of gaseous matter. As the spectrum of the most 
 important terrestrial substances is known, the composition 
 of bodies may be determined by the spectroscope, and several 
 new substances have been discovered by its use. It has been 
 used to detect adulteration of liquids and diseased conditions 
 of the blood. By it iron, sodium, calcium, nickel, copper, 
 zinc, cobalt, manganese, aluminum, and other metals are shown 
 to exist in the sun. Hydrogen has been shown to exist in 
 hundreds of different stars. In the star Aldebaran, hydrogen, 
 iron, sodium, mercury, and five other elements common on the 
 earth are shown to exist, Some stars are so far from the earth 
 
LESSONS IN PHYSICS. 85 
 
 that light traveling with the inconceivable velocity of 186,000 
 miles per second would be fifty years or more in traversing the 
 profound space, yet with the spectroscope we can analyze that 
 light and make it tell what substance sent it out. 
 
 The rainbow is a beautiful and gigantic solar spectrum, which 
 has been formed by the refracting power of thousands of rain- 
 drop prisms. The bow is seen when the sun is back of the ob- 
 server, and sometimes a second bow may be seen outside of the 
 primary one. The primary bow is formed by light that enters 
 the upper part of the drop, is refracted, reflected and refracted 
 
 again to the observer. The second bow is formed by the light 
 which enters the lower part of the drop, is refracted, reflected 
 twice, then refracted to the observer. (See Fig. 20.) R indicates 
 red ray, V violet ray and S" the sun. 
 
 The white light of the sun falls upon all bodies alike. This 
 light is decomposed in different ways by different bodies, some of 
 it being absorbed and some reflected. One body is red because it 
 reflects the red rays, absorbing the others; another is blue be- 
 cause it reflects only the blue rays, absorbing the others. The 
 foliage of plants receives the sun's white light, decomposes it, 
 reflecting only the green rays. The petals of the rose decompose 
 the sunlight, reflecting to us the colors peculiar to itself. A body 
 
86 PRACTICAL LESSONS IN SCIENCE. 
 
 which reflects all the colors of the light it receives is white; when 
 it reflects none it is black. The clouds both refract and reflect 
 the sun-light, and all their varied colors are due to the decompo- 
 sition of light by the water vapor in the clouds of the morning 
 or evening sky. 
 
 The color of objects depends upon light. All objects are black 
 in the dark. When we paint our houses we apply to them a sub- 
 stance that has the property of reflecting the colors we desire 
 and absorbing the others. Thus bodies have no color of their 
 own. If a white body in a dark room be successively illuminated 
 by the colors of the spectrum, it appears red, yellow, orange, 
 green, etc., according to the light which illuminates it. 
 
 Red, green, and violet are called fundamental colors, since, 
 with these, all possible colors may be formed by mixture. 
 
 Two colors or tints which together give white are called com- 
 plementary colors. The following pairs of colors give white: 
 Red and bluish-green; orange and blue; yellow and indigo; 
 violet and yellowish-green. 
 
 Spectrum colors differ from pigment colors. Pigment yellow 
 and pigment blue produce green, not white. 
 
CHAPTER X. 
 
 FRICTION AL ELECTRICITY AND MAGNETISM. 
 
 IF a dry glass tube, as a lamp chimney, is rubbed vigorously 
 with a piece of dry flannel for a moment or so, it will attract 
 small pieces of paper or pith, which, after remaining a short 
 time in contact, are repelled. After being rubbed, if the glass 
 tube is held near the cheek, a gentle breeze will seem to blow 
 against the cheek, and perhaps a pricking sensation may be felt 
 and crackling sounds be heard. Like phenomena sometimes occur 
 when stroking a cat or while combing the hair with a hard-rub- 
 ber comb. Sealing wax when rubbed in the same way exhibits 
 the same property. Bodies having this property are said to be 
 electrified. 
 
 When a glass tube is rubbed with a piece of flannel, only 
 the part rubbed will be electrified, and the same is true of sealing 
 wax. In these bodies electricity does not pass from one part to 
 another; that is, they do not conduct electricity, but when met- 
 als become electrified by friction or otherwise in any of their 
 parts the electricity immediately spreads out over the en- 
 tire surface, that is, metals do conduct electricity. Bodies 
 which resist the spread or passage of electricity through them 
 are called poor conductors, or non-conductors; while others 
 which resist the passage of electricity but slightly are called 
 good conductors. The difference between these two classes of 
 bodies is in the quantity of electricity they convey, as no body 
 is absolutely a non-conductor. Nearly all the metals are good 
 conductors of electricity, and so are graphite, water, charcoal, 
 animal and vegetable bodies and other substances, while lime, 
 India rubber, silk, diamond, wax, resin, air and other bodies are 
 poor conductors. A good conductor retains electricity only so 
 
 (87) 
 
88 PRACTICAL LESSONS IN SCIENCE. 
 
 long as it is surrounded by poor conductors, as glass or air, 
 which are sometimes called insulators. 
 
 It is often desirable to detect the presence of electricity, which 
 is done by the use of the electroscope. This, in the simplest 
 form, consists of a ball of pith from a cornstalk or elder, hung 
 by a silken thread from a glass support. Now, if a glass rod 
 which has been electrified by friction is brought near the ball of 
 pith it will attract the ball, but on coming into contact with 
 the rod the ball receiving electricity from the rod is instantly 
 repelled. Now, if an electrified stick of sealing wax and an elec- 
 trified rod of glass are alternately brought near the pith ball the 
 glass rod will repel and the wax attract the ball, which seems to 
 show that the glass and wax have different kinds of electricity, 
 and that the same kinds of electricity repel each other while un- 
 like kinds attract each other. The electricity produced on the 
 glass is called vitreous or positive electricity ; that developed in 
 the wax is called resinous or negative. They are developed to- 
 gether, positive in the glass and negative in the rubber, the nega- 
 tive in the wax and positive in the rubber. The supposition is 
 that each body is endowed with neutral electricity, and by fric- 
 tion this is decomposed, one body retaining the positive and the 
 other the negative. Another curious phenomenon which compli- 
 cates matters somewhat occurs when glass is rubbed with cat- 
 skin, in which case negative electricity is developed in the glass 
 instead of positive, as when rubbed with the flannel. 
 
 In all electrical experiments the air and the apparatus should 
 be dry, many delicate experiments fail by loss of electricity 
 through the conduction of moisture in the air. 
 
 Frictional electricity seems to rest only on the surface of bod- 
 ies. An insulated conductor charged with either kind of elec- 
 tricity decomposes the neutral electricity of bodies near it, 
 attracting the opposite and repelling the like kinds. The action 
 thus excited is called induction. 
 
 Machines are made for developing electricity by friction, and 
 with them are condensers of some kind for the accumulation of 
 the electricity developed ; sometimes the condenser is part of the 
 
LESSONS' IN PHYSICS. 89 
 
 machine and sometimes separate. A common form of condenser 
 is the Ley den jar, which is a wide-mouthed jar covered inside and 
 out with tin foil for about two-thirds its height. Through the 
 wooden stopper passes a brass rod, terminating at the upper 
 extremity in a ball and at the other in a chain, which rests on 
 the bottom of the jar. The condenser in this case consists of two 
 good conductors separated by glass, a poor conductor, or insula- 
 tor. The jar is charged by connecting the inner coating with the 
 electrical machine, the other with the earth, the electricity inside 
 the jar holding or developing the opposite kind on the outside of 
 the jar by induction. The jar may be discharged by connecting 
 the two coatings of tin foil by holding the jar in one hand and 
 touching the ball with the other, which maybe done with safety if 
 the jar is a small one, or by connecting them by a wire attached 
 to a glass handle. 
 
 It has been found that smooth bodies without angles or 
 points retain electricity best. It is usually impossible to charge 
 the condenser of an electrical machine if it has points or angles, 
 as electricity passes away so quickly through them, but in 
 such cases it passes away very quietly, while in the case of 
 a smooth body the electricity is retained until the accumula- 
 tion is so great that disastrous results are liable to follow its 
 discharge. 
 
 The electricity of the atmosphere is of the same nature as 
 the frictional electricity. The air is usually positively elec- 
 trified, while the earth is negatively electrified. It is stronger 
 in summer than in winter, and during the day than in the 
 night. During cloudy weather, and on the approach of thun- 
 der storms the electrical condition of the air changes frequently 
 and rapidly. Clouds separated by dry air become Leyden jars 
 or condensers, and the electricity bursting across through the 
 non-conducting air causes lightning and thunder and often rain ; 
 again the clouds and the earth separated by dry air form a con- 
 denser, and while electricity is streaming toward the clouds 
 from every angle and point, from every tree and shrub, in some 
 places the accumulation becomes so great that it bursts through 
 
90 PRACTICAL LESSONS IN SCIENCE. 
 
 the air and lightning and thunder follow, and sometimes with- 
 ered trees, burned buildings, and loss of life is the result. 
 
 As some protection from accidents from this cause lightning 
 rods have been devised. They consist of metal, usually of iron, 
 although copper is a better material. The lightning rod should 
 be of ample size, and attached securely and closely to the build- 
 ing and to all metallic pipes about the building. It should reach 
 downward to ground that is permanently moist, and it would 
 be better if it terminated in a broad plate of metal. It should 
 extend upward for some distance above the building and termi- 
 nate in bright, sharp points. When first invented it was thought 
 necessary to separate the lightning rod from the building, but it 
 was soon discovered that it was better to connect the whole 
 building with the rod, which discharges electricity so rapidly 
 that no accumulation occurs to cause dangerous results. The 
 effects of lightning, so well known to all, show that electricity 
 can do mechanical work, as in the tearing of trees, shattering of 
 walls, etc. 
 
 To Doctor Franklin belongs the immortal honor of provingthe 
 identity of electricity and lightning. A kite was the simple instru- 
 ment which he employed. Having made a kite by stretching a silk 
 handkerchief over two sticks in the form of a cross, he went out 
 into a field accompanied only by his son; raised his kite; fast- 
 ened a key to the lower end of its hempen string ; insulated it by 
 fastening it to a post by means of a silk cord, and anxiously 
 awaited the approaching storm. A dense cloud, apparently 
 charged with lightning, soon passed over the spot where he 
 stood, without causing his apparatus to give any sign of elec- 
 tricity. He was about to give up in despair, when he caught 
 sight of some loose fibers of the hempen cord bristling up as if 
 repelled. He immediately presented his knuckle to the key, and 
 received an electric spark. The string of his kite soon became 
 wet with the falling rain ; it was then a better conductor, and he 
 was able to obtain an abundance of sparks from the key. By 
 this experiment he furnished a decisive proof of the identity of 
 lightning and electricity. 
 
LESSONS IN PHYSICS. 91 
 
 Magnetism. A magnet is a body which has the property of at- 
 tracting iron, and when suspended, so as to turn freely, of assum- 
 ing a north and south direction. The end toward the north is 
 called the north pole of the magnet, while the other end is called 
 the south pole. An ore of iron, called magnetite or lodestone, is 
 found in many localities. Lodestone was known to the ancients, 
 being found in Asia Minor, in Sweden, in the region of Lake Super- 
 ior, and in many other localities. The name lodestone or leadstone 
 seems to have been derived from the Saxon laedan,to lead. When 
 a steel bar or needle is rubbed by a natural magnet, it acquires 
 magnetic qualities and becomes an artificial magnet. Artificial 
 magnets are more powerful and convenient than lodestone mag- 
 nets, and are the only ones in ordinary use. 
 
 Magnets maybe straight, when they are bar magnets; or they 
 may be in the shape of a letter U, when they are called horseshoe 
 magnets. A bar of soft iron, called an armature, laid across the 
 poles of a magnet enables it to retain its magnetism for a longer 
 time. In the case of bar magnets they are laid in pairs, an arm- 
 ature connecting the north pole of one with the south pole of the 
 other. 
 
 If a magnet is rolled in a mass of fine iron filings, it will be 
 seen that the attractive force is stronger at the ends, gradually 
 diminishing to zero at the center. If a bar magnet, as an ordinary 
 knitting needle, is broken at the zero point, each end instantly 
 becomes a complete magnet, with strong poles and zero center 
 as before, and the same will be true however short the pieces be- 
 come. Either pole of the magnet attracts iron, but if we experi- 
 ment with two magnets, one of which is suspended, we find that 
 the north pole of one attracts the south pole of the other, but 
 repels the north pole, and vice versa; that is, poles of the same 
 name repel each other, while poles of different names attract 
 each other. The iron or steel attracted by a magnet becomes 
 itself a magnet, has a north and south pole, is polarized, and in 
 turn may polarize other pieces of iron or steel, as is shown by 
 the experiment of rolling the magnet in iron filings. If a piece 
 of writing paper is laid over a strong magnet, and then fine iron 
 
92 PRACTICAL LESSONS IN SCIENCE. 
 
 filings be sprinkled over the paper, on tapping the paper gently 
 the filings will arrange themselves in beautiful curves about the 
 poles of the magnet, showing that a magnet makes magnets 
 without contact, and all these iron filings, as secondary magnets, 
 are arranged pole to pole in regular order according to the laws 
 mentioned above. The most important use of the magnet is in 
 the construction of the compass. A slender bar magnet bal- 
 anced on a pivot, is called a magnetic needle. The compass con- 
 sists of a circular box, usually of brass, with a glass cover, in 
 which a magnetic needle is balanced over a card on which the 
 different directions are marked. The mariner's compass is so 
 mounted that whatever the motion of the ship the compass is 
 always horizontal. With it the mariner, aided by observations 
 of the sun and stars, finds his way across the trackless sea. 
 
 In general, the needle varies more or less from the true 
 north. The line of no variation passes near Cape Lookout, 
 Cleveland, Ohio, thence across Hudson's Bay to the pole, enter- 
 ing Europe just east of the White Sea, thence across the Caspian 
 Sea, and through Western Australia to the south pole, thence 
 northward through eastern South America. West of this line the 
 needle varies west, east of it the needle varies east. This line itself 
 varies east and west. In 1580, the variation of the needle, at 
 Paris was 11 30' east, showing that the line of no variation was 
 west of Paris. In 1663 this line was at Paris, while in 1825 the 
 variation was 22 22' west, showing that the line of no variation 
 was far to the east. Besides this slow variation there are annual 
 and daily variations, and variations due to volcanic eruptions 
 and earthquakes, and variations attended upon marked displays 
 of the Aurora borealis, and disturbances in the sun as shown by 
 sun spots. These latter variations are said to be due to mag- 
 netic storms or disturbances. 
 
 The magnetic needle does not remain in a horizontal position, 
 but north of the equator the north end dips, while south of the 
 equator the south end dips, so that in practice one end must be 
 weighted to keep the needle horizontal. Here again we have no 
 rational explanation of the phenomena. 
 
CHAPTER XI. 
 
 DYNAMICAL ELECTRICITY. 
 
 ABOUT the year 1786, Luigi Galvani, a professor of anatomy, 
 discovered that in the case of a recently killed frog, if one end of 
 a metal conductor, composed of zinc or copper, was placed in 
 contact with the nerves of the lumbar region and the other with 
 muscles of the thigh or leg, a prompt contraction of the muscles 
 ensued. He assumed that the electricity was inherent in the 
 animal substance; but Professor Volta from his experiments, 
 attributed to the metals the active part of the phenomena of 
 contraction. The investigations of these men and their suc- 
 cessors have led up to the dynamical electricity of to-day. 
 
 A little experiment will help us to understand how this form of 
 electricity is developed. Get a strip of sheet copper and two pieces 
 of zinc, each about five inches long and one and one-half inches 
 wide; and have a piece of No. 16 copper wire about ten inches 
 long soldered to one end of each. Fill a tumbler about two-thirds 
 full of water and add to it two tablespoonfuls of strong sulphuric 
 acid. Amalgamate one piece of zinc as follows: Dip it into the 
 acidulated water, and then pour a little mercury over the surface, 
 rubbing off any excess with a cloth. Put a piece of copper and a 
 piece of zinc that is not amalgamated into the liquid without 
 allowing them to touch each other, and vigorous action takes 
 place between the acid and the zinc, but none between it and 
 the copper. Now substitute amalgamated zinc for the other 
 and no action appears on either plate. Now, if the wires of the 
 two plates are brought in contact, gas is given off from the cop- 
 per but not from the zinc plate; and, if we separate the wires care- 
 fully, we may see a little spark of light, and the action in the fluid 
 ceases. There is no action between the liquid and the amalga- 
 mated zinc, unless it is connected with the copper. The wire 
 
 (93) 
 
94 PRACTICAL LESSORS IN SCIENCE. 
 
 conductors seem to be necessary to the action which takes 
 place. Do they acquire any new properties? Place a magnetic 
 needle near the tumbler and hold the connecting wires over 
 it, and the needle will be deflected from its north and south 
 direction, which indicates the presence of electricity in the wire. 
 
 This action is explained as follows : the zinc takes the place 
 of the hydrogen of the acid, forming zinc sulphate which re- 
 mains dissolved in the liquid, and the hydrogen is forced 
 along from molecule to molecule through the acid until it 
 reaches the copper plate where it escapes in bubbles. This action 
 is so rapid as to appear continuous, and it is believed to be the 
 cause of the electricity or electrical current in the wire, as the 
 result of the conversion of chemical energy into potential energy. 
 If this action continues the acid becomes weaker, and the zinc is 
 dissolved so that it must be renewed from time to time. 
 
 In order that water may flow from one place to another there 
 must be a difference of level ; so in the case of electricity, there 
 must be a difference in electrical conditions before there can be a 
 flow of electricity. When electricity at any place is greatly in 
 excess of that in the earth it is described as high potential, when 
 slightly in excess as low potential; when there is more electricity 
 in one body than in another again the terms high and low poten- 
 tial are used. Electricity moves from the place of high potential 
 to the place of low potential. Differences of potentials and elec- 
 tromotive force are commonly used in the same sense. The zinc 
 is positive, that is, has a higher potential than the copper, and 
 the electricity passes from the zinc through the liquid to the cop- 
 per in the attempt to restore the equilibrium of the potentials. 
 But as the chemical action is practically continuous the motion 
 toward the copper is continuous, and we have what is called an 
 electrical current. The current passes through the liquid between 
 the metal plates and through the wire connecting them, and to 
 this whole path or course of the current the term circuit is applied. 
 The wires are called the conductors, the end of the wire from the 
 copper plate is called the positive pole and the other the negative 
 pole. Separating the poles is called opening the circuit, bringing 
 
LESSONS IN PHYSICS. 95 
 
 them together is called closing the circuit. Opening the circuit 
 and filling the gap with an instrument of any kind is called intro- 
 ducing the instrument into the circuit. 
 
 The tumbler of acid with the two metals is called a voltaic cell, 
 the metals are called elements. There are several different kinds 
 of cells, but all are constructed on the same general principle. A 
 number of cells working together form a battery. By enlarging 
 the plates of the cells batteries of low resistance are made, but 
 they furnish great quantities of electricity. By increasing the 
 number of cells, batteries of high resistance and great intensity 
 may be made. No conductor, whether liquid or solid, is perfect ; 
 each resists the passage of electricity more or less. The resist- 
 ance in a circuit is principally in the cells, when it is called 
 internal, or in the conductors, when it is called external. 
 
 The greatest difference between current electricity and fric- 
 tional electricity is this : Current electricity is remarkable for 
 its great quantity but feeble intensity, while frictional elec- 
 tricity is equally remarkable for its great intensity and small 
 quantity. 
 
 If a bar of soft iron be inclosed in coils of wire, and the ends 
 of the wire be attached to the poles of a battery, the current 
 passing through the wire makes the bar of iron a magnet. Break 
 the current and the magnetism is gone. The rapidity with which 
 an iron bar may receive and part with magnetism as the current 
 is made or broken is very great; it may occur as many as 8,000 
 or 10,000 times per minute. Such magnets are called electro 
 magnets, and may be made much stronger than permanent mag- 
 nets. The induction of magnetism by current electricity is the 
 principle on which depends the working of the electric telegraph. 
 The wire connecting the battery and the coil about the soft iron 
 may be very long, even miles in length ; so the battery may be in 
 one city or town and the coil in another, and still the magnet is 
 made and an armature may be attracted every time the circuit is 
 closed. For a long time two wires were thought necessary , but it 
 was discovered that if one pole of the battery was connected with 
 the coil by a wire, and both the battery and coil connected with 
 
96 PRACTICAL LESSONS IN SCIENCE. 
 
 the earth, that the earth would complete the circuit. As the re- 
 sistance of the earth is practically nothing, less powerful batteries 
 were needed, as they had only to overcome the resistance of one 
 wire instead of two. The distance may be so great that the bat- 
 tery at one end cannot entirely overcome the resistance, in which 
 case relay batteries are introduced. In addition to the battery, 
 coil and line wire, an instrument called a key for opening and 
 closing the circuit is necessary, and a mechanical device for the 
 purpose of registering the action of the armature, which may be 
 by blows on a sounder or by marks on paper moved by clock 
 work. If the circuit is closed for an instant a dot is made on the 
 paper, or a short sound on the sounder; if for a longer time, a 
 line is made on the paper or a longer sound, and the differences 
 between the blows on a sounder, made by the dot or line closure 
 is easily distinguished by the ear, so that all first-class operators 
 work by sound. The telegraphic alphabet, consisting of dots 
 and dashes, is called the Morse alphabet, and the telegraph is 
 usually known as the Morse telegraph. But there is reason to 
 believe that while Morse introduced them to the world, they were 
 really invented by another man of whom the world has seldom 
 heard. Electric bells and electric clocks are based on the same 
 principle as the telegraph. 
 
 The magnetic needle whose deflection indicates electricity in the 
 connecting wires of the voltaic cell, is in fact a galvanoscope. 
 It may be made so that the needle hangs over a graduated circle 
 under which a coil of wire is placed, and so arranged that the 
 instrument may be introduced into a circuit. 
 
 Make two coils of wire, one containing a few feet of stout copper 
 wire, called the primary coil; and another containing a much 
 greater length of fine copper wire, called the secondary coil, and 
 make them so that the primary coil may be placed inside the 
 secondary, or removed at pleasure; connect the primary coil with 
 the battery and the secondary with the galvanometer. Now, 
 lower the primary coil into the secondary coil and the galvano- 
 meter shows the presence of a current in the secondary coil, but 
 the needle of the galvanometer soon settles to zero, showing that 
 
LESSONS IN PHTSICS. 97 
 
 the current was temporary. Draw out the primary coil and again 
 the current is shown, but in the opposite direction, and again it 
 appears to be temporary. Again place the primary coil inside 
 the secondary, then break and close the circuit and in each case 
 we have a current in the secondary coil as before. When intro- 
 ducing the primary coil, and when closing the primary circuit, an 
 inverse induction current is formed in the secondary coil, while 
 on withdrawing the primary coil or breaking the primary circuit 
 a direct current is formed in the secondary coil. 
 
 Further, it has been discovered that the same results are 
 reached by using a magnet with the secondary coil, as are 
 reached by using a primary coil. That is, if a magnet be lowered 
 into the secondary coil, an inverse current is indicated in the 
 coil, and if the magnet is removed, a direct current is indicated. 
 Now, if a bar of soft iron be placed in the secondary coil, and the 
 pole of a permanent magnet be brought near it, the soft iron 
 becomes a magnet by induction and a current is manifested in 
 the secondary coil. Now, remove the permanent magnet and the 
 soft iron ceases to be a magnet, and a current is again indicated, 
 but in the opposite direction. 
 
 Again, a permanent magnet is placed within the secondary coil 
 and a bar of soft iron is moved toward it; the magnet causes the 
 soft iron to become a magnet by induction, and this seems to 
 increase or change the magnetism of the permanent magnet, and 
 a current is indicated in the secondary coil, and a current in the 
 opposite direction is shown on the removal of the soft iron. 
 
 The same effect maybe obtained if an electro-magnet be placed 
 within the secondary coil and a strong magnet rotate rapidly 
 in front of it, so that its pole acts inductively upon the branches 
 of electro-magnet in succession. 
 
 Similar results may be obtained by passing coiled wire around 
 the poles of a permanent horseshoe magnet, and revolving the 
 plate of soft iron in front of the poles of the magnet. The soft 
 iron becoming magnetized acts on the permanent magnet, and 
 alternate currents are induced in the coils of the wire. 
 
 On the principles just mentioned many different kinds of ma- 
 
 L. S. 7 
 
98 PRACTICAL LESSONS IN SCIENCE. 
 
 chines or dynamos have been constructed by which electricity 
 may be transformed into work. 
 
 The dynamo electric machine, or the dynamo, consists of an 
 iron core wound with long coils of wire constituting the arma- 
 ture, which revolves between the poles or within the field of a 
 powerful electro-magnet, called a field magnet. The armature is 
 rotated by steam, and the currents induced are gathered up for 
 transmission by brushes of copper wire. These machines vary 
 greatly in detail, but all contain the above essentials. The 
 energy generated in the dynamo is transmitted through wires to 
 a similar machine called a motor, which transforms the electrical 
 energy into mechanical work. 
 
 The energy developed in the dynamo may be transmitted to 
 electric lamps where it is transformed into light. If the termi- 
 nals of the wires from a dynamo are connected with pencils of 
 carbon and these brought near each other, their tips are intensely 
 heated, some of the carbon being volatilized. This vapor, a con- 
 ductor of high resistance, attains a very high temperature, 
 emitting intense light. The light of the incandescent lamps is 
 produced by introducing some refractory substance of lower con- 
 ducting power into the circuit, which soon becomes heated to 
 incandescence. The substance commonly used is carbon, inclosed 
 in a glass bulb from which the air has been exhausted. 
 
 The value of the dynamo machines and the conducting wires 
 is not in gain of power, but in the distribution of power. The 
 heat energy which drives a great engine may through the dynamo 
 and conducting wires be distributed to hundreds of motors in 
 different parts of a city, to hundreds of arc lamps or thousands 
 of incandescents. 
 
 The power of falling water, as at Niagara Falls, may be trans- 
 formed through turbine wheels and dynamos into electric energy, 
 which may be transferred through long distances, even as far as 
 Buffalo, and then through motors be transformed to light or 
 mechanical work. In this way water power becomes as available 
 as steam power, and much cheaper. 
 
 The dynamo is also used in charging storage batteries, A 
 
LESSONS IN PHYSICS. 99 
 
 storage battery consists of two lead plates, which have been 
 coated with the red oxide of lead, and these with a layer of paper 
 or cloth between them suspended in dilute sulphuric acid. When 
 these plates are connected with the terminals of a dynamo, a 
 portion of the water is decomposed, the lead oxide of the posi- 
 tive pole is peroxidized, and that of the negative pole reduced 
 to metallic lead of a spongy form. The electrical energy has been 
 transformed into chemical energy. The plates will remain in 
 this condition for several days if the circuit is left open, and may 
 be transported for long distances and used as ordinary voltaic 
 cells are used. They are used for moving cars, boats, wagons, etc. 
 The principles just given enable us to explain the action of the 
 Bell Telephone. It consists of a permanent bar magnet with a 
 coil of wire about one of its poles; a thin disk of sheet iron, 
 called a diaphragm, very near but not touching the pole of the 
 magnet ; two wires, one leading from the coil to the second in- 
 strument, the other to the earth. At the other end of the line is 
 a second instrument of the same kind. The speaker puts his lips 
 to the mouth of the instrument and speaks, while the listener at 
 the other end hears what is said. The air waves of the voices 
 vibrate the diaphragm of soft iron ; these motions to and from 
 the pole of the magnet strengthen or weaken the magnetism, and 
 this sends electric pulses through the wire to the distant station ; 
 the electric pulses from the transmitting telephone act through 
 the coil of the receiving telephone at the other end of the line, 
 and alternately strengthen and weaken its magnetism, and as 
 the strength of the magnet varies the thin disk springs back and 
 forth. These vibrations of the disk produce air waves, which 
 enter the ear of the listener. Vibrations in the disk of the re- 
 ceiving instrument are the same as those of the disk in the trans- 
 mitting instrument, and the air waves formed by the disk in the 
 receiving instrument are the same as those which caused the 
 vibrations of the disk in the transmitting instrument; and the 
 two sets of air waves will affect the ear in exactly the same way, 
 so that the voice at the transmitting instrument is reproduced in 
 the receiving instrument; hence by the telephone sound waves 
 
100 PRACTICAL LESSONS IN SCIENCE. 
 
 are converted into electric pulses in the transmitter, and these 
 electric pulses reaching the receiver are converted back again 
 into sound waves. 
 
 The Telautograph is an electrical instrument by which writing 
 or drawing may be reproduced at a distant station. "A common 
 lead pencil is used to write the message; near its point are fast- 
 ened at right angles to each other, two silk cords, which, con- 
 necting with the instrument, follow the motion of the pencil and 
 control the receiving pencil at the other end." 
 
 "At the receiving station two aluminium arms hold the ca- 
 pillary glass tube which serves as a pen. This pen is guided by 
 the electrical impulse from the sender, and moves simultaneously 
 and in like direction and extent with every motion of the distant 
 pencil, so that the ink tracing which results must be a fac-simile 
 of whatever the sender writes or draws." It conveys a written 
 message, as the telephone conveys a spoken message. 
 
 A piece of No. 30 copper wire about 9.7 feet long has a resist- 
 ance of one ohm, and is used as a unit in measuring the resistance 
 of wires to the passage of electricity. The difference in potentials 
 is measured in volts, and the unit of current strength is the 
 ampere, but these units are not as definite as the ohm. Many 
 other interesting subjects might be discussed under the head of 
 physics, but the subjects considered seem to be sufficient for the 
 development of the general principles of this branch of science 
 and for the illustration of their more important applications. 
 
CHAPTER XII. 
 
 CHEMISTRY HISTORICAL AND GENERAL. 
 
 CHEMISTRY is a branch of natural science which has always 
 been of great interest to mankind. There is ample evidence to 
 show that even before historic times men were able to extract 
 several of the useful metals from their ores, knew something of 
 the processes of tanning, dyeing, soap making and glass making; 
 could mix mortar and paints, and do many other things which 
 indicate considerable knowledge of practical chemistry. 
 
 But these ancient people do not seem to have had any knowl- 
 edge of the laws of chemical changes or any definite idea of the 
 chemical elements. In the time of Aristotle, 350 B.C., the four 
 elements were fire, hot and dry, air, hot and wet, earth, cold 
 and dry, and water, cold and wet. The qualities mentioned are 
 physical, not chemical. The elements, according to the Hindoos, 
 were earth, air, fire, water and ether. Among the Chinese they 
 were earth, fire, water, metal and wood; but in no case do the 
 ancients seem to have recognized chemical qualities. 
 
 The first mention of chemistry is found in a dictionary of the 
 llth century, where it is defined as the preparation of silver and 
 gold. In the 16th century Paracelsus says the true use of chem- 
 istry is not to make gold but to prepare medicines. In the works 
 of Glauber (1604-1668) he speaks of various compounds of iron 
 and copper, and of sulphuric, nitric, and hydrochloric acids, but 
 gives no idea of their composition. He also states that salt and 
 mercury are the principles of all metals, and that salt is the 
 origin of all things, and that water and earth have produced all 
 the minerals and metals. 
 
 Georg E. Stahl (1660-1734), whose researches gave rise to a 
 marked advance in chemistry, enumerated four elements, water, 
 acid, earth, and phlogiston. Phlogiston was supposed to be a 
 constituent of all combustible bodies, and it was believed that 
 
 (101) 
 
102 PRACTICAL LESSONS IN SCIENCE. 
 
 when bodies burned the phlogiston made its escape, and the resi- 
 due was regarded as the substance with which the phlogiston 
 had been combined. The British chemist, Black, about 1750, 
 began to use the balance as an aid in chemical investigation. 
 
 About 1774 Dr. Joseph Priestly discovered and isolated 
 oxygen, but called it dephlogistigated air. Scheele, a Swedish 
 chemist, discovered oxygen the next year, and the French chem- 
 ist, Lavoisier, claimed to have discovered the same gas independ- 
 ently of the others. He at least understood the nature of the 
 gas better than the others, and in 1781 gave it its present name, 
 oxygen, " acid-former," as he had recognized that it was an 
 essential ingredient in several important acids. Lavoisier pointed 
 out the fallacies of the phlogiston theory, and gave the received 
 explanation of combustion. He also introduced system into 
 chemistry and chemical research, and by many is called the 
 father of modern chemistry. 
 
 The discovery of oxygen has been called the capital discovery 
 of the last century, rivaling in importance the great discovery 
 of Newton in the previous one. It formed one of the great eras 
 in human progress. It resulted in gradually putting away old 
 and fanciful theories, the outgrowth of limited knowledge, and 
 laid the foundation of modern chemical science. It opened a 
 way to a knowledge of the composition of the air and of water, 
 of plants and animals. It may be said to have changed the 
 manners, customs and business habits of the world. More than 
 anything else it has explained the phenomena and opened up 
 the resources of the material universe. 
 
 The introduction of instruments for weighing has been of im- 
 mense value in chemical science, even rivaling the discovery of 
 oxygen. One of the greatest discoveries of modern times is the 
 truth that nature works with the same exactness on the small 
 scale as on the large. It is the glory of Newton to have proved 
 that the movements of all celestial and terrestrial bodies are 
 regulated by mathematical law. "It has been established by 
 chemists that the minutest particles of matter, in their actions 
 and reactions, obey law, and that every chemical compound has 
 
LPJSSONS IN CHEMISTRY. 103 
 
 a mathematical constitution as fixed as that of the solar system 
 itself. The stones and soil beneath our feet, and the ponderous 
 mountains, are not mere confused masses of matter; they are 
 pervaded throughout their innermost constitution by the har- 
 mony of numbers, The fuel we burn wastes away before us, dis- 
 solves in air, and passes beyond the reach of sight ; but the in- 
 visible changes among the unseen particles are definite, exact, 
 and harmonious. And so it is with all chemical mutations." It 
 was found that, however often matter might change its form, 
 nothing was either gained or lost that its quantity always re- 
 mained the same ; and it was likewise discovered that the con- 
 stituents of chemical compounds are always combined in the 
 same definite proportions. 
 
 Chemistry deals with those phenomena of matter and energy 
 which involves some change in the composition of bodies. The 
 combination of two or more simple substances into one substance 
 possessing properties different from those of either of the compo- 
 nents is a chemical process. If we mix carefully powdered sulphur 
 and copper filings, they remain sulphur and copper and may be 
 separated ; but if they are heated strongly the sulphur combines 
 with the copper forming a compound which shows none of the 
 peculiar properties either of copper or sulphur. This illustrates 
 something of the difference between a physical mixture and a 
 chemical combination. The liquid, water, may be separated into 
 the gases oxygen and hydrogen. A piece of wood is composed 
 mainly of the gases, oxygen and hydrogen, and the solid, carbon. 
 When wood is burned, oxygen of the wood and of the air unites 
 with the hydrogen forming steam, which may be condensed into 
 water. Other portions of oxygen unite with some of the carbon 
 forming carbonic acid gas ; some of the carbon may be left as 
 charcoal; some, very finely divided, may be carried away with 
 the steam, making a black smoke from which the carbon may be 
 collected as soot; and in the ash are several mineral ingredients 
 which existed in small quantities in the wood. The various 
 reactions which take place in all kinds of combustion, whether 
 alow or rapid, are chemical changes. 
 
104 PRACTICAL LESSONS IN SCIENCE. 
 
 Another difference between a physical mixture and a chemical 
 combination is that the former may consist of any possible 
 proportion of the ingredients, while in the case of chemical com- 
 binations the proportions are definite. Take the case of sulphur 
 and iron; they may be mixed in any proportion, but they com- 
 bine in the proportion of 56 parts of iron to 32 parts of sulphur. 
 If there is either too much sulphur or too much iron, the surplus 
 does not enter into the combination. In the case of oxygen and 
 sulphur the proportion of the chemical combination is 32 of oxy- 
 gen and 32 of sulphur. Experiments with many substances have 
 led chemists to the conclusion that chemical combinations always 
 occur between definite weights of substances. In some cases the 
 weight of a substance may vary in different combinations, but in 
 every such case some number can be found which shall express 
 the combining weight, or the weight will be some simple multiple 
 of that number. 
 
 Some of the ancients considered matter as made up of atoms, 
 but the idea was never more than a speculation. And when it 
 had been proved that chemical combinations were in definite 
 proportions, the old idea of atoms assumed a different position. 
 Dr. Dalton, who, early in this century, discovered and announced 
 the law of definite and multiple proportions, saw that the con- 
 ception that matter is made up of indivisible particles or atoms 
 might have some connection with this law. As a result of his 
 studies he conceived that the law might be explained by assum- 
 ing that all matter consists of indivisible, unchangeable par- 
 ticles, or atoms; that atoms of the same kind have the same 
 weight, while those of different kinds have different weights, and 
 that the combining weights of chemistry represent these atomic 
 weights. The supposition is that atoms of iron and atoms of 
 sulphur unite to form molecules of the compound substance, 
 sulphide of iron, so of the oxygen and sulphur, and other chem- 
 ical combinations. Atoms are considered the units of simple 
 substances or elements, and molecules, made up of atoms, are 
 the units of compound substances. The artomic theory, and the 
 law of definite and multiple proportions in chemical combinations 
 
LESSONS IN CHEMISTRY. 105 
 
 may not be at once apprehended, but they underlie the whole 
 work of chemistry and will become clearer and more satisfactory 
 with every step of chemical investigation. 
 
 Chemists have discovered and isolated some seventy or more 
 elements which make up the earth as we know it. The composi- 
 tion by weight, of the crust of the earth is as follows : Oxygen 
 45 per cent., silicon 25 per cent., aluminium 9 per cent., iron 
 8 per cent., calcium 5 per cent., magnesium 2 per cent., so- 
 dium 2 per cent., potassium 2 per cent. If we add to these 
 elements hydrogen, nitrogen, carbon, chlorine, iodine, phos- 
 phorus and sulphur we not only have those that make up the 
 solid crust of the earth, but the constituents of the air, water, 
 plants and animals as well, fifteen elements which those must 
 study who pursue chemistry as a branch of general education, 
 since a knowledge of their properties is essential to the expla- 
 nation of those chemical changes which are common about us 
 everywhere. Several other elements are interesting and will re- 
 ceive brief consideration. It is the study of the laws in accord- 
 ance with which the elements combine with one another, and of 
 the properties of the elements and of the compounds formed by 
 them, which constitutes the science of chemistry. 
 
 The elements are divided into metallic elements, as iron, copper, 
 aluminium, sodium, mercury, etc., and non-metallic elements, as 
 oxygen, hydrogen, nitrogen, silicon, etc. The metals generally are 
 better reflectors of light and heat, better conductors of heat and 
 electricity, and as a rule have a higher specific gravity than the 
 non-metals. All these elements are designated by symbols, which 
 usually consist of the initial letter of the English or Latin name 
 of the element, as for oxygen, C for carbon, Si for silicon, Cl 
 for chlorine, Fe for iron, from its Latin name ferrum; Na for 
 sodium, from its Latin name natrium; K for potassium, from 
 its Latin name kalium ; Ca for lime, from calcium, its Latin 
 name. The symbols for other elements will be given as they are 
 described. The various sub-groups into which the elements seem 
 to be naturally divided can be more intelligently considered as 
 the elements are studied more in detail. 
 
CHAPTER XIII. 
 
 OXYGEN, HYDROGEN AND WATER. 
 
 OXYGEN is a colorless, odorless, tasteless gas that constitutes 
 nearly one-half the weight of the solid crust of the earth, eight- 
 ninths of the water, one-fifth of the air, and enters largely into 
 the composition of all vegetable and animal bodies. Its symbol 
 is 0, and its combining weight 16. While it is so abundant, so 
 important in every way, it was not known, or isolated so that 
 its properties could be studied until the year 1774. Its discovery 
 marks an era not only in the growth of chemical science, but in 
 the progress of human affairs. 
 
 Oxygen may be prepared by heating crystals of potassium 
 chlorate in a test tube over a spirit flame; it soon melts into a 
 clear liquid which presently begins to boil from the escaping 
 bubbles of gas. That the gas is oxygen may be shown by 
 thrusting into the tube a stick whose end is a glowing coal, when 
 it will burst into flame, burning with great vigor. Any substance 
 that burns in air burns much more rapidly in oxygen. Take a 
 piece of wire and wind about one end of it a piece of twine 
 and soak the twine in melted sulphur, then ignite the sulphur 
 and thrust the wire into a jar of oxygen, the burning sulphur 
 ignites the iron, which burns brilliantly as long as the oxygen 
 lasts. 
 
 Another very common method of preparing oxygen in a small 
 way, is from the red oxide of mercury, which yields, when heated, 
 the liquid mercury and the gas oxygen. If the oxide be weighed 
 carefully, and after the decomposition the mercury and the 
 oxygen are weighed, their weight will be found to be equal to the 
 original weight of the oxide, which is thus shown to have con- 
 tained only oxygen and mercury in chemical combination. The 
 heat applied overcame the force of chemical attraction and the 
 (106) 
 
LESSONS IN CHEMISTRY. 107 
 
 compound was decomposed into its original elements. The red 
 oxide of mercury is represented in chemistry by the symbol 
 HgO, which signifies that it is a compound whose molecule con- 
 tains one atom of mercury and one atom of oxygen, and the 
 proportion of the components by weight is 200 parts of mercury 
 and 16 parts of oxygen. 
 
 The chemical formula of potassium chlorate from which 
 oxygen is usually prepared for laboratory purposes is KC10 3 , 
 which indicates a compound body whose molecule is com- 
 posed of one atom of potassium, one atom of chlorine and 
 three atoms of oxygen; by weight there are 39 parts of 
 potassium, 35.5 parts of chlorine and 48 (16X3) parts of oxy- 
 gen. Potassium chlorate however made, wherever found al- 
 ways contains these substances, and in the proportions named. 
 The decomposition may be represented by an equation as 
 KC10 3 , after heating strongly equals KC1, potassium chloride, 
 +0 8 , the atoms of oxygen. The KC1 a solid, remains in the tube 
 or retort, and the oxygen is collected in jars over water. 
 
 The heat, strong enough to separate all the oxygen from the 
 original compound, was not sufficient to separate the chlorine 
 from the potassium. This shows that the attraction of the 
 potassium for the chlorine is stronger than the attraction of the 
 two, as combined, for the oxygen, which illustrates the general 
 fact that the elements differ widely in their attractions for each 
 other, which is a prominent feature in all chemical reactions. 
 
 In preparing oxygen in quantity a glass or metal flask of ap- 
 propriate size is used, and the gas is collected in jars over water, 
 or in regular gas receivers. The jars are immersed in water, then 
 inverted and placed on a perforated shelf so adjusted that the 
 mouth of the jar will be just below the surface of the water. The 
 delivery tube conducts the gas under the mouth of the jar, which, 
 rising through the water crowds it out, occupying its place in the 
 jar. When wanted for experiment, a piece of glass or board may 
 be slipped under the mouth of the jar, which may then be in- 
 verted. As the gas is heavier than air it can be retained in the 
 jar for some time, even though it be covered loosely. 
 
108 PRACTICAL LESSONS IN SCIENCE. 
 
 The most marked characteristic of oxygen is its prompt and 
 vigorous support of combustion. But combustion, whether slow 
 or rapid, is a chemical process, and when we remember the wide 
 dispersion of oxygen, being found in chemical combination every- 
 where, we judge that it must be an extremely active chemical 
 agent, and yet at ordinary temperatures its action is by no 
 means vigorous. But if substances are heated to a greater or 
 less degree before being brought into contact with oxygen, it 
 unites promptly with most of the elements, making an endless 
 variety of compounds. 
 
 Sulphur burns in the air; it burns with greater vigor in oxy- 
 gen than in air. Sulphur has but a slight odor, oxygen has 
 none; and yet, after burning sulphur, whether in air or oxygen, 
 a pungent, suffocating odor is present, the odorless sulphur and 
 oxygen have disappeared and something with a pungent odor 
 remains. If a piece of charcoal, nearly pure carbon, be ignited 
 and thrust into a jar of oxygen it burns fiercely for a few moments, 
 then gradually ceases. Some of the charcoal has disappeared, 
 the oxygen is gone and in their place is a gas in which the char- 
 coal will not burn and which quickly extinguishes a lighted candle 
 thrust into it. 
 
 In the first case, the oxygen combined with the sulphur form- 
 ing a gas whose molecule contains one atom of sulphur and two 
 atoms of oxygen, its chemical symbol is S0 2 and it is called sul- 
 phur dioxide. The chemical equation is S + 2 = S0 2 . In the 
 other case, oxygen united with carbon forming a compound 
 whose molecule contains one atom of carbon and two atoms of 
 oxygen called carbon dioxide. The equation is C + 2 = C0 2 . If 
 we had used phosphorus, only a slight elevation of temperature 
 would have been necessary to start the chemical action. More 
 was needed in the case of sulphur, more still in the case of carbon ; 
 but when started in each case it continued vigorously till the 
 oxygen was all gone. 
 
 As soon as one atom of sulphur or carbon combined with 
 two atoms of oxygen their activity ceased, their attractive 
 powers had been satisfied. As these atoms rushed together 
 
LESSONS IN CHEMISTRY. 109 
 
 under the action of chemical attraction, the collision gave rise 
 to the heat and light which attended the action. The heat 
 and light of chemical action being due in reality to atomic per- 
 cussion as the hammer and iron become warm from the blows 
 necessary to shape the iron. As the sulphur and carbon burn in 
 the air, forming the sulphur dioxide in one case and carbon 
 dioxide in the other, we have reason to suppose that oxygen 
 exists abundantly in the air. 
 
 Combustion means any chemical action attended by the evolu- 
 tion of heat, but is usually restricted to the union of oxygen with 
 other substances which results in the evolution of heat and light. 
 Substances which unite with oxygen are said to be combustible, 
 those that do not are incombustible. Most of the elements are 
 combustible, but the compounds resulting from combustion, as 
 the sulphur arid carbon dioxides, are incombustible. Chemical 
 action, or combustion, always produces the same amount of heat 
 whether the action be rapid or slow. When it is slow the heat 
 escapes by conduction or otherwise almost as rapidly as it is 
 formed, so that there is at no time any great intensity of heat and 
 no light, while if the combustion is rapid the heat becomes intense 
 and is accompanied with light as well. 
 
 . The amount of heat generated by chemical action may be 
 measured. This is done by causing the action to take place 
 in such a manner that the heat resulting may, without waste, 
 be applied to raising the temperature of water. The quantity 
 of heat is shown by the number of grams of water it will 
 raise one degree in temperature. From careful experiments in 
 this direction, it has been shown that the chemical combi- 
 nation not only contains definite unvarying proportions of 
 simples, but that in its formation a definite unvarying amount 
 of heat was generated. Chemical combination and the evolution 
 of heat represent work done. When the carbon united with the 
 oxygen forming carbon dioxide, a certain amount of heat was 
 given off, a definite amount of work was done, and the same 
 amount of work will be necessary to separate the oxygen from 
 the carbon as was developed in bringing them together. The law 
 
110 PRACTICAL LESSONS IN SCIENCE. 
 
 of conservation of energy holds in chemical as well as in physical 
 phenomena. 
 
 Combustible substances are endowed with potential energy; 
 they can do work. The carbon of the coal, uniting with oxygen 
 generates heat which converts the water into steam, whose ex- 
 pansive force acting through machinery does manifold kinds of 
 work. The carbon dioxide formed by the respiration of animals 
 by many kinds of slow combustions has no potential energy, 
 but plants under the influence of sunlight can separate the carbon 
 from the oxygen and the carbon stored up in wood, coal, oil, or 
 gas, has acquired potential energy, can do work. Potential en- 
 ergy, derived from the sun, stored up in coal, oil and gas, millions 
 of years ago, is now doing a great part of the work of the world. 
 This is an interesting illustration of one of the wonderful econo- 
 mies of nature. 
 
 The compounds of oxygen with other elements are called ox- 
 ides. Thus the union of oxygen and mercury forms mercuric 
 oxide, composed of one part of mercury to one part of oxygen. 
 In some compounds, called dioxides, there are two atoms of oxy- 
 gen, as the carbon dioxide, and sometimes there are trioxides, as 
 in the case of sulphur. In the case of copper there are two oxides, 
 whose formula are Cu 2 0,the oxide of copper, or cupric oxide, 
 and CuO, suboxide of copper, or cuprous oxide. 
 
 HYDROGEN is a colorless invisible gas having neither odor nor 
 taste, and is the lightest substance known. Its symbol is H and 
 its combining weight I. Its weight is considered as the unit of 
 the system of combining weights. It has been found free in vol- 
 canic gases, but usually exists in combinations with other sub- 
 stances, making up one-ninth of the weight of water, and forming 
 a constituent part of all vegetable and animal bodies. Hydro- 
 gen is in many respects the most interesting of all the elements. 
 It unites with oxygen to form water, and by the decomposition 
 of water we may obtain both of these gases. 
 
 Water may be decomposed by the voltaic current, oxygen be- 
 ing given off at the positive pole and hydrogen at the negative. 
 
LESSONS IN CHEMISTRY. Ill 
 
 Some of the metals decompose water. Throw a small piece 
 of the metal potassium on water ; it takes fire, burning with a 
 fine violet flame floating about as a melted globule on the sur- 
 face of the water. The potassium unites with the oxygen in the 
 water, and the heat generated is intense enough to ignite the 
 hydrogen which has been set free, and is also sufficient to 
 vaporize some of the potassium which gives the violet color to 
 the flame. 
 
 The metal sodium behaves much like potassium, only that the 
 heat is not quite sufficient to ignite the hydrogen. These experi- 
 ments are interesting, but for preparing hydrogen in quantity, a 
 simple process consists in passing steam over red-hot iron. The 
 iron combines with oxygen of the water, forming the black oxide 
 of iron (Fe 3 4 ) the hydrogen passes on and is collected in jars over 
 water. The equation is as follows : 4H 2 0, steam -f- Fe 3 = Fe 3 4 , 
 oxide of iron -f H 8 . While the decomposition of water by po- 
 tassium and sodium at ordinary temperatures is prompt and 
 spontaneous, iron must be heated to a red heat before it can sep- 
 arate oxygen from hydrogen. 
 
 The most convenient method of preparing hydrogen for use 
 is by treating a metal, as zinc, with a strong acid. Put two 
 or three pieces of granulated zinc into a test tube and pour 
 upon them some dilute sulphuric acid. A brisk action takes 
 place immediately, gas being given off in abundance. After 
 the action has continued for a few moments, bring a lighted 
 match to the mouth of the tube and the gas takes fire with a 
 slight explosion, burning with a pale flame. In preparing the 
 gas in a larger way, use a wide-mouthed bottle with a cork hav- 
 ing two holes ; through one of these pass a glass funnel whose 
 stem is long enough to reach nearly to the bottom of the bottle; 
 through the other hole pass the delivery tube. Use zinc and acid 
 as before, being sure that the funnel tube extends below the sur- 
 face of the acid in the bottle. After the chemical action has con- 
 tinued long enough so that all of the air has been driven out of 
 the bottle, the gas may be collected over water as in the case of 
 oxygen. Acid may be added through the funnel if the action 
 
112 PRACTICAL LESSONS IN SCIENCE. 
 
 becomes too weak. Care should be taken to see that the bottle 
 is closely corked so that the gas shall be free from air, as hy- 
 drogen with a little air makes an explosive mixture of great 
 vigor. 
 
 The chemical equation in the preparation of hydrogen by this 
 method is as follows : Zn, Zinc-f-H 2 S0 4 , sulphuric acid ZnS0 4 , zinc 
 sulphate +2H, that is one atom of zinc has taken the place of two 
 atoms of hydrogen, forming zinc sulphate and free hydrogen. 
 Hydrogen may be kept in an inverted jar for some time, but 
 quickly escapes from one that is upright. It can be poured up 
 but not down. Hydrogen or some of its compounds is used for 
 filling balloons. It is combustible, but must be heated up to the 
 kindling temperature when it unites vigorously with oxygen. The 
 temperature of the hydrogen flame is higher than that of any 
 other flame known. The oxyhydrogen flame, while giving very 
 intense heat gives but little light. But if a cylinder of lime be 
 put in the focus of this flame, it is soon heated to incandes- 
 cence and gives out a light second only to that developed by 
 electricity. 
 
 Oxygen and hydrogen combined form water, whose molecule 
 is composed of one atom of oxygen and two of hydrogen ; for- 
 mula H 2 0. Two volumes of hydrogen combined with one volume 
 of oxygen forming two volumes of water vapor or steam. 
 
 Water can be produced from a mixture of oxygen and hydro- 
 gen. If we introduce into a stout test tube a mixture of two 
 volumes of hydrogen and one of oxygen, on touching a lighted 
 match to the mixed gas it explodes, the hydrogen burning rap- 
 idly, so that a flash of flame fills the tube. After the explosion 
 water will be found deposited as dew on the sides of the tube. In 
 this experiment there is no attempt to measure the waterformed, 
 but careful experiments show that all the oxygen unites with all 
 of the hydrogen, forming the corresponding amount of water 
 vapor or steam. 
 
 In the decomposition of water by the voltaic current the 
 volume of the hydrogen is double that of the oxygen, and that 
 experiment seems to show that water contains only oxygen and 
 
LESSONS IN CHEMISTRY. 113 
 
 hydrogen in its composition. Pure water has been decomposed 
 by the action of several different metals and by the electric 
 spark. It has been analyzed and found to contain only the gases 
 oxygen and hydrogen. 
 
 Pure water at ordinary temperature is a clear transparent 
 liquid, tasteless, odorless and neutral in its reactions. It is es- 
 sential to the life of plants and animals, forming the chief in- 
 gredient of all the liquids they contain. It is the standard for 
 obtaining the specific gravity of solids and liquids. It is the 
 standard for the measurement of specific heat. It is an abundant 
 ingredient of many rocks. Its presence or absence determines 
 whether a region shall be a barren waste or a teeming garden. As 
 a chemical compound, the combining tendencies of water extend 
 over a wider range than those of any other compound. Its com- 
 binations with other substances are usually called hydrates. 
 Water combines with the elements bromine and chlorine, forming 
 an exception to the general rule that combinations do not take 
 place between elementary and compound bodies. Water dis- 
 solves more substances than any other liquid known, so that in 
 nature pure water is seldom or never seen. But it may be easily 
 purified by filtration and distillation. 
 
 The purest water in nature is rain water, which falls after it has 
 rained for some time. During the first part of the storm the rain 
 washes dust and impurities out of the air, so that later the water 
 is nearly pure. Large quantities of natural waters contain car- 
 bonate of lime in solution, and are called hard waters, forming 
 deposits on the inside of boilers and kettles. Others contain iron, 
 salt, soda and other minerals, some of which are of medicinal value. 
 The solvent power of water is of great value in chemical operations, 
 as well as in the operations of nature. In some cases substances 
 which do not act upon one another when dry act promptly when 
 in solution, the particles come into more intimate contact and 
 chemical action seems to be facilitated. In solutions the particles 
 of the dissolving liquid seems to have some attraction for the 
 particles of the dissolved substances so that they are uniformly 
 distributed through the solution, but this attracting power may 
 
 L.S. 8 
 
114 PRACTICAL LESSONS IN SCIENCE. 
 
 be saturated, and any amount added beyond this limit gradually 
 settles to the bottom of the solution. 
 
 Oxygen and hydrogen, whether free or combined as water, are 
 the most important and interesting substances within the do- 
 main of chemistry. They are alike in most of their physical 
 qualities, but differ widely in their chemical properties. Oxygen 
 combines with many substances with which hydrogen does not 
 combine, while hydrogen combines with some substances which 
 do not readily combine with oxygen, but under favorable condi- 
 tions they combine with each other. In fact, in this case and in 
 many others, unlike elements combine more freely than those 
 which have many properties in common. 
 
CHAPTER XIV. 
 
 NITROGEN, THE AIR, AMMONIA AND NITRIC ACID. 
 
 THE air, an invisible, tasteless, odorless gas surrounds us every- 
 where. In motion it is wind, from which we may recognize not 
 only the existence of the air but something of its power as well. 
 It has weight, as shown by the action of the common pump and 
 mercurial barometer. 
 
 The air contains oxygen as shown by the fact that the same 
 products arise from burning sulphur, carbon and other sub- 
 stances in the air, that arise from burning those substances in 
 oxygen. But combustion in the air is not as prompt and vig- 
 orous as it is in oxygen, so that the oxygen of the air seems to be in 
 a sense diluted. On a broad piece of cork, or bit of board, fasten a 
 porcelain, crucible or a piece of earthenware; place it on the surface 
 of water; put on the porcelain a piece of phosphorus about the 
 size of a pea and set fire to it, then invert a jar over the burning 
 phosphorus, at first the heat of combustion may drive out a 
 few bubbles of air, but soon the water will rise in the jar, taking 
 the place of oxygen used in the combustion. The white clouds 
 which fill the jar at first is oxide of phosphorus, which the 
 water at length absorbs, and a transparent, tasteless, odorless 
 gas remains, but does not fill the jar. If we measure the jar 
 carefully it will be found that water occupies about one-fifth of 
 its capacity, the gas occupying the balance. 
 
 This gas is called Nitrogen, its symbol is N, and its combining 
 weight 14. If an experiment is carefully performed it will show 
 that the air is composed of about 21 per cent, of oxygen to 79 
 per cent, of nitrogen. Close the jar and invert it, then lower into 
 it a lighted candle and it is extinguished. Confine in it a mouse 
 or a bird and it dies ; the gas will not support combustion, it will 
 not support life. Nitrogen is prepared in quantity by passing 
 
 (115) 
 
116 PRACTICAL LESSONS IN SCIENCE. 
 
 air over red-hot copper, the oxygen combines with the copper 
 forming copper oxide, leaving the nitrogen free. Oxygen enters 
 into many combinations, and compounds of oxygen are gener- 
 ally stable, while nitrogen enters into comparatively few combi- 
 nations and they are generally unstable, breaking up under the 
 least provocation. 
 
 Besides occurring in the air nitrogen is an essential ingredient 
 of animal and vegetable substances, and is an important ingredi- 
 ent in many other interesting compounds. Besides the oxygen 
 and nitrogen the air always contains more or less water vapor, 
 carbon dioxide or carbonic acid, ammonia and small quantities 
 of other gases, and the lower portions are often loaded with 
 various kinds of dust. The air seems to be simply a mechanical 
 mixture of these various gases and not a chemical compound. 
 If the oxygen and nitrogen were in chemical combination we 
 would expect the proportions by weight to be as 14 of nitrogen 
 to 16 of oxygen, or in some multiple of those numbers, but the 
 proportion is as 23.10 of oxygen to 76.90 of nitrogen, and when 
 these gases are mixed in this proportion, under no circumstances 
 is there any generation of heat, light or electricity, as occurs in 
 chemical combinations. As far as known the gases of the air 
 exist everywhere in uniform proportions. The carbon dioxide 
 and ammonia are small but important ingredients of the air, as 
 it is from the air that plants get the greater part of the carbon 
 dioxide and ammonia necessary to their existence. 
 
 Ammonia is a colorless gas, formula NH 3 , composed of one 
 atom of nitrogen and three atoms of hydrogen. Formerly it 
 was made from the horns of harts, hence the name spirits of 
 hartshorn. The chief source of ammonia and ammonium com- 
 pounds is now the ammoniacal liquors of gas works derived as a 
 by-product in the distillation of coal. It is greedily absorbed by 
 water, and a solution of the gas in water is the ammonia of the 
 shops. This solution has a strong alkaline reaction, turning red 
 litmus to blue, neutralizing strong acids, forming salts of 
 
 ammonium. 
 
 
 
 In certain compounds a group of nitrogen and hydrogen 
 
LESSONS IN CHEMISTRY. 117 
 
 atoms, represented by NH 4 , behave very much like some metals, 
 as potassium and sodium, and the name of ammonium has been 
 applied, but no such substance has ever been isolated. Ammo- 
 nia gas at a temperature of 40 F. becomes a liquid and at 
 103 it becomes a white crystalline solid. It can be reduced to 
 a solid by a pressure of about 10 atmospheres. When the pres- 
 sure is removed it expands into a gas by the action of heat de- 
 rived from surrounding objects. On this principle machines for 
 making ice are constructed. 
 
 Ammonia and hydrochloric acid, whether as gases or in 
 solution, unite to form ammonium chloride, a white solid. 
 If bottles containing the gases in solution be uncorked and 
 brought near each other, a cloud of the ammonium chloride 
 will be formed by the volatile gases. The chemical equation is 
 2NH 3 -f HC1=2NH 4 C1. This compound, called salammoniac, is 
 found in volcanic regions in considerable quantities. 
 
 Pure nitrogen may be prepared from the air, but the com- 
 pounds of nitrogen have never been prepared successfully from 
 the nitrogen of the air. It is difficult to cause nitrogen to 
 combine directly with either hydrogen or oxygen, but through 
 the action of myriads of minute organisms in some soils, atmos- 
 pheric nitrogen and decaying nitrogenous matters are trans- 
 formed into nitrates of lime or potassium. 
 
 One of the most important compounds of nitrogen is nitric 
 acid, whose molecule is composed of one atom of hydrogen with 
 one atom of nitrogen and three atoms of oxygen. Its symbol is 
 HN0 3 . It is prepared by the action of sulphuric acid on potas- 
 sium nitrate or sodium nitrate. The action is as follows: 
 KN0 3 +H 2 S0 4 =HN0 3 +KHS0 4 . Nitric acid is a colorless, cor- 
 rosive liquid whose applications in the arts and manufacturing 
 industries are very extensive. 
 
 Dilute nitric acid by adding an equal bulk of water, then add 
 ammonia water in small quantities from time to time, as long as 
 the mixture shows an acid reaction. If this mixture be evapo- 
 rated slowly, a solid substance with many transparent crystals, 
 called ammonium nitrate, will be formed. This experiment is a 
 
118 PRACTICAL LESSONS IN SCIENCE. 
 
 good illustration of what is meant by chemical combinations. 
 Two liquids of strongly marked qualities, one an acid, one an 
 alkali, united forming a solid as unlike its constituents as could 
 well be imagined. Neither acid nor alkaline, neither sour nor 
 bitter, and with but slight odor. The chemical equation is 
 NH 3 +HN0 3 =NH 4 N0 3 . 
 
 If the ammonium nitrate obtained above be heated moder- 
 ately, it melts and a colorless gas is given off which supports 
 combustion almost as vigorously as oxygen. The equation is, 
 NH 4 N0 3 ==2H 2 0-f N 2 0. This gas, the sub-oxide of nitrogen or ni- 
 trous oxide, is the laughing gas used by dentists as an anaesthetic. 
 
 The several compounds of oxygen and nitrogen that occur are 
 of little value beyond illustrating the law of multiple propor- 
 tions. They are the nitrous oxide, N 2 0; nitric oxide, NO; 
 nitrous anhydride, N 2 3 ; nitrogen peroxide, N0 2 ; and nitric 
 anhydride, N 2 5 . An anhydride is an oxide which combined with 
 water, forms an acid, as nitrous anhydride N 2 3 fH 2 2HN0 2 , 
 nitrous acid; and nitric anhydride N 2 5 4-H 2 O=2HN0 3 nitric 
 acid. 
 
 Acids are composed of hydrogen and some other non-metallic 
 element, and in most cases they contain oxygen, as hydrochloric 
 acid, composed of hydrogen and chlorine, formula HC1, nitric 
 acid, composed of hydrogen, nitrogen and three atoms of oxy- 
 gen, formula HN0 3 , and sulphuric acid composed of hydrogen, 
 sulphur and oxygen, formula H 2 S0 4 . Acids usually have a sour 
 taste, turn vegetable blue colors to red and are often poisonous. 
 
 The combination of a metal with hydrogen and oxygen, non- 
 metals, forms a compound called a base, as sodium hydroxide 
 composed of sodium, hydrogen and oxygen, formula NaHO, called 
 caustic soda, as potassium hydroxide, composed of potassium, 
 hydrogen and oxygen, formula KHO, called caustic potash, and 
 as calcium hydroxide, formula Ca0 2 H 2 , called caustic lime. The 
 bases are sometimes bitter corrosive poisons, turning red colors 
 to blue, but generally they are mild compounds. 
 
 The customary method of testing a substance for acid or 
 basic reaction is by the use of paper colored by the dye litmus. 
 
LESSONS IN CHEMISTRY. 119 
 
 Acids change litmus blue to red, while a basic solution changes 
 the red to blue again. 
 
 When a base and an acid are mixed in solution they neutralize 
 or change the properties of each other, forming water and a com- 
 pound called 3, salt. If we mingle hydrochloric acid and sodium 
 hydroxide the salt, sodium chloride will be formed, together with 
 one molecule of water, according to the following equation, HC1 
 -j-NaHO=NaCl, common salt,-hH 2 0. The hydrogen of the acid 
 exchanges places with the metal of the base, as shown in the 
 equation. The following equation shows the same exchange. 
 Sulphuric acid, H 2 S0 4 -f-2NaHO, sodium hydroxide, Na 2 S0 4 , 
 sodium sulphate, H-2H 2 0. 
 
 The names of the stronger acids end in ic, as nitric, sulphuric 
 and hydrochloric. If an acid containing the same elements has 
 a less proportion of oxygen the name ends in ous, as nitrous 
 acid, sulphurous acid. In the case of acids of which chlorine is 
 a distinguishing element we have a hypo or subchlorous acid 
 and a perchloric acid; the former contains less oxygen than 
 the ous acid, the latter more than the ic acid. 
 
 The bases are metallic hydroxides, and the metal of the com- 
 pound is the distinguishing part of the name, as sodium hydrox- 
 ide, potassium hydroxide and calcium hydroxide. Such com- 
 pounds are sometimes called hydrates, as they may have been 
 formed by the metal replacing one atom of hydrogen in water, as 
 H 2 0+K KOH-f-H, one atom of free hydrogen. 
 
 Salts are named from the acids forming them, as nitrates, 
 sulphates, chlorates, etc., and they are further distinguished by 
 the name of the metal of the base, as potassium nitrate, sodium 
 sulphate, etc. The salts formed by nitrous acid are called nitrites 
 and those by sulphurous acid are called sulphites, etc. If the 
 name of the acid ends in ic, the name of the salt ends in ate, if the 
 name of the acid ends in ous, the name of the salt ends in ite. The 
 reciprocal action of chemical agents, as in the case of an acid and 
 a base, or the action of some form of energy causing chemical 
 changes, is called a reaction, and a substance capable of producing 
 with another substance a chemical reaction is called a reagent. 
 
CHAPTER XV. 
 
 CHLORINE, BROMINE AND IODINE. 
 
 CHLORINE is a greenish yellow gas, never found free in nature, 
 but existing in great quantities as an ingredient of common salt. 
 It also occurs in combination with potassium, magnesium and 
 silver. Its formula is Cl and combining weight 35.5. If common 
 salt be mixed with sulphuric acid and heated, a transparent in- 
 tensely acid gas will be given off, which must be collected over 
 mercury, as water absorbs it greedily. The sodium of the com- 
 mon salt and hydrogen of the sulphuric acid change places and 
 the acid is formed, which, dissolved in water, is the hydrochloric 
 acid of commerce. The equation is common salt, 2NaCl-KH 2 S0 4 
 =Na 2 S0 4 , sodium sulphate, -+-2HC1, hydrochloric acid. 
 
 This acid is one of the most useful agents in the chemical labor- 
 atory, and is extensively used in manufacturing industries. As 
 an acid it forms the class of salts called chlorides, as sodium chlo- 
 ride, or common salt. A mixture of hydrochloric and nitric acids, 
 called aqua regia, is the only solvent for gold, the acids decom- 
 pose each other, and the chlorine, when set free, attacks the gold. 
 
 If hydrochloric acid be well mixed with the binoxide of man- 
 ganese, and the mixture heated gradually, chlorine gas will be 
 set free. As it is heavier than air it may be collected in an open 
 jar by carrying a delivery tube to the bottom of the jar, its 
 color enabling one to see when it has filled the jar. The equa- 
 tion is, Mn0 2 +4HCl=MNCl 2 -f 2H 2 0+2C1. Chlorine is usually pre- 
 pared by heating a mixture of common salt, oxide of manganese 
 and sulphuric acid. 
 
 Chlorine combines readily with many elements and decom- 
 poses many compounds from its strong affinity for hydrogen. 
 If a piece of paper, soaked in oil of turpentine that has been 
 slightly warmed, be dropped into a jar of chlorine there will be 
 (120) 
 
LESSONS IN CHEMISTRY. 121 
 
 a flash of flame, followed by a dense black smoke; the turpen- 
 tine is composed mainly of hydrogen and carbon, the chlorine 
 uniting with the hydrogen leaves the carbon free, which helps to 
 form the dense black smoke. 
 
 Chlorine is a powerful bleaching agent. Pieces of calico or 
 other colored fabrics placed in chlorine gas, if dry, will remain 
 unchanged for some time, but when moistened the color will in 
 most cases disappear promptly. Some of the hydrogen is taken 
 from the coloring matter and oxygen set free, which doubtless 
 assists in decomposing the compounds which constitute the color, 
 but the action must not be allowed to continue long or the 
 fabric itself will be destroyed by the chlorine. 
 
 For bleaching purposes chlorine is usually prepared from cal- 
 cium chloride, which readily gives off chlorine when acted on by 
 dilute sulphuric acid. An interesting experiment illustrating 
 the difference in specific gravity between chlorine and air may be 
 shown with the chloride of lime. On the bottom of a glass jar or 
 wide-mouthed bottle place a much smaller bottle containing some 
 bleaching-powder, add a little sulphuric acid, diluted by an equal 
 bulk of water and partly cover the larger bottle with a piece of 
 glass or pasteboard. Chlorine gas will be set free, will gradually 
 fill the smaller bottle, and failing over the sides to the bottom of 
 the larger one will gradually crowd out the air till it fills the bottle. 
 With a small bottle as a dipper the gas may be dipped out and 
 poured into other jars. Care should be taken not to breathe 
 the gas. 
 
 Hydrogen is an important ingredient in many unpleasant, un- 
 healthful odors, and the strong affinity of chlorine for hydrogen 
 makes it a valuable disinfecting agent in such cases. It removes 
 the hydrogen, breaking up the compounds, and the oxygen set 
 free oxidizes or burns other parts into harmless compounds. 
 
 Chlorine combines with hydrogen even more promptly than oxy- 
 gen does. If hydrogen and oxygen be mixed in the proper pro- 
 portion for water, they will not combine except by the aid of heat, 
 as the electric spark. While if hydrogen and chlorine be mixed 
 in the same way the combination takes place with explosive vio- 
 
122 PRACTICAL LESSONS IN SCIENCE. 
 
 lence under the influence of direct sunlight, taking place slowly 
 and quietly in moderately strong, diffused light. The action of 
 sunlight in this and other cases of chemical action, as in photog- 
 raphy, is not well understood. It does not seem to be the heat, 
 as even a higher degree of heat without light has no such effect. 
 Compounds of oxygen with elements are called oxides, the com- 
 pounds of chlorine with elements are called chlorides. 
 
 Chlorine combines energetically with bromine, iodine, sulphur, 
 phosphorus and arsenic, and with most of the metals also, mak- 
 ing it the rival of oxygen in the extent of its combinations. Chlo- 
 rine forms several interesting compounds with hydrogen and 
 oxygen. They are, hypochlorous acid, HC10; chlorous acid, 
 HC10 2 ; chloric acid, HC10 3 ; perchloric acid, HC10 4 . 
 
 The chloric and hypochlorous acid are the most important, 
 but the whole series is interesting as illustrating the law of mul- 
 tiple proportions. Chloric acid may be prepared by treating po- 
 tassium chlorate with sulphuric acid. The reactions are as 
 follows : 2KC10 3 +H 2 S0 4 =K 2 S0 4 +2HC10 3 . The potassium tak- 
 ing the place of the hydrogen in the sulphuric acid forms po- 
 tassium sulphate, and the hydrogen with the chlorine and 
 oxygen forms the chloric acid. The chloric and hypochloroun 
 acids form salts as the calcium hypochlorite, usually called 
 chloride of lime, or bleaching powder, and the potassium chlorate. 
 These compounds of hydrogen, chlorine and oxygen are not very 
 stable. The affinity with oxygen is not strong. 
 
 In considering the composition of hydrochloric acid it is found 
 that one volume of hydrogen unites with one volume of chlorine 
 to form two volumes of hydrochloric-acid gas. In the compo- 
 sition of water, two volumes of hydrogen combine with one 
 volume of oxygen forming two volumes of water-vapor. In the 
 case of ammonia, three volumes of hydrogen combined with one 
 of nitrogen to form two volumes of ammonia, and in marsh gas 
 we have four volumes of hydrogen combined with one of carbon 
 into two volumes of marsh gas. 
 
 These facts were discovered and have been abundantly verified 
 by experiment ; but how are they explained ? Dr. Dalton formu- 
 
LESSONS IN CHEMISTRY. 123 
 
 lated the atomic theory. Avogadro, after a careful study of 
 gases, formulated this theory, that equal volumes of all gases, 
 whether simple or compound, under the same conditions of tem- 
 perature and pressure, contain the same number of molecules. 
 Elements differ in their chemical combinations, as HC1, hydro- 
 chloric acid, H 2 water, NH 3 ammonia, CH 4 marsh gas. The 
 atom of chlorine can hold one atom of hydrogen, the atom 
 of oxygen holds two, the atom of nitrogen three and the 
 atom of carbon four. On examination it is found that a sim- 
 ilar difference occurs among other elements. An element, whose 
 atom can hold only one other atom is called univalent, as 
 hydrogen and chlorine. An element whose atom can hold two 
 others in union is called a bivalent, as oxygen and mercury. An 
 element whose atom can hold three atoms in combination is 
 called trivalent, as nitrogen and antimony, and one that can 
 hold four is called quadrivalent, as carbon and tin. In the forma- 
 tion of salts elements of the same valence replace each other, as 
 in the formation of potassium, nitrate, the univalent potassium 
 replaces the hydrogen in HNO and the compound becomes KNO. 
 In the case of potassium sulphate two atoms of the univalent 
 metal replace the two atoms of hydrogen and H 2 S0 4 becomes 
 K 2 S0 4 . In zinc sulphate one atom of zinc, a bivalent metal, re- 
 places the two atoms of hydrogen and H 2 S0 4 becomes ZnSO 4 
 sulphate of zinc. From the foregoing data we may form a theory 
 for the peculiarities of combination by volume. 
 
 If we suppose our unit volume to contain 1,000 molecules then, 
 according to the law of Avogadro, one volume of hydrogen con- 
 taining 1,000 molecules unites with one volume of chlorine con- 
 taining 1,000 molecules forming two volumes of hydrochloric-acid 
 gas containing 2,000 molecules. But each molecule of the hydro- 
 chloric acid contains two atoms, and in the two volumes there 
 must be 4,000 atoms. From this we judge that the molecules of 
 hydrogen and chlorine are each made up of two atoms. In the 
 case of water we have two volumes of hydrogen containing 2, 000 
 molecules or 4,000 atoms, combining with one volume of oxygen 
 containing 1,000 molecules or two thousand atoms, forming 
 
124 PRACTICAL LESSONS IN SCIENCE. 
 
 two volumes of water vapor, containing 2,000 molecules or 6, 000 
 atoms. The two-atom molecules of hydrogen and oxygen were 
 rearranged into three-atom molecules of water vapor, diminish- 
 ing the bulk by one-third. With ammonia the case is similar, one 
 volume of nitrogen containing 1,000 molecules or 2,000 atoms, 
 unites with three volumes of hydrogen containing 3,000 mole- 
 cules or 6,000 atoms, forming two volumes of ammonia, con- 
 taining 2,000 molecules with 8,000 atoms. The two-atom 
 molecules were broken up and rearranged into four-atom mole- 
 cules and the volume diminished by one-half. Thus the atomic 
 theory, Avogadro's principle, the theory of valence and the 
 phenomena of combination by volume, all seem to harmonize 
 with the facts of definite and multiple proportions in chemical 
 combinations, and to sustain and mutually verify each other. 
 The law of definite proportions has been demonstrated, the 
 others are still theories. 
 
 It has been found that elements at the instant they are set 
 free from compounds are much more active and can effect 
 changes which they cannot effect under other circumstances. 
 Hydrogen gas passed into nitric acid causes no change, but 
 hydrogen liberated in direct contact with nitric acid reduces the 
 acid and forms the lower oxides of nitrogen. Examples of simi- 
 lar action are of frequent occurrence. An element at the instant 
 of its liberation is said to be in the nascent state or atomic state 
 when it seems to be more active than after the atoms have com- 
 bined into molecules. 
 
 BROMINE (Br) is a dark brown liquid heavier than water having 
 an irritating disagreeable odor, hence the name, meaning a stench. 
 It is the only non-metal which is a liquid at ordinary tempera- 
 tures. It occurs in seawater and other natural brines, as 
 magnesium bromide, which is the main source of the bromine of 
 commerce. It is generally obtained from bittern, the residue 
 which remains after sodium chloride has been crystallized out 
 from the natural brines. Bromine forms compounds with hydro- 
 gen and oxygen, which are analogous to those of chlorine, and in 
 physical and chemical properties is somewhat similar to that 
 
LESSONS IN CHEMISTRY. 125 
 
 element. Some compounds of bromine are used as bleaching and 
 disinfecting agents. Some are used in photography, and bromide 
 of potassium is used extensively in medicine. 
 
 IODINE (I) is also found in seawater. Certain varieties of sea- 
 weed separate the sodium iodide from the seawater and concen- 
 trate it in their tissues. The seaweed is collected, dried and 
 burned. The ashes and other residue are leached with water, 
 which dissolves out the sodium iodide, and this solution yields 
 the iodine of commerce. Iodine is a grayish black crystalline 
 solid of metallic luster. It melts at 225 F. and boils at 356, 
 forming a beautiful violet-colored vapor, which is the heaviest 
 known, being 872 times heavier than air. Drop a piece of iodine 
 as large as a grain of wheat into a test-tube and apply heat; 
 observe the vapor, notice the coating it forms on the tube; apply 
 heat to different parts of the tube and study the effects. Exam- 
 ine the coating for crystals. 
 
 Iodine is soluble in alcohol or ether and is sparingly soluble 
 in water. Iodine colors starch paste a deep blue ; this reaction 
 constitutes the most delicate test of its presence. Take a thin 
 solution of starch paste and add to it a few drops of an aqueous 
 solution of iodine and notice the color. Dip a piece of white pa- 
 per in the paste and suspend it while moist in a bottle or jar on 
 the bottom of which has been placed a small piece of iodine. In 
 a few moments the paper begins to show a blue color, indicating 
 that iodine is volatile at ordinary temperatures. Iodine stains 
 the skin yellow but is not as corrosive as either chlorine or bro- 
 mine. A solution of iodine in alcohol is familiarly known as 
 tincture of iodine and much used as a liniment. Iodide of mer- 
 cury is sometimes used in painting as a pure scarlet; the iodide 
 of lead has a bright golden color; the iodide of silver is yellow 
 and the iodide of potassium is white. The iodide of potassium 
 is extensively used in photography and in medicine. 
 
 Iodine combines with hydrogen forming hydriodic acid, a 
 colorless gas, with a suffocating odor. One part of hydrogen, 
 weight one, combines with one part of a highly colored iodine 
 vapor, weight 127, and the one part discharges the color and 
 
126 PRACTICAL LESSONS IN SCIENCE. 
 
 changes the properties of the 127 parts forming a colorless 
 gas, formula HI. 
 
 Iodine forms an acid with hydrogen and oxygen called iodic 
 acid, formula HIO, analogous to chloric and bromic acid. 
 
 Chlorine, bromine and iodine constitute a well-defined natural 
 group of elements. They each unite with hydrogen in the same 
 proportions, forming acids of similar properties and each form- 
 ing similar salts. Each of these elements forms a powerful acid 
 containing three atoms of oxygen. With nitrogen they each form 
 explosive compounds. At ordinary temperatures chlorine is a 
 gas, bromine a liquid and iodine a solid. Chlorine is yellow, 
 bromine reddish-brown and iodine violet. In general chlorine is 
 more energetic and its compounds more stable, while iodine is 
 least energetic except in its combinations with oxygen. 
 
 FLUORINE is an element, known only in its compounds, of which 
 the most common is the mineral fluor spar. It occurs in vegetable 
 and animal substances and in several other minerals. Fluorine 
 forms an acid with hydrogen analogous to hydrochloric acid, 
 which is very corrosive, attacking glass vigorously, so that it 
 must be collected in lead, rubber, or platinum vessels. It is used 
 for etching glass. The glass is covered with a thin coat of wax, 
 and lines or figures are drawn with a pointed instrument so as 
 to cut through the wax. The glass is then exposed to the action 
 of the acid, and soon the figures drawn are corroded into the 
 glass. Fluorine seems to have affinities with the chlorine group 
 of elements, but so little is known of it that no extensive com- 
 parison can be made. 
 
CHAPTER XVI. 
 
 CARBON, SILICON AND BORON 
 
 CARBON (C) is an essential constituent of all animal and vege- 
 table bodies. It is found in the air, in many kinds of rocks and 
 soils, and in many natural waters, but is especially the element of 
 organic bodies. Every living body from the microscopic animal- 
 cule up to the giant whale, from the tiniest vegetable to the lofty 
 red- wood contains carbon. It occurs in its purest form in the 
 crystalline transparent diamond, the hardest substance known. 
 Another form of nearly pure carbon is graphite, and another 
 still is common charcoal. Diamonds are found in South America, 
 South Africa, in the East Indies and in Australia, and to some 
 extent in other localities. They are usually found in alluvial de- 
 posits as water-worn pebbles whose crystalline form and trans- 
 parency have been obscured by abrasions. It is the most beauti- 
 ful and highly prized of all the gems. It is a powerful refractor of 
 light, and is sometimes employed in making the lenses of micro- 
 scopes. Small, dark stones are much used for cutting glass, 
 drilling gems and in making the cutting edges of core drills. If 
 heated to a very high temperature in oxygen gas it burns up, the 
 sole product of the combustion being carbon dioxide. 
 
 Graphite, another form of carbon, occurs in great quantities 
 among the older rocks of Canada and other localities, and is often 
 associated with iron ores. It sometimes occurs in six-sided plate- 
 like crystals, while the diamond usually has the form of an octa- 
 hedron. Graphite has a grayish black color with a metallic 
 luster ; has an oily feel, and is often used in place of oil to prevent 
 friction in machinery. Graphite resists a very high degree of 
 heat, and is used in manufacturing crucibles for melting steel and 
 other refractory substances. When subjected to a high degree of 
 heat in oxygen it burns, evolving intense heat nnd light, but the 
 
 (127) 
 
128 PRACTICAL LESSONS IN SCIENCE. 
 
 sole product, as in the case of the diamond, is carbon dioxide. 
 Graphite is insoluble and unaffected by moisture or air, and 
 forms a valuable coating for protecting iron from the effect of the 
 weather. Its chief use is, perhaps, the manufacture of pencils. 
 For this purpose it is reduced to a powder and subjected to great 
 pressure. It is then sawed into little bars which are cased with 
 wood. A mass of graphite seems soft and friable, but the par- 
 ticles are extremely hard, and soon wear out the steel saws used 
 in cutting it into shape. 
 
 We know nothing about the formation of diamonds, but 
 geologists consider graphite to be the residue of some of the 
 forms of life occupying the earth when the materials of the older 
 rocks were being deposited . 
 
 Another form of nearly pure carbon is charcoal. It is formed 
 when any organic substance, as wood, sugar, flesh, bone or blood 
 is burned in a limited supply of air. It is a black, brittle, tasteless, 
 solid. It is not easily affected by the action of air or water at 
 ordinary temperatures; charred cloths, grains, fruits, and other 
 remains of the Lake Dwellers of Switzerland, are as perfect to-day 
 as when entombed in the mud and waters of the lakes thousands 
 of years ago. The charcoal of commerce is formed from wood 
 by burning it in a limited supply of air. Wood is made up 
 mainly of carbon, oxygen and hydrogen, and when burned in the 
 open air the oxygen combines with the hydrogen forming water, 
 and with the carbon forming carbon dioxide until only a few 
 ashes are left ; but if the supply of oxygen is limited the hydrogen 
 and part of the carbon are driven off, but the main part of the 
 carbon remains as charcoal. Charcoal is used as a fuel, burning, 
 when dry, without flame, yielding a high degree of heat. Burned 
 in oxygen the sole product is carbon dioxide, as in the case of 
 diamond and graphite. 
 
 Charcoal is very porous, and possesses in a remarkable degree 
 the power of absorbing gases, some specimens absorbing 90 
 times their bulk of ammonia, 35 times their bulk of carbon diox- 
 ide. It is said that freshly burned charcoal will absorb moisture 
 from the air so as to increase at least 10 per cent, in weight. 
 
LESSONS IN CHEMISTRY. 129 
 
 The absorbing properties of charcoal make it a good deodor- 
 izer and a powerful disinfectant, and it is much used in making 
 water filters. Charcoal from bones is much used in sugar refin- 
 eries to decolorize sirups. It destroys bad odors, and discharges 
 colors, not only by absorbing gases, but the absorbed oxygen 
 acting chemically on the noxious gases and other substances 
 changes them to harmless compounds. 
 
 Soot is another form of nearly pure carbon. It is carbon which 
 has been released by heat from its combinations, without being 
 burned, it helps to form the smoke of combustion. It may be 
 condensed from the smoke as a fine black powder. It is used for 
 making printers' ink, black paint, etc. .In the distillation of coal 
 for the manufacture of illuminating gas, there is deposited on the 
 inside of the retort a grayish coating called gas carbon. It is 
 quite as nearly pure carbon as any of the other forms, but 
 whether it is a variety of graphite, or a fourth form is not 
 settled. Gas carbon is a good conductor of electricity, and is. 
 used for electric-lamp carbons and other purposes. Coke and an- 
 thracite coal are nearly pure carbon. The different kinds of soft 
 coal and peat all have carbon as the basis of their composition 
 but associated with various impurities. 
 
 All these forms of carbon seem to be the result of the slow 
 decomposition of organic matter, mainly vegetation, usually 
 under water, so that the supply of oxygen was limited. This 
 mass of decomposing matter covered with sand or clay, sub- 
 jected to pressure and heat, gradually changed into various kinds 
 of coal and graphite. It seems hardly possible that the black, 
 brittle, porous charcoal, and the soft compact graphite are chem- 
 ically identical with the beautiful diamond. They are specimens 
 of the same element appearing in different or allotropic forms, 
 and notwithstanding their marked differences, they have well- 
 marked properties in common. The explanation of these differ- 
 ent forms of carbon is one of the unsolved problems of chemistry. 
 
 Carbon combines freely with oxygen in all forms of combus- 
 tion and combines also with hydrogen, nitrogen and other ele- 
 ments. When any of the forms of carbon is burned in oxygen 
 
 t S.-9 
 
180 PRACTICAL LESSONS IN SCIENCE. 
 
 the product is carbon dioxide, formula C0 2 , one atom of car- 
 bon uniting with two of oxygen. It is ordinarily prepared by 
 treating calcium carbonate, limestone, with hydrochloric or some 
 other strong acid. It may be collected over water, or as it is 
 much heavier than air it can be collected in an open jar. The 
 chemical equation is CaC0 3 -f2HCl CaCl 2 -f H 2 0-fC0 2 . Calcium, 
 a bivalent element, replaces two atoms of hydrogen forming 
 calcium chloride, the two atoms of hydrogen taking one atom 
 of oxygen form water setting free (C0 2 ) carbon dioxide, which at 
 ordinary temperatures is a colorless, tasteless, odorless gas. If 
 a lighted stick or candle be put into a jar of this gas, it is extin- 
 guished as promptly as if thrust into water; if a bird or mouse 
 be confined in it, life is quickly destroyed. 
 
 Carbon dioxide will not support combustion, will not sup- 
 port animal life, and for the same reason that water does not, 
 they each contain plenty of oxygen, but it is so firmly bound 
 to the other members of the compound that it cannot be 
 utilized for the processes of life or combustion. Water and 
 the dioxide of carbon are cinders, the affinities of the oxygen, 
 hydrogen and carbon have been satisfied, their energy has been 
 expended, they are like rocks at the foot of a hill, work must 
 be done on them before they are in a condition to do any more 
 work ; and that work must be equal to the work they did as they 
 clashed together into molecules of water and carbon dioxide. 
 
 This gas sometimes accumulates in wells, abandoned mines and 
 caves. As a test of its presence a lighted candle is lowered into 
 places where its presence is suspected ; if the light is not extin- 
 guished or dimmed, the air does not contain a dangerous amount 
 of the dioxide. Carbon dioxide is a product of respiration. Im- 
 merse a jar in water and invert it so as to keep the mouth under 
 water; then through a tube fill the jar with air from the lungs, 
 displacing the water; cover the mouth of the jar with the hand 
 or piece of board and place it upright on the table and test the 
 contents with a lighted candle for carbon dioxide. If the air is 
 held in the lungs for a little time before being breathed into the 
 jar the effect will be more marked. This experiment will show 
 
LESSONS IN CHEMISTRY. 181 
 
 that air that has been breathed once is not safe for breathing a 
 second time. But lesser quantities of the dioxide are harmful, 
 and a more delicate test of its presence is often desirable. Put a 
 small piece of quick lime into a tumbler or jar of water, after a 
 few minutes stir it well, and when the sediment settles pour off 
 the clear water for use. Fill a test-tube about two-thirds full of 
 lime water and force air from the lungs through the water by 
 means of a tube, and quickly the water becomes cloudy and 
 milky. This makes a delicate test for the dioxide. The lime of 
 the water combines with dioxide forming calcium carbonate 
 which is insoluble in water. If lime water is exposed to the air 
 in an open dish, the dioxide of the air uniting with the lime 
 soon forms a thin coating of calcium carbonate on the surface of 
 the water. 
 
 The dioxide of carbon accumulates so rapidly as the pro- 
 duct of combustion and respiration that the air of a room 
 occupied by a number of people soon becomes loaded with 
 this gas unless special arrangements have been made for free 
 ventilation. Tests of the* air of almost any school or assembly 
 room, especially when fires or lights are in use, will show dan- 
 gerous quantities of a gas which cannot support life, and which 
 by limiting the supply of oxygen becomes detrimental to health. 
 
 Under a pressure of 36 atmospheres (about 450 Ibs.) carbon 
 dioxide becomes a liquid; when the pressure is removed it begins 
 to evaporate rapidly, the evaporating portion absorbing so 
 much heat from the other that it freezes into a snow-like solid. 
 
 Carbon dioxide is absorbed freely by water and other liquids, 
 the sparkling appearance of wines and mineral waters, the foam 
 of beer and " soda water " are due to the presence of this gas. It 
 is also used in the manufacture of fire extinguishers. An English 
 coal mine that had been smouldering for years was extinguished 
 completely by the use of carbon dioxide. This gas combined 
 with water forms carbonic acid, formula H 2 C0 3 , and it is prob- 
 able that in the tests with lime water we find the carbonic acid 
 not the dioxide. 
 
 When coal is burned without a free supply of air, a gas is 
 
132 PRACTICAL LESSONS IN SCIENCE. 
 
 formed called carbon monoxide. It is colorless, tasteless, odor- 
 less, but exceedingly poisonous when inhaled. We often hear of 
 deaths caused by coal gas, and the gas from a pan of smoulder- 
 ing charcoal is often the cause of suicidal death, especially in 
 France. In an open coal fire, before all the coal is fully ignited, 
 the pale blue flames flickering over the mass are burning moxideof 
 carbon. It is probably the cause of death in the cases mentioned. 
 
 All forms of artificial light, except the electric light, are flames 
 due to the combustion of some gas. In the case of illuminating 
 gas, the source of the light is made and stored as gas, in the case 
 of oil, the wick is ignited and as the oil comes up by capillary at- 
 traction it is expanded into gas and burns as a flame, and so 
 with the candle. At first a flame seems a simple thing and illumi- 
 nation seems as simple as the flame, but when one attempts to 
 explain the phenomena, the simplicity vanishes. We have already 
 learned that the hydrogen flame, while intensely hot yields but 
 little light. If we pulverize a little charcoal and dust it into a flame 
 of hydrogen it gives out an intense light; or if the hydrogen flame 
 be turned upon a piece of lime or other refractory substance it is 
 soon heated to incandescence giving out intense light, which leads 
 us to suspect that an illuminating flame must contain some solid 
 incandescent substance which is the cause of the illumination. 
 
 If we examine a flame, as of a candle, we find it conical in 
 shape, pale blue below, dark in the center and yellow at the sides 
 and at the apex. Put a piece of porcelain or any solid substance 
 into the flame and the coat of soot deposited indicates the pres- 
 ence of solids in the flame. Pass a piece of paper into the flame 
 just above the wick, hold it there a moment, then remove it, and 
 if skillfully done there will be a ring of burnt paper with a little 
 portion uncharred within it, which indicates that the outside of 
 the flame is hotter than the inside dark portion. The substances 
 used for illuminating flames, as gas, oils and fats are composed 
 largely of compounds of hydrogen and carbon. About the wick 
 of a lamp or candle or the opening of the gas jet the unburned 
 gas makes the cool dark center of the flame. The oxygen uniting 
 more readily with the hydrogen than with the carbon forms 
 
LESSONS IN CHEMISTRY. 133 
 
 the hydrogen flame just outside the dark center and the 
 liberated carbon passing through the hydrogen flame is heated 
 to incandescence, and just outside this hydrogen flame it com- 
 bines with the oxygen forming the dioxide of carbon. 
 
 If air is admitted to the center of the flame, as in an Argand 
 burner, the dark center is lessened and the light increased. In 
 the case of the Bunsen burner air is allowed to mingle with the 
 gas so that the combustion is practically complete, yielding 
 a hot flame but very little light; for use in chemistry it is 
 better as it gives greater heat and leaves no deposit of soot. 
 The flame of alcohol yields but little light and deposits no 
 soot. Within certain limits the amount of light depends upon 
 the temperature of the flame. The temperature may be so low 
 as to hardly heat the carbon to incandescence when the light 
 must begin to fail. If by any means the temperature of the flame 
 falls below a certain limit it is extinguished. 
 
 A piece of fine wire gauze held across the flame of a lamp or 
 candle cools the combustible gases below the ignition point so 
 that they rise through the gauze in the form of smoke, the gauze 
 may become red hot and still not allow the flame to pass, so 
 rapidly does the wire conduct the heat away, and yet the gases 
 may be ignited above the gauze. On this principle the miner's 
 safety lamp is constructed. Light carbureted hydrogen or marsh 
 gas, abundant in some coal mines, forms with air an explosive 
 mixture of great power, but the mixture must be raised to the 
 igniting temperature before explosion takes place. As the gas 
 is odorless often the first intimation of danger was the fatal explo- 
 sion of fire damp, lighted from the miner's open lamp. Sir Hum- 
 phrey Davy studied the problem, and at last made a lamp in 
 which the flame was surrounded by a wire gauze which so con- 
 fined it that the explosive gases outside could not be ignited. 
 As the gauze restricted the light it soon became the custom to 
 explore the mine for dangerous gas with a safety lamp and if 
 none was found the men wnt to work with open lamps. Aflame 
 seems a little thing, but the full discussion of a candle flame would 
 make quite a complete treatise on chemistry. 
 
134 PRACTICAL LESSONS IN SCIENCE. 
 
 Cyanogen, formula, C 2 N 2 , is a colorless poisonous gas composed 
 of carbon and nitrogen, which is best known in combination with 
 the metals potassium and iron, in connection with which it will 
 be more fully discussed. 
 
 No other two elements are capable of occurring in so many 
 different combinations as carbon and hydrogen. Compounds of 
 these elements are known as hydrocarbons, and include most of 
 the inflammable gases and a great many essential oils, naphthas 
 and other interesting substances. It is supposed that all these 
 compounds were originally derived from the vegetable kingdom, 
 and they may be considered under the head of organic chemistry. 
 Three members of this group of compounds may be mentioned 
 here for the purpose of affording a little insight into the mutual 
 relations of these important elements. When intensely heated, 
 as by the electric spark, carbon combines with hydrogen forming 
 a colorless gas called acetylene, formula C 2 H 2 . This gas is found 
 among the products of incomplete combustion, having a peculiar 
 odor something like that of geranium. It burns with a smoky 
 flame in the air, bursting spontaneously into flame when brought 
 into contact with chlorine. Olefiant gas, formula C 2 H 4 , is also a 
 product of the action of heat on coal, and is one of the illumi- 
 nating gases. This gas derives its name from its property of 
 uniting with chlorine and bromine, forming oily liquids. 
 
 If the mud and decaying vegetable matter at the bottom of 
 stagnant pools is stirred up, bubbles of gas rise more or less 
 abundantly to the surface. This gas has received the name of 
 methane, or marsh gas. It is abundant in coal mines, as the fire 
 damp of the miners ; it is a constituent of petroleum oil and is 
 the initial member of an interesting series of hydrocarbons. It 
 is a colorless, odorless, inflammable gas, burning with a lumi- 
 nous flame. When petroleum is brought up to the air several 
 gases are given off. The simplest of these is methane, formula 
 CH 4 , the next Ethane, C 2 H 6 , the next Propane, C 3 H 8 , the next 
 Butane, C 4 H 10 , the next Pentane, C 5 H 12 , and so on, each member 
 differing from the preceding one by CH 2 , altogether forming what 
 is called an homologous series. Such series are distinguishing 
 
LESSONS IN CHEMISTRY. 135 
 
 marks of the hydrocarbons. The ordinary illuminating gas 
 consists of free hydrogen, marsh gas, olefiant gas, carbonic 
 oxide, acetylene and other substances. 
 
 SILICON (Si), next to oxygen, is the most abundant element in 
 nature. It has never been formed in an uncombined state, occur- 
 ring most abundantly as silicon dioxide or silica, formula, Si0 2 . 
 The dioxide uniting with water forms silicic acid, H 2 Si0 3 . This 
 acid forms silicates of sodium, potassium, aluminium, calcium 
 and other metals. These silicates are very abundant, silica and 
 the silicates make up the greater part of the crust of the earth. 
 The granite rocks, volcanic rocks, sand rocks, clay or slate rocks 
 everything except limestone and coal is composed largely of 
 the compounds of this element. Silica is not only abundant and 
 useful but is beautiful as well. The purest natural variety is the 
 transparent, colorless quartz crystal or rock crystal, occur- 
 ring in six-sided prisms terminated by six-sided pyramids. They 
 may be distinguished from most other crystals not only by their 
 form, but by their hardness, scratching glass almost as readily 
 as the diamond. With a little tinge of purple, the rock crystal 
 becomes the beautiful amethyst; when brown or smoky, Scotch 
 pebbles. Losing its transparency and crystalline form, we have 
 the translucent chalcedony, the brilliant carnelian, the banded 
 agate, the catseye, the onyx and the opal. Each of these forms 
 beautiful and enduring. Flint is a dark colored variety of silica 
 which is proverbial for its hardness. The percussion of flint and 
 steel for many years served our forefathers as a source of light 
 and heat in place of the lucifer match. 
 
 While silica is insoluble, some of its compounds are soluble, 
 and plants contain considerable quantities in their composition, 
 and animals as well. Many natural waters contain silica in solu- 
 tion, as in the Geysers of Iceland, and petrified wood indicates 
 that silica is soluble to some extent in water, but probably only 
 in hot water and under considerable pressure. 
 
 Hydrofluoric acid is the only substance that can decompose 
 silica at ordinary temperatures. Silicic acid does not appear to 
 be a very strong acid, seeming to be of about the same strength 
 
136 PRACTICAL LESSONS IN SCIENCE. 
 
 as carbonic acid, and yet the silicates generally are quite stable 
 compounds. Glass is manufactured from the silicates of sodium, 
 potassium, calcium, etc., with other ingredients. 
 
 Silicon has been obtained as a brownish powder and in the 
 form of crystalline scales with metallic luster resembling graphite. 
 Carbon and silicon are similar in some respects, as both form 
 dioxides and weak acids, and the same hydrides and chlorides, 
 but differ in that most of the compounds of carbon are derived 
 from the hydrocarbons, while the compounds of silicon are derived 
 from silicic acid. 
 
 Boron (B)is an element which has not been found in vegetable 
 or animal bodies ; is never found free ; is not abundant ; is not es- 
 sential to life, and yet in many ways it is an interesting element, 
 similar in some respects to carbon and silicon. It forms with 
 oxygen boric trioxide, B 2 3 , which uniting with water forms 
 boracic, or boric acid, H 3 B0 3 . 
 
 This acid is found issuing from the earth as vapor, accom- 
 panied with steam in certain volcanic regions, as Northern Italy. 
 This steam is passed into water, which absorbs the acid yielding 
 boracic acid crystals on evaporation. Boracic acid is feeble like 
 silicic and carbonic acids. It fuses at high temperatures, when 
 it dissolves many of the metallic oxides forming glassy berates 
 which are of characteristic and often beautiful colors. On this 
 property depends the chief value of boron in the arts and in 
 chemistry. It forms a good test for detecting the presence of 
 metals, and is valuable in the manufacture of colored glass and 
 porcelains. It is used in hard soldering and in brass manu- 
 facture. The most important borate is the sodium borate called 
 borax, which is the form under which boron is best known. 
 
 Boron has been isolated as an olive-green powder; also in 
 copper-colored scales similar to graphite; also in transparent 
 octahedral crystals, rivaling diamonds in brilliancy and hardness. 
 Carbon, silicon and boron seem to form a natural group; each 
 has a crystalline, amorphous and graphite-like form. Neither 
 can be made a vapor, and each is practically insoluble. 
 
CHAPTER XVII. 
 
 SULPHUR, PHOSPHORUS AND ARSENIC. 
 
 SULPHUR is an element that has been known from the earliest 
 times, as it is found in great quantities in volcanic regions, 
 especially in those of Southern Europe. It occurs as hydrogen 
 sulphide in mineral waters. It forms compounds with several 
 metals, as the bisulphide of iron, sulphide of iron and copper, 
 sulphide of lead, zinc, antimony and mercury. It also is a con- 
 stituent of numerous sulphates, as the sulphates of lime, baryta, 
 strontia, magnesia and soda. It is also found in small quanti- 
 ties in animals and some plants. 
 
 Sulphur is a yellow brittle solid. It melts at 239 F. to 
 a thin straw-colored liquid; when heated to a higher temper- 
 ature it becomes darker in color, and at 350 F. becomes a 
 dark viscid body. At this point the temperature remains 
 stationary for some time, although heat is applied continu- 
 ously, showing that heat is doing other work besides raising 
 temperature. As it begins to rise in temperature again it 
 becomes liquid at about 500 F., and at 836 F. it boils, form- 
 ing a brownish-yellow vapor, which burns in oxygen or in the 
 air with a bluish flame. When a liquid at about 500, if poured 
 into water, it becomes a dark plastic mass much like india rub- 
 ber, but this form is not permanent it soon changes back to the 
 yellow brittle form. 
 
 The plastic sulphur not only differs from brittle sulphur in 
 physical properties but it differs in chemical properties as well, 
 for brittle sulphur dissolves readily in bisulphide of carbon while 
 the plastic form is entirely insoluble ; and further, they differ in 
 their electrical relations, the plastic form is electro-positive while 
 the other is electro-negative. 
 
 The diamond crystallizes in the form of an octahedron and 
 
 (137) 
 
138 PRACTICAL LESSONS IN SCIENCE. . 
 
 so does sulphur. Nearly all the compounds of sulphur as 
 well as most other substances of the mineral world have defi- 
 nite crystalline forms, and so constant and definite is this 
 form that it is one of the marks for the identification of min- 
 erals. The natural crystallization of sulphur is the octahedra, 
 and it takes this form when crystallizing from solutions, but 
 when crystallizing from the melted state it takes the form of 
 oblique prisms. The difference between these two crystalline 
 forms of sulphur extends to their specific gravities and the tem- 
 peratures of their melting points. Ordinary rolled sulphur con- 
 tains many prismatic crystals when first made which gradually 
 change to octahedra. This change in structure of the solid gives 
 rise to a state of tension which accounts for the extreme brittle- 
 ness of sulphur. 
 
 Sulphur is one of the most interesting of the non-metallic ele- 
 ments, and it may serve as the basis of many interesting and 
 instructive experiments . A large part of the sulphur of commerce 
 comes from Sicily. As the melting point and boiling point of 
 sulphur are low it is comparatively easy to separate it from im- 
 purities by the aid of heat. Large quantities of sulphur are also 
 obtained by decomposing iron pyrites or bisulphide of iron. 
 Sulphur is used in the manufacture of gunpowder and matches. 
 
 Sulphur unites with oxygen, forming many interesting com- 
 pounds. When sulphur is burned in the air, sulphur dioxide, 
 formula S0 2 , is formed with the evolution of light and heat. It 
 occurs among the products of volcanic action, is a transparent 
 colorless gas, having a pungent suffocating odor, such as arises 
 from a burning match. It may be prepared for examination 
 by treating copper with sulphuric acid. It is readily absorbed 
 by water but may be collected by displacement, as in the case of 
 chlorine or carbon dioxide, as it is heavier than air. It may 
 be condensed to a liquid by cold or pressure, and is a solid at 
 105 F. Sulphur dioxide S0 2 -hwater, H 2 forms sulphurous 
 acid, H 2 S0 3 . When neutralized by a base this acid forms a class 
 of salts called sulphites, as the sulphite of soda. 
 
 Sulphur dioxide is extensively used as a bleaching agent. Al- 
 
LESSONS IN CHEMISTRY. 139 
 
 though less powerful than chlorine it is preferred in some cases, 
 because it is less liable to injure the fabric. The articles to be 
 bleached are moistened and hung in a chamber in which sulphur 
 dioxide is produced by burning sulphur. The coloring matters 
 seem to form colorless compounds with the acid and in some cases 
 the colors maybe restored by neutralizing the acid. Sulphur diox- 
 ide, like carbon dioxide, will not support combustion and is used 
 to stop combustion. This acid is an antiseptic promptly arrest- 
 ing fermentation. It is used as a disinfectant and as an insecti- 
 cide. The dioxide becomes an acid so readily by taking water 
 from the air that it is often difficult to decide whether a given 
 result is due to the dioxide or the acid. 
 
 While sulphurous acid is useful in many other ways its principal 
 use is in the manufacture of sulphuric acid, formula H 2 S0 4 . It 
 is a powerful acid which has very many practical uses. It is said 
 that more than 100,000 tons of it are used each year in England 
 alone. The steps involved in the manufacture of sulphuric acid are 
 the formation of the sulphur dioxide, and sulphurous acid H 2 S0 3 , 
 which combined with one atom oxygen forms sulphuric acid. The 
 last step is the most difficult and most interesting. The sulphur- 
 ous acid cannot readily get the necessary oxygen from the air, 
 but nitric oxide, formula NO, takes oxygen from the air forming 
 nitrogen peroxide N0 2 . The peroxide gives off one atom of oxy- 
 gen to the sulphurous acid and sulphuric acid is formed, the nitric 
 oxide simply carrying oxygen from the air to the sulphurous acid. 
 Sulphurous acid is supplied from burning sulphur or decomposing 
 iron pyrites. Nitric acid, from which the nitric oxide is formed, 
 is supplied by the decomposition of niter by sulphuric acid. 
 A mixture of sulphurous and nitric acids, air and steam are 
 conveyed into a leaden chamber containing a layer of water. 
 The nitric acid by the action of the sulphurous acid is reduced to 
 nitric oxide, which takes oxygen from the air and gives it up to 
 the sulphurous acid, converting it into sulphuric acid. This is 
 absorbed by the water forming a weak acid which is concentrated 
 by evaporation, at first in leaden pans and then in glass retorts 
 or platinum stills. 
 
140 PRACTICAL LESSONS IN SCIENCE. 
 
 This acid is a heavy corrosive liquid, colorless when pure, but 
 usually brownish from charred organic matter. It blackens 
 wood and cloth and almost every form of organic matter is ut- 
 terly destroyed by this powerful acid, even when much diluted. 
 If a few lumps of sugar be dissolved in a little water and mixed 
 with sulphuric acid, a violent action takes place and a black mass 
 of semi-solid substance results. Some varieties of shoeblacking 
 are made by the action of sulphuric acid on molasses or treacle. 
 Sulphuric acid has a strong affinity for water; if exposed to the 
 air in an open dish it soon absorbs water from the air so as to 
 greatly increase its bulk. It is frequently used in the laboratory 
 for drying substances without heat. 
 
 A high degree of heat is developed by the action of sulphuric 
 acid on water, when the two are mixed, which leads one to sus- 
 pect chemical action. The diluted acid has a smaller bulk 
 than that occupied by the acid and water before mixing. The 
 corrosive action of this acid seems largely due to its power of 
 absorbing water from the objects with which it conies in con- 
 tact. 
 
 Sulphuric acid acts on all the metals except gold and platinum, 
 and has a more powerful attraction for bases than any other 
 acid, displacing all other acids from their salts. Some bases 
 form two salts with sulphuric acid, as H 2 S0 4 +KOH KHS0 4 -f 
 H 2 0, acid potassium sulphate, and H 2 S0 4 +2KOK=K 2 S0 4 +2H 2 
 neutral potassium sulphate, while in the case of nitric acid only 
 one salt seems possible, as HN0 3 +KOH=KN0 3 +H 2 0. An acid 
 as sulphuric, which has the power to form two salts with one 
 metal, is called dibasic, while others that can form but one are 
 called monobasic. 
 
 Sulphuric acid is one of the most important substances used in 
 manufacturing. It is used in making sodium carbonate, citric, 
 tartaric, acetic and nitric acids, sodium and magnesium sul- 
 phates, and various paints. It is used in calico printing, in dye- 
 ing, in gold and silver refining, in purifying oil and tallow. It is 
 used in medicine and is invaluable about the chemical laboratory. 
 
 Hyposulphite of soda is a salt used extensively in photog- 
 
LESSONS IN CHEMISTRY. 141 
 
 raphy. There are other hyposulphites, but no hyposulphurous 
 acids have ever been isolated. 
 
 When sulphur vapor is passed over red-hot charcoal the sul- 
 phur combines with carbon, forming carbon sulphide, formula 
 CS 2 . It is a volatile liquid of high refractive powers. It has never 
 been frozen and is used in making thermometers. It dissolves 
 crystalline sulphur, phosphorus, India rubber, fatty matters, and 
 is one of the most injurious impurities of illuminating gas. 
 
 When hydrogen passes over heated sulphur the two elements 
 combine forming hydrogen sulphide, a colorless gas of disgusting 
 odor, whose formula is H 2 S. It occurs in some natural waters, 
 and is formed in the decomposition of some organic substances, 
 as the albumen of eggs. It is soluble in water, and is usually 
 prepared by treating sulphide of iron with diluted sulphuric 
 acid. The chemical equation is FeS+H 2 S0 4 =FeO-fH 2 S. This 
 gas acts promptly on nearly all the metals forming sulphides. 
 Nearly every sulphide has a characteristic color, so that this 
 gas is an important reagent in chemical analysis. This gas 
 becomes a liquid under a pressure of 255 pounds, and a solid 
 at -122 F. 
 
 PHOSPHORUS combined with calcium exists in the older rocks 
 and the soils formed from them. Its compounds are abundant in 
 plants, especially in the seeds of the cereals which furnish such a 
 large portion of the food-supply of men and domestic animals. 
 Its compounds are abundant in all parts of the animal body, 
 especially in the bones, three-fifths of whose weight consists of 
 calcium phosphates. Formerly bones were the chief source of 
 phosphorus, but extensive deposits of phosphatic rocks have 
 been discovered in Florida and other localities, from which phos- 
 phorus and its compounds may be obtained. These deposits 
 are among the later rocks, and probably derive their phos- 
 phorus from decomposing animal matters, so that our supply 
 of phosphorus comes from the older rocks through the medium 
 of plants and animals. 
 
 In the preparation of phosphorus the animal matter is dis- 
 solved out of the bones by hot water at a high pressure, and 
 
142 PRACTICAL LESSONS IN SCIENCE. 
 
 used in the manufacture of glue. The mineral matter of the bone 
 is then subjected to distillation, from which results ammonia 
 and bone charcoal. The charcoal is used by the sugar refineries 
 until its decolorizing power has been exhausted, when it is 
 strongly hearted, burning away the carbon, leaving the bone-ash, 
 consisting largely of calcium phosphate. This bone-ash is heated 
 with diluted sulphuric acid, which forms with the lime a nearly 
 insoluble calcium sulphate, leaving phosphoric oxide, P 2 5 , in 
 solution. This solution strained and evaporated to the consist- 
 ency of sirup is mixed with charcoal and strongly heated, when 
 the oxygen unites with the carbon, and the phosphorus rising as 
 vapor is condensed in water. 
 
 Phosphorus is a soft, yellowish, semi-transparent, waxy solid, 
 which exposed to the sunlight soon becomes darkened. It is 
 extremely inflammable, taking fire in the air by the heat arising 
 from the slightest friction. It is kept under water to protect it 
 from oxygen, and it should be kept and handled under water, as 
 the heat of the hand will cause it to burn. It not only burns in 
 oxygen and the air, but burns in chlorine, bromine, or iodine. 
 When exposed to the air it undergoes slow oxidation, giving off 
 a white vapor of a garlic odor. In the dark phosphorus gives 
 out light; hence its name, meaning bearer of light. 
 
 If phosphorus is heated without access of air a second variety 
 called red phosphorus is formed. Ordinary phosphorus is soluble 
 in the bisulphide of carbon, is poisonous and easily inflammable. 
 The red phosphorus is insoluble, not poisonous, not easily inflam- 
 mable. The allotropic forms of phosphorus are as well marked 
 as those of sulphur and carbon, and are as yet unexplained. 
 
 The principal use of phosphorus is the manufacture of 
 matches. Matches were invented early in the present century, 
 but the phosphorus friction match was first produced on a com- 
 mercial scale about 1832. A match consists of a splint of wood, 
 one end of which has been dipped in melted sulphur or wax, or 
 paraffine, and this substance covered with the " match composi- 
 tion," which is generally composed of chlorate of potash, phos- 
 phorus, red lead and glue. The match depends for its action 
 
LESSONS IN CHEMISTRY. 143 
 
 on the easy ignition of phosphorus by friction, when mixed with 
 oxidizing agents, like chlorate of potash, the glue only servingto 
 bind the other parts together and attach them to the wood. The 
 phosphorus ignited by friction sets fire to the sulphur or paraf- 
 fine, which in turn ignites the wood. Several different " match 
 compounds" are made. When chlorate of potash is used there 
 is a slight explosion when the match is lighted. When potassium 
 nitrate is used a silent match is made. This form is most com- 
 mon in Germany, while the other is more common in this country 
 and in England. 
 
 A single match is a little thing, but the manufacture of matches 
 for the use of mankind is one of the great industries of the world. 
 More than 2,000 tons of phosphorus are used annually with cor- 
 responding amounts of the other ingredients, and thousands of 
 acres of forests are necessary to supply the splints used every year. 
 It is estimated that forty thousand millions of matches are used 
 annually in the United States alone. Matches made with red 
 phosphorus, called safety matches, are sometimes manufactured, 
 but for some reason they are not in general use. A match is 
 made in France, using red phosphorus, which is ignited by break- 
 ing the match and rubbing the ends together. In Mexico matches, 
 as generally made, are little wax tapers, tipped at both ends 
 with the " match compound." 
 
 Phosphorus forms several compounds with oxygen and hy- 
 drogen. When phosphorus burns in air or oxygen, the dense 
 white fumes formed are phosphoric oxide. This oxide com- 
 bines with water forming two acids as P 2 5 -j-H 2 0=H 3 P0 4 meta- 
 phosphoric acid and P 2 5 -h3H 2 0=2H 3 P0 4 orthophosphoric acid 
 commonly called phosphoric acid. It is the most important of 
 the compounds of phosphorus. It is tribasic, forming three 
 salts with the same metal, but the most common and important 
 salt is calcium phosphate, the chief mineral constituent of the 
 bones, and the form in which phosphorus usually occurs in 
 nature. 
 
 Phosphorus (P) is an indispensable ingredient in the food of 
 animals and plants. No other mineral substances can bear com- 
 
144 PRACTICAL LESSONS IN SCIENCE. 
 
 parison with it as a measure of the capability of a country to 
 support life. Hence substances containing phosphate of lime are 
 of great value as fertilizers. The phosphate being practically 
 insoluble, is not easily distributed through the soil. But by 
 treating the phosphate with sulphuric acid it is transformed into 
 a soluble lime salt called superphosphate, which is easily distrib- 
 uted to the soil by water. It is said that in England alone more 
 than 500,000 tons of phosphate materials are used annually in 
 the manufacture of artificial manures. Phosphorus forms a 
 compound with hydrogen called phosphine, formula PH 3 . It is 
 somewhat analogous to ammonia. It has no economic value, 
 and is characterized as having the most villainous odor known. 
 
 ARSENIC (As) is often classed with the metals because of its 
 metallic luster, but it forms no base with oxygen, and in many 
 respects is similar to phosphorus. It is sometimes found pure 
 in nature and sometimes as an oxide, but more commonly in 
 combination with various metals, as the arsenides of nickel, co- 
 balt and iron. The principal source of arsenic and its compounds 
 is arsenical pyrites, formula, FeAsS. Arsenic is also obtained as 
 a by-product in working ores of tin, nickel and cobalt. 
 
 When arsenic is heated in the air it burns with a bluish flame, 
 giving off fumes which have the odor of garlic, and are very 
 poisonous. These fumes condense into a white solid called 
 arsenic trioxide, formula As 2 3 . It is the arsenic of the shops. 
 It is used in glass-making, in the manufacture of coloring mat- 
 ters; with water it forms a weak acid which forms salts, called 
 arsenites. An arsenical soap made of arsenite of potash, soap 
 and camphor is sometimes used by naturalists to preserve the 
 skins of birds and animals. Arsenite of copper, called Scheele's 
 green, is much used in coloring wall papers, feathers, muslin, etc. 
 
 In quantities less than poisonous doses arsenic trioxide has pe- 
 culiar effects on the animal body; it seems to favor the deposition 
 of fat ; grooms use it to improve the appearance of their horses, 
 and in some parts of Europe men and women take it for the 
 same purpose. A solution of arsenite of potash is much used 
 in medicine as Fowler's solutions. Arsenic pentoxide, formula 
 
LESSONS IN CHEMISTRY. 145 
 
 As 2 5 , combined with water, forms arsenic acid, which forms 
 arseniates. Arsenic acid by its action upon aniline forms the 
 beautiful dye called magenta. It is also much used in calico 
 printing. There are three sulphides of arsenic. Kealgar, or red 
 orpiment, formula As 2 S 2 , is a beautiful mineral crystallizing in 
 orange red prisms. It is an important ingredient in compositions 
 used for fire-works and signal lights. Yellow orpiment, As 2 S 3 , 
 is found native as yellow prismatic crystals. A fine yellow paint 
 is made from this substance. The other sulphide is not of special 
 interest. 
 
 Arsine is a compound of arsenic and hydrogen, formula, 
 AsH 3 , analogous to ammonia and phosphine. It is a color- 
 less, poisonous gas, having an unpleasant odor. Arrange an 
 apparatus as in preparing hydrogen, adding a little arsenic. 
 Arrange a delivery tube so that the gas formed may be burned. 
 When the gas is burning freely bring into the flame a piece of 
 porcelain, and a dark spot is formed by the condensed arsenic 
 called a mirror of arsenic. When carefully performed this is 
 a very delicate test for the presence of arsenic, and is exten- 
 sively used in examining the contents of the stomach of per- 
 sons in cases of suspected poisoning. It is known as Marsh's 
 test. Arsenic and its compounds are notable for their poisonous 
 properties, and for their bright and beautiful colors. 
 L. s. 10 
 
CHAPTER XVIII. 
 
 SODIUM AND LITHIUM. 
 
 WE have discussed briefly the non-metal or acid-forming ele- 
 ments that seem of most importance, considering some of their 
 compounds, and we have developed and illustrated some of the 
 principles of chemical action. This work has, however, been 
 somewhat fragmentary and incomplete, because at every step it 
 was necessary to refer to and employ the aid of metallic or base- 
 forming elements, and of salts, that great class of compounds 
 resulting from the combinations of both acid and base-forming 
 elements. In the study of the more important metals, we must 
 at every step invoke the aid of the non-metallic elements in ex- 
 plaining the varied actions and other chemical phenomena that 
 occur. The work will consist, then, in taking new steps in re- 
 viewing and completing many steps already taken, and in the 
 practical application of chemical ideas and principles to the ordi- 
 nary affairs of life. 
 
 Potassium and sodium are typical representatives of the alka- 
 line metals, and from the number of times they have been men- 
 tioned while studying the non-metals we may form some idea of 
 their importance in all lines of chemical phenomena. 
 
 POTASSIUM (K), best known in its hydroxide called potash, is 
 a silver-white metal, lighter than water and so soft that it can be 
 cut and molded like wax. When thrown upon water it unites 
 rapidly with the oxygen, generating heat enough to ignite the 
 hydrogen set free and to vaporize some of the metal, which, burn- 
 ing with the hydrogen, gives the flame the beautiful violet color 
 characteristic of potassium. The oxide formed is dissolved in 
 the water, giving it a soapy feel which is a common property of 
 alkaline solutions. 
 
 Potassium compounds are components of many of the older 
 (146) 
 
LESSONS IN CHEMISTRY. 147 
 
 rocks, and these, broken down and pulverized, yield up a 
 portion of their potassium to growing vegetation. When 
 vegetable structures are burned, the potassium forms a por- 
 tion of the ash in the form of a carbonate, formula K 2 C0 3 . 
 When the wood ashes are leached with water the potassium car- 
 bonate is dissolved out and the solution evaporated yields an 
 impure salt, called potash, which is much used in the manufacture 
 of soft soap and of glass. It is also a valuable fertilizer. The 
 hydroxide or caustic potash is obtained from the solution of po- 
 tassium carbonate by treating it with slaked lime. The chemical 
 equation is K 2 C0 3 +CA0 2 H 2 , calcium hydroxide, =CaC0 3 , calcium 
 carbonate +2KOH, the potassium hydroxide. This compound 
 is a brittle, white solid , having a strong affinity for water, so that 
 it rapidly deliquesces in the air. It is the most powerful alkali 
 in use, and its activity as a chemical agent makes it of great 
 value to the chemist. It is used in medicine as a caustic. It re- 
 places the hydrogen of acids forming salts, as the carbonates, 
 nitrates and sulphates. It decomposes animal and vegetable 
 substances, whether living or dead. Potassium bicarbonate, for- 
 mula HKC0 3 ,is a salt much used in medicine for making efferves- 
 cent solutions by adding citric or tartaric acids. 
 
 Another very common and important salt of this metal is 
 potassium nitrate niter, or saltpeter, formula KN0 3 . It is a nat- 
 ural product of some parts of India and is produced in an artifi- 
 cial way, by heaping up organic matter with lime, ashes and 
 soil, keeping the mass well moistened with urine for two or three 
 years. In the mass nitrates are slowly formed and may be 
 leached out with water and purified for use. The potassium 
 nitrate may also be prepared from the sodium nitrate by treating 
 it with potassium chloride, according to the following equation : 
 NaN0 3 , sodium nitrate, +KCL, potassium chloride, KN0 3 
 niter, -hNaCl sodium chloride, all in solution together. In evap- 
 orating this solution the sodium chloride, being less soluble in 
 boiling water, crystallizes out, leaving the niter still in solu- 
 tion. When the solution is allowed to cool the niter crystallizes 
 out, as it is less soluble in cold water, leaving some chlorides 
 
148 PRACTICAL LESSONS IN SCIENCE. 
 
 still in solution. In refining the niter it is dissolved in boiling 
 water, filtered, then allowed to cool and crystallize while kept in 
 constant motion, so that the salt may be deposited in smaller 
 crystals than if allowed to crystallize from a quiet liquid. The 
 crystals are thoroughly washed, then dried for use. 
 
 These operations illustrate some curious and interesting prop- 
 erties of the substances spoken of, and how these properties have 
 been studied out and made use of in preparing the substances for 
 use, and in most cases they were discovered and utilized by non- 
 scientific men, under pressure of business competition long before 
 they were even partially explained by a scientific man. 
 
 Potassium nitrate is a crystalline salt that readily dissolves 
 in water, having a cooling saline taste, and strong antiseptic 
 powers, so that it is often used in preserving meats. Potassium 
 forms an interesting compound with chlorine, called potassium 
 chloride, formula KC1, which occurs in great masses in the salt 
 mines in Saxony, and is an important source of potassium and 
 its compounds. It resembles rock salt in appearance. Another 
 important salt of potassium is potassium chlorate, formula 
 KC10 3 . It is prepared by passing chlorine gas through a solu- 
 tion of potassium carbonate. As this salt gives up its oxygen 
 freely to other bodies, it is called an oxidizing agent. 
 
 Pulverize carefully a small piece of potassium chlorate and mix 
 with it an equal bulk of sugar ; put the mixture on a brick in the 
 open air, then let a drop of sulphuric acid fall on it and a vivid 
 combustion will follow. Care should be taken both in pulverizing 
 and mixing not to use percussion or heavy pressure, and small 
 quantities should be used at least until one is familiar with the 
 explosive powers of this salt. Cream of tartar, much used in 
 cooking, is potassium tartrate, mainly obtained from fermenting 
 grape juice. 
 
 Potassium as a metal is of no economic value, but some of its 
 compounds are among the most important known. The use 
 of the carbonate as an alkali in making soap, the use of the 
 chlorate as an oxidizing agent in the manufacture of matches, 
 and the use of the nitrate as an oxidizing agent in the manufac- 
 
LESSONS IN CHEMISTHY. 
 
 ture of gunpowder, puts potassium in the front rank of useful 
 metals. 
 
 Gunpowder is an intimate mixture of potassium nitrate, sul- 
 phur and powdered charcoal. The nitrate furnishes oxygen in 
 great abundance, charcoal, carbon in available form, and the 
 sulphur ignites at a low temperature, altogether tending to 
 rapid and intense combustion. The nitrate for the manufacture 
 of gunpowder should be free from the chlorides of potassium and 
 sodium, should be free from coloring matter and should show 
 neither acid nor alkaline reaction. The charcoal for gunpowder is 
 best made of some light wood, as alder or willow, as charcoal 
 from these woods is lighter and more easily combustible. The 
 wood is burned in a retort at a temperature of about 1,000 F. 
 which yields a charcoal of the most desirable density. The char- 
 coal is allowed to cool slowly, and is then exposed to the air for 
 several days, so that it may absorb moisture ; for if ground be- 
 fore it is liable to spontaneous combustion. It is then ground 
 and sifted to free it from dust. Distilled sulphur is used, as it is 
 soluble and free from sulphurous and sulphuric vapors. The pro- 
 portions of these ingredients varies among manufacturers. Eng- 
 lish government powder contains 75 per cent, of saltpeter, 15 
 per cent, charcoal and 10 per cent, sulphur. These substances 
 are first thoroughly mixed, and the mixture, in charges of about 
 50 pounds each, is subjected to the action of the incorporating 
 mill, which is something like the dry pan used in preparing clay 
 for brick making, consisting of heavy iron rollers with scrapers 
 and plows so as to keep the mass well mixed while it is being 
 pressed by the rollers. This process continues about three hours 
 for slow-burning cannon powder, and about five hours for rifle 
 powder. The mass is sprinkled with water during the time, so 
 that at the close of the process the grayish mass of mill cake 
 contains from 2 to 3 per cent, of water. The mill cake is broken 
 up and packed in layers about half an inch thick between copper 
 plates and subjected to great pressure under the hydraulic press. 
 This not only makes the powder compact, but it seems to have 
 less capacity for absorbing moisture. But this mass will not 
 
150 PRACTICAL LESSONS IN SCIENCE. 
 
 burn rapidly enough. It must be broken up into grains, which 
 are separated by sieves, so that the grains of the same size go 
 together. These grains are polished by friction among them- 
 selves in revolving barrels, sifted from dust, dried and sifted 
 again, when the powder is ready for packing. For cannon powder 
 the grains are sometimes a half inch in diameter, and sometimes 
 they are made in molds, so that the form is definite. 
 
 Good powder should be composed of hard angular grains 
 which do not soil the fingers, and when fired on a sheet of paper 
 should burn without sparks and without scorching the paper or 
 soiling it to any great degree. The products of the combustion 
 of powder are chiefly potassium carbonates and sulphates, with 
 carbon dioxide, carbonic oxide, hydrogen and marsh gas. The 
 solid powder changing into these gases, which are expanded by 
 the great heat of the combustion, accounts for the mechanical 
 effects of the explosion. 
 
 It is estimated that the temperature resulting from the ex- 
 plosion of powder as ordinarily used is over 5,000 F., at which 
 temperature some of the gases might be separated into their 
 elements, which would increase the expansive force. It has been 
 estimated that the explosion of a cubic inch of good gunpowder 
 would exert a pressure of about fifteen tons to the square inch if 
 it could all be burned on the instant. It is at present impossible 
 to fully explain the phenomena of the combustion of powder, as 
 the products and conditions at the time of explosion must be 
 different from what they are afterward when the products may 
 be collected and studied. Gunpowder is of very great value. 
 Some have considered its influence on civilization as next in im- 
 portance to the discovery of the printing press and application 
 of steam to machinery. Besides its use in war it is of immense 
 value in all mining and quarrying industries and in many en- 
 gineering operations, although other explosives are supplanting 
 it in some directions. Gunpowder is superior to most other ex- 
 plosives in the uniformity of its action, in that its manufacture 
 and transportation are less dangerous, in that it is not liable to 
 change when stored, and for use in gunnery its slower action 
 
LESSONS IN CHEMISTRY. 151 
 
 exerts less strain on the gun. The early history of powder is 
 obscure. Our first knowledge of its use as a military agent dates 
 from the seventh century, while its first use as a propelling agent 
 was in Spain in the 12th century. It was known and used in Eng- 
 land early in the 1.4th century. 
 
 Potassium and its compounds have been derived from the rocks 
 through the medium of plants, but sodium and its compounds 
 are derived from seawater, which derived them from the older 
 rocks by solution. While land plants gather up potassium com- 
 pounds along with some sodium compounds from the soils, 
 water takes up sodium compounds, with some potassium com- 
 pounds, and carries them down to the sea. These sodium com- 
 pounds are taken up to some extent by seaweeds, and we can 
 obtain sodium compounds from sea plants as we obtain po- 
 tassium compounds from land plants; but it is more profit- 
 able to take them directly from the seawater, or from beds of 
 rock salt which are supposed to have been deposited from sea- 
 water. 
 
 Rock salt is sometimes mined as other rock is mined ; some- 
 times water is let into the mine, then pumped out after it has dis- 
 solved its load of salt. Again in connection with these salt beds 
 natural brines are abundant, which flow out as springs or may 
 be pumped out for use. In some places seawater is pumped into 
 shallow ponds or lakes and allowed to evaporate in the sun until 
 it becomes strong enough to pay for artificial evaporation. In 
 Russia, sometimes a portion of the pure water is allowed to 
 freeze out of the brine. Seawater, rock salt, and natural brines, 
 besides the sodium chloride, contain also magnesium and potas- 
 sium chlorides, and sulphates of magnesia and lime. But as the 
 water is evaporated, most of the sodium chloride crystallizes out, 
 leaving the other substances in solution with iodine, bromine, 
 etc. From the sodium chloride, chlorine, hydrochloric acid and 
 the metal sodium with its various compounds are derived. So- 
 dium chloride, common salt, formula NaCl, is too well known to 
 need any description. Its usefulness in preserving meat, and as 
 an article of food for man and beast make it almost essential to 
 
152 PRACTICAL LESSONS IN SCIENCE. 
 
 the existence of animal life. It is also used in glazing pottery 
 ware. 
 
 Previous to the war of the French Revolution most of the car- 
 bonate of soda came from Spain. As the supply became scanty 
 and the prices high, Napoleon offered a premium for the discov- 
 ery of a process by which the carbonate could be made in France. 
 The chemist LeBlanc discovered the process now in use for the 
 manufacture of sodium carbonate from sodium chloride, a case 
 in which science took the lead in an economic process. By this 
 process sodium chloride is mixed with an equal weight of sul- 
 phuric acid and strongly heated, which results in the formation 
 of the sodium sulphate, called salt cake and hydrochloric acid, as 
 follows: 2NaCH-H 2 S0 4 =Na 2 S0 4 -f2HCl. Arrangements are 
 usually made so that the acid passing off as a gas is absorbed 
 by water. The sodium sulphate is then mixed with about an 
 equal weight of limestone and about half its weight of fine coal, 
 and strongly heated, when the carbon takes up the oxygen of 
 the sulphate which reduces it to sodium sulphide, Na 2 S, and this 
 acted upon by the carbonic acid liberated from the limestone, 
 forms sodium carbonate Na 2 C0 3 and sulphide of calcium CaS, 
 according to the following equations : Na 2 S0 4 -f-4C=Na 2 S+4CO, 
 and Na 2 S+CaC0 3 limestone Na 2 C0 3 +CaS. The sodium car- 
 bonate is dissolved from the mass and crystallized from the 
 evaporating solution. Sodium bicarbonate HNaC0 3 is the sal- 
 eratus or soda used in bread making, etc. 
 
 The metal SODIUM (Na) is prepared from the carbonate by 
 heating it with coal when the carbon takes the carbon dioxide 
 from the sodium forming carbonic oxide, and the sodium passing 
 over as vapor is condensed under oil or naphtha. Equation, 
 Na2C0 3 +2C=2Na-h3CO. This metal is similar to potassium, 
 but does not decompose water as vigorously, and burns with a 
 yellow flame. It is used for the extraction of the metals alumi- 
 num, magnesium, gold and silver from their ores. 
 
 Sodium hydroxide, formula NaOH, is prepared by treating 
 sodium carbonate with calcium hydroxide, equation Na 2 C0 3 -f-Ca 
 O 2 H 2 =CaC0 8 +2NaOH. It is a white solid somewhat similar to 
 
LESSONS IN CHEMISTRY. 153 
 
 caustic potash in appearance and quality. It is usually obtained 
 as a by-product in the manufacture of sodium carbonate. It is 
 used in the manufacture of hard soap. Sodium sulphate, Na 2 S0 4 , 
 is a salt called Glauber's salt. It is produced as a by-product in 
 the manufacture of hydrochloric acid. 
 
 Nitrate of soda, or Chili saltpeter, is imported from Peru. It 
 is used as a fertilizer and in the manufacture of potassium ni- 
 trate. Fifteen parts of clean sand fused with eight parts of car- 
 bonate of soda form a silicate of soda, which is soluble in hot 
 water, forming a strongly alkaline solution called soluble glass. 
 It is sometimes used to lessen the inflammability of wood, and 
 sometimes as a matrix in forming some kinds of artificial 
 stone. 
 
 Ammonia, NH 3 , and the hypothetical metal ammonium, NH 4 , 
 have been mentioned ; but several salts of ammonium are inter- 
 esting, and may be considered here as they are somewhat similar 
 to corresponding compounds of sodium and potassium. Am- 
 monium chloride is sometimes found in nature, but is usually 
 prepared from the ammoniacal liquors of gas works. These 
 liquors are treated with hydrochloric acid, the solution evapo- 
 rated and the residue heated, when the ammonium chloride vap- 
 orizes without melting, and is condensed on cold surfaces in a 
 crystalline form. It has a sharp salty taste, and is freely soluble 
 in water, lowering the temperature considerably, so that it is 
 frequently used in making freezing mixtures. From it ammonia 
 and carbonate of ammonia are prepared, and it is used in dye- 
 ing, in soldering copper and brass, and in galvanizing iron. 
 
 Ammonium sulphide (NH 4 ) 2 S,is prepared bypassing hydrogen 
 sulphide through aqua ammonia, 2NH 3 H-H 2 S=(NH 4 ) 2 S. This 
 compound is a colorless liquid of unpleasant odor, which soon 
 becomes yellowish from partial decomposition. It is a very use- 
 ful agent in the laboratory. 
 
 Bicarbonate of ammonia H(NH 4 )C0 3 , called "smelling salts," 
 is frequently used in medicine, and it is also used by bakers and 
 confectioners. Ammonium sulphate, (NH 4 ) 2 S0 4 , is used in the 
 manufacture of artificial manures and ammonium alum. 
 
154 PRACTICAL LESSONS IN SCIENCE. 
 
 LITHIUM, the lightest metal known, occurs in small quantities 
 in some kinds of mica and other minerals ; is found in the waters 
 of many springs; in tobacco, milk, blood, sea water, etc. It is 
 somewhat similar to potassium and sodium in its properties. It 
 gives a bright carmine color to flame. Lithia water is much used 
 in medicine. Potassium, sodium and lithium are alike in the 
 powerful alkalinity of their oxides and in the solubility of their 
 salts, and in that they give bright colors to flames, sodium 
 yellow, potassium violet or lilac, and lithium red. 
 
CHAPTER XIX. 
 
 CALCIUM, BARIUM, STRONTIUM, MAGNESIUM AND ZINC. 
 
 CALCIUM (Ca) is a very abundant element, as calcium carbon- 
 ate it forms the limestones, the marbles and the chalk of the 
 earth. Calc spar, the marbles and many limestones are crystal- 
 line forms of this mineral. It occurs in bones, corals and the 
 shells of mollusks are nearly pure calcium carbonate. 
 
 Calcium oxide called lime or quick lime is formed by heating 
 the carbonate which drives off the carbon dioxide, leaving the 
 oxide as a white infusible solid, formula CaO. The oxide, com- 
 bines vigorously with water, forming the calcium hydroxide 
 Ca0 2 H 2 . In this process a high degree of heat is evolved, often 
 enough to ignite wood, the oxide swelling up and crumbling to a 
 white powder, called slacked lime, which is somewhat soluble in 
 water forming what is called lime water. If exposed to the air 
 the oxide taking water from the air slowly changes to the hydrox- 
 ide. The hydroxide is the most important of the bases, and is 
 used in almost every art or manufacture which involves chemical 
 changes. It is used in making mortar, glass and soap. 
 
 Calcium sulphate (CaS0 4 -|-H 2 0) occurs in nature as the trans- 
 parent selenite and the opaque gypsum, which is often beautifully 
 colored, sometimes it is pure white when it is called alabaster. 
 When heated to a temperature of 350 to 400 F. the water of the 
 gypsum is driven off and it becomes, what is called, plaster of 
 Paris. When this powder is mixed with water a combination 
 takes place forming a solid nearly as compact and strong as the 
 original gypsum. In the act of setting the plaster expands 
 slightly which makes it especially valuable for taking casts of 
 objects. It is much used in the reproduction of statues and other 
 sculptural forms. The walls and ornamentation of the Colum- 
 bian Fair buildings were made of light wood covered with 
 
 (155) 
 
156 PRACTICAL LESSONS IN SCIENCE. 
 
 plaster of Paris, and at a little distance they have the appearance 
 of stone. Stucco is plaster of Paris sometimes colored, and some 
 cements are made by mixing alum with the plaster. Its property 
 of quickly assuming a solid condition makes it an interesting 
 and very valuable substance. It is interesting to note that 
 plaster of Paris cannot be used a second time, indicating that it 
 is not the same as the gypsum. 
 
 Calcium chloride (CaCl 2 ) is a crystalline substance which has a 
 strong affinity for water and is much used as a drying agent in 
 chemical work. The bleaching powder, called chloride of lime, is 
 an impure hypochlorite of lime which depends for its action on 
 the chlorine it contains. 
 
 MORTAR is a compound of one part of freshly slacked lime 
 and two or three parts of clean sand mixed with water enough 
 to form a stiff paste. When this mixture is exposed to the air 
 the water evaporates, carbon dioxide from the air combines 
 with the calcium oxide forming the calcium carbonate. In this 
 way the mortar becomes very hard so that however massive the 
 structure the mortar can bear its share of the load. 
 
 COMMON GLASS is a silicate of calcium and sodium made by 
 melting together sand (silica) and the carbonates of sodium 
 and calcium. Bohemian glass, used in the manufacture of chem- 
 ical apparatus is a silicate of calcium and potassium. It is not 
 as easily fusible as common glass. Plate glass contains some 
 potassium silicate in addition to the silicate of calcium and so- 
 dium. Flint glass is a silicate of potassium and lead. It has a 
 high refractive power, is easily fusible and easily cut. It is much 
 used for optical instruments, and ornamental glassware. Glass 
 of various colors is produced by melting with it certain metallic 
 oxides, as the oxide of iron gives a green color, the suboxide of 
 copper a red color, the oxide of cobalt a blue, etc, 
 
 BARIUM (Ba), a yellowish malleable metal, is of little value 
 but some of its compounds are interesting. Barium sulphate, 
 called heavy spar, occurs abundantly as an associate of lead 
 ores in the mineral regions of Missouri. It is a white, heavy 
 mineral sometimes used to adulterate white lead paint, and for 
 
LESSONS IN CHEMISTRY. 157 
 
 glazing cards, etc. Barium chloride, BaCl 2? is much used in lab- 
 oratory work as a test for the presence of sulphuric acid. Barium 
 compounds give a yellowish green flame. 
 
 STRONTIUM is less abundant than barium and is of little interest. 
 It occurs in nature chiefly as the mineral celestine which is the 
 strontium nitrate. This salt gives a bright red color to flames, 
 and is often used in the preparation of fire works. 
 
 MAGNESIUM (Mg) is a silver white metal. It burns at a low 
 temperature with a brilliant white light, which may be used to 
 illuminate objects for photographing. It is widely distributed 
 in nature as an ingredient of dolomite or magnesian limestone, 
 soapstone, asbestos, horenblend and talc. Most of these min- 
 erals have a soapy feel. Magnesium sulphate MgS0 4 H-7H 2 is 
 the epsom salts of the shops, and the oxide is the common mag- 
 nesia. When dolomite is burned it becomes what is called water 
 lime, which makes a mortar that will harden under water. 
 
 ZINC (Zn) is a bluish white metal of a crystalline structure, 
 light, easily fusible, but not easily corroded by atmospheric 
 influences. The strength of iron and durability of zinc are com- 
 bined in the so-called galvanized iron, which is made by dipping 
 well cleaned iron in melted zinc, much as tin plate is made. Zinc 
 is an ingredient of brass and German silver. 
 
 Zinc oxide is used in painting as zinc white, and zinc sulphate 
 (ZnS0 4 -h7H 2 0) is used in calico printing and to some extent in 
 medicine as white vitriol. Zinc is easily attacked by acids, and 
 the chemical action of acids on zinc is the most common source 
 of the galvanic current. Zinc precipitates lead, copper and silver 
 from solutions. A very interesting experiment is to place a strip 
 of zinc in a solution of acetate of lead. The lead quickly begins 
 to collect on the zinc forming what is called the lead tree. Zinc 
 occurs in nature most abundantly as the carbonate and as the 
 sulphide, which is the black jack of the lead miner. 
 
CHAPTER XX. I 
 
 COPPER, MERCURY, SILVER AND ALUMINIUM. 
 
 COPPER (Cu) is a reddish, malleable, ducile metal found abund- 
 antly in nature as native copper, and as an ore combined with 
 sulphur and iron. Copper is used for coins in all parts of the 
 world, and is an ingredient of most of the gold and silver coins, 
 giving them additional hardness. Brass is an alloy of copper, 
 tin and zinc; bell metal and gun metal are alloys of copper and 
 tin, and aluminium bronze consists of 90 parts copper and 10 
 parts of aluminium. Hard solder contains equal parts of cop- 
 per and zinc. Copper is extensively used as a protection for 
 wooden ships; copper wire of different sizes is the substance gen- 
 erally used in transmitting electricity for power and lighting 
 purposes. As copper is found pure, or nearly so, in nature, it 
 was one of the earliest metals worked by man. The early inhab- 
 itants of America made cutting tools and ornaments of copper. 
 
 In Europe and the east brass or bronze was extensively used 
 for many purposes before the discovery of methods for working 
 iron. While iron has supplanted copper in many places, it still 
 remains one of the most useful and valuable of the metals. 
 Copper sulphate (CuS0 4 -f-5H 2 0), blue vitriol, is largely used by 
 the dyer and calico printer, and in the manufacture of pigments. 
 It is also used in electrotyping, in galvanic batteries, and in 
 medicine. When heated the crystals lose their water of crys- 
 tallization, crumbling down to a whitish powder, which again 
 becomes blue when allowed to combine with water. 
 
 Copper is precipitated from the solutions of its salts by the 
 metals zinc and iron and by the galvanic current. If a strip of 
 zinc is placed in a solution of copper sulphate it will soon become 
 covered with a layer of copper, the zinc displacing the copper in 
 the sulphate as follows : Zn-f-CuS0 4 =ZnS0 4 in solution -j-Cu as a 
 (158) 
 
LESSONS IN CHEMISTRY. 159 
 
 coating on the zinc. A knife blade placed in the solution is 
 quickly covered with copper. Objects are plated with copper by 
 placing them in a solution of copper sulphate and connecting 
 them with a galvanic current, when the sulphate is decomposed 
 and the copper deposited on the article. There are oxides, 
 sulphides, chlorides, carbonates and arsenites of copper, but 
 perhaps the most interesting are the blue and green malachites, 
 carbonates of copper which are highly prized for their beauty. 
 
 The metals generally are solids, but mercury is a liquid at 
 ordinary temperatures, having none of the properties usually 
 ascribed to metals except its brilliant luster and high specific 
 gravity. The pure mercury is sometimes found in nature, but it 
 more commonly occurs as a sulphide in the mineral cinnabar. 
 
 MERCURY (Hg) is obtained from cinnabar by the heat, which 
 burns out the sulphur, vaporizing the mercury, which is con- 
 densed in brick chambers or flues. It forms alloys, called amal- 
 gams, with most of the other metals, especially with gold and 
 silver. This property makes mercury a valuable agent in sepa- 
 rating gold and silver from their ores. 
 
 Mercury is used in making thermometers and barometers, but 
 its chief use is in silvering mirrors. The silvering of a mirror 
 consists of an amalgam of tin. A sheet of tin foil is laid on a 
 table and rubbed over with mercury, and then another thin 
 layer of mercury is poured over it. The glass is then carefully 
 slid over the foil so as to push off some of the superfluous mer- 
 cury, together with impurities; then heavy weights are laid on 
 the glass to squeeze out any excess of mercury, and in a short 
 time the amalgam adheres firmly to the glass. 
 
 The mercurous chloride is the calomel used in medicine, and the 
 mercuric chloride is the active poison, corrosive sublimate. An 
 oxide of mercury is an ingredient of red precipitate ointment, and 
 the pigment vermillion is the sulphide. The vapor of mercury, and 
 nearly all its compounds, are poisonous, and all those who work 
 with mercury in any of its forms suffer from its effects. 
 
 SILVER (Ag) is a white, malleable, ductile metal which is not 
 easily tarnished or corroded. Pure silver is often found in na- 
 
160 PRACTICAL LESSONS IN SCIENCE. 
 
 ture, but it occurs most abundantly as the silver sulphide, com- 
 bined with lead sulphide and other substances. It also- occurs as 
 the chloride and bromide. The process of obtaining silver from 
 its ores is somewhat complicated and costly. In a general way 
 it is accomplished by heat aided by chlorine from common salt, 
 and by the dissolving power of mercury or lead, or both. 
 
 Silver is used for coin, for plate and for ornaments. Pure 
 silver is so soft that it is usually hardened by the addition of 
 from 7 per cent, to 10 per cent, of copper, so that coins and sil- 
 verware are in fact alloys of silver and copper. It is exten- 
 sively used in plating ware made of cheaper metals or alloys. 
 The chloride of silver, formula, AgCl, is one of the richest ores 
 of silver, and is the form into which silver is usually converted 
 in extracting it from ores. The chloride, bromide and oxide of 
 silver are insoluble in water and change color on exposure to 
 the light. There are many other compounds of silver of which 
 silver nitrate, AgN0 3 , called lunar caustic, is the most important. 
 It is used in surgery, and as it blackens on exposure to light is 
 made the basis of indellible inks. Silver may be precipitated 
 from solutions by zinc, copper, mercury and other metals. 
 
 The chemical changes which silver salts undergo on exposure to 
 light is the basis of the art of photography. To get a photograph 
 on glass pour over the glass a mixture of collodion and potas- 
 sium iodide, which forms a thin film over the glass, which is 
 then placed in a bath of silver nitrate, here a layer of silver 
 iodide is formed in the film. The plate is then exposed in the 
 camera to the action of light from some object to be photo- 
 graphed. When removed from the camera no image is percepti- 
 ble, but on treating the film with a "developer" as a solution 
 of gallic acid in alcohol and acetic acid, the illuminated por- 
 tions appear black while the shaded portions retain the yellow- 
 ish color of the iodide. When the details come out clearly, the 
 developer is washed off and the film treated with a solution of 
 sodium hyposulphite, which dissolves out the iodide that has not 
 been affected by the light, then the hyposulphite is washed away 
 and the plate dried and varnished to protect the film. 
 
LESSONS IN CHEMISTRY. 161 
 
 After oxygen and silicon the most abundant element is the 
 metal ALUMINIUM (Al). It is a tin- white, malleable, ductile, 
 sonorous metal. It is lighter than most other metals and yet 
 it is very strong, approaching iron in this respect. It is never 
 found pure in nature, but is an abundant ingredient in many 
 minerals. The double silicate of aluminium and potassium 
 AlKSi 3 8 a constituent of feldspar, is abundant in trap rock, 
 basalt, mica, and porphyry. Aluminium silicate is the chief 
 ingredient of clay, shale and slate. Aluminium oxide, A1 2 3 , 
 called alumina is nearly pure in the ruby, sapphire and emery. 
 This metal is an ingredient of several double sulphates called 
 alums, as AlK(SO- 4 ) 2 +12H 2 potassium alum, AlNa(S0 4 ) 2 4- 
 12H 2 sodium alum, A1NH 4 (S0 4 ) 2 -|-12H 2 ammonium alum. 
 
 Aluminium hydrate (A10 3 H 3 ) combines readily with many or- 
 ganic coloring matters, forming insoluble compounds. To a so- 
 lution of common alum add a solution of cochineal, and to the 
 mixture add a little ammonia when a colored precipitate of alu- 
 minium hydrate and cochineal will be formed, which is called 
 carmine lake. Similar precipitates may be formed with other or- 
 ganic coloring matters. Fiber of cotton that has been soaked in 
 a solution of alum will retain colors which the cotton alone can- 
 not hold. Soak a piece of cotton cloth in alum water and let it 
 dry a day or two, then treat it and a piece of ordinary cotton 
 with a solution of logwood an*d observe the difference in the 
 amount and permanence of the color taken by the two pieces. 
 Substances having this property are called mordants. 
 
 Clay, aluminium silicate, is the material of which all grades of 
 porcelain and pottery ware and all kinds of brick, tile and terra 
 cotta are made. Clay mixed with water may be moulded in any 
 required shape and after drying may be burned so as to become 
 firm and durable, but pure clay shrinks so much in burning that 
 articles made of it lose their shape and often crack, so that in 
 making bricks, pottery, etc., more or less sand is added to the 
 clay making a mixture which shrinks less and holds its form 
 better than pure clay. 
 
 Bricks are made of a great variety of material and vary in 
 I., s.-u 
 
162 PRACTICAL LESSONS IN SCIENCE. 
 
 quality from the heavy compact vitrified brick that will absorb 
 not more than two or three per cent, of water to the light porous, 
 fragile brick that will absorb half of its weight of water. Bricks 
 are made by hand as they were in Egypt four thousand years 
 ago, and they are made by different kinds of machinery. 
 
 Pottery ware that is designed to hold water must be glazed, 
 which is done by dipping the ware in a mixture of fine sand and 
 water and heating it intensely, in a kiln into which a quantity of 
 wet salt has been thrown. The water, sand and sodium of the 
 salt from a sodium silicate glass, which fuses on the surface of 
 the ware, making it impervious to water. 
 
 In the manufacture of porcelain great care is used in the 
 selection and preparation of the material, definite proportions 
 are used and all the manipulations approach mathematical 
 exactness. One very fine ware is made as follows : The purest 
 materials are selected in the following proportions: Kaolin, 
 Al 4 (Si0 4 ) 3 +4H 2 0, 62 parts, chalk, CaC0 3 , 4 parts, sand Si0 2 , 17 
 parts and feldspar AlKSi 3 8 , 17 parts. These materials are 
 ground up with water and allowed to settle. The water is 
 drained away and the mass well kneaded, then stored away in 
 a damp place for some months, during which time any organic 
 matter is oxidized and the texture of the mass seems to be im- 
 proved. It is then moulded, dried in the air, and strongly heated 
 in a kiln with a wood fire. After burning, the ware must be 
 glazed, care being used to get a glaze that will expand and con- 
 tract with the ware so that it will not crack or craze. The glaze 
 employed at Sevres is a mixture of finely ground feldspar and 
 quartz. When the ware is dipped in this mixture some of it is 
 absorbed, a thin coating remaining on the surface. It is now 
 baked the second time when the glaze fuses, forming aglass var- 
 nish, which covers the surface penetrating the ware to someextent. 
 If the ware is to have a uniform color, some mineral pigment is 
 mixed with the glaze. If designs are to be painted, glasses 
 colored with metallic oxides ground up with the oil of turpentine 
 are used. After painting, the ware is again burned so that the 
 paint is fused upon the glaze. 
 
CHAPTER XXI. 
 
 IRON, NICKEL, COBALT, GOLD AND PLATINUM. 
 
 IRON (Fe) is the most useful, the most widely diffused, and 
 next to aluminium, the most abundant of the metals. Meteoric 
 iron is nearly pure, but native iron is seldom found. Minerals in 
 great numbers contain iron; in fact there are few substances, 
 liquid or solid, that do not contain more or less of this element. 
 The most important ores of iron are the oxides and carbonates, 
 as the magnetic oxide, hematite, or sesquioxide, which consti- 
 tute the great bodies of ore found in the old rocks of New York, 
 Canada, Michigan and Missouri. Clay-ironstone, abundant in 
 the coal measures, is the carbonate of iron, FeC0 3 , mixed with 
 clay. It is the chief ore of England. 
 
 Iron is reduced from its ores by the action of heat and fluxes 
 in a blast furnace. The steps in the process are to expel the 
 water, sulphur, carbonic acid, etc., by heat reducing the ores to 
 oxides. Next reducing the oxides to the metallic state by heat- 
 ing them with carbon, and third, the separation of the earthy 
 impurities by fusion with limestone or clay into a glass or slag, 
 and lastly the carbonizing and melting of the iron. The blast 
 furnace is charged at the top with coal, ore and flux in alternate 
 layers. The air for the support of the combustion is forced in by 
 a powerful blast. The melted iron sinks to the bottom and is 
 drawn off into molds, forming the pig iron of commerce. The 
 lighter slag is also drawn off from time to time. The resulting 
 gases are collected and used in raising the temperature of the air 
 of the blast. This iron contains from two to five per cent, of 
 carbon, is hard, crystalline and easily fusible, being generally 
 contaminated with silicon, sulphur and phosphorus. 
 
 This pig iron is subjected to heat in the puddling furnace, 
 which oxidizes most of the impurities, finally reducing it to a 
 
 (163) 
 
164 PRACTICAL LESSONS IN SCIENCE. 
 
 pasty mass, when it is carried to a squeezer which drives out the 
 slag, welding the iron into a compact body called wrought iron. 
 Wrought iron may be obtained from some of the purer ores by 
 heating them with charcoal in an open forge. It is such ores that 
 are worked by the natives of Africa and Southern Asia. 
 
 The pig iron or cast iron is capable of bearing great pressure, 
 and is useful in the manufacture of articles which are not sub- 
 jected to heavy tension. Wrought iron is tough, and when 
 heated slightly may be drawn into wire or rolled into bars or 
 plates, and is extensively used, especially where toughness is a 
 quality desired. Steel, in composition, is intermediate between 
 cast iron and wrought iron. They are each compounds of iron 
 and carbon, the wrought iron containing very little carbon, one 
 or two parts in a thousand only, while steel contains from three 
 to ten parts and cast iron from fifteen to twenty-five parts. In 
 neither case does there seem to be a definite chemical combination. 
 
 Steel is made by heating wrought iron bars with charcoal to a 
 temperature of about 2,000 for several days, during which time 
 carbon penetrates the iron and the fibrous structure changes to 
 a fine granular form. This process is called cementation. These 
 bars broken up, heated and hammered become more uniform in 
 texture, more tenacious and ductile, forming what is often called 
 shear steel. Steel from the cementation furnace is melted in cru- 
 cibles and molded, forming cast steel, which is more dense, uniform 
 and hard than the shear steel. 
 
 Cast iron is converted into steel by melting it in a large vessel 
 called a converter, and then oxidizing the mass by currents of air 
 forced through it. When the oxidation is nearly complete cast 
 iron enough is added to furnish carbon for converting the whole 
 mass to steel, when it is cast into ingots. This is called the Bes- 
 semer process. Steel becomes very hard and brittle when heated 
 and suddenly cooled, but when allowed to cool slowly it can be 
 given almost any degree of hardness, with some degree of elas- 
 ticity. Pure iron is almost unknown, and of no value in the arts. 
 With all the care exercised in working iron and steel it is almost 
 impossible to secure uniform product. 
 
LESSONS IN CHEMISTRY. 165 
 
 Ferrous sulphate (FeS0 4 -f7H 2 0) is commonly known as 
 green vitriol or copperas. It is manufactured from iron pyrites, 
 so common in the coal measures. It is used in the manufacture 
 of ink and black dyes. There are ferrous and ferric oxides and 
 chlorides, sulphates, nitrates and silicates, and many other in- 
 teresting compounds of iron, but they are of little value in the 
 arts and need not be discussed. 
 
 Iron oxides, hydrates and other compounds yield a large 
 variety of colors, and these compounds are so abundant every 
 where that iron has been called the pigment of nature. 
 
 There are ferrous and ferric cyanides of iron. Common Prus- 
 sian blue seems to be a mixture of these cyanides, formula 
 (Fe 7 C 18 N 18 ). It is largely used in dyeing and calico printing. 
 Potassium ferrocyanide is a mordant of great value. 
 
 NICKEL (Ni)is a metal sometimes found in meteoric iron, and is 
 found associated with cobalt arsenic and sulphur. It is chiefly 
 valuable from its property of imparting a white color to alloys 
 of copper and zinc, as German silver and the five-cent coins. The 
 salts of nickel form green solutions. 
 
 COBALT (Co) is a metal somewhat similar to iron, but is not 
 abundant enough to be of great value, but some of its com- 
 pounds are important on account of their brilliant and perma- 
 nent colors. The salts of the oxides have a fine red color in the 
 hydrated state, while they are blue in the anhydrous. Cobalt 
 blue is the more common color. Chloride of cobalt is used as a 
 sympathetic ink. It has a slight pink color when cold and turns 
 blue when heated. 
 
 MANGANESE (Mn) is a hard, grayish-white metal resembling iron 
 in some of its physical and chemical qualities, and is often asso- 
 ciated with iron in nature. The principal ore of Manganese is 
 the dioxide, Mn0 2 . The compounds of Manganese give up their 
 oxygen readily ; the use of the dioxide in preparing oxygen has 
 been noted. One of the most interesting and valuable com- 
 pounds of Manganese is potassium per manganate, KMn0 4 ; it 
 is soluble in water, forming a dark purple solution. It gives up 
 its oxygen easily, losing its color, and is much used in purifying 
 
166 PRACTICAL LESSONS IN SCIENCE. 
 
 water, as well as in disinfecting or deodorizing decaying animal 
 and vegetable substances. 
 
 CHROMIUM (Cr) is found in nature chiefly as chrome iron ore, 
 Fe 2 Cr 2 4 . When this ore is heated with potassium carbonate and 
 potassium nitrate, potassium chromate is formed. And this salt 
 treated with nitric acid yields potassium dichromate, K 2 Cr. 2 O 7 , 
 the most important form of chromium. It occurs as beautiful 
 red tabular crystals, which dissolve in about ten parts of water. 
 It is sometimes used in electrical batteries, and is a good oxidiz- 
 ing agent. Lead chromate is the chrome yellow used in painting 
 and calico printing. 
 
 BISMUTH (Bi) is a grayish brittle metal of crystalline form. 
 It is used in some alloys as type metal, giving them the property 
 of expanding slightly in the mold so that they are forced into 
 the finest lines. Two parts of bismuth, one of lead and one of 
 tin forms an alloy which melts below the temperature of boiling 
 water. The nitrate of bismuth is used in medicine. 
 
 LEAD (Pb) is a soft grayish metal which is useful in many 
 ways. Its most common form in nature is the sulphide which 
 occurs in connection with sulphides of copper, iron, zinc and 
 silver, with quartz, barium sulphate, calciun fluroide and some- 
 times with bismuth and antimony. Sulphide of lead or galena 
 crystallizes in cubes, having a bright metallic luster. Lead is 
 obtained from galena by heating it with iron, when the latter 
 combines with the sulphur and the lead is set free. Or the sul- 
 phide is roasted in the air until some of it is converted into lead 
 oxide and the lead sulphate, then heated without the access of 
 air when the lead and sulphur are set free as represented in the 
 following equations : PbS-f 2PbO=3Pb-f SO 2 and PbS+PbS0 4 = 
 2Pb-f-2S0 4 . 
 
 Lead is malleable, and in the form of sheets is used to line 
 tanks, cover roofs, make pipes, etc. Lead oxide, PbO is litharge 
 which heated in the air becomes red lead, Pb 3 4 . The red lead 
 is used in storage batteries, where it takes up oxygen becoming 
 lead peroxide Pb0 2 . The red oxide is used as a paint, and in the 
 manufacture of glass and matches and as a glaze for pottery. 
 
LESSONS IN CHEMISTRY. 167 
 
 One part of litharge, and ten parts of brick dust with enough 
 linseed oil to form a paste makes a cement often used by build- 
 ers in repairing broken stone. Acetate of lead, or sugar of lead, 
 is formed by dissolving litharge in vinegar. Lead carbonate, 
 PbC0 3 is the well-known and much-used white lead. 
 
 Lead resists the action of most acids, but when exposed to the 
 air the surface is soon covered by the lead oxide, which with a 
 little moisture becomes lead hydrate, which, combined with car- 
 bon dioxide of the air, becomes lead carbonate. The salts of lead 
 are in general poisonous, and lead in all forms should be used with 
 care. Nearly all natural waters act on lead, forming dangerous 
 compounds. Lead is a constituent of several alloys, as type 
 metal, and solder; bird shot are an alloy of arsenic and lead, and 
 some bullets are an alloy of lead and antinfony, the alloys being 
 harder than lead. 
 
 TIN (Sn) is a soft, malleable white metal, having something of 
 the appearance of silver. The principal ore of tin is the stannic 
 oxide, Sn0 2 , from which the metal is obtained by heating it with 
 coal. Tin does not tarnish in the air at ordinary temperatures, 
 and is largely used as a coating for other metals, as copper and 
 iron. It is also an ingredient of several alloys, as bronze, solder, 
 pewter and type metal. The stannic oxide, when melted with 
 caustic soda, forms the sodium stannate, Na 2 Sn0 3 . This sub- 
 stance is largely used as a mordant by calico printers. Stannous 
 and stannic chlorides are also used in calico printing. Stannic 
 sulphide, SnS 2 , is known as mosaic gold, or bronze powder. 
 
 GOLD (Au) is a beautiful yellow metal, surpassing all others in 
 malleability and ductility. It may be beaten into sheets so thin 
 that 282,000 of them would make a pile only one inch high. 
 Gold is less affected by exposure to the air than any other metal, 
 and is used as a coating of other metals for their protection and 
 to increase their beauty. Gold is usually found free in the veins 
 of rocks, or in the sands resulting from the disintegration of the 
 rocks. It is sometimes so associated with iron, sulphur and cop- 
 per that it is very difficult of reduction. There are oxides and 
 chlorides of gold, but they are of little importance. Gold is so 
 
168 PRACTICAL LESSONS IN SCIENCE. 
 
 soft that for coin and most other purposes it is alloyed with at 
 least 10 per cent, of copper. 
 
 PLATINUM (Pt) is a grayish-white metal, which is very malleable 
 and ductile. It resists the action of most non-metallic substances, 
 and is valuable to the chemist in many ways. It is used for cru- 
 cibles, forceps, tubes, stills, etc. It forms alloys readily, so that 
 it should not be used with easily fusible metals. It is much used 
 in connection with voltaic electricity. None of the platinum com- 
 pounds are of much value. It usually occurs as an alloy with 
 palladium, iridium and other metals. 
 
CHAPTER XXII. 
 
 ILLUMINATING GAS, ANILINE DYES AND RESINS. 
 
 ILLUMINATING gas is one of the products of the destructive 
 distillation of coal. The coal is heated in earthenware retorts 
 without access of air till all the volatile matters are driven off, 
 leaving only gas carbon and coke in the retort. The volatile 
 products passing through water and coolers loses ammoniacal 
 liquids and tarry matters by condensation, then through beds of 
 lime or the ferric hydrate, which removes the sulphur and car- 
 bon dioxide, and thence to the gasometer. The gas in the 
 meter consists of marsh gas, hydrogen and carbon monox- 
 ide, with some vapor of benzole, olefiant gas and other hydro- 
 carbons. 
 
 The ammoniacal liquids are the main source of ammonia and 
 the ammonium salts. The coal tar contains, or is made up of 
 many substances which are volatilized at different temperatures. 
 The first to pass over is water with salts of ammonia in solution, 
 then a brown, oily liquid, lighter than water, containing benzole 
 toluole, etc., then a yellow oil heavier than water, containing 
 napthaline, aniline, carbolic acid, etc., and a black residue called 
 pitch remains, which is employed in making Brunswick black and 
 asphalt for paving. The benzole from the light oil is a colorless 
 liquid with the odor of coal gas. The fact of its dissolving 
 caoutchouc and gutta percha, and that it removes grease from 
 cloth and other objects, makes it a valuable substance. 
 
 The chief purpose to which benzole is devoted is the prepara- 
 tion of aniline, which may be converted into the brilliant dyes 
 now so extensively used. Benzole treated with nitric acid forms 
 a dark red liquid from which water precipitates a yellow oily 
 liquid called nitrobenzole. Benzole, C 6 H 6 +HN0 3 =C 6 H 5 (N0 2 ) , 
 nitrobenzole. When nitrobenzole is treated with sulphuric acid 
 
 (169) 
 
170 PRACTICAL LESSONS IN SCIENCE. 
 
 and zinc the hydrogen set free from the acid replaces the oxygen 
 of the nitrobenzole as follows: C 6 H 5 (N0 2 )+6H=C 6 H 5 NH 2 or 
 C 6 H 7 N aniline, -j-2H 2 0. Aniline is colorless when pure, becom- 
 ing brown if exposed to the air. Aniline mixed with a little tolui- 
 dine derived from toluole, and treated with chloride of lime, 
 yields a beautiful violet dye. What share the toluidine has in 
 the production of the color is not known, and the chemical 
 changes are not understood, but it is known to be an oxida- 
 tion. Red, blue, green, black, yellow, etc., in varying shades 
 may be obtained from these substances by the action of various 
 chemical agents. 
 
 Carbolic acid (C 6 H 6 2 ) makes up the greater part of commer- 
 cial kreasote, which is extensively used as an antiseptic to pre- 
 vent the decay of wood. Carbolic acid is much used as a 
 disinfectant. The value of aniline dyes and other products from 
 coal tar manufactured in Europe amounts to about $30,000,- 
 000 annually. The recovery of the materials for aniline dyes, 
 carbolic acid and other substances from the waste products of 
 gas manufacture is a striking example of the utility of purely 
 scientific work. 
 
 While aniline dyes have superseded many of those formerly used, 
 yet a few are worthy of mention. Madder, furnishing beautiful 
 red and purples, is derived from the root of a plant much grown in 
 Europe. The essential ingredient of madder is alizarin, which 
 has been prepared artificially from coal-tar products, so that the 
 madder industry is fast passing away. Brazil wood and log- 
 wood, quercitron from oak bark, fustic and indigo are important 
 dyes. Indigo is prepared from various species of plants by al- 
 lowing them to ferment in water, and when a blue scum appears 
 on the surface of the water a little lime is added, when the indigo 
 is precipitated. Cochineal, a dye prepared from an insect, gives 
 a beautiful red. 
 
 The art of coloring fabrics of various kinds has been practiced 
 by man everywhere from the earliest times. The process varies 
 with different colors and different fibers. To obtain the finest 
 shades of mauve, magenta, purple and many other colors on 
 
LESSONS IN CHEMISTRY. 171 
 
 silk or wool fiber the whole process consists in placing the ma- 
 terial in a solution of the desired color; it absorbs the color 
 becoming dyed. The color enters into such intimate combination 
 with the fiber that it cannot be washed out. There is probably 
 no chemical action between the fiber and the coloring matter, 
 although the union is very close and some have considered it a 
 chemical union. 
 
 In the case of the same kind of fibers, with cochineal, logwood 
 or madder, there would be no permanent color. In such cases 
 another class of bodies called mordants is necessary. They in 
 some way help to make the coloring matters adhere to the fiber. 
 The substances commonly used as mordants are the salts of 
 aluminum, iron, tin, chromium, copper and a few other metals. 
 Woolen goods, after boiling in salts of tin, will take on a brilliant 
 scarlet in a solution of cochineal. The process of dyeing calico 
 with logwood is first to pass the calico through a hot solution 
 of sulphate of iron, then through lime water, which decomposes 
 the iron salts, setting free the iron oxide, which remains in the 
 fiber ; the excess of lime is then washed away, preparing the calico 
 for the logwood. The calico, now of a buff color from the oxide, 
 when placed in the hot solution of logwood, speedily acquires a 
 dark hue, and in about half an hour has become dyed a dense 
 black color. The above will give some idea of the methods em- 
 ployed in one of the most important industries we have, and 
 that at every step from the preparation of the dye or mor- 
 dant it is mainly a chemical process. And a very large propor- 
 tion of all the chemical elements are in some way used in this 
 industry. 
 
 Some interesting products arise from the destructive distilla- 
 tion of wood. Wood and coal are both of vegetable origin, but 
 coal, having suffered partial decomposition, has lost much of its 
 original oxygen, so that the products of wood and coal differ 
 somewhat. The gases derived from wood are marsh gas, and 
 the carbon oxides. Among the liquids are toluole, kreasote, 
 acetic acid and wood spirit. Paraffin, a beautiful, semi-trans- 
 parent, waxy substance, is the most important solid. It is used 
 
172 PRACTICAL LESSONS IN SCIENCE. 
 
 extensively as a lubricating oil. It burns with luminous flame, 
 and is used in the manufacture of candles. 
 
 Petroleum oil is a mixture of hydrocarbons of the marsh gas 
 and olefiant gas series, which makes it valuable for lubricating 
 and lighting purposes. Bitumen, or asphaltvm, is a hydrocar- 
 bon something like turpentine, which seems to be derived from 
 petroleum oil. It is soluble in turpentine, and is used as a water- 
 proof varnish and in making roadways, walks, etc. 
 
 When incisions are made in the bark and wood of the different 
 varieties of pine, spruce and allied trees, a viscous substance 
 flows out called pitch, gum, turpentine or balsam. It consists of 
 resin mixed with the essential oil of the plant. When this sub- 
 stance is distilled with water the oil passes over and the resin 
 remains, which is called rosin. Turpentine obtained from the 
 pine yields from 75 to 90 per cent, of rosin (C 20 H 30 2 ), and from 
 10 to 25 per cent, of essential oil commonly called spirits of tur- 
 pentine, C 10 H 16 . 
 
 Rosin burns with a smoky flame, and is used in the prepara- 
 tion of lampblack and varnish. The resins generally are in- 
 soluble in water, but dissolve in alcohol, naphtha and the oil of 
 turpentine. The solutions thus obtained are called varnishes. 
 When exposed to the air in a thin layer the solvent evaporates, 
 leaving a layer of resin over the substance which is impervious to 
 air and water. Gum copal, shellac, amber and the balsams are 
 resins similar to common rosin. 
 
 The oils of bergamot, cloves, lemons, tolu, valerian and 
 others are similar to the oil of turpentine, having about the 
 same composition. 
 
 Camphor, obtained from the camphor laurel of Japan, is 
 similar to the resins, having the formula C 10 H 16 0. It is a crys- 
 talline substance, melting at 175 F., burning with smoky flame, 
 and passing into vapor at ordinary temperatures. It is almost 
 insoluble in water, but is dissolved by alcohol and ether. The 
 alcoholic solution is known as spirits of camphor. 
 
 Asafoetida, aloes, gamboge, myrrh and others are gum-resins 
 which exude from plants in a milky state, gradually solidifying 
 
LESSONS IN CHEMISTRY. 173 
 
 on exposure to the air. They consist of a mixture of gum, resin 
 and essential oil. They are partially soluble in alcohol, and are 
 used in medicine. 
 
 Caoutchouc is prepared from the milky juice of several varieties 
 of tropical plants. It is insoluble in water, but soluble in tur- 
 pentine and naphtha. It is elastic, and when warmed becomes 
 soft and pliable. It is not acted on by alkalies or dilute acids. 
 In time it oxidizes into a resin, losing its strength and water- 
 proof qualities. It is extensively used in the manufacture of 
 waterproof goods, water tubes, springs, elastic fabrics, gas 
 holders, etc. In many cases it is used in the manufacture of 
 waterproof cloth or felt, which is prepared by dissolving the 
 caoutchouc and spreading it over the cloth or felt, which is then 
 passed between rollers, which causes firm union, waterproofing 
 the cloth and strengthening the caoutchouc. 
 
 Caoutchouc placed in fused sulphur will absorb large quantities 
 of that element, and if heated to about 300 F. it becomes vul- 
 canized, and if heated to a higher degree it at length becomes 
 vulcanite, which is used in the manufacture of combs, etc. Vul- 
 canized caoutchouc is not soluble in turpentine or naphtha, and 
 is not sticky when warmed. 
 
 Gutta percha is similar to caoutchouc in many respects, but is 
 only slightly elastic at ordinary temperatures. It is insoluble in 
 water and a poor conductor of electricity, so that it is much 
 used for water pipes and as an insulator for electric wires, etc. 
 Gutta percha is a hydrocarbon, C 20 H 32 , often mixed with resins. 
 Caoutchouc, C 5 H 8 , has the same composition with the same pro- 
 portion of elements, but of different-sized molecules. Such bodies 
 are said to be isomeric (equal parts) . There are many instances 
 of isomerism among organic compounds. 
 
 Gums, as gum arabic, gum tragacanth appear like resins, but 
 unlike them are soluble in water, and contain oxygen, gum 
 arabic having the formula C 12 H 22 O n , and tragacanth C 15i H 20 10 , 
 differing by only one molecule of water. 
 
 Wood, free from sap, consists of cellulose (C 6 H 10 5 ),lignine and 
 some mineral substances. The cellulose composes the wood cells, 
 
174 PRACTICAL LESSONS IN SCIENCE. 
 
 and is the most abundant constituent; the lignine is the material 
 lining the cells, and is more abundant in the harder varieties of 
 woods. Woods differ widely in their physical properties, but are 
 quite similar in their chemical composition. Beech, birch, oak, 
 aspen and willow each contain about the same amount of car- 
 bon. Aspen 49.26 per cent., birch 50.29 percent., and the others 
 between these amounts varying less than 1 per cent. Of oxygen 
 willow contains 39.38 per cent., beech 42.36 per cent., the others 
 between, varying less than 4 per cent. The hydrogen, sulphur, 
 nitrogen and ash are also nearly the same in each. Cellulose is 
 nearly pure in cotton, linen and the best kinds of paper. If dry 
 white paper, pure cellulose, be drawn through a cooled mixture 
 of two parts of strong sulphuric acid and one part of water, and 
 then thoroughly washed, it is changed into a semi-transparent 
 substance called vegetable parchment; when dried it is found 
 that there has been no alteration in weight or composition, but 
 it is at least five times as strong as before, and is waterproof. 
 This change is supposed to be due to change in the molecule. 
 Cellulose treated with a mixture of nitric and sulphuric acids is 
 converted into nitrocellulose or gun cotton. Gun cotton dis- 
 solved in a mixture of alcohol and ether is the collodion much 
 used by photographers. 
 
CHAPTER XXIII. 
 
 STARCH, SUGAR, ALCOHOL AND OILS. 
 
 STARCH, C 6 H 10 5 , is a product prepared by growing plants, 
 as food, for the nourishment of succeeding plants of their kind. 
 The starch of commerce is prepared from potatoes, rice and wheat. 
 Starch has the appearance of a white powder, but when examined 
 under the microscope it is found to consist of grains which vary 
 somewhat in size and appearance in different plants. The grains 
 of potato starch are about ^-^ of an inch in diameter, those of 
 wheat about y-oVo"' and of rice about 3-^^ of an inch. 
 
 Starch is insoluble in cold water but if heated with water to a 
 temperature of about 140 F. the grains swell up, burst and 
 yield the well-known paste used for stiffening linen and other 
 fabrics. A dry heat of 140 will also cause the grains to burst, 
 as in a roasted potato. A few drops of iodine added to a solu- 
 tion of starch gives a deep blue color, which disappears as the 
 solution is heated, reappearing as it cools. 
 
 When starch is heated to a temperature of about 400 F. it is 
 converted into a substance, called dextrine, which is soluble in 
 water. Dextrine has all the properties of gum, and is used by calico 
 printers for thickening their colors. It is also used as a muci- 
 lage, and for immovable surgical dressings. Dextrine (C 6 H 10 5 ), 
 i&isomerie with starch. 
 
 When starch is boiled with water containing a few per cent, 
 of sulphuric acid it is first converted into dextrine, and then into 
 glucose or grape sugar (C 6 H 12 6 ). These changes are usually 
 explained by supposing that in dextrine the starch molecule has 
 been changed in form, and in glucose has taken up one molecule 
 of water. Cellulose may be changed to grape sugar by the same 
 process. 
 
 SUGAR (C 12 H 22 O n ), occurs in the juices of several plants, as in 
 sugar-cane, sugar-maple, and sugar-beet. In this country most 
 
 (175) 
 
176 PRACTICAL LESSONS IN SCIENCE. 
 
 of the sugar is made from the juice of the sugar-cane, while in 
 Europe the juice of the sugar-beet is generally used. In the 
 manufacture of cane-sugar the canes are crushed between 
 grooved iron rollers and the juice mixed with the milk of lime is 
 boiled in open pans. The lime neutralizes the acids and hardens 
 some of the impurities; the albuminous matters, hardened by 
 heat, entangle these impurities and rise as a thick scum. The 
 scum is removed and the clear liquid remaining is evaporated to 
 such a consistency that on cooling it separates into two parts, 
 one crystalline, called brown sugar, the other unerywtalline, 
 called molasses. These products are purified, refined and con- 
 verted into the various grades of sugar and sirup of commerce. 
 
 Sugar melts to a colorless liquid which on cooling forms an 
 amber colored mass called barley sugar. When heated to about 
 400 F. sugar is changed to a dark brown substance called cara- 
 mel, which is soluble in water, being used for coloring sauces, 
 gravies, wines, brandies, etc. 
 
 The white of an egg is a typical form of an interesting and 
 important substance called albumen, which is found in all ani- 
 mals and vegetables. It is composed of carbon, hydrogen, 
 oxygen, nitrogen and sulphur, but the chemical formula is not 
 fully known. It seems to be about C 108 H 169 N 27 034S. It is found 
 in the blood and milk and in lean meat; it is associated with 
 starch in plants, as the gluten of wheat, and the legumin of 
 beans. The elements which compose albuminous compounds are 
 not firmly bound together; they break up and decompose very 
 readily, and in many cases promote change and decomposition 
 in other substances. 
 
 In addition to the starch, seeds and grains contain some form 
 of albumen. When placed in warm moist air the albumen 
 takes up oxygen forming carbon dioxide, and a substance, con- 
 taining carbon hydrogen, nitrogen and oxygen, called diastase. 
 Diastase has the power to set up changes by which the insoluble 
 starch is converted into the soluble glucose, which can be used 
 by the growing plant as food. If the seed is kept dry or cool it 
 will remain dormant for thousands of years, but expose it to air, 
 
LESSONS IN CHEMISTRY. 177 
 
 warmth and moisture and at once the seed becomes a theater 
 of activity. Substances similar to diastase occur in the saliva 
 and other digestive fluids. 
 
 In the manufacture of ale and beer the barley is caused to 
 germinate for a short time and then it is dried at a high tem- 
 perature which stops the germination, forming what is called 
 malt. The malt is ground and heated with water for some 
 hours, during which time the diastase formed, has converted the 
 starch into glucose and the liquid is called the wort. Yeast is 
 then added to the wort, which by the process of fermentation 
 changes some of the glucose to alcohol. 
 
 YEAST is a fungoid plant, made up of minute cells, which con- 
 tain cellulose albuminoid matter and mineral salts. These cells 
 multiply rapidly in solutions of sugar containing albuminoid 
 and mineral substances, changing cane-sugar to grape-sugar, 
 and grape-sugar into alcohol and carbon dioxide. This decom- 
 position is called alcoholic fermentation. The changes may be 
 represented by the following equation: cane-sugar (G 12 H^flii^~ 
 H 2 0=C 12 H 24 ]2 or 2(C 6 H 12 6 ) grape-sugar, and grape-sugar, 
 C 6 H 12 6 =2(C 2 H 6 0) alcohol, +2C0 2 . 
 
 ALCOHOL is the important ingredient in all fermented and dis- 
 tilled liquors, and is obtained from fermented liquors by distilla- 
 tion. Alcohol dissolves resins, oils and other vegetable substances, 
 and is much used in preparing medicines and varnishes. It is used 
 as a fuel and as a preservative fluid, preventing from decay ani- 
 mal or vegetable substances immersed in it. Wood spirit, or 
 methyl alcohol, is often used in place of ordinary alcohol. 
 
 When a mixture of strong sulphuric acid and alcohol is heated 
 in a retort there distills over with water a highly volatile inflam- 
 mable liquid called ether. When ether is inhaled for a few mo- 
 ments it produces insensibility, and is extensively used in surgical 
 operations. 
 
 When a fermented liquor is exposed to the air it gradually 
 
 becomes sour ; the alcohol taking up oxygen is converted into 
 
 acetic acid as follows : C 2 H 6 0-h0 2 =C 2 H 4 2 , acetic acid +H 2 0. 
 
 The chief source of this acid is the destructive distillation of 
 
 L. s. 12 
 
178 PRACTICAL LESSONS IN SCIENCE. 
 
 wood. Vinegar is a dilute acetic acid which is prepared in various 
 ways. It is made from alcohol treated with yeast. It is made 
 from wine or cider by adding a ferment called the mother of 
 vinegar, and is prepared from dilute solutions of sugar. Acetate 
 of lead, or sugar of lead, is used in medicine, and aluminum ace- 
 tate is used in dyeing. 
 
 The process of fermentation is intimately related to bread- 
 making. Flour is composed of starch, an albuminoid substance 
 called gluten, with some mineral substances. The flour is mixed 
 up into a dough with water, yeast and salt, and allowed to stand 
 for some hours at a temperature of between 70 and 75 F., 
 during which time some of the starch has been broken up by 
 fermentation into alcohol and carbon dioxide, which causes the 
 dough to swell up and become porous. The bread is then baked 
 at a temperature of about 500 F. The dioxide expanded some- 
 what by the heat increases the lightness of the bread, finally 
 escaping with the alcohol and some of the water. The internal 
 portions of the bread do not rise above the temperature of 
 boiling water, but the outside becomes much hotter and is 
 hardened into a crust, and some of the sugar is converted into 
 a caramel-like substance which gives the crust a sweetish taste. 
 Sometimes the fermentation is caused by leaven, being dough in 
 which fermentation has already commenced, and sometimes the 
 gas for making the bread light is formed from soda bicarbonate 
 and hydrochloric acid. 
 
 The various fats and oils, whether of vegetable or animal 
 origin, are mixtures of three well-defined bodies, stearin and 
 palmatin solids and olein, a liquid. Tallow is mainly stearin, 
 olive oil mainly olein, lard a mixture of olein and palmatin. They 
 are composed of carbon, hydrogen and oxygen of a complicated 
 formula, but are in effect salts of glyceryl. When stearin is boiled 
 with milk of lime, calcium stearate and glycerin are formed, and 
 when olein is boiled with litharge (PbO) lead oleate and glycerin 
 are formed. Glycerin (C 3 H 8 3 ) is a sweet, colorless, sirupy 
 liquid which dissolves in water or alcohol, but not in ether. It 
 is used in medicine and ag a preservative fluid. 
 
LESSONS IN CHEMISTRY. 179 
 
 
 
 When glycerin is poured slowly into a mixture of sulphuric 
 and nitric acids a yellowish oil, called nitroglycerin, is formed. 
 It is insoluble in water, but very explosive. For use it is mixed 
 with some inert matter, as finely divided silica, when it is known 
 as dynamite. 
 
 One of the oldest industries involving chemical principles is 
 soap-making from natural fats and oils. Hard soap is made as 
 follows: A solution of carbonate of soda is boiled with lime, 
 forming an insoluble calcium carbonate and a soluble sodium 
 hydrate, called soda lye. Tallow is then boiled with a weak 
 lye, and as the process continues, stronger lyes are added until all 
 of the tallow has disappeared. In order to separate the soap 
 from the solution, a quantity of salt is thrown into the liquid, 
 when the soap rises to the surface, and is transferred to molds. 
 As tallow contains both stearin and olein the soap formed con- 
 sists of a mixture of sodium stearate and oleate, while glycerin 
 remains in solution. When a lye of potassium hydrate is used, 
 soft soap is formed. A great variety of soaps are made, but in 
 every case the essentials of the process are the same. Soaps con- 
 tain from 30 to 80 per cent, of water, which evaporates slowly, 
 so that in general soap that has been well dried is more econom- 
 ical than that which is freshly made. 
 
 Tallow is extensively used in the manufacture of stearine 
 candles. For this purpose the tallow is first converted into lime 
 soap, which is decomposed by sulphuric acid, causing the fatty 
 matters to separate from the other parts of the solution. They 
 are then strongly compressed to squeeze out tha olein, leaving 
 the solid elements for manufacture into candles. 
 
 Palm oil, cocoanut oil, olive oil, castor oil are common and 
 useful oils. Linseed oil has a tendency to become solid when ex- 
 posed to the air, and is called a drying oil. This tendency is 
 increased by heating the oil with litharge or the bin oxide of man- 
 ganese, when it is called boiled linseed oil. This oil is extensively 
 used by painters everywhere. 
 
 Several interesting acids of vegetable origin are used exten- 
 sively in the arts. Of these, perhaps the most interesting is 
 
180 PRACTICAL LESSONS IN SCIENCE. 
 
 9 
 
 oxalic acid occurring in sorrel, rhubarb and other plants. It 
 is prepared by mixing sawdust into a paste with a strong solu- 
 tion of the potassium and sodium hydrates, and heating the 
 mixture on iron plates. The wood fiber is converted into oxalic 
 acid, which combines with the potassium and sodium forming 
 oxalates, from which the pure acid is obtained . Oxalic acid is 
 very poisonous ; the best antidote is chalk or magnesia. It is 
 much used in calico printing, in cleansing articles of brass and 
 copper, in removing stains of iron rust or ink and as a solvent 
 of Prussian blue in the manufacture of blue ink. 
 
 Wine during fermentation deposits on the inside of the cask a 
 crust called argol. It is a hydrogen potassium tartrate, and 
 when purified it is called cream of tartar. From argol, or cream 
 of tartar, tartaric acid (C 4 H 6 6 ) is prepared by the aid of lime 
 and sulphuric acid. It occurs in many fruits besides the grape 
 and is extensively used in dyeing and calico printing. It is also 
 used in medicine, as Eochelle salts and tartar emetic. 
 
 The acid of lemons, oranges and some other acidulous fruits, 
 called citric acid, is used in the preparation of acidulated drinks. 
 It is also used in medicine and in dyeing operations. 
 
 In the bark of the oak, pine, hemlock and other trees, in the 
 roots of many plants, in tea, coffee, and many other vegetables 
 is found an astringent substance called tannin or tannic acid. 
 Tannic acid may be extracted from its various sources by water, 
 and is chiefly valuable from the fact that it forms a black preci- 
 pitate with the salts of the peroxide of iron, and that it forms a 
 tough insoluble compound with gelatine, a form of albumen, and 
 with gelatinous membranes. The first characteristic makes it 
 useful in the manufacture of inks, and the second in the prepara- 
 tion of all kinds of leather. 
 
 In the process of tanning the skins are first soaked for three 
 or four weeks in strong lime water which removes the fat and 
 loosens the hair. They are then washed and treated with very 
 dilute sulphuric acid which removes any remaining lime and 
 opens the pores of the skin fitting it better for the action of the 
 tanning solution. They are then soaked in tannic acid solution 
 
LESSONS IN CHEMISTRY. 
 
 181 
 
 for five or six weeks, then packed with alternate layers of coarsely 
 ground oak or hemlock bark and covered with water for six or 
 eight months, changing them occasionally so that all shall be 
 treated by a uniform strength of the tannic acid. By this time 
 the hide or skin has increased in weight from 30 to 40 per cent., 
 has acquired a uniform brown color and is chemically leather, 
 ready for various mechanical operations which give it the de- 
 sired texture and finish. Special processes are used in preparing 
 kidskins, buckskins, etc. Tannic acid is used in medicine. 
 
 Morphine obtained from opium, quinine derived from Peruvian 
 bark, both used extensively in medicine, are vegetable alkaloids. 
 Strychnine from nux vomica, and nicotine from tobacco, two of 
 the most active poisons, are alkaloids, as are theine and caffeine, 
 the active elements of tea and coffee. 
 
 A list of the more important elements, with the symbol and 
 combining or atomic weight of each. 
 
 NON-METALLIC ELEMENTS. 
 
 Name. Symbol. Weight. 
 
 Oxygen O 15.96 
 
 Hydrogen H 1.00 
 
 Nitrogen N 14.00 
 
 Chlorine Cl 35.36 
 
 Bromine Br 79.75 
 
 Iodine I 126.53 
 
 Fluroine.... ...F 19.10 
 
 Name. Symbol. 
 
 Carbon C 
 
 Silicon Si 
 
 Boron B 
 
 Sulphur S 
 
 Phosphorus P 
 
 Arsenic... ...As 
 
 Weight. 
 12.00 
 28.00 
 11.00 
 31.98 
 30.96 
 74.90 
 
 METALLIC ELEMENTS. 
 
 Potassium (Kalium)...K 39.04 
 
 Sodium (Natrium) Na 23.00 
 
 Lithium Li 7.01 
 
 Calcium Ca 39.90 
 
 Barium Ba 136.80 
 
 Strontium Sr 87.20 
 
 Aluminium A! 27.30 
 
 Magnesium Mg 23.94 
 
 Zinc Zn 64.90 
 
 Silver (Argentum) Ag 107.66 
 
 Copper (Cuprum). .^....Cu 63.30 
 
 Mercury (Hydrargyrum) Hg 
 
 Iron (Ferrum) Fe 
 
 Nickel Ni 
 
 Cobalt Co 
 
 Manganese Mn 
 
 Chromium Cr 
 
 Bismuth Bi 
 
 Lead (Plumbum) Pb 
 
 Tin (Stannum) Sn 
 
 Gold (Aurum) Au 
 
 Platinum..., ...Pt 
 
 199.80 
 
 55.90 
 
 58.60 
 
 58.60 
 
 54.80 
 
 52.40 
 
 207.50 
 
 206.40 
 
 117.80 
 
 196.20 
 
 196.70 
 
CHAPTER XXIV. 
 
 BOTANY GENERAL AND STRUCTURAL. 
 
 THE science of Botany includes everything relating to the 
 vegetable kingdom. It considers the external forms of plants, 
 their anatomical structure, however minute, their classification, 
 geographic distribution, and economic value. It treats of the 
 varied relations of plants among themselves, and of their rela- 
 tions to minerals on the one side, and to animals on the other. 
 It attempts to examine plants in their earliest form, as single 
 cells, and to follow them through all their stages of development 
 until they reach maturity; in short, endeavors to learn the life 
 history of plants. 
 
 Many plants are minute in size, and much of the structure of 
 all plants is microscopic, so that there is considerable botanical 
 work which can be done only in well equipped laboratories, with 
 microscopes, re-agents, and mechanical appliances beyond the 
 reach of most individuals; but wide and interesting fields, the 
 greater part of botany, lie easily within the range of the unaided 
 vision. A good pocket magnifying glass will, however, be found 
 useful in the study of plants, animals or minerals. 
 
 Plants are composed of carbon, hydrogen, oxygen, nitrogen, 
 sulphur, iron and potassium as essential elements, necessary to 
 their life and growth, and sometimes they contain phosphorus, 
 calcium, sodium, silicon, magnesium or chlorine, as elements of 
 secondary importance in the vegetable structure. While the plant 
 is made up of the elements mentioned, it cannot feed on them as 
 elements, they must be united into compounds as water, carbon 
 dioxide, ammonium nitrate, calcium phosphate, etc., before the 
 plant can utilize them for food. Oxygen seems to be the only 
 exception to this rule, being an elemental plant food. 
 
 The living portion of the plant, that which moves, appropri- 
 (182) 
 
LESSONS IN BOTANY. 183 
 
 ates food and grows, is a transparent, semi-fluid, albuminous 
 substance, called protoplasm. It is the protoplasm that takes 
 up these mineral compounds and transforms them into the struc- 
 tures and compounds of the vegetable kingdom. It is impossible 
 to distinguish the protoplasm of plants from that of animals. 
 We cannot say that they are the same for the precise nature of 
 living matter cannot be determined, but we know that the "physi- 
 cal basis of life "has in all cases some common characteristics of 
 structure and behavior, diverse as are the ways in which its 
 activity may be manifested. 
 
 Corn, beans, wheat or other grains growing by themselves or 
 in pots with other plants, are interesting objects for observation 
 and comparison, whether in the home or schoolroom. If the tip 
 of the root of a grain of corn or the bean be divided lengthwise 
 with a sharp knife, then moistened with a solution of iodine, it 
 will assume a yellowish or brownish color indicating the presence 
 of protoplasm. If the tip of the root is dipped in a solution of 
 sugar and then moistened with a dilute sulphuric acid, a reddish 
 color will show the presence of protoplasm. 
 
 Sometimes in the lower order of plants, as in slime-moulds, the 
 protoplasm is without form, but in general it occurs in somewhat 
 definite forms of minute size called cells, which are enclosed by a 
 wall of cellulose, secreted by the protoplasm. The protoplasm 
 contains carbon, oxygen, hydrogen, nitrogen, sulphur, and pos- 
 sibly iron ; and in addition the cellulose contains potassium and 
 possibly lime, so that the cell contains the essential elements of 
 the plant. The cell is the unit of all vegetable structures from 
 the simplest to the most complex. In some cases it performs all 
 the functions of a plant; it takes food, grows, reproduces its 
 kind, and dies. 
 
 Free cells are in general somewhat spherical in form, but when 
 grouped in masses they are more or less angular from pressure 
 upon each other, so that they may be cubical, tabular or many- 
 sided. It frequently happens that cells grow more in some direc- 
 tions than in others, and thus elongated cells are formed which 
 are sometimes cylindrical and sometimes angular. The walls of 
 
184 PRACTICAL LESSONS IN SCIENCE. 
 
 cells are often thickened in various ways, forming wood cells, 
 spiral or banded cells, etc. 
 
 New cells are formed by the division of old cells, each division 
 soon growing to the size and form of the original, as in the 
 growth of some of the lower forms of plant life, and in the tips 
 of growing roots. And new cells are also formed by the union of 
 the contents of two cells, as in the reproduction processes of some 
 of the lower plants. 
 
 Besides the protoplasm within the cell wall there is often a 
 delicate green coloring matter called chlorophyll, which may be 
 dissolved out with alcohol. The chlorophyll gives the green 
 color to the leaves, stems and other parts of growing plants. 
 Another product of plant cells is starch, as in the potato, wheat, 
 corn and other grains. In addition to other substances many 
 cells contain solutions of various forms of sugar, as cane sugar, 
 grape sugaT, beet-root sugar, etc.; and the cells of some plants 
 secrete oils, as olive, castor, linseed and palm oil, the oils of tur- 
 pentine, lemon and thyme. Others secrete such substances as 
 camphor, essence of cinnamon, wintergreen, etc., and as the es- 
 sential oils of onions, mustard, asafcetida, etc. Others again 
 secrete gums, as gum tragacanth, gum arabic, and many others. 
 Several important acids are the product of vegetable cells, as 
 tartaric, citric and tannic acids. In addition to those mentioned, 
 opium, quinine, and other valuable medical substances, and many 
 valuable dyes are the products of cell action. 
 
 The embryos of all plants begin as single cells, and some of 
 the lower plants during their whole existence consist only of 
 single cells. In some cases cells at first distinct become united 
 more or less closely into a common mass, each cell to a great ex- 
 tent remaining a distinct individual. Sometimes the partitions 
 between contiguous cells are dissolved away, and the two cells 
 are merged into one. In this way long tubes or vessels are 
 formed. But in the great majority of plants the cells are com- 
 bined into tissues. They may be joined end to end, form- 
 ing threads, filaments or hairs, or they may be joined end- 
 wise and sidewise, forming cell surfaces, or they may be joined 
 
LESSONS IN BOTANY. 
 
 in three directions forming masses of greater or less size and 
 solidity. 
 
 At the tips of young stems and roots there are groups of ac- 
 tive cells which, multiplying by division and growing rapidly, 
 form what is called the vegetative cone of the root or stem. This 
 mass of cells is sometimes called the primary meristem, the sec- 
 ondary meristem being a layer of cells between the bark and 
 wood of plants called the cambium layer. From the meristem 
 tissue all the other tissues of the higher plants are developed. 
 
 The next most important tissue is called parenchyma. It is 
 composed of cells whose walls are thin, nearly colorless and 
 transparent, and which vary greatly in form. This tissue makes 
 up the whole substance of many plants of the lower order, and 
 the essential portions of the green or assimilative, growing and 
 reproductive parts of the higher plants. Another tissue, perhaps 
 developed from parenchyma by thickening the walls of the cells 
 along their angles, is called collenchyma, or thick angled tissue. 
 It is found beneath the epidermis of many plants, for the pur- 
 pose, doubtless, of giving support and strength to it. Another, 
 in which the cell walls are somewhat uniformly thickened, is 
 called sclerenchyma. It occurs in the mosses, ferns and higher 
 plants. 
 
 The most abundant and important tissue after parenchyma is 
 the fibrous tissue. It is composed of long thick-walled cells, 
 which constitute the tough, flexible part of the bark, called bast, 
 and the hard woody parts of the stems of plants and the frame- 
 work of leaves. In some plants, as the milkweeds, there are nu- 
 merous vessels, containing a milky or colored fluid, which form 
 what is called the lactiferous or milk tissue. Another group of 
 vessels having numerous openings in their thin walls constitute 
 what is called the sieve tissue, which is abundant in the grape 
 vine, in ferns and other plants. Besides those mentioned, there 
 are in the higher orders of plants elongated cells whose thickened 
 walls are perforated at places where similar vessels touch each 
 other. They are called spiral, pitted or banded vessels, etc., and 
 together make up the tracheary tissue. While young these cells 
 
186 PRACTICAL LESSONS IN SCIENCE. 
 
 contain protoplasm, but as they become older it disappears and 
 the tissue only contains air. 
 
 These various tissues are grouped into three systems : the epi- 
 dermal, the fibro-vascular, and the fundamental. Neither of 
 these systems occur in the lowest plants. The epidermal system 
 is the most simple, and appears earlier in the life of the individ- 
 ual, and earlier in passing from lower to higher forms than the 
 other systems. The first indications of this system is in smaller, 
 darker colored surface cells in some of the lower fungi and their 
 allies, while in some of the mosses a distinct epidermis occurs, 
 becoming well developed in the ferns and flowering plants. The 
 epidermis proper consists of modified parenchyma, the cells 
 changing form, thickening and hardening their walls and finally 
 losing their protoplasm. 
 
 From these epidermal cells hairs are produced, especially on 
 young roots, which vary somewhat in form and are active agents 
 m absorbing nutritive matters for the plant. And in the epider- 
 mis there are numerous stomata or breathing pores, which open 
 directly into intercellular spaces below. They are more numer- 
 ous on the under surface of leaves; on the lower surface of a 
 black walnut leaf there are nearly 300,000 stonmta in one square 
 inch of surface, with none on the upper side; while in the case of 
 a leaf of corn or maize, there are about 60,000 to the square 
 inch on the upper surface and about 100,000 on the lower sur- 
 face. In the case of the iris leaf and oat leaf there are more on 
 the upper surface. 
 
 In most of the higher orders of plants the fibrous, sieve and 
 tracheary tissues, with some parenchyma, form bundles of com- 
 pact tissue running through the plant from roots to leaves. 
 They are called the fibro-vascular or vascular bundles. The 
 young radish is crisp and brittle the vascular bundles are not 
 noticeable; but later, as they are more fully developed, the rad- 
 ish becomes stringy and woody. They constitute the framework 
 of leaves and may be separated from the more delicate tissues by 
 maceration, and they are easily found as threads in the pith of 
 the cornstalk. The components of the bundles vary in their pro- 
 
LESSONS IN BOTANY. 187 
 
 portions in different plants ; but in every case they serve to 
 strengthen the plant structure and as a means for conducting 
 liquids from roots to leaves. 
 
 The fundamental system includes all the tissues not found in 
 the other systems, being made up mainly of parenchyma, thick 
 angled tissue, milk tissue, etc. 
 
 An examination of a green stem of Indian corn will give one a 
 good idea of the vascular bundles and the parenchyma surround- 
 ing them. An examination of the leaf stalk of the squash shows 
 whitish bands extending from end to end just beneath the epi- 
 dermis. They are masses of thick angled tissue, which may be 
 torn out, when the stalk becomes weak and flexible. The large 
 pores seen in cross sections of oak, ash and other woods are 
 pitted vessels. 
 
 Plants are made up of the various tissues and systems men- 
 tioned. The lower plants consist mainly of parenchyma, while 
 all three systems unite to form the bodies of the higher plants. 
 Such plants are made up of stem, leaves and roots. 
 
 The typical stem is illustrated in the trunk of a tree or the 
 body of an upright plant, bearing branches and leaves and sup- 
 ported by roots; but it also appears in many other forms : First, 
 as runners, which are slender and weak, creeping along the ground 
 and bearing stunted leaves or bracts, as in the case of straw- 
 berries. Second, rootstocks, scale-bearing underground stems, 
 as in the case of ferns. Third, tubers, scale-bearing, thickened 
 and subterranean, as the potato. Fourth, the cormb, a thick, 
 solid body with thin leaves, subterranean, as the Indian turnip. 
 Fifth, bulbs, small bodies covered by the thickened bases of 
 leaves, as the onion. Sixth, tendrils, slender branches usually 
 destitute of leaves. Seventh, thorns, short, thick, pointed 
 branches without leaves. 
 
 The leaves are broad, flat expansions of chlorophyll-bearing 
 tissue, supported by a framework of fibrous tissue. They may 
 be reduced to bracts, or scales, which have but little chlorophyll, 
 or, modified in form and color, they make up the different parts of 
 the flower, as the sepals, petals, stamens, pistils, and sometimes 
 
188 PRACTICAL LESSONS IN SCIENCE. 
 
 they become tendrils, spines, and in some cases cups. Besides 
 these there are numerous outgrowths of the epidermal system, 
 known as bristles, prickles, scales, glands, root hairs, etc., which 
 are called trichomes. 
 
 The roots which fix the plants in the ground, or on some sup- 
 port, and absorb nutriment for the plant, show little variation 
 in form. The roots of parasites are usually short and thick, and 
 sometimes provided with sucker-like organs. And the aerial 
 roots of orchids, and similar plants, often have a thickened 
 epidermis containing more or less chlorophyll. 
 
 All parts of a growing plant are abundantly supplied with 
 water; it makes up about 75 per cent, of the weight of plants. 
 Water is constantly being taken up by the roots, and as con- 
 stantly being evaporated from the leaves. It has in solution, 
 materials from the soil and soluble products of plant action. 
 The tissues are constantly taking materials from this liquid for 
 their growth, and the various secretions, as oils, gums, acids, 
 etc., are formed from materials taken from the same source. The 
 cause of the movement of water or sap in plants is not fully 
 understood. 
 
 In the chlorophyll parts of plants during the daylight water 
 and carbon dioxide are broken up into materials for starch, cel- 
 lulose and other hydrocarbons, and oxygen is set free. This pro- 
 cess is called assimilation. These materials are then changed to 
 sugar, cellulose, protoplasm, etc., by a process called metastasis, 
 or metabolism. This process is not understood, but it seems to 
 go on more rapidly at night, and to be attended with the evolu- 
 tion of carbon dioxide, while assimilation is attended by the 
 evolution of oxygen. 
 
 In many plants starch or other material is stored up for the 
 future use of the plant in modified stems, as potatoes, onions, 
 etc. ; in seeds, as in the various grains, and in buds. In most 
 cases this material is used as a supply of food for the growth of 
 young branches or the young plant. Some plants are parasites, 
 taking materials already assimilated from other plants. Again, 
 they are partially parasitic, where some food is assimilated in the 
 
LESSONS IN BOTANY. 189 
 
 plant. Many plants are saprophytes or partly so, deriving their 
 food wholly or partly from decaying matters. 
 
 The processes of assimilation and metabolism can only be car- 
 ried on within certain degrees of temperature; the limits vary with 
 different plants. In many plants these changes progress at tem- 
 peratures very little above freezing point, and in some plants 
 they are carried on freely at a temperature of from 110 to 120 
 F. Many of the subjects mentioned in this chapter will be more 
 fully discussed and illustrated in subsequent chapters. 
 
CHAPTER XXV. 
 
 BACTERIA, ALG.E, FUNGI, AND LICHENS. 
 
 AMONG living things two processes must be maintained; first, 
 the nutritive, on which the life and vigor of the individual plant 
 or animal depends; second, the reproductive, on which the life of 
 the race, the perpetuation of the species, depends. The differences 
 in structure among plants, and the modifications of structure by 
 which the plant adapts itself to its surroundings, are important 
 items to consider in the study of plants. The structure of plants 
 and the processes of nutrition and reproduction comprise nearly 
 all the work of botany. 
 
 There are a great many kinds of plants, and it would be an 
 endless task to try and study each one ; but many plants are 
 similar to other plants in structure, in methods of reproduction, 
 etc., so that a careful study of one plant gives a good idea of 
 many similar plants. Plants are divided into species, genera , 
 families, orders, divisions, etc. On the basis of structure we have 
 cellular plants, made up wholly of parenchyma, and vascular 
 plants in which the vascular bundles are prominent features of 
 the structure. These groups are separated into divisions mainly 
 on the basis of differences in the reproductive processes. 
 
 The division including the lowest plants is called PROTOPHYTA, 
 first plants. These are the lowest and simplest plants, usually of 
 minute size; the cells are poorly developed, and often there is no 
 cell wall. In many cases the plants consist of only one cell, and 
 when there is an aggregation of cells, the union is usually so 
 slight that each cell is practically an individual. 
 
 If we add a few drops of yeast to a solution of sugar and keep 
 
 it in a warm place, the mixture will soon become turbid and then 
 
 frothy, will lose its sweetness and acquire a spirituous odor, and 
 
 at length a scum of yeast will collect on the surface of the liquid. 
 
 (190) 
 
LESSONS IN BOTANY. 191 
 
 If some of this scum be spread out on a piece of glass and exam- 
 ined with a pocket magnifier, fine grains may be seen scattered 
 through the mass. These grains, called torulse, are the active 
 part of the yeast. They are living bodies, as shown by the ra- 
 pidity with which they grow and multiply. Each torula is a cell 
 tvhich gives rise to minute buds, which grow rapidly and finally 
 become detached from the parent cell, though generally not till 
 they have themselves developed other buds. When yeast is dried 
 and burned it gives rise to an odor similar to that which arises 
 from burning meat. Dried yeast forms a fine powder which dif- 
 fuses itself rapidly through the air, so that a solution of sugar 
 open to the air, if kept warm, will soon begin to ferment from 
 yeast particles received from the air. 
 
 Infuse or steep some hay in warm water for an hour or so, 
 then filter it and set the filtrate in a warm place, and from time 
 to time notice the changes which take place in it. At first the 
 solution is clear, after 24 or 36 hours it becomes turbid, as did 
 the yeast solution, and at length a scum forms on the surface 
 and the solution acquires a putrid odor. These changes are due 
 to the growth and multiplication of Bacteria. All forms of putre- 
 faction are due to fermentation set up by bacteria of different 
 kinds. A living thing dies, other things still living attack the 
 dead body and speedily convert it into gases and liquids which 
 may be used for food by the same or other forms of life. 
 
 Bacteria may be developed in almost any vegetable infusion. 
 They are minute ; they cannot be studied in detail without pow- 
 erful instruments, but it is interesting to note the work of these 
 minute but numerous beings, which in some sense are the sub- 
 stratum of life. When dry the bacteria forms a dust of minute 
 grains which is diffused through the air everywhere, furnishing 
 the material for fermentation wherever the air can go freely. 
 They have size and form, for they may be filtered out of the air. 
 
 Take three test tubes and fill each about one-third full of 
 freshly made hay infusion; cause the solutions in two of the 
 tubes to boil for a few minutes, then while it is boiling cork one 
 of the tubes with a mass of cotton wool and let it boil for a min- 
 
192 PRACTICAL LESSONS IN SCIENCE. 
 
 ute or so after closing; put the three tubes in a warm place and 
 note the results. Bacteria are developed promptly in the un- 
 boiled solution, and also appear in the boiled solution of the 
 unclosed tube, but not as promptly as in the first, while none ap- 
 pear in the other if the experiment was well performed. Experi- 
 ments show that every form of bacteria may be filtered out of 
 the air by a mass of cotton wool and in other ways; that they 
 may be filtered out of water by such material as porous pottery- 
 ware, and that if a body of air remains at rest for a few days 
 these germs of bacterial life will settle out of it so that it is as 
 pure as if filtered. 
 
 It is by excluding the germs of bacteria that vegetable and 
 animal substances are preserved from decay by the process of 
 canning. The discovery of bacteria and the recognition of their 
 importance in the economy of nature has been of great value to 
 man. It has promoted a more rational treatment of disease, 
 and has greatly extended the domain of surgery. 
 
 Another interesting one-celled plant, sometimes called a green 
 slime, is found as a green coating on the north side of old fences 
 or trees, especially after a few days of wet weather. Pieces of 
 wood or bark bearing this plant may be kept dry for a long time, 
 becoming fresh when moistened. Notice the color, and with the 
 pocket lens notice that it appears as if dusted over the surface. 
 Scrape off some of the slime and put it in a little alcohol, and after 
 an hour or so notice the color of the alcohol. The green color of 
 the plant and the color it imparts to the alcohol is due to the 
 delicate coloring matter called chlorophyll, which, in general, is 
 formed only in the sunshine. Potato stems growing in the sun- 
 light are bright green, but are nearly white when growing in the 
 dark. This slime is called Protococcus. It multiplies rapidly, 
 not by the process of budding, as did the torula, but by division, 
 one cell dividing into two and these dividing again, etc. 
 
 A dark blue-green scum is very common on stagnant water 
 about watering troughs, along street gutters and other places. 
 It can be kept for observation in water in an open dish. If a 
 small portion of this scum be allowed to remain for a few hours 
 
LESSONS IN BOTANY. 193 
 
 in a saucer with a little water it will spread out in good shape 
 for study. Then notice the form and color of the hairlike fila- 
 ments and possibly careful observation will allow one to see the 
 slow vibratory movements which give this plant the name of 
 Oscillaria. The filaments are composed of cells attached end to 
 end in colonies, but each is an individual as fully as the cells of 
 protococcus. 
 
 These minute plants all live in water or in damp shady places, 
 yet all retain their vitality for a long time when dried so as to 
 form an impalpable dust. While these plants are minute in size 
 and simple in structure they constitute an important branch of 
 the vegetable kingdom. 
 
 On the surface of stagnant water and in quiet water along the 
 edges of streams, in the early spring, little patches of a frothy 
 substance appears, sometimes called frog spittle, later the sur- 
 face is covered with a bright green scum, and during June and 
 July great patches of a dirty brownish scum is present with the 
 green. When lifted from the water it has a slippery feel, and 
 strings out like wet hair. The plant is some species of Spirogyra 
 or Zygnema. It may be grown for observation in an open dish 
 of water, with some soil at the bottom, in which some water lov- 
 ing plant is growing. 
 
 The long hairlike filaments are colonies of cells attached end 
 to end as in oscillaria. The cells in spirogyra are marked by 
 spiral bands of chlorophyll, while in zygnema there is a central 
 starlike nucleus, with the chlorophyll in bands or plates. They 
 multiply by division as do protococcus and oscillaria, but in ad- 
 dition there is another form of reproduction. At the close of their 
 growth in the spring, the cells push out little processes from 
 their sides, which meet similar processes from other cells of par- 
 allel filaments. They flatten upon each other, the walls fuse and 
 are absorbed, leaving a connecting channel between the two cells, 
 through which the protoplasm of both cells become one mass. 
 This mass secretes a wall of cellulose forming a zygospore or 
 germ, which has much thicker walls than the ordinary cell, and 
 from which a colony of cells or plants may be developed. 
 L. S.-43 
 
194 PRACTICAL LESSONS IN SCIENCE. 
 
 These bodies sink to the bottom of the water, when released 
 by the decay of the old cells, resting there till the next season. 
 With the warmth of spring, the zygospore becomes active, little 
 bubbles of gas are formed, which float it to the surface of the 
 water, the central portion lengthens, partitions are developed 
 forming cells, which multiplying by division extend intoahairlike 
 filament. Some idea of the cell markings and of the fruiting 
 stage can be gained by examination with the naked eye or with 
 the simple magnifier, but these plants are interesting if we can 
 do no more than observe the different stages of growth, the 
 changes in color, the rapid increase in bulk, their complete disap- 
 pearance at the end of the growing season and other phenomena 
 visible to the naked eye. 
 
 Another interesting plant colony common in ponds and sluggish 
 streams is the Water net. It is a tubular net composed of elon- 
 gated cells which, when full grown, are sometimes one-third of an 
 inch in length. The protoplasm of some of these cells breaks up 
 into a great number of daughter-cells which arrange themselves 
 into a miniature net inside the mother-cell which is set free by the 
 absorption of the enclosing walls. In other cells thousands of 
 little ciliated swarm spores are formed, which, after swimming 
 about for a time, thicken their walls and sink to the bottom of 
 the water, where they remain for a time in a resting stage, as in 
 the case of spirogyra. 
 
 The Fungi or Moulds are closely akin to the plants just consid- 
 ered. A common one forms a greenish coating upon bread, leather 
 and other substances left in damp places. When examined the 
 green color seems to be due to a fine powder which is apparently 
 the same as the torulae. Each of these grains or spores gives 
 rise to a long tubular filament called a hypha,, and a number of 
 these hyphae, make up the body of the fungus, which is called the 
 mycelium, hyphae projecting downward and upward like roots 
 and shoots from the mycelium. Some of the hyphae projecting 
 upward develop spores at their summit. 
 
 Moulds are easily grown for observation. A little moistened 
 horse dung placed in a, dish and covered with a glass will furnish 
 
LESSONS IN BOTANY. 195 
 
 a vigorous growth of Mould. When these are full grown, some 
 of the spores may be sown on a piece of moistened bread, 
 which, under a glass will soon develop a fine crop of Mould. 
 The moulds do not contain chlorophyll and are saprophytes, 
 living upon decaying vegetable or animal matter, or they are 
 parasitic. 
 
 With the moulds, spirogyra and water net are associated des- 
 mids which are found abundantly in shallow fresh water, and 
 diatoms which occur in both salt and fresh water, often forming 
 a thin yellowish layer at the bottom of the water. These forms 
 of life are beautiful and interesting objects of study, but their 
 minute size makes their observation difficult. This group of 
 plants is called ZYGOPHYTA,from the fact of their forming a zygo- 
 spore or yoke spore. The plants of this group differ considerably 
 among themselves but are similar in their modes of reproduction, 
 but not alike, as in some cases the spores have organs of locomo- 
 tion while in others they do not have them. Yet in this respect 
 this class is clearly superior to the protophyta. 
 
 The next division of plants is called OOPHYTA, egg-spore-plants. 
 The distinguishing characteristic of the plants of this group 
 is that they develop special cells which contain one or more 
 rounded masses of protoplasm which are fertilized by the con- 
 tents of another special cell of smaller size, which results in the 
 production of an oospore from which a new plant may be de- 
 veloped. 
 
 In streams and ponds tufts of da,rk green plants may be seen 
 floating in the water from stones or sticks or other objects to 
 which they are attached. These masses of vegetable matter are 
 probably the simple or branching filaments of some species of 
 (Edogonium. These plants multiply by the sexual process of re- 
 production as above, and by an asexual process as well. 
 
 The Vaucheria is another member of this division of plants. 
 It forms dense felt-like masses in water, or on damp ground or 
 rocks. They do not have the slippery feel of spirogyra but 
 change to a dingy color at the fruiting stage and the filaments 
 are coarse enough so that many things can be learned about 
 
196 PRACTICAL LESSONS IN SCIENCE. 
 
 them from observation with the naked eye. In studying the 
 vaucheria during the fruiting stage, it will be found interesting 
 to observe them carefully several times during the day, especially 
 late at night, and early in the morning. 
 
 Other members of this group are the seaweeds, Fucus and Sar- 
 gassum. They grow from just below low- tide to just above high- 
 tide, and often attain great size. They are washed ashore in 
 great quantities during storms, and are much used for manure, 
 and from their ashes Iodine and Bromine may be obtained. 
 
 The CARPOPHYTA or spore-fruit-plants are distinguished by the 
 formation of a sporocarp as the result of the fertilization of the 
 female element. The sporocarp usually consists of a fertile part 
 which produces spores, and a sterile part, so formed as to inclose 
 the fertile portion. The spores are not the direct but a secondary 
 result of the fertilization. The plant body usually has a more 
 perfect development than in the previous divisions. 
 
 To this division belong the large and interesting class of sea- 
 weeds called Florideae, which are noted for their delicate forms 
 and rich coloring. They are mostly of a red color, due to a pig- 
 ment soluble in cold fresh water. The color varies through every 
 shade of red from bright rose to purple. Irish moss used for 
 making blanc mange is one of the best known. 
 
 To this division also belong a great group of parasitic plants 
 or fungi, and while they are too minute for detailed study, yet 
 their presence in patches on plants and something of their effects, 
 their color, their changes when fruiting, etc., are interesting sub- 
 jects of study. A species occurs on the leaves of the apple and 
 cherry, another on the leaves of the willow; another on the 
 leaves of the grape, doing much injury, is called Oidium Tuckeri. 
 One occurs on the leaves of the maple and a very common spe- 
 cies is found on the leaves of the lilac. They occur on the leaves 
 of the oak, elder, mandrake, pea, and many other plants. 
 
 In the study of these fungi or mildews, or any other plant, it 
 is interesting to watch several plants of the same species through 
 the whole growing season, noting all changes, so as to get some 
 idea of the life history of the plant. By watching several plants, 
 
LESSONS IN BOTANY. 197 
 
 mere accidental changes may be eliminated, so that at the end 
 of the season a clear and complete history can be given of the 
 particular species studied. 
 
 Lichens, a large and well-known group of plants, belong in this 
 division. These plants are common everywhere and have been 
 carefully studied, yet there has been much difference of opinion 
 about their true nature. The idea seems to prevail that they are 
 fungi which live in association with algse, which may be proto- 
 phytes or zygophytes, plants of a higher order as parasites on 
 those of lower orders. A lichen of Asia Minor is used for food, 
 and the so-called Reindeer moss is a lichen. They grow on the 
 bark of living trees, on rocks and decaying wood, and on the 
 ground ; they vary greatly in form and color, and are interesting 
 subjects for study. The ergot of rye, the rust of wheat, and the 
 smut of wheat, oats and barley and their allies, belong to this 
 division of plants. 
 
 The most valuable and best known group of this division are 
 the mushrooms. They are saprophytes, and the largest of the 
 Fungi, growing with great rapidity and decaying rapidly after 
 maturity is reached. Many species are poisonous, but many are 
 edible, and in France they are extensively cultivated for food ; in 
 one cave there are over six miles of mushroom beds. 
 
 The only chlorophyll-bearing plants in this division are the 
 Characese. They are submerged water plants, slim and delicate 
 in structure, sometimes attaining the height of two or three feet. 
 They grow in close patches at the bottom of fresh-water lakes, 
 ditches and streams ; in deep or shallow, stagnant or running 
 water. They are easily grown in an open dish, and associated 
 with spirogyra, or some other of the scums, make an attractive 
 and entertaining addition to a group of house plants. 
 
 The divisions already considered constitute the Thallophytes 
 of some authors, who generally divided them as follows : Algse, 
 aquatic chlorophyll-bearing plants; Fungi, terrestrial, sapro- 
 phytic, or parasitic plants destitute of chlorophyll; and Lichens, 
 terrestrial plants containing green gonidia. But the classifi- 
 cation already given, based mainly on the character of the 
 
198 PRACTICAL LESSONS IN SCIENCE. 
 
 reproductive apparatus, has the sanction of the latest and best 
 authorities. 
 
 These plants show no indication of true roots, stems or leaves. 
 They are made up mainly of parenchyma cells showing no 
 wood cells, tubes or other characteristics of stems. Yet while 
 they are low in form and structure, and are of comparatively 
 small economic value, they are numerous, far exceeding the num- 
 ber of the higher plants. We cannot learn many things about 
 them by examination with the naked eye; but what we can learn 
 is of great interest, leading us into comparatively untrodden 
 fields of nature. 
 
 Among these cellular plants the nutritive processes go on in 
 all parts of the organism, there being little or no division of 
 labor, each cell acting a.s an individual. In the study of these 
 plants we have found three classes: the chlorophyll plants that 
 absorbed their nourishment, as carbon dioxide, water, etc., from 
 the mineral kingdom these in the sunlight were changed into 
 such compounds as the plant could build into tissue; others, 
 called parasites, absorbed compounds already prepared for use 
 from the juices of chlorophyll plants, and from them built up 
 their tissues; others called saprophytes absorbed compounds 
 from decaying vegetable substances, from which their tissues 
 could be nourished. 
 
 The members of this group of plants affect man in various 
 ways; directly, in causing such diseases as intermittent, typhoid, 
 yellow, scarlet and typhus fevers, cholera, smallpox, croup, con- 
 sumption, erysipelas, and many other diseases; and indirectly, 
 in causing diseases of domestic animals, as splenic fever, fowl 
 cholera, swine fever, rabies, glanders and others. And they are 
 the cause of the various kinds of fermentation, some of which 
 are valuable and some harmful. Some fungi are valuable for 
 food, but many of them are injurious. They cause skin diseases, 
 as ringworm. They infest almost every useful plant, lessening 
 the quantity of the food product, injuring its quality, as in the 
 case of the rust of wheat, the potato fungus and those which 
 infest the grape. 
 
LESSONS IN BOTANY. 199 
 
 They attack many kinds of insects, as flies, wasps, beetles, 
 spiders, butterflies, etc., in some cases causing their death. Fish 
 are subject to attack from fungi. As saprophytes fungi are 
 doubtless in many cases beneficial; but they promote the decay of 
 timber, whether in the house, ship, bridge, furniture, or the piece 
 thrown aside as useless. Without going into further detail it 
 seems clear that Bacteria, Fungi and Algae are important mem- 
 bers of the vegetable kingdom , that they are present everywhere, 
 and that their general effect is to disintegrate and destroy the 
 more highly organized groups of plants and animals. 
 
CHAPTER XXVI. 
 
 BRYOPHYTA, MOSS PLANTS AND PTERIDOPHYTA, FERN 
 
 PLANTS. 
 
 N 
 
 THE BRYOPHYTA are in some sense a transition group between 
 
 the cellular plants below and the well developed vascular plants 
 above. A plant called Marchantia polymorpba is a good repre- 
 sentative of a portion of this group. It is found in damp shady 
 places, growing on the rocks or on moist ground. It consists 
 of flat leaf-like stems, producing fine silky hairs from the lower 
 surface which serve to attach it to its resting place, and they 
 probably absorb nourishment as well, acting as true roots. The 
 dark green upper surface is covered with minute diamond-shaped 
 markings. 
 
 The reproductive organs occur on separate plants as disk- 
 crowned stems about an inch high. The antheridia or male ele- 
 ments have a scalloped disk, while the archegonia or female ele- 
 ments have the disk cut into finger-like rays. After fertilization 
 a sexual spore, called an oospore, is formed in the archegonium, 
 from which a sporogonium is developed. In the sporogonium 
 asexual spores are formed from which new plants grow. On the 
 upper surface of the plant little cups or cupules occur which con- 
 tain bright green scale-like bodies called gemmse. The gemmae 
 grow into new plants. 
 
 In studying this plant notice carefully the points already men- 
 tioned, note the difference in color between the upper and lower 
 sides of the plant, note the mode of branching, the indented 
 apex, the median line or midrib. Note also the pores on the 
 upper surface. Remove some of the gemma? and placing them 
 on a white surface, study their form. Examine carefully the 
 orchegomal and antheridial branches, and compare them with 
 (200) 
 
LESSONS IN BOTANY. 201 
 
 each other. Write out an account of everything observed, with 
 a description of the locality in which the plant was found. 
 
 In the plants heretofore studied there was little differentiation 
 of parts, but in the marchantia the upper surface seems to have 
 been specialized for the purpose of assimilation and reproduc- 
 tion, and the under side for the absorption of nourishing liquids. 
 And there is some thickening of cell walls, and some indications 
 of the development of a vascular system. Marchantia grows 
 well in greenhouses and may be grown for observation on moist 
 earth anywhere about the house. 
 
 The true Mosses are common wherever moisture is abundant, 
 in swamps, on the ground, on trees, rocks and decaying vegeta- 
 tion. The stem, roots or root hairs and leaves in form and func- 
 tion are similar to those of the higher plants. The spore formed 
 by the sexual organs produces a branching body called the pro- 
 tonema, from which the moss plant proper grows, producing at 
 length the archegonia and antheridia. Mosses may be grown 
 for observation on moist decaying wood or earth under a glass. 
 
 In studying mosses, notice the following: the stem, its height, 
 shape and color, make a cross section of it and note different 
 tissues as shown by different colors. Note the shape, color and 
 arrangement of the leaves; study the flowering heads, the male 
 with its rosette of green leaves, and the female with the 
 leaves folded into a bud ; compare them in other respects ; note 
 the fruit which is a cylindrical pod or capsule, and the hood fit- 
 ting over the pod, remove the hood and note appearance and 
 contents of the pod. Make full notes of what you observe and 
 describe the locality in which the moss was found. 
 
 In the groups previously studied the sexually formed spore 
 produced a plant like the parent, but in this group it grows into 
 a fruit or sporogonium, which forms asexual spores that pro- 
 duce plants like the original. This process is known as an alter- 
 nation of generations. 
 
 In the economy of nature Mosses, with Lichens and other 
 plants of the lower orders, are precursors of higher plants; they 
 appear first on rocks and sterile places ; sand and dust collecting 
 
202 PRACTICAL LESSONS IN SCIENCE. 
 
 around them with the decaying leaves and stems at length form 
 soil suitable for higher plants. Some species of Sphagnum grow- 
 ing in swamps enter largely into the formation of peat bogs, and 
 perhaps helped to form some varieties of coal. This moss is ex- 
 tensively used in packing trees and plants for shipment, and some 
 species are used for stuffing mattresses. Some species of mosses 
 and lichens are almost the only flora of the polar and high 
 mountain regions. 
 
 Pteridophytes or Ferns, produce no highly colored flowers, yield 
 no rich perfume, yet no group of plants attracts more notice, are 
 more sought for cultivation, or more enjoyed than the ferns, 
 whose sole charm consists in their delicate, graceful, feathery foli- 
 age. Ferns are abundant in all parts of the world, but exist in 
 greatest variety in the hot moist regions of the tropics. There 
 are said to be some 3,000 species ranging in size from less than 
 an inch to the gigantic tree ferns of Australia, some of which 
 reach an elevation of 75 feet, with leaves or fronds which exceed 
 in size those of any other plants. While in general they seem to 
 enjoy rich soil and warm, moist, shady localities, they do grow 
 on exposed hillsides, on rocky cliffs, and sometimes on trees 
 as air plants. They are not only abundant now, but they 
 have been a marked feature in the flora of the earth from very 
 early times. Their remains are found in the rocks of the Devo- 
 nian age, while the coal of the succeeding age is made up mainly 
 of the stems and leaves of ferns and allied plants. 
 
 Ferns consist of a stem, rootstock or rhizoma which is usually 
 horizontal and subterranean, but in some cases it creeps along 
 the surface ; and sometimes it is erect, as in the case of tree ferns. 
 From the rhizoma arises the leaf which consists of a stalk or 
 stipe and the blade or frond. The stipe may be green or black ; 
 may be smooth and polished or covered with scales or hairs; 
 the frond may have an even, uniform outline, like the leaf of an 
 apple tree, or it may be divided and subdivided into many dis- 
 tinct parts, as in the case of the maiden hair fern, so common 
 everywhere. 
 
 The continuation of the stipe through a simple frond is called 
 
LESSONS IN BOTANY. 203 
 
 the mid vein, in a divided frond it is called the rachis. When a 
 frond is cut into lobes extending halfway or more toward the 
 mid vein, it ia pinnatified ; when the divisions extend to the mid- 
 vein the frond is simply pinnate, and the divisions are called pinnae. 
 When the pinnae are lobed the frond is bipinnatified and the lobes 
 are called segments. When these divisions extend to the mid vein 
 of the pinnae the frond is bipinnate and the divisions are called 
 pinnules, and the midvein of the pinnae becomes a secondary 
 rachis. The delicacy and extent to which this division is carried 
 is the chief beauty of many ferns. 
 
 Besides the leaves, the stem gives rise to roots, so that the 
 ferns and their allies are the first plants to show distinct stems, 
 roots and leaves; and in them the three tissue systems first make 
 their appearance. If the stipe of almost any fern be crushed or 
 broken, the vascular bundles, as yellowish bands, are easily found 
 and with a little care may be traced into the stem or rhizoma, 
 and also into the divisions and subdivisions of the frond. The 
 epidermal and'fundamental tissues can easily be made out at the 
 same time. 
 
 The reproductive process in the ferns is interesting and some- 
 what peculiar. On the under surface of the frond bodies called 
 sporangia are developed, in which spores are formed. The 
 spores, when mature, develop into a flat roundish body, deeply 
 notched on one side, so that it is sometimes heart-shaped, which 
 is called the prothalium. The prothalium develops the sexual 
 organs, archegonia and antheridia. After fertilization an ovum 
 is developed in each archegonium which produces a young fern. 
 The prothalia in most cases are small, and they escaped the eye 
 and investigation of the botanist until about 1848, when they 
 were discovered and the mystery of the reproduction of ferns 
 was cleared up. 
 
 Some variety of the maiden-hair fern may be found in almost 
 any locality. It may be recognized by its black polished stem, 
 which divides into two equal recurved branches, from these arise 
 secondary branches which support oblong leaflets. On the under 
 side of the leaflets, along their margins are the crescent-shaped 
 
204 PRACTICAL LESSONS IN SCIENCE. 
 
 masses of sporangia called sori. The plant should be gathered 
 for study some time in August, and the fresh specimen may be 
 studied, or the stem and roots may be preserved in alcohol, and 
 the stipe and frond dried in a plant press or book, and the study 
 made at some other time. 
 
 With the complete plant in hand, notice the dark brown stem, 
 from which the slender branching roots arise, then the leaf with 
 its polished stipe and green leaflets, and lastly the hairs on the 
 roots, the scales on the rhizome, and the sori on the leaflets, which 
 together are called trichomes. Each of these parts is worthy of 
 study. Notice the shape, size and surface of the rhizome, its 
 growing apex and dying base. Those places on the rhizome from 
 which leaves grow are called nodes and the intervals between the 
 nodes are the internodes. Examine the buds at and near the 
 growing end of the rhizome; some show rudimentary leaves with 
 coiled stalks, and one or more are simply continuations of the 
 stem. Notice the arrangement of the buds and leaves on the 
 rhizome. 
 
 Crush a portion of the rhizome and then pick out the whit- 
 ish bands of vascular tissue, trace this tissue into buds, leaves 
 and branches of the stem. Make cross sections of the rhizome at 
 the nodes and between them and note the outer ring of brown 
 tissue, and the somewhat horseshoe-shaped whitish mass, the 
 vascular bundle; examine several sections so as to get a clear idea 
 of the position of this tissue in the internodes, at the nodes and 
 other places. Split a portion of the rhizome with a sharp knife 
 and examine the sections carefully. Notice the shape of the roots, 
 their mode of branching, the root hairs, the growing tip, make a 
 cross section and look for the vascular bundle. 
 
 Note the color, form and mode of branching of the stipe .or 
 rachis of the leaf, trace the vascular tissue into branches and 
 smaller divisions of the rachis. Make cross sections at different 
 places along the rachis, and compare with sections of the rhizome. 
 Study the shape of the leaflets and compare the one at the apex 
 with others on the seconday branches. Note the surface, texture, 
 color and framework or veins of the leaflet. 
 
LESSONS IN BOTANY. 205 
 
 On the under side of some leaflets note the crescent-shaped sori, 
 find out if there is any law as to which leaflets carry sori. After 
 soaking in water open a sorus, and note what forms the cover, 
 called the indusium. The yellowish spheroidal bodies in the sorus 
 are the sporangia, notice that they are attached to the veins of 
 the leaflet. Study a sporangium noting its shape, stalk, and the 
 ridge, called the annulus, extending part way round it. Burst a 
 sporangium and note the minute bodies called spores. The spor- 
 angium is opened by the straightening of the annulus; place some 
 sporangia that have been soaked in water on a piece of glass, 
 watch them through a lens, noting the process of opening. Make 
 a diagram of the mode of branching, and write out a description 
 of what has been observed. A larger fern might be more interest- 
 ing and easier to examine in some respects. The same general 
 plan can be followed in examining any fern. 
 
 Such a study gives one some idea of the gross anatomy of the 
 fern and is full enough for purposes of classification. For classi- 
 fication the maiden-hair fern Adiantum pedatum is described as 
 follows by Prof. L. M. Underwood : Root, many delicate fibers 
 somewhat matted. Rhizome, scaly somewhat creeping. Stipe, 
 slender, polished, black, forked at base of frond forming two 
 recurved rachises. Frond, roundish in outline, formed of sev- 
 eral pinnse, which branch from the recurved rachises; pinnules 
 unequal sided, oblong or deltoid ; upper margins irregularly lobed, 
 surfaces smooth. Veins, free, several times forked. Sori, borne 
 at the end of the veins on the under side of the reflexed margins 
 of the lobes, which form somewhat kidney-shaped membranous 
 indusia. Sporangia, globose with a nearly complete vertical ring. 
 Spores, too minute for examination with an ordinary lens. 
 
 The germination of fern spores may be studied by sowing them 
 on closely pressed muck, or even on a piece of glass, and keeping 
 them warm and moist. In this way the prothalium may be ob- 
 tained for study. 
 
 The method of veining varies somewhat and often serves as an 
 aid in classification. In many cases the veins are free, that is 
 arising from either side of the midvein they do not unite with 
 
206 PRACTICAL LESSONS IN SCIENCE. 
 
 any other vein. In other cases the branches of adjacent veins 
 unite forming a net work near the margin of the leaflet. The 
 sporangia in the true ferns are collected in clusters on the back of 
 the frond or are variously arranged in lines along the veins or 
 around the margins. The sporangia may be naked or covered 
 by an indusium. In the case of the ostrich fern, the sensitive and 
 cinnamon ferns there are sterile fronds, and fertile fronds, the 
 latter bearing large globose sporangia, appearing very little like 
 fronds; only a careful study of their life history would make one 
 sure of their origin. 
 
 Besides the ferns, the pteridophyta include the Equisetacese, 
 called horsetails or scouring rushes, and the Lycopodiacese called 
 lycopodium or club-moss. No member of the pteridophyta is of 
 great economic value, yet as the source of our coal supply they 
 have an honorable historical record. 
 
CHAPTER XXVII. 
 
 THE ANTHOPHYTA, LEAVES, REPRODUCTIVE ORGANS AND 
 
 FRUIT. 
 
 THE anthophyta, or flowering plants, make up the greater 
 part of the vegetable kingdom. They include the common herbs, 
 shrubs and trees, the plants that are cultivated for pleasure and 
 profit, the plants that furnish materials for the food, clothing 
 and shelter of man. 
 
 Among these plants, the stem, roots and leaves are usually well 
 developed and the three tissue systems are clearly defined. And 
 there is a strict division of labor in all physiological functions, 
 indicating a more complex and highly developed organism than 
 among the plants already studied. 
 
 Leaves are organs of assimilation, and in a modified form 
 constitute the organs of reproduction for this group of plants, 
 so that they seem the most important parts of the plant. A 
 leaf consists of a vascular framework covered by a mass of par- 
 enchyma, whose cells are well supplied with chlorophyll, and the 
 whole covered with a delicate epidermis. The parts of a leaf are 
 the stalk or petiole, and the blade or expanded portion, and at 
 the base of the petiole there are sometimes leaf-like bodies called 
 stipules. The petiole continued through the leaf is the midrib, 
 and its branches and subdivisions are called ribs, veins and vein- 
 lets. The framework of the leaf is a branch from the vascular 
 system of the stem. 
 
 On the basis of the arrangement of the veins, leaves are 
 divided into two classes, namely netted- veined, as the leaves of 
 the apple and oak, the veins forming a conspicuous net work, and 
 the parallel- veined, as the leaves of corn and grass, in which 
 there are few branches, and no net work is formed. 
 
 Leaves vary greatly in form, some of the more common forms 
 
 (207) 
 
208 PRACTICAL LESSONS IN SCIENCE. 
 
 are: linear, when the leaf is several times longer than wide 
 and of the same width throughout; lanceolate, when sev- 
 eral times longer than wide and tapering upwards and down- 
 wards from the lower third of the leaf; oblong, when two or 
 three times as long as broad with rounded base and apex ; 
 elliptical and oval, much the same as oblong but taper- 
 ing more toward the ends of the leaf; ovate, when the out- 
 line is like the lengthwise section of a hen's egg, the broader end 
 downward; orbicular, when nearly circular in outline. When 
 the leaf tapers toward the base it may be oblanceolate, spatu- 
 late, obovate, or wedge-shaped. 
 
 If we consider the base of the leaf it may be cordate, or heart- 
 shaped, reniform or kidney-shaped, auriculate or eared, sagi- 
 tate or arrow-shaped, and hastate or halberd-shaped. The leaf 
 of the water-lily and mandrake are peltate or shield-shaped. 
 
 When the apex of the leaf is considered it may be acuminate 
 or pointed, acute or obtuse; truncate, when the end appears as if 
 cut off square ; retuse, when the rounded summit is slightly in- 
 dented; emarginate, when the summit is decidedly notched; 
 obcordate, when the apex is heart-shaped; cuspidate, when 
 tipped with a sharp rigid point ; aristate, when the apex is like 
 a bristle. 
 
 Leaves also vary in outline. When the margin is an even line 
 without teeth or notches the leaf is entire. It is serrate or saw- 
 toothed when the margin is cut into sharp teeth pointing to ward 
 the apex of the leaf. Dentate, when the teeth are wider and point 
 outward; crenate, when the teeth are rounded; repand or 
 wavy; sinuate, like repand with deeper waves; incisid, when 
 the margin is cut into sharp, deep and irregular teeth. 
 
 When the incisions do not extend more than halfway to the 
 midrib, dividing the leaf into a definite number of somewhat 
 rounded parts, it is said to be lobed, and the divisions are called 
 lobes, and their number is expressed by the phrase three-lobed, 
 five-lobed, etc. If the divisions extend more than halfway to the 
 midrib, the leaf is said to be cleft, and it may be three-cleft or five- 
 cleft, etc. If the incisions go nearly to the midrib or base of the 
 
LESSONS IN BOTANY. 209 
 
 blade, the leaf is parted. If the divisions extend to the midrib, 
 or petiole, the leaf is said to be divided. 
 
 In studying leaves it will be noticed that the lobes, divisions, 
 etc., correspond to the veining of the leaf, the veins and divisions 
 in some cases radiating from the base of the leaf blade, when they 
 are said to be palmately veined, lobed, parted, etc., as in the 
 maple leaf; in other cases the branching, lobes and divisions are 
 related to the midrib rather than to the base of the leaf, when it 
 is said to be pinnately veined, lobed, parted, etc., as in the leaves 
 of the oak. 
 
 When a leaf consists of two or more parts, each part with a 
 distinct petiole, joined to the midrib or common petiole, it is a 
 compound leaf. It is often difficult to determine whether a leaf 
 is compound or simply divided. Leaves may be palma tely com- 
 pound, as in the case of the horsechestnut, or pinnately com- 
 pound, as in the case of the locust and pea. 
 
 A pinnately compound leaf may terminate with a single leaflet, 
 a pair of leaflets, or a tendril. The leaflets of compound leaves 
 may be divided and subdivided, and the leaf be bipinnate or tri- 
 pinnately compound, or twice palmate, etc. 
 
 Sometimes the stem grows through the base of the leaf, when 
 the leaf is called perfoliate. Sometimes two opposite leaves seem 
 to have grown together at the base, forming one roundish leaf 
 with the stem through the center. Such leaves are said to be 
 connate-perfoliate. 
 
 Many leaves are nearly horizontal with an upper and lower 
 side. Many others are nearly vertical, having inner and outer 
 surfaces, as the leaves of the iris. An examination of the leaves 
 of the iris shows the older straddling over the younger, as a man 
 straddles a horse, hence the leaves are called equitant leaves. 
 Equitant leaves, and many others, have no distinction of petiole 
 and blade, as the lea.ves of the pine, spruce and juniper. The 
 stipules are sometimes large and conspicuous, as in the case of 
 the pea and clover. Sometimes they form a sheath around the 
 stem, as in some grasses, where they serve as petioles. 
 
 Leaves sometimes take the form of cups, as in the pitcher 
 L. s.u 
 
210 PRACTICAL LESSONS IN SCIENCE. 
 
 plants ; sometimes they are so formed as to serve as insect traps ; 
 sometimes they serve as storehouses for food and as foliage also, 
 and sometimes they appear as spines, tendrils or scales. Foliage 
 leaves are the most prominent parts of the plant, and are much 
 used in describing and classifying plants ; hence the necessity of 
 studying carefully the forms of leaves, and of naming them ac- 
 curately. Leaves differ in color. The under side differs from the 
 upper side. Sometimes they are smooth, sometimes hairy or 
 woolly, etc., all of which may be important details in the identi- 
 fication of a plant. To gather leaves, to study them in all their 
 details, to describe them accurately, is an interesting and valu- 
 able educational exercise. 
 
 Leaves usually arise from definite places on the stem called 
 nodes or joints. If two arise from the same joint, they are on op- 
 posite sides of the stem, the pair above stand at right angles 
 with the first pair and the third pair above are directly over the 
 first, so that there are four ranks or rows of leaves along the 
 stem. Another arrangement is when the second leaf is opposite 
 but on the joint above, the third being over the first, when there 
 are only two rows of leaves along the stem. Another is when the 
 second leaf is on the joint above, but only one-third the way 
 around the stem, so that the fourth above stands over the first 
 and there are three rows of leaves along the stem. Sometimes 
 there are several leaves on one joint when they are called whorled 
 leaves, and sometimes, as in the pine, they form a cluster or fas- 
 cicle which appear to be the leaves of a whole branch, which is so 
 short that the leaves seem to arise from one joint, but examina- 
 tion shows a spiral arrangement. Other arrangements occur, 
 any of which can easily be made out from the careful study of 
 young stems. 
 
 The buds from which branches grow are developed in the axils 
 of leaves, so that the branching of a plant or tree follows the 
 arrangement of the leaves and is always definite, although it is 
 often difficult to discover the law on the older parts of the stem 
 as many branches have been destroyed. This same arrangement 
 extends to the location of flowers on the stalk, so that while on 
 
LESSONS IN BOTANY. 211 
 
 a hasty glance, one might think the top of a plant, shrub or tree 
 a mass of disorder, yet a careful investigation would show that 
 everything was in a definite place according to a plan. 
 
 The flower consists of parts or organs designed for the produc- 
 tion of seeds from which new plants may grow. The parts of a 
 complete flower are the calyx, the corolla, the stamens and pistil 
 or pistils. The flower is a short branch and the parts are com- 
 posed of more or less modified leaves arranged according to the 
 leaf plan of the plant. 
 
 The calyx is the lowest or outer whorl of leaves, they usually 
 have about the same color as the foliage leaves, and are called 
 sepals. Sometimes the sepals grow together forming a cup or 
 tube, when the calyx is called monosepalous. When the sepals 
 are distinct the calyx is polysepalous. The calyx may be regular 
 when all the sepals are alike, or they may vary in form when it 
 will be irregular. 
 
 The second whorl of leaves called petals make up the corolla. 
 They are usually of some attractive color differing widely from 
 that of the foliage leaf. The corolla may be monopetalous or 
 polypetalous, and it may be regular or irregular, and in some 
 cases it is wanting, when the flower is said to be apetalous, the 
 sepals sometimes having the appearance of petals. 
 
 The next whorl of leaves have been changed into stamens. A 
 stamen consists of a filament or stalk and the anther. The fila- 
 ment, usually slender, is sometimes broad and leaf-like. Some- 
 times the stamens are distinct, sometimes united into a tube, 
 when they are said to be monodelphous. Sometimes they stand 
 on the common receptacle of the flower, as an independent 
 group of organs, when they are said to be hypogynous, under 
 the pistil ; they maybe on the calyx around the pistils, when they 
 are perigynous ; they may be on the ovary, when they are epigy- 
 nous; they are sometimes united with the pistil, when they are 
 gynandrous; and again they may stand on the petals, when they 
 are epipetalous. Sometimes the anthers are united, when they are 
 syngenesious. The filaments may be of different length ; if there 
 are four stamens, two long and two short, they are didynamous. 
 
212 PRACTICAL LESSONS IN SCIENCE. 
 
 When there are six, four long and two short, they are tetradyna- 
 movs. The variety of positions in which stamens are found has 
 led some authors to doubt whether they are changed leaves, 
 considering them as possibly outgrowths from the epidermal 
 system of the plant. 
 
 The anther consists of two lobes or cells in which pollen grains 
 are formed, that contain the fertilizing element of the plant. 
 When the anther is attached by its base to the apex of the fila- 
 ment, it is innate; when attached for its whole length to the side 
 of the filament, it is adnate, and when fixed near the middle to 
 the apex of the filament, it is versatile. When it faces inward, it 
 is introi'se; when outward, it is extrorse. 
 
 The upper or innermost whorl of the floral leaves form the 
 pistil or pistils. A pistil consists of a stigma, style and ovary. 
 The ovary is the enlarged hollow part of the pistil in which the 
 ovules are formed, the part from which the ovules arise being 
 called the placenta. Above the ovary the pistil narrows into the 
 style which bears the stigma, which is a moist, glandular body of 
 varying shape. There may be several pistils in one flower; or two 
 or more may unite, forming a compound pistil. If we think 
 of the ovary as formed from a leaf by bringing its edges to- 
 gether, the line of union is called the inner suture, and a line cor- 
 responding to the midrib of the leaf is called the outer suture. 
 The inner or ventral suture is the placenta. When two or more 
 ovaries unite to form a compound ovary, the union is usually 
 along their ventral sutures so that the ovules are attached to a 
 column in the center of the ovary; and sometimes the partitions 
 dissolve away and a one-celled compound ovary results with the 
 ovules on a stalk in the center. 
 
 In some compound ovaries the ovules are on the walls and not 
 in the center. We may imagine in such cases that the three 
 or four or more leaves forming the ovary united with each 
 other by their edges, thus forming ventral sutures at the junc- 
 tion of two leaves instead of at the junction of the edges of the 
 same leaf. In one case the placenta is central, in the other it is 
 said to be pariet&l. 
 
LESSONS IN BOTANY. 213 
 
 Ordinarily the calyx is below the ovary, but sometimes the 
 calyx adheres to the ovary, so that the stamens and petals are 
 around or above the ovary, when the ovary is said to be inferior, 
 half inferior, or superior, as the case may be. Sometimes the 
 leaf forming the pistil is not closed, the pistil being a scale-like 
 leaf bearing the ovules on its upper or inner face near the base. 
 This form of pistil is peculiar to the pine family which is named 
 gymnospermous, or naked-seeded. 
 
 The ovule at first is a mass of parenchyma, a little later an 
 integument grows over the mass called the secundine coat, and 
 later another integument is formed called the primine coat. These 
 coats do not completely cover the ovule, a small opening called 
 the micropyle always remaining over its apex. Later an embryo 
 sac forms near the apex of the ovule. 
 
 In fertilization, the pollen grains are conveyed to the stigma 
 by the wind, by insects, or birds, or in some other way. The 
 grain resting on the moist surface of the stigma, absorbs mois- 
 ture and germinates, sending out a tube which penetrates the 
 soft tissues of the stigma and style, to the cavity of the ovary 
 where it enters the micropyle of an ovule, and through its tissues 
 to the embryo sac, where fertilization takes place. 
 
 As a result of the fertilization there is formed a proembryo, 
 from which is developed the embryo, which consists of one or two 
 leaves or cotyledons, the plumule and the root or radicle. 
 With the embryo in the embryo sac is formed the endosperm 
 which serves to nourish the embryo. The walls of the ovule 
 thicken and harden and the seed is formed. 
 
 Fruit usually consists of the seeds inclosed in a variously 
 modified ovary. Sometimes the wall of the ovary thickens and 
 becoming soft as it ripens, forms such a fruit as the currant, 
 gooseberry, grape and tomato. This softened wall may be cov- 
 ered with a thick skin as in the orange and lemon, or a hard rind 
 as in the melon and squash. While in the cherry and peach the 
 inner part of the ovary forms a stony wall about the seed while 
 the outer forms the delicious fruit. The blackberry consists of 
 the softened end of the stem on which the flower stood, covered 
 
214 PRACTICAL LESSONS IN SCIENCE. 
 
 with little stone fruits. In the case of the apple, pear and quince 
 the thick fleshy part is not the wall of an ovary but a thickened 
 calyx. 
 
 Sometimes the wall of the ovary becomes thin like a mem- 
 brane, or hardens, or remains herbaceous, forming fruits, that 
 in some cases open at maturity for the escape of the seed, while 
 in other cases they remain closed, having the appearance of sim- 
 ple seeds, and are called akenes. The fleshy part of the straw- 
 berry is the softened end of the stem on which the flower stood 
 and the real fruits are ripened ovaries, usually called seeds, 
 scattered over its surface. The fruit of the sunflower, dandelion 
 and many others are akenes. In the case of wheat, corn and 
 other grains, the seed and ovary wall adhere so as to form one 
 body, so that a grain of wheat is a true fruit, called a caryopsis. 
 
 Capsule or pod is the name for dry seed vessels that split open 
 at maturity. The pea-pod is a good illustration. Fruits were 
 designed to help in some way toward the reproduction of species; 
 in many cases they serve as storehouses of food to aid in the 
 growth of the young plant. And they are the most valuable 
 sources of food for man and domestic animals. 
 
CHAPTER XXVIII. 
 
 THE GYMNOSPERM.E. 
 
 THE Anthophyta are divided into two classes, the Gymno- 
 spermte, in which the ovules and seeds are not inclosed in an 
 ovary, and the Angiospermse, in which the ovules and often the 
 seeds are inclosed in an ovary. 
 
 The AngiospermaB are divided into two subclasses, the mono- 
 cotyledons, in which the embryo has one cotyledon, and the 
 plants generally have parallel veined leaves, and the numerical 
 plan of their flowers is three ; and the dicotyledons, in which the 
 embryo has two cotyledons, and the plants generally have netted 
 veined leaves, and the numerical plan of the flowers is five. This 
 subclass includes the greater part of plants and trees of the tem- 
 perate zones. 
 
 The gymnosperuise all have woody stems, and generally nar- 
 row, needle-shaped, parallel veined leaves. The members of this 
 class are mostly trees, including the redwood, pine, spruce, cedar, 
 fir and cypress. The male and female organs are in different 
 flowers, which are very simple, consisting of one or more stamens 
 in the one case, and naked ovules in the other. After fertilization 
 the embryo, consisting of root, stem and leaves, is soon formed. 
 The various parts of the reproductive organs are homologous 
 with those of the pteridophyta, the material from which the em- 
 bryo sac and embryo are developed corresponding with the 
 prothallium. 
 
 A careful study of the Scotch or the Austrian pine will give us 
 clearer ideas of the whole class than to spend the same amount 
 of time on several members of the group. 
 
 The Scotch pine is a species often planted for ornament. The 
 leaves, from two to four inches long, occur in pairs, and are cov- 
 ered with a whitish powder which gives a peculiar color to the 
 
 (215) 
 
216 PRACTICAL LESSONS IN SCIENCE. 
 
 tree. The cones are small, about two inches in length, the free 
 ends of the scales being produced into protuberances, which are 
 sometimes recurved. The Austrian pine has longer leaves of a 
 dark green color, without powder. The Cones are much larger, 
 but without the recurved protuberances. 
 
 As plants vary considerably during the growing season, a com- 
 plete study necessitates continuous observation during the inter- 
 val between fertilization and maturity, with a study of every 
 phase of growth ; or specimens of the different stages of develop- 
 ment may be collected and preserved in alcohol, so that the study 
 can be made at any time of the year. 
 
 The male flowers of the Scotch pine form a catkin or spike-like 
 cluster at the base of the young shoots, and should be gathered 
 for study in May or June. The female flowers form inconspicuous 
 clusters toward the end of the young branches. Specimens should 
 be gathered as above, and later in the season also. Leaves and 
 stems and young cones, found just below the new shoots, should 
 be gathered in July or August, and the terminal buds and mature 
 cones in late autumn. Fresh leaves and stems may be used at 
 any time, but the resin which abounds in fresh material often 
 makes it unpleasant to work with. 
 
 In studying the pine notice the central shaft or trunk of 
 the tree, extending without division to the very summit. Note 
 the whorls of branches at definite places on the stem, and 
 also the angle they make with the main stem, and compare the 
 pine with other kinds of trees in these respects. . In young trees 
 or branches of older trees note the difference in vigor between the 
 terminal and lateral shoots. Make cross sections of the smaller 
 stems and branches, then counting the rings of growth, notice if 
 there is any relation between the age of the stem and the number 
 of whorls of branches. Note the short branches bearing the pairs 
 of green leaves, pull out the leaves and then from the scars study 
 the numerical arrangement, also study the arrangement of the 
 scales on a mature cone and compare the two. Notice the surface 
 of the youngest shoots, then following the branch back to the 
 main stem note any changes as to bark, scales, etc. 
 
LESSONS IN BOTANY. 217 
 
 Notice the position, shape and size of the buds; split a terminal 
 bud lengthwise and study carefully the relative position and the 
 form of the different parts; carefully take off some of the scales 
 with needles and note the character of their edges, and the differ- 
 ences between the apex arid base; note the secondary or new 
 buds, their form, position, etc. Compare the bud with a branch, 
 and observe whether the bud is a branch or not. Make a cross 
 section of a stem which is a half inch or so in diameter, and note 
 the central pith, the woody portion with its rings of growth, and 
 the bark outside the wood. Notice the fine lines radiating from 
 the pith to the bark, called medullary rays, and note that many of 
 them do not reach the pith. Notice also many scattered openings 
 from which resin exudes, they are resin ducts occurring both in 
 the wood and in the bark. Study the rings of growth noting the 
 difference between the inner and outer portions. 
 
 The bark may be divided into three layers an inner, whitish, 
 fibrous layer, the middle green layer and the outer brownish por- 
 tion. Note the relative thickness of these layers and the resin 
 ducts in the middle one. Split a portion of the stem and study 
 the appearance and relation of the various parts in the longitu- 
 dinal as well as in the cross section. 
 
 Notice the color, shape and texture of the leaves, note theapex, 
 edges, base and surface. Make cross sections and longitudinal 
 sections and notice the fibro-vascular bundles, resin ducts, the 
 green tissue and the epidermis. 
 
 Take a cluster of male flowers and note that it is made up of a 
 central axis on which are arranged the short-stalked bodies, called 
 stamens. Each stamen consists of a flat scale, bearing on its in- 
 ferior surface two enlargements, the pollen sacs. Find a pollen 
 sac that has burst and note the location and character of the 
 opening, burst a pollen sac and notice the yellowish grains of 
 pollen that escape. The flowers on a very short stalk are crowded 
 on an axis forming a cluster called a spike. Notice that the 
 flowers each replace a "branch on the young shoot. 
 
 Taking a spike of female flowers, notice the stalk or peduncle 
 by which it is attached to the stem, and that the spike is com- 
 
218 PRACTICAL LESSONS IN SCIENCE. 
 
 posed of thin scales or bracts and thicker ones called carpellary 
 scales. Dissect out one of thicker scales and study its shape and 
 texture and compare it with the thinner bract. Note the promi- 
 nent ridge or keel on the upper surface and the two enlargements 
 near the base, the ovules. Notice the position of the ovules and 
 the opening at the free end called the micropyle. Note that the 
 cluster seems to take the place of a branch. 
 
 Split a one year old cone and examine carefully all the parts 
 in section, notice the ovules, the abortive ovules, the scales, and 
 make a diagram showing the relation of the parts to each other. 
 Dissect out an ovule and bisect it through the micropyle, and 
 notice the nucleus, and a large cavity called the embryo sac, 
 enclosing a soft substance called the endosperm. 
 
 In the mature cone notice the heavy carpellary scales, and the 
 smaller bracts, and along the inner surface of the scales will be 
 found a pair of thin wing-like scales, each bearing at its lower 
 end a seed or an abortive ovule. 
 
 In the case of the seed, note its form, character of surface, 
 micropyle, etc. Bisect the seed lengthwise, parallel with its nat- 
 ter faces, and notice the firm outer coat, the embryo and the 
 food for the embryo, the endosperm. Carefully pick out the 
 embryo with needles and note the short stem, and the young 
 leaves. 
 
 A study of the pine according to the foregoing scheme will give 
 one a good idea of the gross features of the pine family. The 
 careful study of one tree or plant is of great value even though 
 it may be far from complete. The scheme suggested may be va- 
 ried to suit individual ideas and opportunities. The idea has 
 been to encourage careful, systematic study, and to this end full 
 notes should be taken, and numerous drawings, diagrams and 
 sketches made and specimens gathered and preserved for reference 
 and study. 
 
 The wood of the pine is composed mainly of tracheides, while 
 the bark is made of sieve tissue and bast fibers. The tree grows 
 from the cambium layer or meristem tissue lying between the 
 wood and the bark. The cells of this tissue undergo division by 
 
LESSONS IN BOTANY. 219 
 
 the formation of partitions, and the new cells develop into trach- 
 eides or wood cells on the one side and into sieve tissue and bast 
 fibers on the other. The new wood incloses the old, while the old 
 bark is outside the new, serving as a protective coating for it. 
 
 In the class Gymnospermse are included the Cycads, Conifers 
 and the Joint Firs. The conifers are the only ones common in 
 the United States, and the only ones of commercial value. The 
 order conifers includes the juniper, cypress, white cedar, arbor 
 vitce, the giant redwood, the silver fir, the tamarack or American 
 larch, the white pine, the sugar pine of California, the yellow pine 
 of Georgia, and many others. There are some 300 species of 
 pine, growing mostly in cool climates. In general, they are rapid 
 growers, furnishing strong and durable timber and lumber. 
 
CHAPTER XXIX. 
 
 MONOCOTYLEDONS. 
 
 THE class Angiospermse includes the great mass of the flower- 
 ing plants. They differ from the gymnospermae in that they gen- 
 erally have the male and female organs in the same flower ; they 
 have the ovules in a closed ovary, and the flower differs more 
 widely from the other parts of the plant. 
 
 The subclass monocotyledons has one cotyledon, parallel 
 veined leaves, and parts of the flower in threes, and the structure 
 of the stem differs from that of the dicotyledons. A cross section 
 of a stalk of Indian corn, which belongs to this group of plants, 
 shows it to be composed of parenchymatous tissue traversed 
 by great numbers of fibro-vascular bundles. These bundles are 
 more numerous toward the surface of the stem, so that it in- 
 creases in density from the center outwards, the central portion 
 often disappearing leaving a hollow stem, as in the grasses. 
 These bundles are closed bundles; as they become permanent 
 tissue no cambium or meristem tissue remains and no further de- 
 velopment is possible, and such plants are usually short-lived. 
 
 The different stages of germination in these plants may be ob- 
 served by planting several grains of corn, and then by examining 
 a different grain every few hours the process may be followed 
 closely. The first leaf of the young plant has its dorsal surface 
 in contact with the endosperm or food supply, curving entirely 
 around the remainder of the embryo. As it begins to grow the 
 root pushes through the root sheath. The plumule, consisting 
 of a minute stem and a few rudimentary leaves, pushes out 
 through the curved cotyledon, which remains in contact with 
 the food supply, absorbing nourishment for the growing parts. 
 Make out these points from the study of the germinating grains, 
 making notes and sketches. 
 
 The monocotyledons include about fifty natural orders of 
 (220) 
 
LESSONS IN BOTANY. 221 
 
 plants. The most important of these is the order graminse, or 
 grass family. The members of this family are herbaceous, rarely 
 woody plants, with round stems, mostly jointed and hollow, 
 bearing alternate two-ranked leaves, each of which has a split 
 sheath or stalk. The flowers are arranged in spikelets, which 
 form a more or less compact cluster, which may be a spike or 
 panicle. The calyx consists of leaves called glumes, and the 
 parts of the corolla are called palets, which often bear bristles 
 called a-wns. There are rarely more than three stamens, and the 
 anthers are versatile. The ovary contains one ovule, which at 
 maturity forms a caryopsis, or grain. This is a large and widely 
 distributed group of plants, including the cultivated grains and 
 grasses, which furnish the major supply of food for man and 
 domestic animals. 
 
 The more important members of this order are wheat, rye, 
 barley, the oat, rice, Indian corn, and the grasses, timothy, red- 
 top, blue-grass, orchard grass, etc.; also the sugar cane, and 
 many others. We may gain some idea of the characteristics of 
 this interesting family by studying the cultivated grass known 
 as the oat. Specimens should be collected when some of the 
 flowers are expanded and others yet in the bud. They should not 
 be pulled up, but dug up with care and the dirt shaken gently 
 from the roots, which may be cleaned by washing. If possible 
 secure specimens with the empty grain from which the plant grew 
 still attached. 
 
 Notice first the parts of the plant, the roots, the stem with its nu- 
 merous branches to ward the top; the leaves, and possibly root hairs 
 may be seen as well as outgrowths from the stem and some parts 
 of the flower. Study carefully the different groups of roots, the 
 points from which they arise, their arrangement, relative size, etc. 
 The strongest root, from t he grain, is called the primary; those 
 from the nodes on the stem are secondary roots. Make a cross sec- 
 tion of a primary root and of a secondary root and notice the 
 parts shown and compare them. Strip off the bark from a root 
 and note its character, and that of the fibrous tissue which re- 
 mainsnote the position of the root hairs. 
 
222 PRACTICAL LESSONS IN SCIENCE. 
 
 Remove the leaves and study the stem, noting its shape and 
 surface; make a section through a joint or node and note the 
 partition separating the cavities of the internodes. Make a 
 cross section and note the vascular bundles and the cortical or 
 bark layer with its clusters of chlorophyll cells. Make longitu- 
 dinal sections and find the parts shown in the cross sections. 
 
 In studying the leaves notice the split sheath with the thin 
 membraneous ligule, and compare the two as to texture, form 
 and use. Notice the shape of the blade, the veins, their direction, 
 and relations to each other; make a cross section and locate the 
 vascular bundles; the green tissue between is the mesophyll, or 
 parenchyma of the leaf. 
 
 The stem of the plant is the main axis of inflorescence; its 
 branches are secondary axes, and some of these are branched, 
 forming a flower cluster called a panicle. At the extremity of the 
 smaller branches there is a cluster of two or three flowers called 
 a spikelet. At the base of the spikelet notice two leaves which 
 enclose the flowers, called the glumes ; notice their position with 
 respect to each other, also note their shape, surface and veins. 
 The flattened axis on which the flowers stand is the rachis of the 
 spikelet; note the relative size of the flower inclosed by the 
 glumes and the tuft of hairs at the base of the lowest flower. 
 
 Take the lowest flower of the spikelet, and note the bract 
 called the lower palet which almost incloses the flower ; notice 
 carefully the size, shape, surface, texture, number of nerves, etc., of 
 the palet. It sometimes bears a bristle or awn ; if so, note its 
 position, length, texture, etc. Cut away the lower palet without 
 injuring the flower, and note another bract called the upper palet. 
 Study all its parts and compare it with the lower palet, also note 
 two little scales at the base of the upper palet. Notice the num- 
 ber of stamens, the character of the filament and anthers, and 
 the appearance of the pollen. Notice the top-shaped ovary, the 
 thread-like styles, and the feather-like stigmas. Compare the 
 lowest flower of the spikelet with the others. 
 
 In studying the ripe grain, strip off the chaff and note the 
 whitish hairs, especially at the upper end; the longitudinal 
 
LESSONS IN BOTANY. 223 
 
 groove, and the scar at the base. Make a cross section and note 
 the white central portion and the darker shell or enclosing mem- 
 brane. After soaking in water for some time, remove the skin 
 and notice the embryo and try to make out the cotyledon, plu- 
 mule, and stem ; if this cannot be done, examine a grain that has 
 just begun to germinate. The process of germination maybe 
 followed step by step in oats germinating on a piece of wet blot- 
 ting paper. Any one of the grasses studied as indicated above 
 will give one some idea of this order of plants, and will enable 
 one to describe the plant examined accurately, so that it can be 
 identified. 
 
 The value of the hay crop of the United States is not far from 
 $300,000,000, and the cultivated grass eaten by domestic ani- 
 mals is worth as much more; and when we add the value of the 
 annual product of wheat, corn, oats, barley, rye, rice and sugar 
 cane, the total amounts to at least $1,500,000,000, as the an- 
 nual value of the grass crop of the United States. Grass is king. 
 
 Another extensive order is the Sedge Family, made up of her- 
 baceous, three-angled, solid-stemmed plants, growing in tufts, 
 generally in wet places. The members of this family are of little 
 economic value to man or beast. The papyrus, which the ancient 
 Egyptians used for paper, was made from the pith of sedges. 
 Ropes and mats are made from some species in India. 
 
 Order Liliacese or the Lily Family contains many interesting 
 and valuable plants. The members of this family are herbaceous, 
 rarely woody plants, with regular, and usually six parted flowers. 
 The different parts of the flower are distinct and free from the 
 chiefly three-celled ovary. Stamens six except in one case, anthers 
 two-celled. Cajyx and corolla colored alike except in trillium. 
 The plants usually rise from a bulb or short root stalk. 
 
 The trillium is a very common flower in the woods during 
 early spring and can easily be obtained for study. Secure 
 several complete plants, and notice the thick horizontal under 
 ground stem or root stalk. It is covered with broad scales, and 
 from it branch the roots, and it also sends up an aerial branch 
 which bears a whorl of three green leaves and a terminal flower. 
 
224 PRACTICAL LESSONS IN SCIENCE. 
 
 Note the arrangement of the unbranched roots, their wrinkled 
 surface and the root hairs. Make transverse and longitudinal 
 sections of the larger roots, and notice the cortical, parenchyma 
 and fibro-vascular regions, and the thickness and peculiarities of 
 each. In the fibro-vascular region several large tracheary vessels 
 may be seen. 
 
 Notice the size and shapeof the root stalk, the number of nodes 
 and scars of former branches, and the number of roots from each 
 node. Make the two sections and note the vascular bundles amid 
 a mass of white material, which is probably reserved food. Crush 
 a bit of the white matter in a little water and add a drop or two 
 of iodine solution and note change in color indicating starch. 
 Compare the ends of the root stalk, studying especially the grow- 
 ing end as a whole and in longitudinal section, and note the form, 
 structure and veining of the scales or leaves of the root stalk. 
 
 Study the aerial stem with its whorl of leaves and flower, note 
 its form, size and the absence of nodes. Make the two sections 
 and note the three tissue systems, especially the two parts of the 
 vascular area, the light colored or cortical portion toward the out- 
 side, and the darker woody portion toward the center of the stem. 
 Notice the number, shape, arrangement and position of the foliage 
 leaves, especially the outline of the apex and base of each. Note 
 also the petiole and the venation or mode of veining of the leaves, 
 which is not usual in this order. Make a drawing of a leaf. 
 
 The flower is composed of four whorls of organs, the lower, of 
 three greenish sepals, the calyx, the next of three colored petals, 
 the corolla,, the next of six stamens, the andrcecium and the in- 
 nermost, of three partly united pistils, the gyncecium, and all 
 these parts stand on the broadened end of the stem called the re- 
 ceptacle. Note that the parts of a whorl alternate with those of 
 the whorl next to them. Notice the color, shape and venation of 
 both sepals and petals. In studying the anthers, notice the 
 pollen sacs, and the connection between them, which is a continu- 
 ation of the filament. In the filament notice the vascular 
 bundles, and the fundamental tissue. Note also the way the 
 anther opens and the character of the pollen. 
 
LESSONS IN BOTANY. 225 
 
 The tapering, divergent styles, stigmatic along the inner sur- 
 face, unite below forming a compound ovary. Study the style, 
 noting its form, size, etc., find also the vascular bundles. Make 
 a cross section of the ovary and notice the form and position of 
 the ovules, especially notice the placenta on which they stand and 
 find out how it is formed. The fleshy pod incloses the seeds. 
 Where the ripe seed breaks away from the stalk a scar called the 
 hilum is formed. A cross section of a seed shows the thin brown 
 coat or testa, and the food material making up the main body 
 of the seed. 
 
 In these plants we have for the first time a complete flower. 
 The calyx and corolla serving in the bud and blossom as organs 
 of protection for the reproductive organs; the corolla in addition 
 serves to attract the attention of insects and birds, whose visits 
 are often beneficial to plants. Sometimes the calyx also becomes 
 colored and attractive. And here first we find the typical closed 
 ovary, the distinguishing characteristic of the Angiospermae. In 
 the oat the ovule and seed are adherent to the ovary, while in 
 trillium they are distinct. The trillium represents the lily 
 family very well except in the veining of the foliage leaves and 
 the color of the sepals. 
 
 Among the useful plants of this order may be mentioned as- 
 paragus and the onion, used for food; the aloe, green hellebore, 
 colchicum, sarsaparilla and others are used in medicine; and a 
 large number of lilies are cultivated as ornamental plants. 
 
 The Palm Family belongs to the monocotyledons, and for eco- 
 nomic value is second only to the grass family. The members of 
 this family furnish enormous quantities of food materials, of, 
 material for house-building, and for an endless variety of house- 
 hold goods and utensils. But nearly all the useful members of 
 the family are natives of the tropical regions. 
 
 The Orchid Family is an interesting member of this group of 
 plants. They are terrestrial plants in some cases, but generally 
 they are air plants, growing most abundantly and in greatest 
 variety in the tropical regions. They all have irregular flowers, 
 often having most grotesque forms, and sometimes simulating 
 
 L. S. 15 
 
226 PRACTICAL LESSONS IN SCIENCE. 
 
 the forms of insects and birds. They are noted for the beautiful 
 color of their flowers and the varied forms of their foliage. They 
 are especially interesting for the many curious devices for cross 
 fertilization by insects and birds. They are very popular as or- 
 namental plants, and are represented in the United States by the 
 lady's slipper and a few other less showy flowers. The vanilla 
 plant is an orchid, and other members of the family are useful, 
 but in general they are of little economic value. 
 
 Another interesting member of this group is the Banana 
 Family. The genus Musa of this family contains the plaintain 
 and the banana of tropical regions. No other genus furnishes 
 food for as many people as does the genus musa. It is estimated 
 that about 25 tons of bananas can be grown upon an acre of 
 ground, furnishing more food per acre than any other plant. 
 
 There are many other interesting plants in this subclass, but 
 the ones mentioned are the most prominent, and will give a good 
 and comprehensive idea of the whole. This monocotyledon group 
 of plants is distinctively the foo d group of the vegetable kingdom. 
 
CHAPTER XXX. 
 
 DICOTYLEDONS. 
 
 IN this group of plants the embryo has two cotyledons, the 
 leaves are netted-veined, and the plants grow in diameter by the 
 addition of new material each year between the bark and wood 
 of the previous year, as among the gymnosperms. This sub- 
 class contains nearly 200 natural orders or families, but only a 
 few of the more interesting and valuable can be noticed here. 
 
 The Willow Family consists of trees or shrubs, with bitter bark, 
 light, soft wood, and dioecious flowers that is, the male and fe- 
 male organs are in separate flowers on separate plants. Both 
 kinds of flowers are in clusters called catkins, which are much like 
 cones, only the scales are more leaf-like and the axis more slender. 
 The staminate or sterile flower consists of stamens only, the 
 pistilate or fertile flower of one pistil with a one-celled ovary. At 
 maturity the ovary contains numerous seeds each of which is fur- 
 nished with a tuft of cotton-like down at one end. This family 
 includes the willows, osiers, aspens, poplars, and the cotton- 
 wood. Some of these trees are grown for ornament; from the 
 aspen, pulp for coarse paper is made, and willow-ware is made 
 from the young shoots of the osier. 
 
 The Oak Family consists mainly of trees, with some shrubs, 
 bearing alternate leaves, which are sometimes entire and some- 
 times pinnately lobed or cleft. The flowers are monecious or di- 
 clinous, both on the same plant; the sterile in slender catkins, 
 the fertile, solitary or clustered. Among the oaks proper, the 
 sterile flowers have a four to seven lobed calyx, and from three to 
 twelve stamens clustered in pendant catkins, while the fertile 
 flower is one pistil in a bud-like involucre that becomes a scaly 
 cup, called the cupule, which partly covers the brown ovoid nut 
 or acorn. 
 
 (227) 
 
228 PRACTICAL LESSONS IN SCIENCE. 
 
 Make a transverse and longitudinal section of an acorn, and 
 notice the pericarp or shell, the thin, brown membrane investing 
 the kernel, called the testa, and the whitish substance making up 
 the bulk of the seed which constitutes the cotyledons, with their 
 store of food for the young plant. Soak the seed of an acorn for 
 several hours in water and it can easily be separated into two 
 parts, but notice that they are united, study this bond of union, 
 and make out the radicle and plumule of the embryo. 
 
 Make a transverse section of an oak stem and note the rings 
 of growth, the medullary rays, the numerous very large openings 
 which are pitted vessels, and the smaller ones, some pitted ves- 
 sels and some tracheids, and wood fibers. Note that the rings of 
 growth are not of uniform thickness, and an individual ring is 
 not uniform throughout. Find out the reason. Make a longi- 
 tudinal section through the heart and notice the numerous shiny 
 plates, the silver grain, or medullary rays. Sometimes the oak 
 has a strong taproot with few spreading ones. Occasionally the 
 taproot is replaced by spreading multiple roots. Find out a 
 reason for the difference. 
 
 Oak timber is usually heavy, tough, durable and beautiful. 
 These qualities make it a valuable tree. It has a history; it is 
 famous in poetry and prose alike; it is especially interesting to 
 us as its history runs back through the early English and Anglo- 
 Saxon periods, and backward to our Aryan forefathers. The 
 tree has always been admired for its qualities, and it has often 
 been invested with superstition and romance. 
 
 The oak grows best in the cooler regions ; it is generally de- 
 ciduous, but many evergreen varieties exist. It varies in size 
 from a tiny shrub to the sturdy forest tree sometimes six to 
 eight feet in diameter. It grows in a great variety of soils, and 
 varies greatly in quality and appearance. There are some 250 
 species of oak which are found mainly north of the equator; 
 about 100 species are found in the United States. The White 
 Oak and its varieties furnish the best timber. The Live Oak of 
 our southern states is especially valuable for shipbuilding. But 
 nothing in North America quite equals the Quercus rohvr. the 
 
LESSONS IN BOTANY. 229 
 
 British oak of England and Europe. The oak family not only 
 includes the oaks, but the beeches, chestnuts and others. The 
 nuts produced by members of this family are valuable food for 
 domestic animals, and the tannic acid of oak bark makes it valu- 
 able in leather making, and some varieties furnish a beautiful 
 yellow dye. 
 
 The Walnut Family includes the walnuts and the hickories. 
 They have alternate pinnately compound leaves and monecious 
 flowers, the sterile of numerous stamens in catkins, the fertile of 
 a single pistil, and but few in a cluster. The calyx is adherent to 
 the two-to-four-celled ovary which has only a single ovule. The 
 outer part of the nut is the thickened calyx, the stone part the 
 ovary walls, and the meat of the nut consists of the curiously 
 crumpled cotyledons of the embryo. The wood of the walnut is 
 highly prized for its beauty and durability. The bark and 
 young branches are aromatic and strong scented, and from the 
 bark a strong dye is made, and sometimes sugar is made from 
 the sap. 
 
 The hickories have a white, tough wood much used as handles 
 for tools, for parts of carriages, etc. Walnuts, butternuts, hick- 
 ory nuts and pecan nuts are highly prized for eating. 
 
 The Elm Family is made up of trees and shrubs, with alternate 
 two-ranked leaves which are usually rough entire and sharply 
 serrate. The fruit is a one-celled, one-seeded samara, or winged 
 fruit somewhat circular in form. Some of the elms are cultivated 
 for ornament and some of them furnish a tough timber that is 
 valuable when kept dry, or when kept continuously under water, 
 otherwise it deca}^s rapidly. The hackberry, the mulberry, and 
 the osage orange are interesting and valuable trees that are 
 closely allied to the elms. 
 
 The Buckwheat Family is represented in this country by a 
 large group of herbs, having entire leaves with stipules in the 
 form of scarious or membranous sheaths at the strongly marked 
 joints of the stem. The flowers have a green or colored calyx, 
 with the stamens on its base. The one-celled ovary ripens into 
 an akene or* nutlet, which is often triangular in form. Buck- 
 
230 PRACTICAL LESSONS IN SCIENCE. 
 
 wheat is perhaps the most important member of the family, as 
 its seeds furnish excellent material for food, and its honey pro- 
 ducing flowers make it valuable to those who are raising bees. 
 The rhubarb used in medicine and the well-known pie-plant 
 are useful members of this family. Besides these there are 
 knot-grass, smartweeds, sorrels, water pepper, and several 
 kinds of Dock, belonging to this family, which are troublesome 
 weeds. 
 
 The Pink Family includes some beautiful and interesting 
 plants, but none that are of any great economic value. It is 
 made up of herbs with opposite entire leaves, and regular flow- 
 ers. The ovary is usually one-celled , with from two to five styles; 
 it ripens into a many-seeded pod which opens at the top and 
 contains a free central placenta. Stamens not more than ten, 
 usually standing on the calyx. The petals with slender stalks or 
 claws are also on the calyx. The calyx is composed of five sepals 
 which are united below into a cup or tube on which the stamens 
 and petals are inserted. Many varieties of pinks are cultivated 
 for ornament and are much prized for their beautiful colors and 
 sweet odor. The corn-cockle so injurious in the wheat fields is a 
 member of the pink family, and so are the different varieties of the 
 catchfly, which forms a sticky exudation on its stems and calyx 
 by which small insects are caught. The chickweeds, which belong 
 with the pinks, are mostly adapted to impoverished soils, sandy 
 and gravely wastes, etc. They are pioneers everywhere in 
 nature's attempts to renew worn out soils and to clothe barren 
 places with verdure. 
 
 The Crowfoot Family is made up mostly of herbs, growing 
 more abundantly in the cooler climates and in moist localities. 
 They have numerous stamens, usually more than one pistil, and 
 distinct carpels. Sepals usually five, deciduous, often petal 
 like; petals five, often wanting; plants usually with a watery 
 acrid juice; leaves sometimes simple and entire, but often much 
 divided ; flowers sometimes regular, but often irregular. Many 
 familiar plants belong to this family, as the clematis, hepatica, 
 anemone, buttercup, the cowslip, columbine, larkspur, aconite, 
 
LESSONS IN BOTANY. 231 
 
 peony, and others. Several of these are cultivated for orna- 
 ment and some are used in medicine, as aconite, goldthread, etc., 
 but no members of this family are of much economic value. 
 
 The Magnolia Family consists of trees and shrubs, with aro- 
 matic, bitter bark, alternate leaves mostly entire, and large, 
 showy, solitary flowers, stamens and pistils numerous on a long 
 receptacle, the pistils imbricated and cohering into a mass form- 
 ing a cone-like fruit. The most important member of this family 
 is the tulip tree or white wood, in some localities called poplar. 
 It is a handsome tree with greenish-yellow flowers and dark green 
 leaves. The leaves are broad, with two short side lobes and a 
 truncate apex. The timber is white, soft and durable. The nu- 
 merous species of magnolia are broad leaved evergreens noted 
 for the beauty of their leaves and flowers, the latter yielding a 
 rich perfume. 
 
 The Water Lily Family consists of numerous aquatic plants 
 having large roundish leaves, which float on the water. The 
 flower is large and showy, varying considerably among the dif- 
 ferent members of the family in color and arrangement of parts. 
 The water-shield, growing in quiet water, has an oval, centrally 
 peltate leaf, and a small purplish flower whose stem is coated 
 with a clear jelly-like substance. 
 
 The Nelumbium has large root-stalks, large leaves, and large 
 pale yellow flowers. The parts of the flower stand on a broad, 
 top-shaped receptacle in which at maturity there are a dozen or 
 more little pits, each containing an acorn-like seed. The seeds 
 and the tuberous root-stalk are edible. The sepals and petals 
 are numerous, passing gradually into each other so that onecan- 
 not tell where the calyx ends and the corolla begins. This plant 
 is sometimes called the lotus. 
 
 The white water lily is a beautiful and highly prized flower 
 with four sepals, but numerous petals, which pass gradually into 
 the numerous stamens, and is given as an illustration of the fact 
 that the stamens are changed leaves. The root-stalks are very 
 large, and the fruit ripens under water. The yellow pond lily is 
 a less showy flower than the others. It has six sepals and nu- 
 
232 PRACTICAL LESSONS IN SCIENCE. 
 
 merous thick, yellow petals, the stigma forming a broad disk in 
 the center of the flower. The Egyptian lotus and the Victoria 
 Regia of the Amazon, with leaves three feet or more in diameter, 
 belong to this interesting family. 
 
 The Poppy Family is made up of herbs which have a milky or 
 colored juice. The calyx consitsof two sepals which are deciduous; 
 the petals and stamens are numerous, the ovary one-celled, rip- 
 ening into a many-seeded pod. Several members of the family 
 are cultivated for ornament. The juice of the opium poppy, fur- 
 nishing the opium and morphine so much used in medicine, makes 
 this one of the noted families of plants. The bloodroot, with its 
 reniform, palmate-lobed leaf, its white petals, and its blood-red 
 juice, is one of the most interesting flowers of early spring. 
 
 The Cruciferse, or Mustard Family, consist of a large group of 
 herbs having a pungent watery juice and four-parted cruciform 
 flowers. The cabbage, turnip, mustard, radish, water-cress 
 and horseradish are members of this family which are used as 
 food. Some are prized as ornamental plants, as candytuft and 
 sweet alyssum, and others are troublesome weeds, as the shep- 
 herd's purse. These plants are widely distributed throughout 
 the temperate regions, especially in southern Europe and south- 
 western Asia. 
 
 The flowers are much alike, having four sepals, four petals, 
 with long claws and spreading blade; the stamens are tetra- 
 dynarnous, four long and two shorter. They have a two-celled 
 ovary which forms a pod called a silique, or if short a silicle. 
 These pods are two-celled by a false partition between the two 
 parietal placenta?. It generally opens from the apex toward the 
 base by the sides splitting off, leaving the partition with the 
 placentae and seeds. The flower cluster is a raceme, often a com- 
 pound raceme. In this cluster each flower has a pedicel which is 
 a branch of a common axis, the lowest blossoms being the oldest, 
 so that often fruit may be found in the lower part of the cluster 
 with buds at the top and all stages between. The flowers of the 
 shepherd's purse are in a compound raceme, and the pod is a 
 silicle. The root leaves are pinnatified, and the stem leaves are 
 
LESSONS IN BOTANY. 233 
 
 sagitate and partly clasping. The pod of the mustard is a 
 silique. 
 
 Many of these plants, as the radish, are biennials, that is, they 
 grow from the seed during one season, storing up in the roots 
 some nourishment for the next season. During the second sea- 
 son they produce flowers, mature seed and die. Many plants 
 live only one season, dying as soon as seed has been matured. 
 Such plants are called annuals, while trees arid many others live 
 on from year to year and are called perennials. 
 
 The Violacese or Violet Family. The members of this family 
 are well-known plants, highly prized for their beautiful flowers. 
 The flower is irregular, with five sepals and five petals, which are 
 more or less unequal, the lower one with a sack or spur at its 
 base. The stamens are five, the broad, flat filaments, slightly co- 
 hering around the pistil. The somewhat showy flowers are sel- 
 dom fertile. Another set of flowers, hidden under the leaves, 
 produce most of the fruitful pods. These flowers are of a green- 
 ish color, and are more nearly regular than the more conspicuous 
 ones above. The irregularity of the aerial flower is supposed to 
 have some relation to insect a,gency in fertilization. Some of the 
 violets send up flower stalks from underground stems, and some 
 have aerial stems. This is a very interesting flower from its 
 various irregularities, and a careful study of it according to the 
 plan followed with the trillium would be a valuable and inter- 
 esting work. 
 
 The members of the Droseracese or Sundew Family are inter- 
 esting chiefly from the fact that they are carniverous or insect 
 eating plants. They are bog plants with regular flowers, on the 
 plan of fives, having a tuft of glandular bristly leaves at the base 
 of the stem, which in the bud are rolled up from the apex, alter 
 the manner of ferns. The common sundew has small roots with 
 five or six root leaves spread out in a rosette around the base of 
 the stalk. The upper surface of each leaf is covered with gland 
 bearing filaments, each of which is crowned by a drop of a trans- 
 parent viscid secretion. Insects are attracted to these leaves, 
 and lighting on them are entangled by the secretion of the ten- 
 
234 PRACTICAL LESSONS IN SCIENCE. 
 
 tacles or filaments, which by a curious waving movement trans- 
 fer the insect to the center of the leaf where it is soon drowned 
 in the liquid, and at length is digested and absorbed. 
 
 In the Venus fly-trap, the leaf with bristles on its edges and 
 filaments on its surface shuts up like a book thus capturing 
 insects, which are digested and absorbed. Neither of these plants 
 are sensitive to wind or rain. The most vigorous leaves rarely 
 digest more than twice, or at most three times. In these cases 
 we have illustrations of movements in plants due to some kind 
 of irritation that simulates very closely reflex action in animals. 
 
 The common pitcher plant, sarracenia, is carniverous. The 
 mouth of the trumpet-shaped leaves is protected by a lid, the 
 inner surface of which is smeared with nectar, and in some cases 
 a pathway, honey baited, lures the insect into the pitcher where 
 they are soon drowned in the liquid secreted wholly or in part by 
 the inner membrane of the leaf. This liquid does not digest the 
 insect, but seems to accelerate decomposition, and if the plant 
 gets any nourishment from the insect, it as a saprophyte, taking 
 nourishment from decaying matter. There are several other 
 pitcher plants which destroy insects, but their process is much 
 the same as given above. The most extensive studies in this 
 direction were made by Charles Darwin. 
 
 The Linden Family consists chiefly of tropical plants. It is 
 represented in this latitude by the lime tree or basswood. It 
 bears dull cream-colored flowers which are rich in honey. They 
 are arranged in a cluster called a cyme, which is united to a long 
 leaf-like bract ; the fruit is a woody globular two-celled nut. The 
 wood is soft, white, elastic, the inner bark rich in bast fibers. 
 The dark green leaves are roundish, serrate and somewhat heart 
 shaped at the base. It is a beautiful tree, much prized for its 
 timber and as an ornament. 
 
 The Mallow Family consists of herbs, shrubs and trees that 
 have alternate simple, palmately veined leaves, but are best 
 known by their monadelphous stamens, which are united into a 
 tube inclosing the pistil. The flowers are regular, sepals and 
 petals five, and there is often an involucre of several green bracts, 
 
LESSONS IN BOTANY. 235 
 
 resembling an outer calyx. In the mallow family the calyx is 
 valvate and the corolla convolute in the bud. By valvate is 
 meant that the edges of the parts meet without overlapping or 
 infolding, while in the convolute arrangement one edge of each 
 leaf covers one edge of the next, so that each leaf has one cov- 
 ered and one free edge. A cross section of a bud of a mallow 
 blossom shows these arrangements nicely. Several members of 
 this family are cultivated for ornament, as the hollyhock, abu- 
 tilon, hibiscus and althea. But the family is best known from 
 the cotton plant, which furnishes more material for cloth and 
 other fabrics than all other plants. The cotton fiber consists of 
 hairs which are developed on the surface of the seed ; at first they 
 are cylindrical, but on drying they become flattened and twisted, 
 so that they are easily distinguished from other fibers. There are 
 several varieties of cotton, the sea island cotton of our southern 
 states being the finest in the world. The general superiority of 
 American cotton is supposed to be largely due to climate. Cot- 
 ton grows in all tropical countries, even as far north as Tennessee 
 and Arkansas. Cotton was extensively grown and manufactured 
 in India and Egypt centuries before the Christian era. The bast 
 fibers of some of the plants of this family are valuable, and are 
 much used in China, India and New Zealand. Besides the cotton 
 fiber, the cotton seed yields an oil that from its cheapness is be- 
 ing extensively used for many purposes, adding much to the 
 value of the cotton crop. 
 
CHAPTER XXXI. 
 
 DICOTYLEDONS CONTINUED. 
 
 THE Linacese or Flax Family is composed of herbs, shrubs, 
 and a few trees, but is represented in this country by the one genus 
 of which the common flax is the only plant of economic value. 
 The flowers are regular, opening for only one day, and the decid- 
 uous petals are especially delicate in texture and color. This 
 plant rivals cotton in importance as a fiber producing plant. It 
 grows best on the borders of the tropical regions, having a much 
 wider range than cotton. The linen fiber consists of bast cells 
 from the stem of the plant, and has been used from the earliest 
 times. The oldest mummies of Egypt are wrapped in linen and 
 its remains are found in the ruins of the Lake Dwellers of Swit- 
 zerland and Italy. 
 
 The Rue Family includes the prickly ash, the hop-tree, the 
 orange, lemon, citron and lime trees. The chief characteristic of 
 the family is the transparent dots or glands in the leaves which 
 contain a pungent aromatic oil. In some cases the juices are very 
 bitter and in some cases acrid enough to blister the skin. The 
 orange, lemon and citron are the most important members of 
 the family. 
 
 TheAcerinese or Maple Family is made up of shrubs and trees 
 that are prized for their beauty and for their timber, and the sap 
 yields a sugar of a fine flavor. The flowers are sometimes per- 
 fect, sometimes dioecious; sometimes with petals, sometimes with- 
 out. They appear in early spring, with or before the leaves, in 
 drooping, umbel-like clusters. The fruit is a pair of samaras, or 
 winged fruits, united at the base. The leaves are palm ate- veined 
 and palmately lobed or parted, and sometimes serrate. There 
 are several varieties, as the sugar maple or hard maple, the soft 
 (236) 
 
LESSONS IN BOTANY. 237 
 
 maple and the red maple. The hard and soft maples furnish ex- 
 cellent timber, much used in the manufacture of furniture. 
 
 The buckeye and the horse-chestnut, near relatives of the 
 maples, have white, somewhat irregular flowers arranged in a 
 conical cluster called a panicle, and large, palmately compound 
 leaves. 
 
 The Ampelideae or Vine Family consists mainly of woody 
 shrubs or vines climbing by tendrils. The leaves are simple, 
 rounded and heart shaped, sometimes lobed. In some cases the 
 leaves and young shoots are covered with a cotton-like down. 
 Flowers small and greenish forming a cluster called a panicle. 
 The calyx is short, and connected by a thick disk with the ovary. 
 On this disk the petals and stamens are inserted, five thick 
 glands or lobes of the disk alternating with the stamens. The 
 petals cohere slightly at the top and the corolla is thrown off 
 without expanding. 
 
 The vine has been cultivated and used by man from the earli- 
 est times. It is indigenous to southern Asia and North America. 
 There are many varieties. The best wine and raisin grapes grow 
 in southern Europe. 
 
 The Virginia Creeper climbing by tendrils and rootlets belongs 
 to this family. The flowers form a cymose cluster and the pal- 
 mately compound leaf with five lance oblong cut tooth leaflets 
 changing to crimson in autumn make it highly prized as an orna- 
 mental vine. 
 
 The Euphorbiaceze or Spurge Family is a vast group of more 
 than 3,000 species, distributed through a wide range of climate, 
 but growing most abundantly in tropical regions. They vary in 
 size and habit from a tiny creeping plant to a giant tree. They 
 usually have a milky, acrid, often poisonous juice, with flowers 
 varying widely in structure, but the ovary and fruit are usually 
 three-celled. Tapioca, castor and croton oil, caoutchouc and 
 several valuable woods are furnished by members of this family. 
 Many species, with thick succulent stems are cultivated for 
 ornament. 
 
 The Umbelliferse or Parsley Family is a large and widely dis- 
 
238 PRACTICAL LESSONS IN SCIENCE. 
 
 tributed group of plants named from the fact that the small, 
 five-parted flowers are grouped in clusters called umbels. The 
 leaves are alternate, compound, and usually finely dissected. 
 Many of these plants contain a poisonous juice, and in general 
 the green parts are acrid and poisonous, while the seeds are aro- 
 matic and harmless. The parsnip, carrot, celery and parsley 
 are food products of this family. Coriander, caraway, fennel, 
 aniseed are aromatic and medical products, while gum asafoe- 
 tida, poison hemlock, sweet cicely and others indicate the great 
 variety of plants included in this interesting family. 
 
 The Saxifrage Family is made up of trees, shrubs and herbs, 
 which are not marked by any distinguishing character. The 
 leaves are opposite or alternate, pinnately or palmately veined. 
 There are usually five petals, with from five to ten stamens. The 
 calyx is generally monosepalous, and on it the petals and sta- 
 mens are inserted. To this family belong the currant and the 
 gooseberry, the syringia, hydrangea and the strawberry ger- 
 anium, and other interesting and beautiful flowers. 
 
 The Cactacete or Cactus Family consists of succulent herbs, 
 shrubs or trees, generally spiny and leafless. They grow mainly 
 in dry regions, and the surface for evaporation has been reduced 
 to the green rind of the stem, sometimes increased by a few 
 branches or thick leaves. These plants are illustrations of the 
 great changes in form which plants may undergo in adapting 
 themselves to varied circumstances. The scanty evaporating 
 surface and the protecting spines seem necessary to their exist- 
 ence. Many of these plants are cultivated as curiosities; some 
 furnish edible fruits; the leaves of others furnish a valuable fiber. 
 Some varieties instead of growing one year and maturing seed 
 the second, grow for eight or ten years, and then send up a flower 
 stalk from ten to twenty feet high, mature seed and die. In 
 Mexico as the flower stalk of the pulque plant begins to grow, it 
 is cut off and a bowl-shaped cavity made from which the juice, 
 designed for the growth of the flower stem, is gathered for use 
 by man. It is the Mexican pulque, and from it a distilled liquor, 
 called mescal, is made. 
 
LESSONS IN BOTANY. 239 
 
 The Rosacese or Rose Family is divided into several tribes, 
 each of which contains interesting plants or shrubs. The Tribe 
 Pomse includes the apple, pear, crab apple, and quince, haw- 
 thornes, etc. They have simple leaves, two to five ovaries, which 
 in the fruit are covered by the thick walls of the calyx tube. 
 
 The Tribe Rosese includes the Roses, which exist in great va- 
 riety. They have pinnately compound leaves with entire serrate 
 leaflets. The calyx is five parted with a globose fleshy tube, 
 which incloses the pistil. The corolla consists of five petals, 
 which are greatly multiplied by cultivation, and the stamens are 
 numerous. 
 
 The Tribe Potentillese includes the potentillas and the straw- 
 berries. They have palmate or pinnately compound leaves. 
 Many of the potentillas are cultivated as ornaments, and the dif- 
 ferent varieties of strawberry furnish a delicious fruit, which is 
 the enlarged and softened receptacle covered with the seeds or 
 akenes which are the real fruit. 
 
 The Tribe Rubese includes the raspberries and the blackber- 
 ries. The raspberries are clusters of little stone fruits, while the 
 blackberry is a cluster of stone fruits with the receptacle on which 
 they stand. They are usually shrubs with prickly stems and 
 compound leaves. 
 
 The Tribe Prunese includes the almond, peach, apricot, plum, 
 and cherry. They have simple, usually serrate leaves, and their 
 stems and fruit yield a gum. The inner part of the ovary 
 wall hardens into a stone inclosing the kernel or seed ; the outer 
 part forms the edible portion of the fruit. The wild cherry of the 
 United States furnishes a timber much prized for its beauty and 
 durability. No other family of dicotyledons furnishes as large 
 quantities and as great a variety of fine fruit as does the rose 
 family, and it easily leads all others in the beauty and fragrance 
 of its flowers. 
 
 The Leguminsose or Pulse Family is made up of herbs, shrubs, 
 and trees, with alternate and usually compound leaves, and more 
 or less irregular flowers. The stamens are ten, generally mona- 
 delphous, forming a tube inclosing the pistil ; sometimes diadel- 
 
240 PRACTICAL LESSONS IN SCIENCE. 
 
 phous, nine in one set and one in the other; and very rarely the 
 stamens are distinct. This great family, containing 1 some 6,000 
 species growing in all parts of the world, is divided into three 
 subfamilies. 
 
 The Papilionacese includes the pea, bean and peanut ; the lu- 
 pine and the clovers; the locust, rosewood and many other fine 
 trees; indigo, camwood and other dyes; the gums tragaeanth 
 and kino; the balsams of Peru and Tolu; and the plant that 
 yields the medicinal product, liquorice, and species that yield good 
 fiber, besides many species that are cultivated for ornament, 
 as the laburnum and wistaria. The name is derived from the 
 corolla, which is composed of five petals of such form and arrange- 
 ment as to resemble a butterfly. The petals of this corolla have 
 received special names. The upper and larger one, which is gener- 
 ally wrapped round the others in the bud, is called the banner ; 
 the two side petals are called the wings, and the two lower ones, 
 the blades of which usually stick together inclosing the stamens 
 and pistil, are called the keel. 
 
 The Csesalpmiese includes the honey locust, coffee tree, and 
 judas tree of the United States, and many valuable timber trees 
 from the tropical regions, as well as many dye-woods, and others 
 that produce valuable gums and balsams. The members of this 
 group have a somewhat irregular corolla, with usually ten dis- 
 tinct stamens, and often twice pinnately compound leaves. 
 
 The Mimosese have regular flowers, distinct stamens, and twice 
 pinnate leaves. The most important product from this group is 
 gum Arabic or acacia, and the different varieties of acacia fur- 
 nish very fine lumber highly prized for furniture, veneers, and 
 ornamental purposes generally. Some members of this group 
 are especially interesting on account of the movements executed 
 by their leaves, expanding in the light, closing in darkness, or 
 upon the slightest touch or jar, opening again in a few moments. 
 Mimosa pudica, is so prompt in its movements that it is called 
 the sensitive plant; numerous others are more or less sensitive. 
 As a whole the pulse family is interesting, important, and well 
 worthy of study. The common bean plant is a good specimen 
 
LESSONS IN BOTANY. 241 
 
 from which to study the characteristics of the dicotyledons ; the 
 same general plan may be followed as in the study of the trillium 
 and oat. The bean plant can be grown easily at any time of the 
 year, and its whole life history can be studied easily by starting 
 a number of plants, and examining different individuals in the 
 various stages of germination, growth and maturity. 
 
 The Ericaceae or Heath Family is composed mainly of shrubby 
 plants which have monopetalous regular or irregular flowers, 
 and the calyx tube sometimes free and sometimes adherent to 
 the ovary. This family includes the huckleberry, cranberry and 
 blueberry; the wintergreen, trailing arbutus, laurel and other 
 beautiful flowering shrubs. 
 
 The Solonacese or Nightshade Family includes the potato, 
 tomato, and tobacco; red pepper, henbane, belladonna, bit- 
 ter-sweet, and other important plants. These plants have regu- 
 lar monopetalous flowers, a two-celled many seeded ovary, and 
 generally a colorless poisonous juice, with a strong unpleasant 
 odor; many of them are cultivated for their beautiful flowers. 
 While this family is important and interesting, it is peculiar, 
 presenting many sharp contrasts. The potato and tobacco, 
 natives of America, are now cultivated and used in all parts of 
 the earth. 
 
 The Figwort Family is made up mostly of herbs and shrubs, 
 with a more or less irregular monopetalous corolla and a two- 
 celled ovary. There is often an interesting irregularity among 
 the stamens, only a portion of them bearing anthers. In the 
 pentstemons and others there are four anther-bearing stamens, 
 the fifth represented by a barren filament or a scale. The family 
 includes many plants that are cultivated for ornament, as the 
 pentstemon, castilleia, veronica and others. Digitalis, used in 
 medicine, and many coarse weeds are also members of this family. 
 These plants are widely distributed from the tropics to the limits 
 of vegetation towards the poles. A castilleia and a mustard 
 were found at higher elevations on Mount Orizaba than any 
 other flowering plants. 
 
 The Labiatss or Mint Family consists of square-stemmed, 
 
 L. S. 16 
 
242 PRACTICAL LESSONS IN SCIENCE. 
 
 opposite-leaved aromatic plants, with an irregular corolla and 
 didynamous stamens, and a deeply four-parted ovary. It in- 
 cludes lavender, hyssop, peppermint, sage, catnip and other 
 interesting plants, but none of great economic value. 
 
 The Oleacese or Olive Family is composed of trees and shrubs, 
 with simple or pinnate leaves, regular flowers, two stamens, and 
 two-celled ovaries. It includes the olive, which yields fruit, oil 
 and lumber, the different varieties of ash, which yield good tim- 
 ber, and some ornamental shrubs, as the lilac, jessamine and 
 others. 
 
 The Asclepiadacese or Milkweed Family. The members of this 
 family are woody or herbaceous plants with an abundant milky 
 juice. The flowers are regular, calyx and corolla five parted; 
 the two distinct ovaries have a common stigma; the five sta- 
 mens monadelphous, the anthers closely surrounding the stigma 
 and partly adhering to it. The pollen is in waxy masses which 
 are distributed by insects. The structure of the flower is peculiar 
 and difficult to describe, but exceedingly interesting to study, the 
 structure no doubt having reference to cross fertilization by the 
 aid of insects. The flowers are arranged in umbels; the fruit con- 
 sists of a pair of pods containing many flat seeds, which are fur- 
 nished with a tuft of soft, silky hairs, called a coma, at one end. 
 The milky juice contains caoutchouc, and some plants are culti- 
 vated for ornament, but the plants are chiefly interesting for the 
 peculiar structure of their flowers. 
 
 The Gourd Family is made up of tendril bearing herbs, with 
 watery juice, alternate palmately ribbed and lobed leaves, and 
 monopetalous flowers. It includes the gourd, pumpkin, squash, 
 watermelon, muskmelon and the cucumber. 
 
 The Composite or Sunflower Family. This immense family 
 including as many as 10,000 species has representatives in all 
 parts of the world. Many of the species are of great beauty and 
 are much admired as ornaments, but few are of any economic 
 value. The small monopetalous flowers with their syngenesious 
 anthers are gathered into compact heads or masses which often 
 resemble single flowers. The tube of the calyx is coherent with 
 
LESSONS IN BOTANY. 243 
 
 the ovary, its margin, consisting of rigid or downy bristles, teeth 
 or scales is called the pappus. The end of the stalk on which the 
 simple flowers stand is the receptacle. The greater part of the 
 flower cluster is made np of tubular flowers, but often around 
 the margin of the cluster there are flowers whose corollas have 
 extended into a strap or leaf-like form called rays, which in many 
 cases seem to be the petals of ordinary flowers. Some well-known 
 members of this family are chickory, lettuce, dandelion, sun- 
 flower, golden-rod, chrysanthemum, thistle and burdock. 
 
CHAPTER XXXII. 
 
 FORM, COLOR AND ODOR OF PLANTS. 
 
 PLANTS seem to differ widely in structure and in the processes 
 of nutrition and reproduction, but a careful investigation shows 
 that all plants are composed of essentially the same elements, so 
 that the processes of nutrition must be about the same among all. 
 And so with the process of reproduction, it is simply the formation 
 of new cells, whether in the humble protococcus or in the stately 
 oak. And the same is true in the matter of structure; every plant 
 structure, however complicated, is made up of modified paren- 
 chyma cells. We have thus far studied typical members of dif- 
 ferent groups of plants, from which the plant world might seem 
 to be composed of several distinct parts. When we try, however, 
 to find the dividing lines between the groups, they continually 
 evade us, one group seeming to merge into another by such in- 
 sensible degrees that the idea of distinct parts soon fades away, 
 and we are more impressed with the fact that the plant world is 
 essentially a unit. 
 
 The plant world, then, is practically a unit in its structure, in 
 its processes and in its relations. But why , in that case, the wide 
 differences in form, color, odor and habit of plants ? If we accept 
 the theory of special creation, nothing came by chance, each 
 peculiarity of form, each shade of color, each odor means some- 
 thing, nothing depends upon accident the form, color and odor 
 of each particular flower are, all things considered, the best pos- 
 sible, no others would do. Again, if we accept some form of the 
 theory of evolution or development the same thing is true. 
 Every peculiarity which distinguishes one group of plants from 
 others is supposed to be beneficial to that group. Such peculiar- 
 ities are not the result of caprice or chance, but of purpose. 
 (244) 
 
LESSONS IN BOTANY. 245 
 
 The air with its changing temperatures, the water with its 
 multiform impurities, the soil with its different qualities, the ex- 
 istence of other plants and animals, all constitute an endless 
 variety of conditions under which plants exist; and which plants 
 have been made to fit, either by their creation in special forms, or 
 in a form adaptable to all the different conditions that might 
 arise. And perhaps here lies the answer to our query the form, 
 color, fragrance and other peculiarities of plants are, or may be, 
 determined by their surroundings. 
 
 The lowest groups of plants, those which are supposed to have 
 appeared first on the earth, are water plants, or are active only 
 when surrounded by an abundance of moisture. The air and 
 water contain all the nutriment necessary to these, so that there 
 is no call for special organs of nutrition, each cell performing all 
 the functions of a plant, and as there is no division of labor the 
 whole body is an organ of nutrition, and of reproduction as 
 well. The ability to survive long periods of dessication, as in 
 the case of protococcus and many others, implies some modifi- 
 cation, some improvement over the organism of strictly aquatic 
 plants. 
 
 As the rocks were broken down and pulverized into soil, plant 
 life began to appear on the land. But water, one of the essen- 
 tials of plant life, was not now present on all sides; the supply 
 was in a sense limited, coming mainly from the soil below. It 
 was not necessary for the upper surface to be fitted to absorb 
 moisture, but it was necessary to so cover it as to prevent the 
 evaporation of moisture, and hence the plant is differentiated 
 into parts, consisting of a body from whose under surface roots 
 are developed to take up moisture and other nourishment, and 
 on the upper surface an epidermis is formed which protects the 
 body from excessive evaporation. 
 
 Another interesting modification arose when plants, as spiro- 
 gyra, in addition to reproduction by simple division became able 
 to form resting spores, which enabled the species to survive ex- 
 treme cold or drought, thus greatly extending the range of plant 
 life. These examples illustrate the first steps in the differentia- 
 
246 PRACTICAL LESSONS IN SCIENCE. 
 
 tion of organs, and in the division of labor, which exist so fully 
 in the higher plants. 
 
 As the conditions became more favorable and plants increased 
 in size, a fibre-vascular system became necessary to strengthen 
 and support the plant, and to convey nutrient fluids to all its 
 parts. As plants grew more numerous the supply of light and 
 air became somewhat limited, the fibro-vascular system was 
 strengthened and an erect form was acquired, thus greatly in- 
 creasing their opportunity for these essentials of plant life. 
 
 The change in form and habit resulting from this struggle for 
 light and air, is often very marked. Trees growing singly in the 
 open field are shorter, thicker and have a relatively broader 
 foliage system than trees of the same species growing in a 
 crowded forest. The purslane, which is usually a prostrate creep- 
 ing plant, when crowded by other plants will assume an erect po- 
 sition, rising to seek the light. 
 
 Coincident with this growth of the stem, the leaves were devel- 
 oped from the vascular system, parenchyma, and epidermis, and 
 so arranged as to serve for digestive organs. As the work of 
 digestion or assimilation can only be carried on in the light, we 
 can easily understand that the struggle for light involves the life 
 or death of the plant. This struggle may account for many in- 
 teresting forms of plants; as vines climbing up the stems of stur- 
 dier plants, in whose shadow they could not live, to expand their 
 leaves in the life-giving light above. In some cases climbing 
 plants become air plants, able to derive nourishment from the 
 air, or parasites, living on the juices of the host plant, in either 
 case having no use for a stem connecting with the ground . In 
 this way plants become permanent residents amid the branches 
 of trees, so that a tree often appears to produce several kinds of 
 foliage. Thus the common ivy, sometimes becomes an air plant, 
 gathering nourishment from the air and from its support. 
 
 In some flowers the stamens and pistil or pistils are so ar- 
 ranged that self-fertilization is possible, but in general self-fertili- 
 zation is difficult or impossible, so that most flowers are fertil- 
 ized by pollen from other flowers. The pollen grains are carried 
 
LESSONS IN BOTANY. 247 
 
 to the stigmatic surfaces by the wind, by insects, or in rare cases 
 by birds. 
 
 The grasses, sedges, pines, oaks and others, having small 
 uncolored flowers, produce great quantities of pollen. As this 
 floats easily in the air it is widely distributed by the wind, so that 
 while there may be instances of self-fertilization, cross-fertiliza- 
 tion is the rule. Other plants have highly colored flowers pro- 
 ducing nectar, which attracts such insects as bees, butterflies, 
 etc. The insects, in their excursions from flower to flower, carry 
 pollen from one blossom to the stigma of another. And this is 
 by no means a matter of accident or chance; in many cases the 
 flower and insect are so adapted to each other that only a par- 
 ticular insect can get nectar from a particular flower, and aid in 
 its fertilization. One case of many maybe mentioned; the yucca 
 in southern climates, ripens its seeds regularly, but while it thrives 
 well in the north it does not mature seed. In the south a little 
 moth called the yuccasella gathers up masses of yucca pollen, 
 and laying its eggs in them thrusts them down a stigmatic tube 
 and thus fertilization is accomplished. The yuccasella cannot or 
 does not live in the north and the yucca ripens no seed in that 
 region. 
 
 It is said that cats saved the clover crop in a certain district 
 in Australia. The cats caught the mice that destroyed the nests 
 of a long-billed bumble bee, which was the principal agent in the 
 fertilization of the clover blossoms. The orchids with their beau- 
 tiful flowers of grotesque forms afford many interesting illustra- 
 tions of mutual adaptation and dependence between flowers and 
 insects. 
 
 The flowers are fertilized, the seeds have ripened and are ready 
 for the soil; if they fall near the parent plant only one or two 
 could find room for growth, so that it seems necessary for seeds 
 to be scattered widely. This is accomplished in various ways; 
 the seeds of the maple and elm are furnished with wings, those of 
 the thistle, dandelion and milk-weed with plumes so that they 
 may be dispersed by the wind. The seeds of many plants are 
 furnished with hooks by which they may become attached to 
 
248 PRACTICAL LESSONS IN SCIENCE. 
 
 animals and are distributed in their wanderings. The seeds of 
 other plants are inclosed in edible fruits and are scattered by 
 the animals using the fruit for food. In some cases the seed 
 pod at maturity opens with a jerk throwing the seeds some 
 distance. 
 
 Many plants, as the strawberry, multiply not by means of 
 seeds alone, but send out runners which, rooting at the tips, de- 
 velop into new plants. Again other plants send up new plants at 
 intervals along an underground stem; such plants aremore com- 
 monly found in sandy soils. 
 
 In general plants seem to spread out as much surface as possi- 
 ble for evaporation, but in the case of the cactaceae and some of the 
 spurges living in hot dry regions, this surface is much reduced, 
 seemingly as a protection against excessive evaporation. Many 
 plants living in cold climates are protected from cold by a thick 
 growth of hairs, which frequently disappear when such plants are 
 acclimatized to warm regions. Buds, the embryos of the next 
 season's branches and flowers, are often furnished with coats of 
 down or wool, and covered with thick varnished scales so that 
 they are protected from moisture and sudden changes of tem- 
 perature. Again, thorns, spines, prickles, stinging hairs, acid 
 and bitter juices, etc., seem to serve plants as a defense against 
 animals. 
 
 Some trees, as the red or soft maple, when cultivated will grow 
 vigorously on the highland, but when left to their own resources 
 other trees soon crowd them into the lowlands along the streams, 
 resulting in more or less change of form. This is an illustration 
 of the struggle going on between plants everywhere, by which 
 many seeds have no chance to grow, and many plants which begin 
 to grow are smothered out or stunted by stronger plants or are 
 crowded into undesirable localities. 
 
 Some spreading plants creep out over rocks or barren places, 
 dust collects along their stems, and mingling with the decaying 
 leaves forms a soil in which other plants may grow, as illustrated 
 by vegetation advancing over brick walks, and similar spaces. 
 Often soil is formed in this way that is deep enough to support 
 
LESSONS IN BOTANY. 249 
 
 forest trees. Sometimes lichens or algae are the pioneers in 
 such invasions, which are often very rapid in tropical regions. 
 It is said that an island of lava, from the eruption of Kraka- 
 toa was covered from shore-line to summit with an abundant 
 vegetation of ferns and allied plants within six years after the 
 eruption. 
 
 The succession of plants on a tract of land that has been 
 cleared and then allowed to go to waste is interesting. In one 
 case a bit of pine forest had been cleared away and the land 
 abandoned. It was soon covered with weeds and grasses, then 
 quaking aspen and other woody plants began to smother out 
 the herbs, and it seemed as if the aspen was the natural occupant 
 of the soil. After a time, however, little pines began to grow; 
 these grew larger and others started; the aspens began to decay, 
 and in less than thirty years the pines were again in full posses- 
 sion of the ground. 
 
 The illustrations given may serve to suggest a possible 
 explanation of many peculiarities of form and structure, of color, 
 odor and other characteristic features, which exist among plants, 
 and to indicate interesting and profitable lines of study and 
 investigation, which may be pursued in almost any locality. 
 
 The collection and preservation of specimens is an important 
 part of botanical work. A specimen, to be of value, should show 
 roots, stem, leaves, buds, flowers, fruit, all with color and form 
 as perfect as possible. And the label should show the locality 
 and any peculiarity of position or surroundings that might in 
 any way modify the character of the plant, and any peculiarity 
 of the plant that cannot be preserved should be noted. 
 
 Most herbaceous plants may be preserved by drying them un- 
 der pressure. The plant, with its leaves and other parts, should 
 be carefully arranged in a fold of paper, and then subjected to 
 pressure in a discarded book or some kind of a press, which 
 may consist of two boards with a weight of stone. The plants 
 should be aired frequently until they are thoroughly dry. A 
 few trials will enable one to make good specimens of most 
 herbaceous plants. In the case of some succulent plants much 
 
250 PRACTICAL LESSONS IN SCIENCE. 
 
 care is necessary to prevent them from decay or from becoming 
 mouldy. 
 
 Parts too thick or heavy for drying may be preserved in alco- 
 hol, or may be described in the label and not preserved. Lichens 
 may be dried and kept in boxes without pressing. Mosses, liver- 
 worts and algae, when it is desirable to preserve color, should be 
 immersed in glycerine or Miiller's solution. 
 
 When dry, the specimen may be transferred to a sheet of heavy 
 paper and fastened by strips of gummed paper, and the label 
 should be written on the paper or fastened to it in some way, so 
 that it may not be lost or separated from the specimen. The 
 size of the sheets commonly used for specimens is thirteen or 
 fourteen inches long by ten to eleven inches wide. 
 
CHAPTER XXXIII. 
 
 ZOOLOGY GENERAL AND STRUCTURAL. 
 
 THE science of zoology treats of everything relating to ani- 
 mals. It considers their external form, anatomical structure and 
 physiological processes, their geographic distribution and eco- 
 nomic value. It attempts to trace out the life-history of animals 
 from the lowest to the highest forms; it considers also their re- 
 lations to one another, to the members of the vegetable kingdom, 
 and to other forms of environment. 
 
 The animal body is made up of about the same elements found 
 in the plant, but the proportions are different; in animals the 
 albuminous and calcium compounds predominate. From these 
 compounds the different tissues of the body are formed, and the 
 tissues variously modified and combined constitute the organs of 
 the animal body, which may be divided into the organs of the 
 mechanical system, the organs of digestion, circulation, respira- 
 tion and excretion, the organs of reproduction and of the nerv- 
 ous system with those of the special senses. To trace the devel- 
 opment of these different groups of organs and to follow out the 
 processes carried on by them is an important part of the work 
 of zoology. 
 
 The living portion of the animal, as of the plant that which 
 moves, assimilates food and grows is protoplasm, and an indi- 
 vidual portion of protoplasm, called a cell, is the unit of all ani- 
 mal structures. Thecell consists of a small portion of protoplasm 
 which is frequently surrounded by a structureless membrane. It 
 usually contains a nucleus, which may contain a nucleolus. The 
 nucleus may take different forms, but it always contains the nu- 
 clear fluid and the nuclear substance, each of which is of a proto- 
 plasmic nature. 
 
 Free, isolated cells exist in the blood, chyle and lymph. Those 
 
 (251) 
 
252 PRACTICAL LESSONS IN SCIENCE. 
 
 occurring in the blood of the invertebrates, or lower animals, and 
 some of those found in the blood of vertebrates, are colorless, ir- 
 regular in form, having the capacity of movement. They can 
 push out processes and draw them in again, by which means they 
 change position. They originate in the lymphatic glands, and 
 pass into the blood with the lymph. Others found abundantly 
 in the blood of vertebrates have a regular form usually coiitam- 
 inga reddish pigment, haemoglobin, which gives color to the blood 
 and is an important agent in the process of respiration. The ova 
 and spermatozoa, active agents in the process of reproduction, are 
 free cells differing widely in form and size. 
 
 The tissue covering the free surfaces of the body, whether ex- 
 ternal or internal, is called epithelium. Thecells forming thistissue 
 are cylindrical, ciliated, or flattened, making cylindrical, ciliated 
 or pavement epithelium. The cells of the lower layers of this 
 tissue have a semifluid consistency, and are active, continually 
 multiplying by division and growing, while those of the upper 
 layer are less active and more firm in substance, which, finally los- 
 ing their vitality, are thrown off, to be replaced by others from 
 the layers below. 
 
 On the outer surface of the body the upper cells of thistissue, 
 as thick horny layers form claws, nails and hoofs, they form 
 the leathery skin of insects, and with a little calcareous matter 
 they constitute the hard shell or outer covering of the craw- 
 fish and lobster. Feathers, hairs, bristles, scales and the horns 
 of some animals, are the outgrowths of the tissue covering the 
 body. 
 
 The epithelium covering the internal surfaces of the body se- 
 cretes a fluid which keeps the tissue moist, and facilitates the 
 movements of objects over its surface. Sometimes tubular, flask- 
 shaped or branching cavities called glands are formed in this 
 tissue, which secrete special fluids, as the saliva, gastric juice, etc. 
 
 The connective tissue, made up of cells separated by various 
 kinds of intercellular substance, is an important part of thebody. 
 In some cases the intercellular substance consists of white inelas- 
 tic fibers, forming a tissue from which the ligaments and tendons 
 
LESSON& IN ZOOLOGY. 253 
 
 are made, and which invests the bones, muscles, nerves, etc. 
 Sometimes these fibers form a network which serves as the basis 
 of the skin and the fatty tissue. 
 
 Cartilage with spherical cells and a firm intercellular substance 
 is another variety of connective tissue. Sometimes the intercel- 
 lular substance contains a network of fibers, forming a fibro-car- 
 tilage, and there are numerous other intermediate forms. 
 
 When calcareous matters are deposited in the intercellular 
 substance of cartilage, it becomes osseous tissue. This bony sub- 
 stance is traversed by numerous canals, through which nutrient 
 fluids may pass to the cells. Sometimes the bones grow in thick- 
 ness by the deposition of calcareous matter in the inner layers 
 of their investing membranes. 
 
 The protoplasm of the cell has the power of contractility, but 
 some aggregations of cells possess this in a high degree, giving 
 rise to the muscular tissue, which is the chief agent in all the 
 movements of the body. When acting, these cells change their 
 form,becomingshorter and broader than when at rest, thus caus- 
 ing the muscle to contract. Two kinds of muscles are recognized, 
 the smooth and the striated. The smooth muscles are made 
 up of flat, spindle-shaped or band-shaped cells, and are somewhat 
 sluggish in their action. They are more common among the in- 
 vertebrata, but constitute the involuntary muscles of the verte- 
 brata. The striated muscles are made up of elongated cells or 
 fibers, across which there are minute lines giving them a striped 
 appearance. These muscles are more prompt and energetic in 
 their action than the smooth muscle, and are usually under the 
 conscious control of the animal. 
 
 The nervous tissue is made up of cells and fibers, which differ 
 not only in form, but in structure and chemical composition. The 
 cells usually contain a nucleus and nucleolus with a fine granular 
 substance, and have one or more branches, one of which is con- 
 tinued into a nerve fiber. The fibers consist of an axis cylinder 
 or thread of grayish matter, covered by a sheath of whitish 
 fatty matter, which in turn is covered by a sheath of connective 
 tissue ; such fibers are called medullated fibers. Sometimes the 
 
254 PRACTICAL LESSONS IN SCIENCE. 
 
 axis cylinder is naked, having no sheath, and sometimes it has 
 only the sheath of connective tissue. 
 
 A group of nerve cells with their branches forms a ganglion. 
 The brain and the spinal cord are simply groups of ganglia. 
 Nerves are made up of nerve fibers; one set serves to connect va- 
 rious sense organs located in the outer surface of the body with 
 the brain and spinal cord, and another set connect the brain and 
 spinal cord with the muscles. 
 
 The lowest organisms consist of a single cell ; the body is the 
 protoplasm and the cell membrane is the skin. The skin absorbs 
 nutriment and removes waste, the protoplasm assimilates 
 material and grows. But as the organism grows, the body in- 
 creases in three directions, while the skin expands only in two di- 
 rections, so that, finally, the area of the skin is relatively too small 
 to furnish material for the growth of the body. Thus the size of 
 a cell or a one-celled animal is limited. If the organism increases 
 in size it does so by dividing into several cells which arrange 
 themselves so as to give the largest extent of surface, eventually 
 forming a cup-shaped organism with an outer and inner surface. 
 In the outer layers organs of motion and sensation, of respira- 
 tion and excretion are developed, carrying on the animal func- 
 tions and some of the vegetative ; while the inner layers or cavity 
 receives -and digests the food. Thus with an increase of size 
 comes a greater complexity of organism, and the essential char- 
 acteristics of the animal. 
 
 The more highly developed the organs, the more complete the 
 division of labor, the better the work done by each organ and the 
 higher and more perfect the life of the organism. The organs are 
 not only correlated in size but in form, so that from one organ a 
 good idea of the size and form of the organism maybe made out. 
 
 The digestive apparatus, at first a mere cavity, then a tube 
 which at length became separable into three parts, the fore part 
 for the reception of food, the middle part for its digestion, and 
 the hind part for the expulsion of the indigestible portions. 
 Then a mouth with masticatory or sucking organs and salivary 
 glands is developed at the fore end of the tube, and from the fore 
 
LESSONS IN ZOOLOGY. 255 
 
 part of it the stomach with its glands and accessory organs is 
 formed. From the middle part, that portion of the intestine 
 in which digestion is completed, by the action of fluids from 
 the pancreas, liver, and intestinal glands, is derived, and from 
 the hind part that portion of the intestine concerned in the 
 collection and expulsion of undigested portions of food had its 
 origin. 
 
 The liver and pancreas appear to be outgrowths of the alimen- 
 tary canal which have become glands. The liver, distinguished 
 for its relatively great size and weight in the higher animals, 
 has been developed from a little patch of colored cells. The se- 
 cretion of the liver sometimes aids in digestion and sometimes it 
 does not. 
 
 Among the lowerformsof animals no circulatory system is nec- 
 essary, as the digestive cavity extends to all parts of the body ; 
 but in animals of a little higher grade the chyle or nutrient 
 fluid circulates in the space between the wall of the digestive cav- 
 ity and the body wall, doubtless due to the ordinary motions 
 of the organism; later a particular portion of this tract ac- 
 quires a muscular structure, which as a special organ maintains 
 the circulation. Between this and the double heart of the mam- 
 malia, with its systems of arteries and veins, all gradations may 
 be found. 
 
 The respiratory organs are appendages of the circulatory sys- 
 tem, arising from arches of the greater arteries, gradually devel- 
 oping from simple tubes, the gills of fish and the tracheae of insects, 
 to the capacious lungs of the warm-blooded mammalia. 
 
 The respiratory organs are to some extent excretory organs, 
 but the most important excretory organs are the kidneys. In 
 the lowest animals they are represented by contractile vacuoles; 
 in the worms they are known as water vascular vessels, and 
 sometimes they are mere appendages of the lower intestine, while 
 in the higher animals they are independent organs made up of a 
 great number of narrow coiled tubes with an abundance of blood 
 vessels. They separate from the blood broken down albuminous 
 matters. The skin is also in some sense an excretory organ, while 
 
256 PRACTICAL LESSONS IN SCIENCE. 
 
 the sweat glands and sebaceous glands serve to equalize temper- 
 ature and keep the skin moist and supple. 
 
 The systems of organs already mentioned are all concerned in 
 the process of nutrition or the vegetative functions. The organs 
 of locomotion arid sensation, however, belong to the phenomena 
 of animal life. The organs of locomotion vary from the cilia of 
 some protozoa, and the muscular walls of worms to the compli- 
 cated mechanical apparatus of the vertebrata. The bones and 
 other hard parts which assist in locomotion frequently serve as 
 protecting organs for more delicate structures. 
 
 Among the higher animals the organs of sensation, in addition 
 to the brain and nerves, consist of certain peculiar-shaped bodies 
 of nervous tissue, which are called the end organs of certain nerves, 
 as the rods and cones of the eye, the auditory hairs, olfactory 
 cells, taste bulbs, and tactile corpuscles. Each of these has acces- 
 sory organs which serve to protect them and at the same time 
 aid them in gaming impressions of the outside world. These or- 
 gans appear in various forms among the lower animals, and 
 some of them are occasionally wanting. 
 
 Animals of the lower orders multiply by division and by bud- 
 ding, but some form of sexual reproduction is more common 
 among animals. Sexual reproduction depends on the formation 
 of two kinds of germinal cells, the combined action of which is 
 necessary to the development of a new organism. 
 
 One of these cells contains the material from which the new 
 individual grows and is called the ovum or egg cell ; the other 
 called the sperm cell contains the fertilizing material, which fuses 
 with the contents of the ovum and in some unexplained way 
 causes its development. The structure of the sexual organs 
 varies widely among the lower animals. 
 
 The simplest and most primitive case is where the ovum and 
 sperm cell are produced in the same individual; this is called 
 the hermaphrodite arrangement, and while it occurs in almost 
 every group of animals, the two cells are more commonly pro- 
 duced by different individuals. Sexual reproduction is in reality 
 a special form of growth, as the egg cell sometimes undergoes 
 
LESSONS IN ZOOLOG Y. 257 
 
 spontaneous development without fertilization. This frequently 
 occurs among insects. Alternation of generations sometimes 
 occurs among animals as with plants. 
 
 The ovum is a cell composed of protoplasm and containing a 
 nucleus or germinal vesicle. In the ripe ovum a portion of the 
 vesicle with some of the protoplasm is forced out of the egg cell 
 forming the polar cells, the remaining portion as the female pro- 
 nucleus fuses with the spermatozoon or male pronucleus and the 
 resulting body is the nucleus of the fertilized ovum. 
 
 After fertilization the ovum divides into a great number of 
 cells, the mass for a time retaining a spherical form; but at 
 length, by invagination, one side is pushed or drawnin so thatthe 
 mass has a flask shape, with an outer layer of cells, ectoderm, 
 and an inner layer called endoderm, and between these layers a 
 third is formed called mesoderm. The skin, the nervous system, 
 and sense organs of the embryo are formed from the ectoderm. 
 The muscular system, the connective tissues, the corpuscles of the 
 lymph and blood, and the vessels carrying the fluids of the body, 
 all arise from the mesoderm. The lining membrane of the digest- 
 ive cavity and of the glands opening into it are derived from the 
 endoderm ; while the urinary and generative organs arise from 
 all three of the layers. The formation of the ovum and its devel- 
 opment is much the same among all classes of animals. 
 L. s. 17 
 
CHAPTER XXXIV. 
 
 PROTOZOA, CCELENTERATA, ECHINODERMATA AND VERMES. 
 
 ANIMALS may be separated into nine groups or divisions, as 
 follows, beginning with the lowest: 
 
 (1) PROTOZOA. These are animals of minute size composed of 
 a nearly structureless substance called sarcode, having no cellular 
 organs, and usually asexual reproduction. 
 
 (2) CCELENTERATA. The coelenterata are radiate animals, on 
 the plan of two, four or six, having a central body cavity com- 
 mon to digestion and circulation. 
 
 (3) ECHINODERMATA. The echinodermata are radiating ani- 
 mals generally on the plan of five, with a calcareous dermal 
 skeleton or shell, often armed with spines, and having alimentary, 
 circulatory and nervous systems. 
 
 (4) VERMES. The vermes or worms are bilateral animals, 
 without limbs, and with paired excretory canals, sometimes called 
 the water vascular system. 
 
 (5) ARTHROPODA. The arthropoda are bilateral animals with 
 the body divided into segments, which carry jointed appendages 
 or limbs, and they have a well-developed nervous system, as in- 
 sects, spiders, crawfish, etc. 
 
 (6) MOLLUSCA. The mollusca are bilateral animals with a 
 soft unsegmented body inclosed in a single or bivalve shell, as the 
 oyster and mussel. 
 
 (7) MOLLUSCOIDEA. The molluscoidea are bilateral unseg- 
 mented animals with a ciliated circlet of tentacles. They usually 
 have a hard shell case and one or two nervous ganglia. 
 
 (8) TUNICATA. These are bilateral, unsegmented animals with 
 barrel-shaped bodies, having a simple nervous ganglion with a 
 heart and gills. 
 
 (258) 
 
LESSONS IN ZOOLOGY. 259 
 
 The divisions mentioned are sometimes grouped together as 
 the invertebrata. 
 
 (9) VERTEBRATA. The vertebrata are bilateral animals with 
 an internal cartilaginous or bony skeleton, prominent in which is 
 the vertebral column, which serves as a protection for the highly 
 developed nervous system. 
 
 This scheme of classification is more or less incomplete and ar- 
 tificial. The knowledge of the animal kingdom is not sufficient 
 to enable zoologists to work out a natural system, if, indeed, such 
 a system exists in fact. 
 
 The Protozoa, the first or lowest animals, like the protophyta, 
 live in the water, and so much alike are these lowest plants and 
 animals that in many cases it is difficult to determine whether a 
 given organism is an animal or plant. One of the simplest forms 
 of animal life is the amoeba. This minute animal may be found 
 on the submerged leaves of plants or in the mud at the bottom of 
 stagnant water. It appears much like a piece of jelly, nearly col- 
 orless, often granular, and more fluid in its central portion. 
 When active, they are constantly changing form , thrusting out 
 rays or arms, called pseudopodia, from one part or another of 
 the mass. In the larger pseudopodia the granular matter passes 
 in a stream toward the extremity and back again, the circulation 
 probably caused by the contractility of the protoplasmic mass. 
 By means of the pseudopodia the animal creeps slowly along, but 
 in no definite direction. The amoeba has no mouth or stomach; 
 it flows around its food, digests and absorbs such parts as it can 
 use, then flows away from the undigested parts. Besides the 
 granular matter they often contain a rounded body called a nu- 
 cleus, and sometimes a contractile vesicle. The amoeba multiplies 
 by simple division as in the case of protococcus. The amoeba, a 
 little mass of protoplasm without organs of any kind lives, 
 moves, absorbs oxygen, expels carbon dioxide, eats, grows and 
 reproduces its kind in short, appears to be a complete organism. 
 
 The foraminiferae are much like the amoeba, except that they 
 secrete a calcareous shell. The earliest and oldest fossil known 
 IB supposed to be a member of this group. The shells of these 
 
260 PRACTICAL LESSONS IN SCIENCE. 
 
 minute animals are the chief constituent of thick beds of lime- 
 stone rocks, as the chalk cliffs of England and nummulitic lime- 
 stone of France. They are exclusively marine animals, and good 
 specimens of their shells may be obtained by shaking a sponge 
 that has not been treated with acid. 
 
 The radiolaria are marine animals whose body contains a 
 capsule in which are oil globules, albuminous bodies, and some- 
 times concretions, with vacuoles and granules. They secrete a 
 silicious skeleton or shell. Their skeletons have given rise to ex- 
 tended rock formations. 
 
 If some vegetable or animal substance be soaked in water for 
 a few days, the water will be found to contain a large number of 
 different kinds of microscopic animals called infusoria. Among 
 them may be vorticella, paramoecium, stentor and others. One 
 group of the infusoria is especially interesting on account of their 
 close relationship to some of the alga3. They consist of a colony 
 of cells united by a gelatinous substance. In the inactive stage 
 they possess a cellulose membrane, exhale oxygen and have an 
 abundance of chlorophyll, and reproduce by simple division. 
 During the active stage the cells give rise to daughter colonies. 
 They are called volvocinidse, and the most common is volvox 
 globater. Some of the infusoria swim freely by means of their 
 cilia; others, fixed in one locality, create currents in the water by 
 the action of their cilia, thus bringing more food within their 
 reach. The usual mode of reproduction is by self-division, some- 
 times by budding and sometimes by conjugation, the nucleus 
 and nucleolus taking an important part in the process. 
 
 The Coslenterata. Among the coelenterata we find organs and 
 tissues composed of cells ; they have external and internal epithe- 
 lium, calcareous and silicious structures, with muscles, nerves and 
 sense organs. To this division belong the sponges, which are 
 composed of a contractile substance made up of amoeba-like cells 
 supported by a framework of horny fibers, or of calcareous or 
 silicious spicules. The sponge is traversed by numerous canals, 
 which open on the surface by larger or smaller openings. At 
 numerous places in the sponge there are little cavities or pas- 
 
LESSONS IN ZOOLOGY. 261 
 
 sages which are occupied by ciliated cells, which, by the motion of 
 their cilia, keep up a circulation of water through the sponge. 
 Reproduction in the sponges takes place by division, by the 
 formation of gemmules, and by the formation of ova and germ 
 cells. The fertilized ova develop into embryos which are pro- 
 vided with cilia, by means of which they swim about until they 
 find some suitable resting place. Spongilla fluviatilis is common 
 in freshwater ponds; all other sponges are found in saltwater. 
 The sponges of commerce are the horny framework of the 
 sponge, and come mainly from the Mediterranean sea. These 
 sponge colonies vary greatly in form ; one can often find a half 
 dozen distinct forms in the display basket of one drug store. 
 
 The coral polyps, or actinozoa, belong to this division. They 
 consist of a cylindrical or club-shaped tube fixed at one end, 
 having a mouth surrounded by tentacles at the other. They 
 have internal generative organs and usually a calcareous skele- 
 ton. The sexes are usually separate, although hermaphrodite 
 individuals are sometimes seen. The embryos are frequently 
 born alive as ciliated larvae. They also multiply by budding. 
 The body has an ectoderm and endoderm and a mesoderna, which 
 in some cases becomes the seat of calcareous deposits. Corals 
 are radiate animals on the plan of four, five or six. They exist 
 in great variety in the shallow waters of the tropical ocean, 
 building extensive reefs ; there are corals having the form and 
 appearance of a human brain ; there are branching corals and 
 fan corals, etc. They are not only abundant in the seas of the 
 present time but their calcareous skeletons have been the most 
 abundant rock-forming material since the earliest geologic time. 
 
 The Medusse have a soft gelatinous semitransparent bell-shaped 
 body, the margin of which is fringed with stinging tentacles. Near 
 the margin are nerve rings and sense organs as auditory hairs, 
 and in some there is an appearance of eye-spots. The medusae 
 are the jelly-fish or sea-nettles so abundant in many parts of the 
 ocean. Many if not all the medusae are simply the free swimming 
 form of some of the fixed polyps. The polyp gives rise to a bud 
 which becomes a free swimming medusae, while the egg or genera- 
 
262 PRACTICAL LESSONS IN SCIENCE. 
 
 tive bud of the medusae produces a polyp. The radiating parts 
 are on the plan of four. 
 
 The Echinodermata are popularly known as sea-urchins, star- 
 fish, feather-stars, etc. They are radiate animals on the plan of 
 five, and have a rough, often prickly skin, which has the power of 
 secreting calcareous matter. They have a distinct digestive canal 
 with mouth and vent, and a water vascular system, and a true 
 circulatory system are sometimes present. The nervous system 
 consists of nerves running down the five rays from a ring sur- 
 rounding the gullet. Sexual reproduction is the rule. These ani- 
 mals are inhabitants of the sea; are generally capable of a slow 
 creeping movement by means of suctorial tubes, feeding mainly 
 on mollusca and seaweeds. Many of them possess great repro- 
 ductive power, being able to replace lost parts with all their ap- 
 paratus of tubes, nerves, etc. 
 
 The Crinoids, during the whole or a portion of their existence, 
 are fixed by a jointed flexible stalk largely composed of calcare- 
 ous matter. The radiating feather-like arms give the organism 
 something of the appearance of a flower, hence the name, meaning 
 lily -form. The crinoids have been very abundant since early geo- 
 logical times, their stems and crowns contributing largely toward 
 building up great beds of limestone. 
 
 The Star-fish are characterized by their obviously star-shaped 
 body, the stomach, reproductive organs and the nervous system 
 all having the radiate arrangement. The color is yellow, orange 
 or red, the upper surface leathery, roughened by calcareous plates, 
 tubercles and spines. The mouth is below and the rays are fur- 
 rowed underneath, having numerous holes through which pass 
 the sucker-like tentacles or feet which serve as organs of locomo- 
 tion and prehension. They are voracious, and the most destruc- 
 tive enemies of the oyster. 
 
 The Brittle-stars are similar to the star-fish, but the long arms 
 are mere appendages of the body and do not contain any portion 
 of the digestive canal. 
 
 The Sea-urchin varies in form from a sphere to a disk. The 
 shell is composed of numerous calcareous plates, the whole cov- 
 
LESSONS IN ZOOLOGY. 263 
 
 ered with numerous tubercles, to which spines of varying lengths 
 are jointed. The mouth on the underside is armed with a com- 
 plicated apparatus of calcareous teeth. From the stomach pro- 
 ceeds a long convoluted intestine, attached to the interior of the 
 shell by a delicate membrane or mesentery. The surface of the 
 mesentery and the lining membrane of the shell are furnished with 
 cilia, and by their motion the fluids of the body cavity are kept 
 in circulation, and in this way respiration is effected, and, in some 
 cases, they are provided with branched respiratory tubes. The 
 reproduction is sexual, the fertilized ova forming ciliated free 
 swimming embryos which pass through a complicated develop- 
 ment. 
 
 The Holothurians or sea-cucumbers are worm-shaped animals 
 with a leathery skin, endowed with longitudinal and transverse 
 muscles, by which, when irritated, some species can break their 
 bodies into several pieces. The mouth is surrounded by a circlet 
 of feathery tentacles. Locomotion is accomplished by the alter- 
 nate extension and contraction of their worm-like bodies. They 
 sometimes attain considerable size, a,nd are highly prized as food 
 by the Chinese. 
 
 Vermes or Worms. The worms are bilateral animals with a 
 much elongated, flat or cylindrical body without appendages. 
 Just beneath the skin there is a strongly developed muscular 
 system. The nervous system consists of a single ganglion, or a 
 pair of ganglia situated toward the anterior of the body above 
 the gullet, and sometimes of a nerve ring around the gullet. The 
 nerves given off are distributed symmetrically, supplying the sense 
 organs and forming two strong lateral nerves. The sense or- 
 gans are eyes or eye spots, auditory apparatus and tactile cor- 
 puscles. The function of respiration is performed through the 
 surface of the body. Sexual reproduction is common, but gem- 
 mation and fission often occur. 
 
 The Tubellaria are worms that have a small flattened body 
 covered with cilia. They occur in salt or fresh water, and lead 
 an independent life. 
 
 The Trematoda are suctorial worms or flukes, and are all in- 
 
264 PRACTICAL LESSONS IN SCIENCE. 
 
 ternal parasites. The mouth is in the middle of a small sucker, 
 and frequently there are small hooks of chitin which may assist 
 the worm in attaching itself to desirable objects, and sometimes 
 there are several suckers. The best known is the liver-fluke, 
 which infests the ducts of the liver in sheep. The fertilized ova 
 produce ciliated embryos, which wander about till they die or 
 find a host, usually a snail, in which they are transformed into 
 sporocysts, which produce redise, that give rise to a generation 
 of tailed cercaria. In this form they leave the snail and encyst 
 on some foreign object, as a blade of grass ; in this state they 
 are swallowed by grazing sheep, and soon form mature flukes in 
 their livers. 
 
 The Cestoda are the tape worms. They have flattened bodies 
 without mouth or alimentary canal. They infest several different 
 animals, but Tssnia solium, which sometimes inhabits the intes- 
 tines of man, is perhaps the most interesting one to study. It 
 consists of a large number of flattened joints, each of which is a 
 complete hermaphrodite organism. At one extremity the organ- 
 ism is fixed to the mucous membrane of the intestine by means 
 of a crown of hooks and suckers. This part is called the head ; 
 the other parts are produced from the head by a process of bud- 
 ding. Each joint is well supplied with eggs. When mature the 
 joint breaks off and is expelled from the body. The eggs are 
 swallowed by the pig; the coat of the egg of the tape-worm is 
 dissolved and the embryo is set free. It soon passes through the 
 walls of the stomach to some of the internal organs of the pig, 
 where it forms a cyst, giving rise to the disease known as measles. 
 Meat containing these cysts is eaten, the worm is liberated from 
 the cyst and fixes itself to the intestine and develops into an 
 adult tape worm. The tape-worm of the cat is the mature cystic 
 worm of the mouse. The tape worm is nourished by absorbing 
 the nutrient fluids elaborated by its host. 
 
 The Nematoda are the round worms and thread worms which 
 are parasites in the lower part of the human intestine, and they 
 include about two hundred species that are not parasitic. The 
 so-called vinegar eel is a familiar member of this group. The 
 
LESSONS IN ZOOLOGY. 265 
 
 
 
 4to 
 trichina is a parasite belonging to the nematoda. There are 
 
 other worms similar to the nematoda, but they need not be con- 
 sidered here. 
 
 The Annelida are worms whose bodies consist of definite seg- 
 ments. The segments are usually furnished with bristles or setae 
 which serve as organs of locomotion. The digestive system con- 
 sists of a mouth, of ten with a proboscis which may be protruded, 
 sometimes with horny jaws, a gullet, a stomach, intestine and 
 vent. The vascular system is sometimes distinct, and sometimes 
 in communication with the body cavity. When distinct the red- 
 dish blood in the vascular system and the fluid in the body cav- 
 ity both contain amoeboid cells. Branchia or gills are often 
 present as respiratory organs, but frequently respiration is car- 
 ried on through the general surface of the body. There are often 
 organs which seem to serve as kidneys, and there are sometimes 
 hepatic appendages. The nervous system consists of a cerebral 
 ganglion above the gullet and a ventral ganglionic chain. The 
 sense organs are paired eye spots, auditory vesicles, and tactile 
 organs. Sexual reproduction is common, but gemmation and 
 fission often occur. Frequently they develop with metamorpho- 
 sis. Sometimes there is a distinct head with tentacles and bran- 
 chia. They are terrestrial and aquatic animals, mostly marine, 
 living generally on animal food; sometimes they are parasitic. 
 
 The Tubicolse feed on vegetable matter and build tubes of 
 sticks, sand, etc., as a protection for their soft bodies. They 
 have external gills and red blood. 
 
 The Oligochseta include the ordinary earthworm or angle- 
 worm. It has but few locomotive bristles, but has well devel- 
 oped digestive organs. Some of this group are, parasitic, but 
 most of them lead an independent life. 
 
 The Hirudinea include the leeches inhabiting both salt and 
 fresh water. The body is ringed but has no appendages. The 
 common medicinal leech has a sucking-disk at each extremity, and 
 the mouth is armed with jaws strong enough to cut through the 
 human skin. When young it feeds on the blood of insects, then 
 of frogs, and not till maturity is a diet of warm blood necessary. 
 
266 PRACTICAL LESSONS IN SCIENCE. 
 
 The Eotifera are worms with a ciliated apparatus at the ante- 
 rior end of the body which vibrates so rapidly as to produce the 
 impression of a rotating wheel; hence the name of wheel-animal- 
 cules. Some are free-swimming and some are fixed. In the free 
 forms the cilia are the organs of locomotion, and in all cases they 
 create currents in the water by which particles of food, as small 
 infusoria, algae and diatoms are brought within their reach. In 
 external appearance they are much like some infusoria, but they 
 are evidently of a higher order. The rotifer can be dried, then 
 brought to life by a little water, for many times in succession 
 without apparent injury. 
 
CHAPTER XXXV. 
 
 ARTHROPODA CRUSTACEA, ARACHNIDA, AND MYRIAPODA. 
 
 THE Division Arthropods, includes a multitude of animal 
 forms which are distinguished from those already considered by 
 the possession of special organs of locomotion, by which they 
 may swim, creep, run, climb or fly. They are for the most part 
 terrestrial or aerial animals. With the organs of locomotion a 
 solid support was necessary for the attachment of the muscles, 
 hence the outer layer of the skin is hardened into a firm exo- 
 skeleton. 
 
 The body among the arthropoda is divided into three parts, 
 the head, thorax and abdomen, the appendages of each having 
 different structure and function. Each of these parts seems made 
 up of segments. The head is covered by a hard integument, in- 
 closes the brain and bears the sense organs and mouth parts. 
 The appendages of this region are changed so as to form antennae 
 and jaws. The thorax is a fusion of seven segments having a 
 hard integument. In some cases the head and thorax are fused 
 together forming the cephalothorax. The thorax bears the 
 appendages most important for purposes of locomotion. The 
 abdomen, composed of distinct rings or segments, seldom has 
 appendages, but when present they aid in locomotion, or in res- 
 piration, or may serve for carrying the eggs. 
 
 The skin is of two layers, a soft growing layer and an outer 
 one that has been hardened by the deposition of calcareous mat- 
 ter in the chitin base, so as to form a fi^m external skeleton. The 
 hairs, setae, spines, bristles and ot' -r appendages of the skin, 
 have their origin in the deeper layer. During the period of growth 
 this shell is cast off and renewed from time to time when the ani- 
 mal is said to moult. The muscles are all of the cross-striped 
 variety. 
 
 (267) 
 
268 PRACTICAL LESSONS IN SCIENCE. 
 
 The nervous system consists of a brain, above the oesophagus, 
 the ventral chain of ganglia and the cesophagal ring connecting 
 the brain and the anterior ganglia of the ventral chain. The 
 sense nerves arise from the brain, while the ventral ganglia 
 send nerves to the muscles, organs of locomotion and skin. These 
 animals usually have eyes, organs of hearing, organs of smell 
 and tactile organs. 
 
 The digestive organs are well developed, with salivary glands, 
 hepatic appendages and excretory organs usually present. The 
 circulatory and respiratory organs exhibit the widest range of 
 form. Circulation is sometimes effected by a pulsating organ, 
 sometimes by the movements of the body, and again by regular 
 movements of certain organs, as the intestines. Respiration is 
 frequently effected by means of the surface of the body, sometimes 
 by branched appendages of thelimbs,and in other Cases by means 
 of internal tubes or tracheae. The reproduction is usually sexual, 
 but modified forms sometimes occur. The most of this group are 
 oviparous, some are viviparous, and in most a somewhat com- 
 plex embryonic development is followed by a complicated meta- 
 morphosis. The Division Arthropods includes four classes, the 
 Crustacea, as the crayfish and lobster, the Arachnida, as the 
 spiders, Myriapoda, as the centipede, and the Insecta. 
 
 The Crustacea are for the most part aquatic, breathing by 
 means of gills; some, however, breathe air and are terrestrial. 
 They vary greatly in size and form, but a study of the common 
 crayfish will give us a good idea of the whole class. Crayfish 
 may be found hidden among sticks and stones of shallow water, 
 and may be caught with a light dip net, which may be made of 
 stout wire and mosquito netting. Preserve a number in alcohol 
 for dissection and keep several in fresh water in a pan or glass 
 jar for observation. 
 
 Notice how the crayfish walks, how and which way he jumps 
 when frightened. Looking down upon the crayfish, notice the 
 cephalathorax, with its smooth horny covering called the cara- 
 pace, and the projection of the carapace forward between the 
 eyes, the rostrum. Count the segments in the abdomen, and, 
 
LESSONS IN ZOOLOGY. 269 
 
 bending it backward and forward several times, notice bow tbe 
 segments are jointed together. With a pair of scissors or a 
 knife separate one of the segments of the abdomen from the 
 others, and notice the upper part or tergite, the lower part 
 or sternite, the side piece or pleurite, and the two appendages 
 or swimmerets. Compare the segment studied with other seg- 
 ments. 
 
 Observe the tail fin; the middle portion is the telson, the side 
 lobes belong to the sixth joint of the abdomen. The abdomen 
 of the female is relatively wider than that of the male, and the 
 genital openings of the male are on the first joints of the last pair 
 of thoracic appendages, while in the female they are on the first 
 joints of the last thoracic appendage but two. The eggs are 
 usually carried on the under side of the abdomen, glued to the 
 swimmerets. 
 
 Placing the crayfish on its back, count the legs and other 
 appendages of the cephalothorax and note if any of them appear 
 to arise from segments. How many joints in each leg, how do 
 the legs differ from each other, and how do the claws differ from 
 the legs. Notice also the three pairs of peculiar appendages an- 
 terior to the claws or chela? ; they are called foot jaws ; test them 
 carefully so as to learn how they work. Compare the foot jaws 
 with each other and with the legs and claws. 
 
 Now remove the legs, claws, and foot jaws from one side, using 
 care not to tear other parts. Then turn back or break away the 
 free edge of the carapace on that side, and the white feathery 
 organs brought to view are the gills, of which there are eighteen 
 pairs; six are attached to the second and third foot jaws, the 
 chela?, and the first, second, and third pairs of legs, the remain- 
 ing are fixed to the sides of the body. Each consists of a central 
 stem bearing a number of delicate filaments. Separate each 
 pair of gills and find out to what it is attached and how it is at- 
 tached. Study carefully the chamber containing the gills and 
 note the parts which compose it. With a probe explore for open- 
 ings from the branchial chamber. Projecting forward there is a 
 well-marked canal ; in this there is a flat oval plate, attached to 
 
270 PRACTICAL LESSONS IN SCIENCE. 
 
 the second pair of jaws, and by its motion a circulation of water 
 is kept up through the gill chamber. 
 
 When the foot jaws are removed two pairs of soft leaf-like 
 appendages, called jaws or maxillse,come into view, and anterior 
 to these are the mandibles, short, hard, toothed organs which 
 seem more like jaws than the softer maxillae. Each mandible 
 bears an appendage, which curves around its anterior border in a 
 groove, and is known as the mandibular palpus. Fitting closely 
 against the posterior margin of each mandible is a soft plate-like 
 organ called the metastoma. Remove each of these organs, not- 
 ing carefully its mode of attachment and its relations, experi- 
 menting with each so as to gain a clear idea of how the mouth 
 parts are arranged, and what part each plays in the process of 
 mastication. 
 
 Just in front of the mandibles are the long feelers or antennae, 
 the antennulae, and lastly the eye stalks. Examine the an- 
 tennae; notice their mode of attachment, freedom of movement, 
 etc. In the basal segment of the antenna? there is an opening 
 leading to the green gland in the extreme front part of the body. 
 It serves the purpose of a kidney. In the basal joints of the 
 antennula? are the auditory organs; notice the auditory hairs 
 and the auditory sac. Examine the eye stalks and find the black 
 tip or cornea, and try if you can tell whether it is simple or com- 
 pound. 
 
 In the larger crayfish the digestive, circulatory, and nervous 
 systems may be studied, but the dissections are best made under 
 water. Wedge a thin board into the bottom of a shallow dish, 
 or cover the bottom with wax, then placing the ventral surface 
 downward, pin the body firmly through telson and claws. Then 
 with a pair of scissors cut from the posterior margin of the cara- 
 pace forward a little to one side of the median line to the cervical 
 groove, then break away the whole side of the carapace. Push 
 away the gills and cut them off at the point of attachment, Cut 
 away the other side of the carapace. With the forceps clear 
 away the lining membrane which discloses a small chamber con- 
 taining a little whitish polygonal sac which is the heart. Notice 
 
LESSONS IN ZOOLOGY. 271 
 
 the tubes or blood vessels leading from the heart. In the heart 
 there are two holes above, two below and one on each side, each 
 hole guarded by a lip-like valve. From the gills the blood passes 
 into the pericardia! cavity; as the heart expands the blood flows 
 through the holes into it; as it contracts, the valves close and 
 the blood is forced into the different parts of the body, then to 
 the gills again. Under the heart are the reproductive organs, 
 the yellowish ovaries, and the oviducts leading to the genital 
 openings already mentioned, while in the male there are the 
 testes with long white coiled tubes leading to the genital opening 
 in the last thoracic leg. 
 
 Cut away the roof of the head. The space within the head is 
 quite fully occupied by the stomach. Pass a probe through the 
 mouth into the stomach. Note carefully the gullet, stomach and 
 intestine, and near the beginning of the intestine some reddish 
 masses, the hepatic glands or liver. Observe the white muscles 
 along each side the body cavity. Cut away the roof of the 
 abdomen, and trace the muscles through it to the telson, the 
 upper thinner layer straightens the abdomen while the thicker 
 lower layer below the intestine bends it. 
 
 Over the gullet there is a large ganglion, extending outward 
 and downward. Around the gullet are two masses of nervous mat- 
 ter connecting the ganglion above the gullet with the anterior 
 of twelve pairs of ganglia that lie along the ventral surface under- 
 neath the intestine and deeper muscles. Trace out the ganglia 
 and principal branches of this system. Try to have some cray- 
 fish for observation during their moulting season in the spring. 
 
 Those members of the Crustacea living in the sea, as the lob- 
 sters, shrimps and crabs are the most numerous, and individuals 
 among them sometimes attain great size. And these members 
 of the class furnish large quantities of food material. 
 
 The Barnacles belong to this class, as did the Trilobites, ani- 
 mals that were so abundant during the early geologic ages. 
 Besides the crayfish, there is a group of minute organisms called 
 Entomostraca that inhabit fresh water. They are an abundant 
 source of food for fish and other forms of aquatic life. 
 
272 PRACTICAL LESSONS IN SCIENCE. 
 
 The Arachnida include the ticks, mites, scorpions and spiders, 
 animals similar to the Crustacea, but differing from them in some 
 particulars. The arachnid a are air-breathing animals, having 
 only four pairs of legs, and usually no antennae. Almost all the 
 arachnida live on animals, a few only living on vegetable juices, 
 and we may expect to find agility and intelligence as character- 
 istics of this class. 
 
 One group of this class are parasites in the nasal cavities of 
 dogs and wolves; the eggs find their way into the stomachs of 
 rabbits, penetrate to the liver and form a cyst ; after six months 
 or so they again become active for a time, and again encyst, in 
 which state they may reach the mouth of the original host. 
 
 Another group including the mites and ticks are called the 
 Acarina. Their mouth apparatus is adapted for biting, or for 
 piercing and sucking. There are no circulatory organs, and the 
 nervous and respiratory organs are of the lowest order, suggest- 
 ing the idea that the class is made up of degraded, depauperate 
 forms, sunk to their present low estate through indolence and 
 high living. Itch-mites, cheese-mites, ticks, water-mites and oth- 
 ers belong to this group of repulsive animals. 
 
 The Araneida, or true spiders, are distinguished by having a 
 much-swollen abdomen, four pairs of legs, an apparatus for spin- 
 ning webs, with from six to eight eyes, and generally poison 
 glands. In studying the spider make out the cephalothorax a.nd 
 abdomen, the mandibles, poison glands, maxillae, and the jointed 
 appendages of the maxillae, the maxillary palpi. Examine the 
 head for the eyes, usually from six to eight in number. Exam- 
 ine the posterior part of the abdomen for the spinnerets. Hold 
 a live spider by one leg with a pair of forceps and watch him 
 while spinning. The spinning glands secrete a viscid material 
 which, forced out through fine holes, hardens in the air to delicate 
 threads used by the spider for many purposes. Spiders differ 
 widely in form, color, and mode of life, but in any event they are 
 clean, active, intelligent and interesting. 
 
 The Mygalidse are large spiders thickly covered with hair, who 
 dig holes in the earth, or appropriate holes already made in 
 
LESSONS IN ZOOLOGY. 273 
 
 wood or elsewhere. These they line with a soft silk web, some- 
 times arranging a cover that opens and closes like a trap door, 
 as the trap-door spider of Southern Europe and the bird spider of 
 South America. 
 
 The Saltigradse are springing spiders with eight eyes grouped 
 in a square; they do not construct webs. They have stout ante- 
 rior legs and a large arched cephalothorax. 
 
 The Lycosidse, or wolf spiders, pursue their prey by running 
 rather than by leaping. They build holes in the ground, often 
 building little walls around the opening. 
 
 The Laterigradse or crab-spiders have a rounded cephalotho- 
 rax and a flattened abdomen, and the two anterior pairs of legs 
 are longer than the others, so that they run sidewise or backward. 
 
 The Tubitelse or tube spinners, have six or eight eyes in two 
 transverse rows. The two middle pairs of legs are the shortest. 
 They weave horizontal webs, with tubes in which they lie in wait 
 for their food. 
 
 The Inaequitelae, or web spinners, have eight eyes of unequal size, 
 and long anterior legs. They construct irregular webs. 
 
 The Orbitelse, or wheel-spinners. Among these spiders the head 
 and thorax are separated by a groove and the abdomen is globu- 
 lar. The anterior legs are longest and the third pair shortest. 
 They spin a geometrical web, often of faultless symmetry. 
 
 Spiders are especially interesting as objects of study. Many 
 of them have fixed homes where they may be watched and studied 
 during the season. Nearly every group of spiders mentioned has 
 representatives in every part of the United States. If you wish 
 to study burrowing spiders, they are everywhere in the fields 
 along paths, about the yard, often between bricks in sidewalks. 
 A little stream of water will usually force them to the surface. 
 Study the spider; study his house, his family relations, his per- 
 sonal habits, his methods of catching food, etc. 
 
 Almost everybody thinks of the web-spinner as the typical 
 spider, and doubtless more will be interested to study the web- 
 weaving spiders. They are abundant everywhere, and at first may 
 be found more easily than the burrowing spiders. But it makes 
 
 L. S. 18 
 
274 PRACTICAL LESSONS IN SCIENCE. 
 
 no difference about the kind ; locate a spider and commence ob- 
 servations on his habits and manners and customs at once, and 
 the work will afford you as much pleasure as any you ever did. 
 
 The Scorpions have jointed bodies, with a hooked telson and 
 poison gland; they have a bilobed brain, and four pairs of lungs, 
 evidently the most highly developed of the arachnida. They 
 are more common in the warmer countries. The results of the 
 bite of the largest spiders, and the sting of the scorpion have 
 doubtless been much exaggerated, but enough is known to make 
 it wise to avoid the bite or sting when possible. 
 
 The gossamer threads floating in great number in autumn 
 are the work of young spiders. Mounting some little elevation, 
 as a fence, in the warmer part of the day, they throw up the ab- 
 domen and allow the thread formed to float away on the ascend- 
 ing warm air until it becomes buoyant enough to carry the spi- 
 der away in the air. Spiders are oviparous, often carrying their 
 eggs on the abdomen until they are hatched. Spiders cast their 
 skin or moult several times before they attain full size. 
 
 The Myriopoda are animals whose bodies are divided into 
 many segments, but without division into thorax and abdomen. 
 They have a distinct head, three pairs of jaws and numerous 
 pairs of legs. The head is much like that of insects, while their 
 form resembles that of worms. The black cylindrical many- 
 legged worm that rolls up into a ball is a myriopod. 
 
 Some species of the centipede living in tropical countries at- 
 tain a large size, and the secretion from their poison gland is 
 dangerous even to man. 
 
CHAPTER XXXVI. 
 
 INSECT A. 
 
 THE forms of life already studied have been for the most part 
 water animals of such low organism and retiring habits that 
 they have never forced themselves upon the notice of mankind. 
 
 But insects are air-breathing animals abounding everywhere, 
 in the air and soil, in our homes and workshops; they are para- 
 sites inside the human body, and often find an abiding place on 
 the outside; they bite and sting and irritate and annoy by night 
 and by day, and so persistent and aggressive are they in their 
 work that only occasionally can humanity turn aside from the 
 irrepressible conflict to notice that insects are intelligent, that 
 some are exceedingly beautiful, that some are useful, and that 
 insects as a class fill an important niche in the scheme of nature. 
 
 Insects are very numerous, outnumbering by far all other 
 forms of animal life; and while they differ widely in size, form 
 and mode of life, they are usually easily distinguished from 
 other kinds of life. Among the insecta there is a well-marked 
 division of the body into head, thorax and abdomen. 
 
 The head appears to be composed of but one mass, but many 
 think it really a consolidation of four segments. The appen- 
 dages of the head are the eyes, the antennae and the mouth 
 parts. The simple eye or ocellus consists of a convex cornea 
 resting on a crystalline lens, which in turn rests on a vitreous 
 humor, forming quite a complete eye; the compound eye is but 
 a collection of these simple eyes. Some think the ocelli are used 
 in the perception of nearer objects. The antennae are tubular 
 bodies well supplied with nerves, seeming to be organs of touch, 
 often appearing to be organs of hearing and smell. They differ 
 widely in form and size. 
 
 (275) 
 
276 PRACTICAL LESSONS IN SCIENCE. 
 
 The mouth parts consist of the labrum or upper lip; the 
 mandibles or larger jaws; the maxillse or lesser jaws, to which 
 are attached little jointed bodies called maxillary palpi; and the 
 labium or lower lip, to which are attached a pair of jointed 
 bodies called labial palpi. These are the mouth parts of biting 
 insects, but some have the maxillae and labium more or less 
 modified so as to fit them for licking or sucking up liquids. 
 Sometimes the first maxillae are changed into a sucking tube, as 
 in butterflies and moths. Sometimes the labium forms a tube 
 and the maxillae forms cutting parts to open the way for the 
 sucking tube, so that the mouth appears in a great variety of 
 interesting forms. 
 
 The thorax consists of three segments, prothorax, meso- 
 thorax and metathorax. The appendages of the thorax are 
 the legs and wings. All true insects have a pair of legs jointed 
 to each segment of the thorax. Each leg consists of basal joint 
 or coxa, the femur, the tibia and the foot or tarsus, which may 
 be armed with a pair of claws. The legs vary widely in form and 
 size, depending mainly on their use. The wings arise from the 
 second and third parts of the thorax. They are considered by 
 many as simply expansions of the integument spread out over a 
 framework of horny tubes. The tubes are really double, consist- 
 ing of a central air tube inclosed in a larger tube which is filled 
 with blood , so that the wings serve the double purpose of organs 
 of locomotion and respiration. In some cases the anterior wings 
 are thickened and hardened by the deposition of horny matter 
 so as to form a protecting case for the other pair of wings and 
 for the abdomen. 
 
 The abdomen consists of nine or ten segments, each of which 
 is made up of a dorsal and a ventral plate. The segments are 
 joined together by soft connecting membranes, and the parts of 
 the segments are united in the same manner, so that the abdo- 
 men is capable of considerable expansion. At the extremity of 
 the abdomen there are terminal appendages, as stings, appa- 
 ratus for depositing eggs, and other organs pertaining to the re- 
 productive process. 
 
LESSONS IN ZOOLOGY. 277 
 
 The digestive organs after the mouth are the (esophagus, into 
 which open the salivary glands; then a suctorial stomach in some 
 cases, and in others a crop or a straight or coiled intestine; but 
 whatever the name or form, one portion is adapted to digestion 
 of food and another concerned in the ejection of feces. There is 
 no liver, but certain glands in the walls of the stomach seem to 
 perform the office of such an organ, and there are also indica- 
 tions of pancreatic glands and urinary glands. 
 
 The circulatory apparatus of insects is a simple dorsal vessel 
 divided into eight chambers; as this vessel or heart expands 
 blood flows into it, and as it contracts the blood is driven into all 
 parts of the body without being conveyed by a distinct system of 
 tubes. The blood is usually colorless, and always contains 
 amoeboid blood cells. 
 
 Respiration by tracheae is one of the chief characteristics of an 
 insect. The tracheae are delicate tubes penetrating all portions 
 of the insect body, which receive their supply of air through 
 openings called stigmata situated in the membrane connecting 
 the dorsal and ventral plates of the abdomen. The number of 
 stigmata vary, but there are seldom more than nine or less than 
 two pairs present. The tracheae are kept open by a tough spiral 
 fiber of chitin, so that their structure is quite like that of the 
 tracheae of higher animals. Many insects seem to be able to de- 
 velop animal heat by increasing the vigor of respiratory move- 
 ments. The nervous system of insects is highly developed, all va- 
 riations between a common ganglionic mass in the thorax and a 
 ventral chain of ganglia occur. In some cases the brain attains 
 considerable size, which, according to one writer, " gives origin to 
 the sense nerves, and seems to be the seat of the will and of the 
 psychical activity." The ventral chain seems to correspond to the 
 spinal cord, and there seem to be instances of a true sympathetic 
 system. The muscular system lies just beneath the integument, 
 and seems to be continuous with it. The muscles are numerous, 
 especially about the head, some larva? having as many as 4,000 
 distinct muscles. They are generally of the cross-striped variety, 
 and give the insect great power and activity of movement. Some 
 
278 PRACTICAL LESSONS IN SCIENCE. 
 
 insects are more powerful, all things considered, than &ny other 
 form of life. 
 
 Insects are supplied with glands somewhat analogous to the 
 cutaneous glands of higher animals, which secrete substances 
 often of the most intense and penetrating odor, which seeroe to 
 be used as a means of protection. Then there are glands that 
 secrete wax, and those that secrete a sebaceous liquid that serves 
 to lubricate the joints; and in some larvae there are spinning 
 glands which serve for the production of webs, pupa cases, etc. 
 And many insects have poison glands in connection with stinging 
 organs. 
 
 The sounds made by insects are produced by the friction of one 
 part of the external skeleton on another, as the legs against 
 wings, or wings against wings, etc., by the passage of air through 
 the thoracic stigmata, by the rapid movement of the wings, and 
 doubtless in other ways not understood. Insects emit odors and 
 doubtless have a sense of smell, but observers are by no means 
 agreed as to its nature or location. So it seems as if there must 
 be a sense of hearing. Among the grasshoppers and crickets 
 there seems to be an auditory apparatus in connection with the 
 anterior legs, but in reality little is known about the sense or- 
 gans among insects beyond what is known of the organs of sight. 
 Among insects reproduction is sexual. In some cases the egg 
 develops into a perfect insect without metamorphosis, but in 
 most cases the embryo passes through a well-marked metamor- 
 phosis, often requiring considerable time before the perfect stage 
 is reached. 
 
 After the egg is fertilized it gradually develops into a worm-like 
 form called the larva, known commonly as caterpillar, grub or 
 maggot. As soon as hatched the larva eats voraciously, grow 
 ing rapidly, moulting from time to time, storing up fat from which 
 to form the tissues of its future body. At length it stops eating, 
 makes a cocoon and, slowly changing form, loses its worm-like 
 body and develops the head, thorax and abdomen of the perfect 
 insect. Sometimes this resting or pupa stage is very brief ; some- 
 times it lasts for a considerable time. 
 
LESSONS IN ZOOLOGY. 279 
 
 As soon as the insect is complete, the sexes meet, and soon 
 afterward the male, no longer useful, dies; the female lays her 
 eggs in or near some food supply, then dies. For most insects 
 this period occurs in the late summer or early antumn, so that 
 the species is represented during the winter by eggs alone. Some- 
 times the winter is passed in the pupal stage, and in some cases 
 in the larval stage. Insects may brood two, three or more times 
 in one season, but in general, insects are annuals. Sometimes 
 the larva live for many years, as in the case of the seventeen-year 
 cicadia. 
 
 The insect-fauna of a locality comprise all the insect forms 
 found in it. The limits of a fauna are usually determined by 
 temperature or some natural barrier, as the ocean or a high 
 range of mountains, etc. Insects may be distributed ,by the 
 wind, by the agency of birds, or other animals, or of man. The 
 life of an insect is short and active, and has but a single purpose, 
 and yet many insects are subject to disease, for the most part 
 diseases due to parasitic plants or animals. The honey bee, the 
 silkworm, and the house fly are each subject to fungoid diseases. 
 
 There are so many different kinds of insects that the names of 
 the principal groups with some distinguishing characteristics may 
 be helpful. The lowest group of insects are the Thysanura, includ- 
 ing wingless insects, with rudimentary mouth parts and setiform 
 anal filaments which of ten serve as springing organs, so that they 
 are sometimes known as spring-tails. They develop without 
 metamorphosis, and seem to be the most ancient insects as well 
 as the lowest. 
 
 The Orthoptersi. The insects of this order including the grass- 
 hoppers, crickets, etc., have biting jaws, and pass through an 
 incomplete metamorphosis. There is no resting stage ; the newly 
 hatched larva differs from the adult only in size, and the pupa is 
 characterized by rudimentary wings. As a rule they are vora- 
 cious eaters and make sounds of piercing shrillness. 
 
 Some of the largest insects are members of this group, and the 
 grasshopper is one of the best subjects for investigation. Have 
 several individuals in different stages of development confined 
 
280 PRACTICAL LESSONS IN SCIENCE. 
 
 for observation, and have several large specimens preserved in 
 alcohol for dissection. In studying the grasshopper note the 
 general divisions of the body ; examine carefully the antennae and 
 eyes, using the lens in looking for the ocelli. Dissect out and 
 place by itself each one of the mouth parts. Notice the divisions 
 of the thorax, and compare them in size and form and as to the 
 appendages they bear. Note the position of the anterior wings 
 when folded, open these wings so that the anterior margin shall 
 be at right angles with the body, and then note the position of 
 the inner wing while folded; spread it out, noting carefully how it 
 was folded. Compare the framework of the two pairs of wings ; 
 also compare them as to size, shape, color, texture, position 
 and use. Study the legs; note their number, arrangement 
 and mode of attachment, and the parts of each. Notice the 
 different ways in which the grasshopper travels, and how he 
 makes sounds. 
 
 Note the number of segments in the abdomen and the two 
 longitudinal grooves on its under surface. That part of the ab- 
 domen between the grooves is the sternum, the side is the pleu rum 
 and the upper part the tergum; and the corresponding parts of a 
 segment are the sternite, pleurite and tergite. Note the spiracles 
 or breathing pores on the sides of the abdomen. On the sides of 
 the first segment find a pair of thin oval membranes called tym- 
 pana, which some think are an auditory apparatus. The four 
 short setae, which may be discovered at the end of the abdomen 
 of a female grasshopper, form an ovipositor by which she can 
 make a hole in the earth as deep as the abdomen is long, at the 
 bottom of which she deposits her eggs. Dissecting a large female 
 grasshopper under water, as in the case of the crayfish, one may 
 make out the air sacs and tubes, the egg masses and the alimen- 
 tary canal. 
 
 The Orthoptera include Forficulidse or earwigs, the Blattidse 
 or cockroaches, the Phasmidss or walking sticks, the Acridiidse or 
 grasshoppers, the Locustidse or locusts, the Gryllidse or crick- 
 ets, the TermitidsBor white ants, the Ephemeridae or the Mayflies, 
 the Libellulidse or dragon flies, and others. They are all inter- 
 
LESSONS IN ZOOLOGY. 281 
 
 eating and many of them familiar insects, well worthy of study 
 and investigation. 
 
 The Neuroptera, includes insects that have biting mouth parts, 
 membranous wings, and that pass through a complete meta- 
 morphosis. They have something the appearance of the dragon 
 flies and May flies. One member of this order has long horns 
 and long delicate wings, and is called the Horned corydalis. 
 
 The Strepsiptera includes a few insects of minute size and no 
 special interest. 
 
 The Rhynchota are insects that have piercing mouth parts, 
 and pass through an incomplete metamorphosis. The Pediculidse 
 and other animal parasites, theAphida? and other plant-lice, and 
 the Cicadidse belong to this order, and so do the Hemiptera or 
 bugs, water bugs, etc. The bugs may be known by their anterior 
 wings which are horny toward the base and membranous toward 
 the tip. The Coccus cacti oi Mexico yields a coloring matter called 
 cochineal, which has considerable commercial value. 
 
 The Diptera. The members of this order are insects with 
 piercing and sucking mouth parts, passing a complete metamor- 
 phosis. The posterior wings are reduced to mere knobs, so that 
 they appear to have but one pair. This group includes insects 
 that are parasites on animals, and sometimes on other insects. 
 The common house fly, the bot fly, gad flies, gnats, fleas, mos- 
 quitoes and others are members of this order. 
 
 The Lepidoptera are insects having suctorial mouth parts, 
 two pairs of wings similar in form, which are covered with deli- 
 cate scales. This group includes the moths with feathery an- 
 tennae, that are active at night, and the butterflies with knobbed 
 antennae that are active during the day. Both moths and but- 
 terflies are noted for their beautiful colors and graceful forms. 
 They pass through a complete metamorphosis, and the cocoons 
 spun by some of the larvae of this group are the source of the 
 silk of commerce, making the silkworm chief among insects for 
 the economic value of its work. 
 
 The Coleoptera are insects with masticating mouth parts, and 
 hardened anterior wings, which are the chief 'characteristic of 
 
282 PRACTICAL LESSONS IN SCIENCE. 
 
 this immense group of insects, numbering some 80,000 species. 
 They are properly called beetles, not bugs, which is the name ap- 
 plied to the Hemiptera. 
 
 The Hymenoptera. This group includes the bees, wasps and 
 ants. They have mouth parts adapted to biting and licking; 
 the head is large with three ocelli and large compound eyes. 
 There are two pairs of membranous wings fitted for prolonged 
 flight. The body is compact, of about average size, the nervous 
 system complicated and highly developed, so that in the matter 
 of intelligence and capacity for work we would expect this group 
 to stand easily at the head of the insect world. In the female 
 the abdomen ends in an ovipositor, or more commonly with a 
 sting and its associate poison glands. The leaf-wasps, wood- 
 wasps, gall wasps, ichneumen flies and others have ovipositors 
 and deposit their eggs in wood, leaves or other vegetable struct- 
 ures, some making quite deep excavations. 
 
 The Formicidae or Ants, live together in communities, which 
 contain winged males and females, but are composed mainly of 
 wingless individuals called workers. The female has a sting and 
 poison gland, and the workers, supposed to be aborted females, 
 also have poison glands. The dwellings of ant communities con- 
 sist of passages and cavities in rotten wood or in the earth. 
 Customs vary in different communities, but the following is per- 
 haps the history of an average colony : Some time during the 
 summer the males and females reach the adult size; soon after- 
 ward they take the marriage flight. The males soon die, and the 
 females attend to the matter of raising their brood or founding 
 new colonies. In general there seems to be a tendency among the 
 young females to form colonies by themselves or with a body of 
 workers, but usually females enough are forcibly retained by the 
 workers of the original colony to continue it as a strong commu- 
 nity. The fertilized eggs are exposed to the morning sun, covered 
 from its heat during midday and removed from the influence of 
 damp and cold at night. The grub is treated in the same way, 
 and besides is fed by the nurse or female with a liquid disgorged 
 from the stomach. After passing into the pupa state they are still 
 
LESSONS IN ZOOLOGY. 288 
 
 under the constant care of the mother or nurse. It is supposed 
 that different care or different feeding develops the male, female, 
 soldier or worker from the same group of eggs, but this matter 
 seems to lack confirmation. Wonderful stories are told of the in- 
 telligence of ants. It is claimed that they carry on war; that 
 colonies are sometimes exterminated, sometimes enslaved, and 
 that some ants keep domestic animals, and that they sometimes 
 undertake migrations in great numbers. 
 
 The Vespidae or Wasps. The life history of a wasp is about as 
 follows : Males and females reach maturity in late summer, and 
 copulate in the air; soon afterward the males die, but many of 
 the females survive the winter. In the spring the wasp begins a 
 nest, making it of gnawed wood which resembles paper. During 
 the spring and summer she begets workers, which help to in- 
 crease the size of her nest, and to rear the perfect insects later in 
 the season. 
 
 The Apidse or Bees. The nest of the bumble bee is founded by 
 a single female which has survived the winter as in the case of 
 the wasp. Some bees excavate cavities in wood for the deposi- 
 tion of their eggs. The common honey-bee is, next to the ants, 
 the most interesting insect. Among them we have the commu- 
 nity of the queen, males and workers, the queen living for four or 
 five years no other perfect insect having as long tenure of life. 
 The wasp builds a cell of paper for its young, the bee builds one 
 of wax. The cells are of hexagonal form, and of a larger and 
 smaller size. In the smaller cells, provisions are stored, and in 
 them the worker brood is placed, while the larger ones are used 
 for the male brood and the reception of honey. On the edge of 
 the comb a few large irregular queen cells are formed. In early 
 spring the queen deposits eggs in the workers' cells, and later in 
 the drone cells, and later still she deposits an egg in each of sev- 
 eral queen cells. The larva in these cells receive richer food, and 
 reach maturity in about sixteen days, while the male requires 
 twenty-four days, and the worker twenty to reach maturity. 
 Just before the oldest of the young queens reaches maturity, the 
 queen mother leaves the hive or nest with a portion of the work- 
 
284 PRACTICAL LESSONS IN SCIENCE. 
 
 ers as a first swarm. The young queen arrives at maturity, is 
 fertilized in marriage flight, returns to the colony, kills the queen 
 pupas in the remaining cells, and reigns undisputed; or, if prevented 
 from this she leads out another colony before the maturity of a 
 second queen. If the queen dies, the workers enlarge the cell of 
 some young worker grub, and feed it with royal jelly, so that it 
 develops into a queen, and the affairs of the colony go on as 
 usual ; but if there are no brood cells, a bee community soon goes 
 to pieces on the loss of the queen. Division of labor is well marked 
 among bees; the queen-mother and ruler, the fathers, gentlemen 
 of leisure, and the workers ; some collecting honey, some secreting 
 wax and building cells, some nursing the brood, some attending 
 to the ventilation of the hive, as their active respiration tends to 
 raise the temperature and foul the air. Bees, silk-worms and the 
 cochineal insects, are the only representatives of the great group 
 of insects that are of much economic value. 
 
 The collection of specimens is an interesting and valuable exer- 
 cise. A pint fruit jar two-thirds full of seventy-five per cent, alco- 
 hol will be a good receptacle for almost anything taken in the 
 field except moths and butterflies. They may be killed with 
 chloroform or cyanide. The cyanide bottle is perhaps the most 
 convenient, and may be made by placing several pieces of cyanide 
 over the bottom of a pint fruit jar, and just covering them with 
 plaster of paris. Insects shut up in the jar are soon killed ; after 
 which they can be transferred to folds of paper and packed in 
 boxes, or pinned in boxes. Great care is necessary in arranging 
 the legs and wings so that when dry the specimen shall look nat- 
 ural, be neat, and well preserved. 
 
CHAPTER XXXVII. 
 
 MOLLUSCA, MOLLUSCOIDEA AND TUNICATA. 
 
 THE Mollusca are soft-bodied animals without internal skele- 
 ton, and without segments or joints. The body is covered loosely 
 with a soft contractile skin which usually secretes a calcareous 
 shell as a protective covering. Most of the mollusca are aquatic 
 animals or live in damp places, and many of them are perma- 
 nently fixed to solid bodies, having no organs of locomotion. A 
 mass of skin and muscular tissue called the foot is developed on 
 the ventral surface of many of this group, by means of which 
 slow movements may be accomplished. 
 
 The alimentary canal consists of the oesophagus, stomach 
 and intestine, and the rectum. Attached to the digesting por- 
 tion of the canal there is quite a complete liver, and kidneys are 
 always present. There is a vascular system with a heart driving 
 the blood through the body, but the system is not completely 
 closed from the body cavity. Respiration is carried on through 
 the general surface of the body, also by means of branchia or 
 gills, and occasionally by means of lungs. 
 
 The nervous system consists of a pair of dorsal ganglia lying 
 above the oesophagus, with pedal and visceral nerve cords; and 
 sometimes it would be better described as consisting of a cerebral 
 ganglion, a pedal ganglion and a ganglion supplying the walls of 
 the body. The cerebral ganglia supply the sense organs, which 
 usually consist of eyes, tactile and auditory organs. But no 
 general description can do justice to this large and interesting 
 group of animals; some notice must betaken of the more im- 
 portant subdivisions. 
 
 The Lamellibranchiata are mollusca without distinct head, that 
 breathe by means of plate-like branchia or gills, and have bivalve 
 shells. To this class belong the oyster, the salt water and the 
 
 (285) 
 
286 PRACTICAL LESSONS IN SCIENCE. 
 
 fresh water mussel. The fresh-water mussel is abundant in the 
 beds of most of the streams and ponds of the Mississippi valley, 
 and can easily be taken during the low water of the summer. 
 They may be kept for observation in a tub or bucket, in which 
 there are two or three inches of mud and sand covered by six or 
 eight inches of water. A few specimens should be preserved in 
 alcohol for dissection. With a live shell in the hand, notice the 
 two parts or valves of the shell : the edge along which the valves 
 are joined is the dorsal margin, and the other is the ventral mar- 
 gin of the shell. The concentric lines parallel to the ventral mar- 
 gin are lines of growth, the raised portion which forms the center 
 of these lines is the beak or umbo which is nearer the front or 
 anterior end of the mussel. Holding the shell with the dorsal 
 margin upward, and the anterior portion forward, notice the re- 
 lation of parts, the anterior and posterior regions, the right and 
 left valves, the ventral and dorsal margins, and the heavy hinge 
 ligament binding the valves together. 
 
 Drop two or three live mussels into water that is nearly boiling 
 hot. The hot water will kill the animal and loosen it from its shell. 
 When cool enough to handle open the shell by turning back the 
 left valve. Notice the white membrane, mantle, adhering to the in- 
 ner surface of the shell; it can easily be removed with the fingers; 
 then notice the glistening inner surface of the shell, and the rough 
 line parallel with the margin of the valve called the pallia! line t or 
 impression, as it marks the line along which the mantle was at- 
 tached to the shell. Notice that this line terminates in two oval 
 rough-bottomed pits near the extremities of the hinge ligament. 
 With the fingers or a thin piece of wood carefully separate the 
 mussel from the other valve, noting the pits near the dorsal 
 margin, and the bodies which occupied them. They are the ante- 
 rior and posterior adductor muscles' by which the mussel closes 
 his shell. Note their relative length and thickness, and their 
 structure. Notice that the shell does not remain closed, the 
 elasticity of the hinge ligament opens it as soon as the muscles 
 are cut or loosened. Notice that the mantle lobes are continuous 
 across the dorsal portion of the mussel. The hatchet-shaped, 
 
LESSONS IN ZOOLOGY. 287 
 
 yellowish or whitish mass of flesh lying between the mantle lobes, 
 and forming the ventral portion of the animal is the foot. On 
 either side the foot find a pair of branchia or gills. Just in front 
 of the gills on each side are a pair of triangular processes called 
 the labial palpi, and between them just back of the anterior ad- 
 ductor muscle is the mouth. Toward the posterior of the ani- 
 mal notice that the mantle lobes coalesce so as to form two slit- 
 like openings called the ventral or inhalent siphon, and the dor- 
 sal or exhalent siphon. By the action of cilia in the ventral 
 siphon and gills, water is driven through the gill chamber, and 
 food materials pass with the water over the palpi to the mouth. 
 Commencing at the mouth with probe, blowpipe and scissors trace 
 out the alimentary canal. This can be done more easily with an 
 alcohol specimen. 
 
 Pry open the shell of a live mussel and insert a little block of 
 wood to keep it from closing; then cut the adductor muscles, 
 separate the mantle lobes from the shell, and on the dorsal 
 border of the animal, near the region of the umbo, notice a thin 
 space in the mantle covering a cavity filled with fluid. In this 
 cavity, called the pericardium, a yellowish transparent sac, called 
 the heart, may be seen pulsating in the pericardial fluid. This 
 dissection can be made more satisfactorily with a live clam, but 
 most of the work can be as well or better done with the alcohol 
 specimen, or one that has been killed with boiling water.' 
 
 Most mussel shells have hinge teeth with corresponding sockets 
 on the dorsal margin of the valves, near the ligament, by which 
 they are more firmly held together when the shell is shut. The 
 anterior is conical, sometimes sharp, the posterior narrow and 
 long. Notice a thin dark-colored membrane bordering the edge 
 of the shell, seemingly an extension of the outer covering or epi- 
 dermis of the shell. Burn some mussel shells in the open fire, 
 and note what properties they lost and what they gained from 
 burning. From the burned shells try to get some idea of how 
 the shell was built up. Test portions of the burnt shell with 
 acid and note results ; also test a fresh shell with acid and note 
 results. In observing the mussel note especially his methods of 
 
288 PRACTICAL LESSONS IN SCIENCE. 
 
 locomotion, his position while lying in the mud, and the currents 
 of water when the siphons are in action. Water snails and land 
 snails having univalve shells are also interesting to keep for ob- 
 servation, as are also garden slugs or snails that have no shells, 
 or only little scales on the dorsal surface. 
 
 The nervous system of this group consists of three pairs of 
 ganglia, the cervical, pedal and visceral. The sense organs are 
 but slightly developed. Usually the sexes are separate, but 
 hermaphrodite individuals occur. They are generally oviparous, 
 but the fertilized eggs are often retained in the pouches of the 
 parent until the embryo is well advanced. 
 
 The Ostridse, or oysters, belong to this class. They have a fixed 
 left valve; the right valve closes upon the oyster held in position 
 by a strong ligament. They have no siphons, and only a rudi- 
 mentary foot. Oysters are either mainly hermaphrodite indi- 
 viduals or females. The fertilized ova, called spat, after escaping 
 from the organs of the parent, swim freely for several days, then 
 settle on some support as sticks, stones, old shells or other ob- 
 jects, and become fixed. The natural oyster beds of the Old 
 World and many of those of the United States have been ex- 
 hausted, and artificial beds have been made and cultivated and 
 protected to such an extent that oyster culture has become an 
 extensive and profitable industry. 
 
 The Gasteropoda, have a distinct head, often with tentacles 
 and stalked eyes, and simple mantle that secretes a plate-shaped 
 or coiled shell. The muscular foot forms the ventral side of the 
 body, hence the name signifying stomach foot. Eyes, olfactory, 
 tactile and auditory organs are fairly well developed. Sometimes 
 the mantle forms a long siphon. This family includes the uni- 
 valve land snails and the fresh water and salt water univalve 
 snails or mollusks, as well as some that do not secrete a shell. 
 
 The Cephalopoda have a circle of arms, bearing suckers round 
 the mouth, and they have a funnel-shaped perforated foot. The 
 water used for respiration, violently driven from the funnel, tends 
 to force the animal backward. This method of locomotion is 
 common among the animals of this class. The octopus, the 
 
LESSONS IN ZOOLOGY. 289 
 
 nautilus, cuttlefish and other interesting mollusks belong to this 
 class. Some attain great size and strength, so that with their 
 long arms, supplied with powerful suckers, they sometimes de- 
 stroy men, and so fierce and destructive are they that one group 
 has received the name of devil fish. 
 
 The Molluscoidea. The bryozoa and brachiopoda, now 
 grouped as molluscoidea are interesting animals whose relations 
 are not well made out, and which do not appear much alike, but 
 a study of their developmental history seems to show them 
 closely related. The bryozoa are small animals usually united 
 together forming colonies so as to present the appearance of 
 sprigs of moss. There is no vascular system, and the nervous 
 system consists of a simple ganglion. The mouth, surrounded 
 by a crown of tentacles, leads to a capacious stomach, the intes- 
 tine terminating near the mouth. The brachiopoda are fixed ani- 
 mals of larger size, having a shell consisting of dorsal and ven- 
 tral valves. A vascular system is present, and the nervous 
 system is a ring about the oesophagus with two ganglia in it. 
 The mouth is provided with two long, coiled arms, which serve 
 as a respiratory apparatus, and aid in gathering food for the 
 animal. The oldest fossils belong to this group. 
 
 The Tunicata. These are saccular or barrel-shaped animals, 
 whose respiratory cavity has two wide openings, between which 
 is placed the simple ganglion which constitutes the nervous sys- 
 tem. Judging from the development of the different systems of 
 organs the ascidians would appear to take low rank in the scale 
 of being, but a study of their embryonic development seems to 
 show that they have close relations to the lower vertebrates. 
 They are nearly all marine animals of little or no economic 
 value, and of no special value for study by beginners in zoology. 
 
 L. S. 19 
 
CHAPTER XXXVIII. 
 
 THE VERTEBRATA, PISCES, AND AMPHIBIA. 
 
 THE vertebrata are distinguished from other forms of animal 
 life by the possession of an internal skeleton. The principal part 
 of the skeleton is the vertebral column composed of several dis- 
 tinct bones called vertebrae. Each vertebra is made up of a body 
 and several processes or projections. Some of these processes en- 
 able the vertebrae to articulate with one another so as to form an 
 elongated, flexible, bony axis. Other processes jut out from each 
 vertebra so as to form a narrow bony tube, or canal on the dor- 
 sal side of the axis, and at least the framework of a much larger 
 cavity on the ventral. And perhaps we find here the chief differ- 
 ence between the two groups of animals : the in vertebrates consist 
 of onebody cavity and its contents; the vertebrates havethesame, 
 and in addition a second cavity, the vertebral canal and its con- 
 tents. While the Vertebrata are alike in many respects they differ 
 widely among themselves, forming five quite well-marked classes : 
 Pisces or Fishes, Amphibians, Reptiles, Aves or Birds, and Mam- 
 malia. 
 
 The class Pisces is made up of cold-blooded aquatic animals 
 that breathe by means of gills. As usually constituted, this class 
 includes several forms that are not regarded as true fishes. Of 
 these the lowest in the scale are the Leptocardii. They have a 
 membrane-cartilaginous skeleton, without a skull, the vertebral 
 column represented by an elastic substance called the notochord, 
 which in the higher vertebrates represents the column in the em- 
 bryo. The colorless blood circulates in pulsating vessels without 
 the aid of a heart; they have no nervous system or sense organs. 
 The mouth without jaws leads into the pharyngeal sac, whose 
 sides are pierced by numerous slits which serve for respiration. 
 (290) 
 
LESSONS IN ZOOLOGY. 291 
 
 The individuals of this group are small, and are found usually in 
 the sands of shallow water along the seashore. 
 
 The Marsipobranchia, are vermiform animals with a cartilagin- 
 ous skeleton, and persistent notochord. The mouth is suctorial ; 
 the alimentary canal a simple tube. The blood is red, and the 
 heart has two valves. The brain is distinct, with three sense 
 nerves: the optic, auditory and olfactory. They have dorsal 
 and caudal fins, but no scales. Respiration by means of five or 
 six pairs of gill sacs. They are all parasites, including the marine 
 hagfish, and the lampreys, living in both fresh and salt water. 
 They attach themselves to dead or living fish, and also eat worms 
 and other small aquatic animals. 
 
 The Selachii have a cartilaginous skeleton, pectoral and ven- 
 tral fins, transverse mouth, and a capacious stomach. Respira- 
 tion is accomplished by means of one or several gill openings. 
 There is no air bladder, and the arterial bulb has three series of 
 valves. The nervous system is well developed, but the optic 
 nerves do not decussate. This group includes the different kinds 
 of sharks, dog fishes, skates and rays. They are carnivorous, 
 and generally marine. 
 
 The Ganoidei and Teleostei are regarded as true fishes. The 
 Ganoidei have a bony or cartilaginous skeleton with enameled 
 scales or osseous plates. The arterial bulb is muscular with 
 numerous valves, and there is a partial decussation of the fibers 
 of the optic nerve. The sturgeons, gar-pikes and mud-fish are 
 the chief representatives of this group in the waters of the present 
 time, but earlier in the history of the earth they were the domi- 
 nant form of fish life. 
 
 The Teleostei are bony fish, and include the great bulk of the 
 fishes of the present time ; they are the typical fish, and perhaps 
 we can best learn something of them by a somewhat detailed 
 study of some common fish, as the yellow or ringed perch ; or a 
 bass or a croppie would serve as well. 
 
 Holding a fish in its natural position, notice that it is symmetri- 
 cal , has an anterior and posterior region, a dorsal and ventral sur- 
 face and a right and left side. A fish may be cylindrical, or flat- 
 
292 PRACTICAL LESSONS IN SCIENCE. 
 
 tened from above downward, but they are usually "compressed," 
 flattened from side to side ; as in the case of the bass or perch. 
 
 The fins are membranous organs, probably folds of skin, sup- 
 ported by spines or rays. The principal one is the caudal or tail 
 fin. Of these there are two kinds, the hoinocercal, when the back- 
 bone ends at the base of the fin and the fin is symmetrical, and the 
 heterocercal, when the backbone extends into the upper lobe of 
 the fin, making it unsymmetrical, as in the sturgeon and shark. 
 The fin along the center of the back is the dorsal; it is sometimes 
 single, sometimes double, and it may be supported by spines or 
 soft rays. Then there are the pectoral or breast fins, the ventral 
 fins and theana7fin. Count the spines in each of the fins, count the 
 soft rays, measure along the base to find the length of the fin, 
 and the length of the longest ray to get the height of the fin. 
 Compare the fins as to length, height, number of rays and spines, 
 and note their relative position. Close the mouth and measure 
 from the tip of the snout to the posterior margin of the bone 
 which covers the gill opening for the length of the head, and to 
 the base of the caudal fin for the length of the fish, and measure 
 from above downward at the widest place for the depth of the 
 fish. Compare the length of the head with the length of the body, 
 and the depth with the length and width, etc. 
 
 The bone that serves as an upper lip for the fish is the premax- 
 illary; note its form, size, and movements; notice also the fine 
 teeth on it, and their shape, size and arrangement. Back of the 
 premaxillary on each side are the oblong maxillary bones, and 
 abovethese in the median line are the nasal, prefrontal and frontal 
 bones, and on the sides of the lower jaw are the dentary bones. 
 
 In the front part of the roof of the mouth find a group of teeth 
 situated on a bone called the vomer. Extending backward on 
 each side of the roof of the mouth find rows of teeth located on 
 the palatine bones. Examine other parts of the mouth and the 
 tongue for teeth ; compare the different sets as to form , size and 
 arrangement. In front of the eye is the anteorbital and below it 
 are the suborbital bones. 
 
 The cavities in the sides of the fish which divide the head from 
 
LESSONS IN ZOOLOGY. 293 
 
 the body are the #7*77 openings, and the bones covering them are 
 the g7*77 covers. The upper posterior part of the gill cover is the 
 opercle; below it is the subopercle; between the opercle and the 
 eye is the preopercle, which is sometimes serrate or toothed, and 
 below it is the interopercle. Below the gill cover find the bran- 
 chiostegal membrane, supported by curved bones called bran- 
 chiostegal rays. The narrow body in the median line separating 
 the right and left branchiostegal membranes is the isthmus. 
 
 Turn back or cut away the gill cover and examine the gills. 
 Notice the central bony arch, and the fringe of red filaments that 
 makeup each gill. On the front and inner border of each arch are 
 teeth-like bodies, called gill-rakers. The slits between the gills 
 are the gill clefts. A red spot on the inside of the gill cover is the 
 false gill. Below the four gill arches is a fifth arch, called the in- 
 ferior pharyngeal bone, and where the gill arches unite above is 
 the superior pharyngeal bone, each of which bears teeth. 
 
 Study a scale; notice its radiate and concentric markings. A 
 scale with an even posterior border is a cycloid scale, and one 
 with a toothed border is a ctenoid scale. Compare scales from 
 different parts of the fish. Notice a line called the lateral line 
 along the side of the fish. Compare a scale from the lateral line 
 with other scales and note the differences. Note that the arrange- 
 ment of the scales is regular and symmetrical. Count the scales 
 in the lateral line. Count the rows of scales above and below the 
 lateral line on the side of the fish. Remove a scale carefully and 
 notice a thin skin or epidermis covering it, and if we examine a 
 dark spot we find that the coloring-matter is in the epidermis 
 and not in the scale. 
 
 Open the fish by cutting from the anus forward in the median 
 line to the isthmus ; just back of the ventral fins, cut toward the 
 spinal column on each side, so as to open the body cavity fully. 
 Notice a silvery white membrane, the peritoneum, and in the front 
 part, a little to the left, a brownish mass, the liver, and under it 
 the hepatic vein. 
 
 Placing the fish on its right side ; turn down the liver, uncover- 
 ing the stomach. Pass a probe through the mouth and gullet 
 
294 PRACTICAL LESSONS IN SCIENCE. 
 
 into the stomach; trace the intestine from the stomach to the 
 anus, and notice the delicate membrane called the mesentery. 
 Near the intestine find a reddish body, the spleen. Find the air 
 bladder', it sometimes communicates with the alimentary canal. 
 Does it in this case? Above the air bladder find two slender, dark 
 red bodies, the kidneys, and in the posterior part of the body 
 cavity find the urinary bladder and the reproductive organs; 
 the yellow single or double ovary with the oviduct in the female, 
 and the two white testes in the male. 
 
 In front of the liver, separated from it by the false diaphragm, 
 is the pericardial cavity. Examine the heart ; note the thin-walled 
 auricle and the thicker walled ventricle. The auricle receives 
 blood from the body through the venous sinus which passes to 
 the ventricle, then through the arterial bulb to the gills, thence 
 to the body ; the blood is usually red. 
 
 The pectoral fins represent the anterior limbs of other verte- 
 brates. They arise from the pectoral arch, which, in some cases, 
 is a simple cartilaginous arch, in others composed of the clavicle, 
 supraclavicle and post-temporal bones. The ventral tins repre- 
 sent posterior limbs. 
 
 Cut down to the ribs by the side of the dorsal fin and dissect 
 away the flesh, studying the relation of the fin to the vertebral 
 column. This, perhaps, can be done more easily in a fish that 
 has been cooked, and in this way the flesh may be removed from 
 the backbone so that it may be studied more satisfactorily. 
 Study a vertebra. Notice the form of the body, the dorsal spine 
 and neural arch and the haemal spine and arch below, and note 
 the neural canal with the spinal cord, and the haemal canal with 
 its contained blood vessels. 
 
 Open the cranial cavity and at least a portion of the spinal 
 canal, and, beginning at the front, notice the olfactory lobes giv- 
 ing rise to the olfactory nerves, then the cerebral hemispheres, 
 then the optic lobes, the widest part of the brain, then the cere- 
 bellum, and the medulla oblongata, merging gradually into the 
 spinal cord. 
 
 Cut away the lower jaw, and, working from the mouth, dissect 
 
LESSONS IN ZOOLOGY. 295 
 
 out the muscles of the eye, and trace the optic nerve to the optic 
 lobes. Notice the form of the eye, its flat cornea and spherical 
 lens; its freedom of motion and the absence of eyelids. 
 
 Auditory organs are usually present, but it is said that fish 
 cannot hear well, and the senses of taste and touch do not seem 
 to be well developed. The olfactory sense is, perhaps, better 
 developed than any other except the sense of sight. 
 
 Open and shut the mouth and note the motion of the different 
 bones which make up that cavity. Cut away the gill cover on 
 one side and note the motion of the gills corresponding to the 
 motions of the jaws and tongue. Keep minnows or small fish in 
 jars for observation, and notice their movements and habits. 
 
 Fish, in general, are carnivorous; they are voracious eaters 
 and rapid growers. The flesh of most kinds is highly prized for 
 food. The fishing industry is one of the great industries of the 
 world . 
 
 Most fish are oviparous, producing vast quantities of spawn, 
 but their natural enemies are so numerous, and the number de- 
 stroyed by man so great, that many of the valuable fish began to 
 diminish in numbers. This fact led several nations to establish 
 departments looking toward the protection and culture of valu- 
 able food-fishes. 
 
 These departments have gathered an immense fund of informa- 
 tion relating^ to the habits and life history of the more valuable 
 food-fishes; to the habits and history of the various forms of life 
 used by them as food ; to the habits and history of those forms 
 of life that prey upon food-fishes, and to the various forms of 
 disease that attack valuable fish. This knowledge has led to the 
 adoption of rational methods of protection and culture, so that 
 waters formerly barren now yield an abundance of good fish, and 
 other waters are furnishing a largely increased product. The 
 more important food-fishes included in this group are the herring, 
 cod, mackerel, shad, salmon, hake, haddock, halibut, white fish, 
 trout, bass, pickerel, and many others. 
 
 The Dipnoi, are scaly animals breathing by means of gills and 
 lungs ; they have the form and appearance of fish, but their lungs 
 
296 PRACTICAL LESSONS IN SCIENCE. 
 
 and the structure of the heart, make them appear as in some 
 sense a transitional group between the true fishes and the am- 
 phibians. They are not found in this country, and are of no 
 economic value, and are not numerous, although, during recent 
 geological periods, they were prominent forms of life. 
 
 The Amphibia are cold-blooded, usually naked-skinned animals 
 that are oviparous. The fertilized egg develops into a larva, 
 somewhat fish-like in form, that breathes by means of gills. The 
 larva eventually develops lungs and anterior and posteriorlimbs, 
 sometimes retaining the gills during life but usually losing them. 
 The lungs are not well organized and much of the respiration is 
 carried on through the skin. The medium of respiration whether 
 by gills, lungs or skin is supposed to be derived from the cutane- 
 ous surface. 
 
 The skeleton varies considerably, but the bones are usually 
 more compact and calcareous than those of fish, and, with the 
 development of the external limbs, the pectoral and pelvic arches 
 are more fully developed and the amphibian is fitted for crawl- 
 ing, swimming, climbing and walking. 
 
 The nervous system seems, on the whole, to be more highly de- 
 veloped than among fishes, although the sense organs do not 
 seem much superior to those of fish unless, perhaps, the senses 
 of touch and taste may be exceptions. Some of the amphibians 
 have a well-developed vocal apparatus in connection with the res- 
 piratory organs, which is a distinguishing mark of some impor- 
 tance. 
 
 The young, while breathing by means of gills, have the single 
 auricle and ventricle and the same arrangement of arterial trunks 
 as among fishes, but with the development of the lungs the auri- 
 cle is divided into two chambers, one receiving blood from the 
 body, the other from the lungs; but the ventricle remains single, 
 containing mixed blood. The lymphatic system is well developed , 
 in some cases the lymph receptacles are contractile, having the 
 value of lymph hearts. 
 
 Some amphibia are terrestrial during the adult state, but usu- 
 ally live in damp localities since cutaneous respiration necessi- 
 
LESSONS IN ZOOLOGY. 297 
 
 tates a moist atmosphere. In larval life they live mainly on 
 vegetable matters, in adult life on insects. 
 
 As a rule, their movements are sluggish, and the need of food 
 is relatively small, so that they live for months without food. 
 They also have the power of reproducing lost parts, as the limbs 
 or tail. 
 
 The Apoda are worm-like amphibia, without limbs, that were 
 for a long time thought to be snakes. They live in tropical 
 climates and are of no special interest beyond the question of 
 relationship. 
 
 The Caudata have four short limbs and a persistent tail, some- 
 times retaining external branchia through adult life. 
 
 This group includes the sirens, the mud puppies, which have 
 external gills, and the land and water salamanders which have 
 no gills. 
 
 The Batrachia are tailless amphibia with naked skin and well 
 developed extremities. This group includes water frogs, land 
 frogs, tree frogs, toad frogs and toads. 
 
CHAPTER XXXIX. 
 
 REPTILIA AND AVES. 
 THE REPTILIA. 
 
 THE Reptilia are cold-blooded animals with a scaly or ar- 
 mored skin. In many cases there are no limbs, and when pres- 
 ent they are usually weak, scarcely raising the body from the 
 ground. In most cases the trunk, even when the limbs are pres- 
 ent, is an important agent inlocomotion, as the vertebral column 
 is adapted to serpentine movements. The internal skeleton is 
 always bony, and generally the ribs are numerous and well de- 
 veloped. Each half of the lower jaw is composed of several 
 pieces joined by sutures, and the two halves are usually only 
 loosely united. The lower jaw is jointed to the skull by means of 
 the " quadrate bone," which enables the mouth to be opened 
 much wider than would otherwise be possible. The jaws are 
 usually supplied with prehensile teeth, and salivary glands are 
 present. The stomach and intestines with pancreas and liver, are 
 well developed. The heart has distinct auricles, but the ventricle 
 is but imperfectly divided, so that mixed blood is distributed to 
 the organs. Respiration is by means of lungs, which often reach 
 considerable size, not being separated from the digestive organs 
 by a diaphragm, as in the higher vertebrates. The nervous sys- 
 tem is more highly developed than among the amphibians, the 
 cerebral hemispheres being relatively large, but the senses arenot 
 specially acute. The reptilia in general are oviparous, the eggs 
 having membranous shells. During the development a mem- 
 brane called the amnion grows out from the blastoderm around 
 the embryo so as to form a sac, which is filled with fluid. In ad- 
 dition the allantois, an extremely vascular organ, is formed, 
 which serves as an embryonic respiratory organ. The appear- 
 ance of the allantois corresponds with the disappearance of 
 (298) 
 
LESSONS IN ZOOLOGY. 299 
 
 branchial respiration, and every form of metamorphosis Rep- 
 tiles generally are tenacious of life ; can to some extent replace 
 lost parts ; can live- for long periods without food, and with but 
 limited respiration. 
 
 The Ophidm, or snakes, have elongated cylindrical bodies, 
 usually without limbs ; sometimes limbs are represented by small 
 spurs on the sides of the vent. They have an epidermal cover- 
 ing of scales, which are usually somewhat elongated, and may 
 be smooth or provided with a longitudinal ridge. The head is 
 covered with irregular-shaped plates, the abdomen with broad 
 band-like plates, while the subcaudal plates are in pairs. The 
 anal plate is sometimes entire and sometimes bifid. The number 
 of rows of scales, the number of ventral plates and the charac- 
 ter of the anal plates and body scales are important specific char- 
 acteristics. The ribs, of which they have great numbers, are the 
 chief locomotive organs of snakes. The free ends of the ribs are 
 attached to the abdominal plates by muscular fibers, so that the 
 ribs serve as legs and the plates as claws. The skin is shed and 
 replaced at somewhat regular intervals ; they have a forked pro- 
 trusible tongue and no eyelids. 
 
 The Colubrifonma, have both jaws armed with solid hooked 
 teeth, with no poison fangs, and no spur-like appendages near 
 the vent. This group includes the spreading vipers, watersnakes, 
 garter snakes, blacksnakes, the racers, milk snakes, and other 
 common snakes of our country. The harlequin, or bead snake, 
 which is much like the members of this group in general appear- 
 ance, has two grooved poison fangs in the upper jaw. It is jet 
 black, with seventeen broad crimson rings, spotted with black, 
 while the tail has yellow rings. 
 
 The Crotalidse have the upper jaw provided with an erectile 
 grooved poison fang on each of the relatively small upper jaws, 
 and the short tail is often provided with a rattle. This group 
 includes the rattlesnakes, massasaugas, .copperheads and moc- 
 casins. 
 
 The Lacertilia or Lizards, are sometimes snake-like in form, 
 but as a rule they have two pairs of limbs, and the body is usually 
 
300 PRACTICAL LESSONS IN SCIENCE. 
 
 covered with scales ; the pectoral and pelvic arches are present, 
 and the bones of the head and jaws are more fully consolidated 
 than in the snakes. This group includes the tree swifts, horned 
 toads, glass snakes, which have hidden rudimentary limbs, lizards, 
 skinks, etc. Lizards are more abundant in the warmer parts of 
 the world, where they are common everywhere about walls, build- 
 ings, rocks, trees, etc. 
 
 The CrocodWaare not only larger than other reptiles, but they 
 seem in every way more highly developed. The alligators of our 
 Southern States are the only representatives of the class in this 
 country. 
 
 Lizards and crocodilian reptiles existed in great numbers and 
 variety and attained to an enormous size during middle geologic 
 times, so that one period is called the Age of Reptiles. 
 
 The Chelonia, are a well-marked group of animals. They have 
 a short stout body, with the dorsal and ventral surface covered 
 with osseous shields, which in turn are covered by horny plates 
 or a leathery skin. The neck and tail are flexible but the dorsal 
 and sacral vertebra? help to form the carapace, uniting with ribs 
 and overlying bony plates. The plastron or ventral plate seems 
 to consist of membrane bones. There are no teeth, but the jaws 
 are incased in horny sheaths which usually have sharp cutting 
 edges. The eye is furnished with eyelids, and respiration is ef- 
 fected by means of air that is swallowed . This group includes 
 the land tortoise, box turtles, terrapins, snapping turtles, soft- 
 shelled turtles, etc. 
 
 The Aves or Birds. The birds are warm-blooded oviparous 
 animals, clothed with feathers. They have four extremities, two 
 adapted for walking or swimming and two fitted for service as 
 organs of flight. 
 
 The bones of birds are more compact and lighter than those of 
 reptiles. The cranial bones are fused together into a light, firm 
 skull, which is articulated to the vertebral column by a single 
 condyle. The face bones unite to form projecting beaks, the mar- 
 gins of which are covered with a horny substance that supplies 
 the place of teeth. The vertebral column has a long, flexible, 
 
LESSONS IN ZOOLOGY. 301 
 
 cervical region, a short, slightly flexible, caudal region and a 
 rigid dorsal lumbar and sacral region. 
 
 The ribs join the broad sternum forming a deep conical body 
 cavity, whose walls are an excellent foundation for a strong 
 shoulder joint. The clavicles unite so as to form an arch or fork, 
 then the scapula and coracoid wedged in between the rigid ver- 
 tebrae and the heavy sternum, making a socket for the broad 
 faced humerus that gives the bird one of the best of shoulder joints. 
 The wing is completed by the ulna and radius, and by the more 
 or less modified parts of the wrist and hand. 
 
 The foundation for the articulation of the legs consists of an 
 elongated pelvis made up of the lumbar and sacral vertebrae 
 fused with the long iliac bones and the shorter ischial and pubic 
 bones, The acetabular cavity is deep and the joint is firm. The 
 short, heavy femur is concealed within the body, the knee joint 
 usually being just at the surface of the body. The first free por- 
 tion of the leg is composed of the tibia, the fibula being rudimen- 
 tary; the second portion is a fusion of tarsal and metatarsal 
 bones, which lead to the phalanges. 
 
 The muscular system is well developed and especially adapted 
 to quick, vigorous movements. The skin is covered with feathers 
 which correspond to the hair of the mammalia. A feather has a 
 shaft and vane and the vane is made up of barbs and barbules. 
 Feathers from different parts of the body vary considerably in 
 appearance and use. Feathers are usually imbedded in the skin, 
 but the larger stiffer feathers of the wing, called quills, are inserted 
 in the bones of the wing. 
 
 The quills on the hand are the primaries, those on the forearm 
 are secondaries, and when found on the arm they are tertiaries. 
 The skin on the legs and toes is usually covered with horny scales 
 or plates. 
 
 The nervous system and the sense organs are well developed. 
 The alimentary canal consists of the mouth with the salivary 
 glands, the oesophagus, crop, pro-stomach, stomach or gizzard, 
 and the intestine with the pancreas and liver. The kidneys and 
 the ovaries evacuate through the intestine. The heart and the 
 
302 PRACTICAL LESSONS IN SCIENCE. 
 
 circulatory organs are double. The lungs are capacious, but in- 
 stead of moving freely, as in the case of mammals, they are fixed 
 to the dorsal aspect of the body cavity. They communicate 
 freely with the cavities of the larger bones. 
 
 The matter of the adaptation of animals to their surroundings 
 is perhaps more easily shown in the study of birds than in the 
 study of any other group. The feet, the bill, the legs, the wings, 
 the neck, the plumage, the whole appearance and habit of the 
 bird depend on whether it is a wader, walker or swimmer; a 
 scratcher, climber or a bird of prey. The idea is common every- 
 where, but in some way it seems more prominent among the 
 the birds. 
 
 Birds are oviparous, the eggs having a large amount of yolk, 
 and requiring a high degree of heat for their development. In 
 the fertilized egg, the process of development begins before it is 
 laid ; the blastoderm is formed, the primitive groove and medul- 
 lary folds appear, then the cranial flexure, the digestive canal, the 
 amnion and allantois membranes, and soon the young bird is 
 ready to open the way to liberty from his stony cell. 
 
 Birds are intelligent; they have beautiful plumage and musical 
 voices, and are interesting to man in many ways. No group of 
 animals yet studied is as intimately related to man; none other 
 more available for study than the birds. Study birds; note the 
 migratory birds, the time they arrive and depart; note the ones 
 that remain during the whole year, and those that only remain 
 during the winter. Note also those birds that pass through your 
 locality in their spring and autumn migrations, stopping only 
 for a few days. Notice the birds that nest in your region ; the 
 kinds of nests they build ; when they build them ; how many eggs 
 are laid, and what was the period of incubation. Make a careful 
 study of the breeding and nesting habits of some particular pair 
 of birds, making full notes. Study the legs, feet, wings, bill and 
 other parts of birds and compare them. Study the bones and 
 skeletons of birds, and compare with those of other animals. 
 Notice that the claws of perching birds close automatically on 
 the perch. Examine the arrangement of tendons in the legs. 
 
LESSONS IN ZOOLOGY. 303 
 
 Scald a bird and remove its feathers; notice if the feathers were 
 uniformly distributed over the body; notice if they are dis- 
 tributed in the same way on different kinds of birds. After 
 removing the feathers dissect the digestive, respiratory and cir- 
 culatory organs, and dissect the brain and the sense organs. 
 Study the development of the chick from day to day, breaking 
 the egg into blood-warm water for observation. Study birds in 
 every way. 
 
 The Natatores or Swimming Birds. These birds are clothed 
 with a thick compact plumage and a heavy coat of down, and 
 are supplied with a large oil gland. They are excellent swimmers 
 and divers, and usually strong flyers. The beak varies from the 
 strong cutting beak of the fish-eater to the soft yielding beak of 
 birds who live on infusoria. They are usually gregarious on the 
 seacoast or on large inland waters. Some species are valuable 
 for food and other purposes. To this group belong the penguins 
 with their fin-like wings, the auks, divers, swans, ducks, geese, 
 pelicans, gulls, the albatross and stormy petrel. 
 
 The Grallatores or Wading Birds. These birds have a long 
 beak, long neck and long legs, and are adapted for taking snails, 
 larvae, worms, frogs, fish and other materials for food from the 
 mud of shallow waters. They are mostly migratory birds, some 
 of them being highly prized for food. The plover, snipe, heron, 
 stork, rail and water hen belong to this group. 
 
 The GalHnacese. These are terrestrial birds, having stout 
 bodies and rounded wings not well adapted to flight. The legs 
 are strong, of medium length and well fitted for running and 
 scratching. To this group belong turkeys, domestic fowls, 
 grouse, quail and partridge. 
 
 The Columbinas or Pigeons. These birds are all of medium 
 size, small heads and short legs, with soft beaks swollen about 
 the nasal openings. They have long, pointed wings well fitted for 
 sustained flight. They live on grains and seeds, and their 
 plumage is often beautiful. To this group belong the pigeons and 
 doves, and the lately extinct dodo was a member of the group. 
 
 The Scansorial or Climbing Birds. These birds in general have 
 
304 PRACTICAL LESSONS IN SCIENCE. 
 
 a powerful beak, sometimes especially fitted for chiseling and 
 hammering. They have strong climbing feet and a stiff plumage 
 that often aids in climbing. They generally inhabit forests, living 
 on insects, small birds, or on fruits and vegetable matters. The 
 toucans, trogans, cuckoos, woodpeckers, parrots, cockatoos, 
 etc., belong to this somewhat miscellaneous group. 
 
 The Passeres or Passerine Birds. The birds of this order are 
 generally of a small size, well fitted for flight, dwelling mainly 
 among the trees and bushes. They are sometimes divided into 
 singing birds or oscinesand shrieking birds or clamatores. They 
 are usually divided on the character of the beak into Levirostres, 
 light beaks, as the hornbills, king-fishers and bee-eaters. Tenui 
 rostres, slender-billed birds, as the humming-birds, honey-suckers 
 and tree creepers. Fissirostres or birds with a deeply-cleft beak, 
 and usually long-pointed wings, as the swallows, swifts, and 
 goat-suckers. Dentirostres, birds with the beak more or less 
 notched at the point, as the crow, starling, shrike, flycatcher, 
 titmouse, warblers and thrushes. And the Conirostres, birds 
 with conical beaks, that feed on seeds, etc., as the larks, spar- 
 rows, buntings and others. 
 
 The Raptores or Birds of Prey. These birds are of powerful 
 build, having strong hooked beak and claws, and they are usually 
 well adapted for vigorous long-sustained flight. Their sense 
 organs in most cases are highly developed, thus fitting them well 
 for their particular mode of life. They live mainly on warm- 
 blooded animals, and the food is softened in the crop before diges- 
 tion, the feathers and hair being rejected. To this group belong 
 the owls, vultures, eagles, hawks, buzzards, kites, etc. 
 
 The Cursores include the ostrich, rhea, cassowary, emu, etc., 
 large birds that are incapable of flight. The sternum has no keel, 
 and the bones generally are massive and dense, more like those 
 of the mammalia. The apteryx sometimes called dwarf ostrich, 
 clothed with long hair-like feathers is also a member of this 
 group. The recently extinct moa, and the dinornis giganteus, 
 both enormous birds, were near relatives of the birds just men- 
 tioned. 
 
CHAPTER XL. 
 
 THE MAMMALIA. 
 
 THE Mammalia are warm-blooded viviparous animals that 
 suckle their young with milk from the mammary glands. The 
 members of this class differ considerably among themselves in 
 matters of detail, but in general the structure is the same, and 
 the processes are carried on in the same way throughout the 
 group. 
 
 A good general idea of the class may be gained by the careful 
 study of some animal, as a rabbit, a cat, a puppy, or any other 
 that is convenient. A good knife and a saw are all the instru- 
 ments necessary, although a pair of forceps, and little hooks to 
 hold parts in position or out of the way are a great convenience. 
 First, go carefully over the external features of the animal, com- 
 paring it with others as far as possible. If not dead, kill it with 
 chloroform and open the body cavity for its whole length, cut- 
 ting a way the breast bone and a portion of the ribs. Notice the 
 diaphragm dividing the abdomen from the chest ; note the form 
 of the two cavities and the lining membrane of each. Study care- 
 fully the relative position of the organs in each cavity, turning 
 them over so as to find them all; do not hurry; try to see every 
 organ in its place, surrounded by its associated organs also in 
 place. Through a tube, inflate the lungs, trying to imitate the 
 breathing of the animal. Then study each organ and group of 
 organs somewhat in detail, so as to get, if possible, some idea of 
 how each organ performs its work. Study the heart carefully, 
 tracing out the distribution of the larger blood vessels. Open 
 the cranium ; notice the protective coverings of the brain, its di- 
 visions and external appearance. Find the origin of the nerves 
 of smell, sight, hearing and taste, and trace them to their respect- 
 
 L. S.-20 (305) 
 
306 PRACTICAL LESSONS IN SCIENCE. 
 
 ive external organs, and make a special study of those organs. 
 Open the spinal canal and study the spinal cord; especially no- 
 tice the origin of the spinal nerves. Study the bones, ligaments, 
 muscles, tendons, joints, etc., in the legs, and in the spinal col- 
 umn. This study should be carried into detail as far as time 
 and circumstances will allow. If it is inconvenient to get animals 
 for dissection, material for an extended study may be obtained 
 at the slaughter-house or butcher shop. 
 
 The Mammalia in general have a skeleton composed of com- 
 pact bones filled with marrow, and the vertebral column is gen- 
 erally divided into five well-marked regions the cervical, dorsal, 
 lumbar, sacral and caudal. There are two pairs of limbs with 
 the pectoral and pelvic arches well developed. The feet are es- 
 pecially interesting from the variety of forms under which the 
 same group of bones appears. The digestive organs are well de- 
 veloped in all, but they vary widely with the nature of the food 
 used by the animal. In nearly all cases the jaws are armed with 
 bony teeth, differing in form, number and arrangement with the 
 kind of food. The heart has four chambers and the circulation 
 is double. The lungs are capacious and free to move in a special 
 cavity, and the skin is usually covered with hair. The brain is 
 relatively large and usually covered with convolutions, and the 
 special senses are all highly developed. They easily lead the ani- 
 mal kingdom in matters of intelligence, and for this reason they 
 are more useful and companionable to man. 
 
 There is considerable variation in the reproductive process, 
 but the young are always born alive, and need the mother's care 
 for considerable time afterward. 
 
 The Monotremata. This order includes the ornithorhyncus, 
 or duck-bill, and the echidna, or porcupine ant-eater, both living 
 in Australia. They have short legs armed with strong claws 
 well adapted for burrowing. The urinary and reproductive or- 
 gans open into the intestine, as with birds. The jaws are elon- 
 gated into toothless beaks. The duck-bill is clothed with fur, 
 has a smooth brain, a flattened body and swimming feet. The 
 echidna is covered with spines, has a protrusible tongue and 
 
LESSONS IN ZOOLOGY. 307 
 
 folded brain; both have marsupial bones, but only the echidna 
 has a pouch, and both live on insects. 
 
 The Marsupialia. This order includes the kangaroo, wombat, 
 bandicoot and others of Australia, and the opossum of the 
 United States. The females of this order are furnished with an 
 abdominal pouch or marsupium, for the immature young after 
 birth. The marsupials form no placenta, so that the young 
 are born early in their embryonic life and transferred to the 
 pouch, where they attach themselves to the nipples of the mam- 
 mary gland and remain there during the remainder of their 
 helpless existence. Some of this order are carnivorous, some 
 herbivorous and others are omnivorous; some are specially 
 adapted for jumping, others for climbing, and others have a 
 naked prehensile tail; so that they are quite varied in form and 
 habits. 
 
 The Edentata. The members of this order are all sluggish, 
 stupid animals, with a small smooth brain; the teeth are fre- 
 quently absent, and when present are usually incomplete or im- 
 mature. To this group belong the ant-eaters, armadillos and 
 sloths. The ant-eaters have an elongated narrow snout, protru- 
 sible tongue and weak jaws; the legs are short and adapted for 
 digging. They live mainly on ants and termites. The armadil- 
 los are covered with bony plates, having legs and claws fitted for 
 digging. They can rapidly bury themselves in the ground when 
 pursued, and most of them can roll themselves into a ball that 
 is well protected by bony plates from the attacks of enemies. 
 The sloths are strictly arboreal, hanging by their curved claws 
 from the underside of branches. The sloth, armadillo and one 
 ant-eater live in South America, while the scaly ant-eater is 
 found in Asia and Africa. The remains of many gigantic edent- 
 ates are found in the later rocks of South America. 
 
 The Cetacea. The members of this order are aquatic mam- 
 malia, with fin-like anterior and no posterior extremities. The 
 body is fish-like in form, only that the caudal fin is horizontal, 
 not vertical as in the fishes. The surface is usually devoid of hair, 
 but a thick subcutaneous layer of fat serves to protect from cold, 
 
308 PRACTICAL LESSONS IN SCIENCE. 
 
 and perhaps lessens specific gravity. This group includes the 
 Dolphins, Whales and Sirenia. 
 
 The dolphin is carnivorous, having both jaws armed with con- 
 ical teeth. They live on fish, and frequent the mouths of large 
 rivers. The narwhals have two upper teeth, which in the female 
 are small, but in the male the one on the left side usually be- 
 comes a spiral tusk, which sometimes attains a length of twenty 
 feet. The sperm whale has an enormous head, nearly one-third 
 the length of the body. The head is swollen by the accumulation 
 of fat spermaceti. They inhabit the colder regions, and live 
 mainly on cephalopoda. The whalebone whales have large 
 heads and wide mouths without teeth. From the palate and 
 upper jaw rows of whalebone plates project downward, forming 
 a kind of sieve which strains the small medusae and other forms 
 of life from the water as it flows out. The sirenia have a dis- 
 tinct neck and no canine teeth, they feed on fuci and seaweed 
 along the coast. They are known as sea cows, or manatees, on 
 the coasts of America, and as dugongs on the coasts of the In- 
 dian ocean. Stellar 's sea cow of the north Pacific has become 
 extinct within the last 200 years. 
 
 The Perissodactyla are large herbivorous animals having one 
 or three hoofs, and in all, the teeth are well developed. The teeth 
 are divided into incisors, canines, premolars and molars. In 
 this group the premolars and molars form a continuous series of 
 broad grinding teeth all much alike. The dorsal-lumbar verte- 
 brae are usually 23, never less than 22. The middle digit or toe 
 is always largest and symmetrical in form. 
 
 The Tapirs are short-haired animals of medium size, having 
 four hoofs on the anterior legs and three on the posterior. There 
 are 6 incisors, 2 canines and 6 molars in each jaw, while there are 
 8 premolars in the upper and 6 in the lower jaw. They have a 
 short proboscis, eat leaves and young twigs, and live in South 
 America and Southeastern Asia. 
 
 The Rhinocerotidse are large, unwieldy, thick skinned animals 
 bearing one or two epidermal horns on the nasal bones. In 
 each jaw there are 4 rudimentary incisors, 8 premolars and 6 
 
LESSONS IN ZOOLOGY. 309 
 
 molars. They are natives of Africa and Southern Asia. They 
 have hoofs on the 2d, 3d and 4th toes of each foot. 
 
 The Equidse are as noted for their graceful, slender forms as the 
 other members of the order are for their bulky, clumsy bodies. 
 The dentition is 6 incisors, 2 canines, 8 premolars and 6 molars 
 in each jaw. Each of the incisors has a little pit near the sum- 
 mit, which, filled with foreign matter, seems like a black spot, that 
 wears away with age. This pit is peculiar to horses, and is not 
 found in the teeth of geological ancestors of the horse. The 
 canines are small, conical teeth and are usually present in both 
 jaws only in the male. The knee and hock joints of the horse 
 correspond to the wrist and ankle joints of man, the bones 
 below to the middle bone of the hand, and the bones of the mid- 
 dle finger are represented by the bones below the fetlock joint. 
 The hoof in all the ungulates corresponds with the nails or 
 claws of other animals. The slender form of the horse fits him 
 for harder ground and more open country than that occupied by 
 the tapir and rhinoceros, and his well developed incisors enable 
 him to take different kinds of food. The zebra, wild ass and 
 quaggas belong to the horse family. The present members of the 
 horse family are natives of the Old World, but in comparatively 
 recent geological times there were several species of horses in 
 America. Some of these ancient horses had three and some four 
 toes instead of one, as does the present species. 
 
 The Artiodactyla, are animals with paired hoofs, the third and 
 fourth digits on each foot supporting the body, the second and 
 fifth digits are generally present but are rudimentary and do not 
 help support the body. 
 
 The dorsal and lumbar vertebrae are 19 or 20 ; the premolars 
 are single, while the molars are two-lobed and the other teeth are 
 variable. This order contains several families. 
 
 The Suidse or swine family have an elongated mobile snout, 
 and the skin is clothed with coarse bristles. There are 6 incisors, 
 2 canines, 8 premolars and 6 molars in each jaw, sometimes an 
 upper incisor and a premolar are suppressed. 
 
 The canines in the male are developed into formidable tusks. 
 
310 PRACTICAL LESSONS IN SCIENCE. 
 
 The wild boar of Europe, Africa and Asia was perhaps the progeni- 
 tor of all the varieties of the domestic pig, but they are so widely 
 distributed and vary so greatly that some have thought they 
 must have originated from several sources. Besides these, there 
 are the wart hogs of Africa, the peccaries of America, and the 
 babyroussa or hog deer of Southeastern Asia. The domestic 
 pig is one of the most important food-producing animals known 
 to man. 
 
 The Obesa, or Hippopotami, are large unwieldly amphibians, 
 vegetable eating animals, living in Southern Africa, that belong 
 in this order. 
 
 The other members of this order are ruminants, distinguished 
 by incomplete dentition and by the peculiarities of the digestive 
 organs. The animal crops the food, and without much mastica- 
 tion it passes from the oesophagus into the paunch, where it soaks 
 in the secretions for a time, then passes to the honeycomb bag, 
 or reticulum, where it is made up into little balls and returned to 
 the mouth by regugitation. After thorough mastication, the 
 food passes to the third stomach, called " many plies " or "psal- 
 teriunii" because its lining membrane lies in many folds. From 
 this cavity the food passes with little change into the rennet 
 stomach, where the food is really digested by the secretion of the 
 peptic glands. 
 
 The Tylopoda include the camel and dromedary of the Old 
 World and the llama, alpaca, etc., of the New. The soles of the 
 feet are covered with horny integument on which the animal 
 walks, and there is no separate psalterium. 
 
 The Arabian camel has numerous large cells in its paunch 
 which enable it to carry several days' supply of water. The gi- 
 raffes and musk-deer belong to this order. 
 
 The Cervidae, or deer, are characterized by a pair of solid dermal 
 horns attached to a bony process of the forehead ; they are cast 
 off and renewed from year to year, the weight and number of 
 parts usually increasing with each renewal. The red deer, the 
 stag, the elk, the reindeer, used as a beast of burden in Lapland, 
 and others, are members of this family. The deer and stag have 
 
LESSONS IN ZOOLOGY. 311 
 
 pointed horns, while the horns of the elk and reindeer are broad 
 and flat at the extremities. The horns are borne only by the 
 males, except in the case of the reindeer. The cervidse have eight 
 incisors in the lower jaw working against a callous pad in the 
 upper jaw; occasionally canines occur in the upper jaw. There 
 are twelve grinders in each jaw, which are separated on the lower 
 by a little space from the incisors. The young of nearly all spe- 
 cies are spotted. The spines of the dorsal vertebrae are long, bet- 
 ter fitting them for the origin of the strong ligaments which 
 support the head with its load of horns. 
 
 The Cavicornia have hollow horns in both sexes, no canines, 
 but twelve grinders in each jaw with six incisors in the lower. 
 In this group belong the antelope, gnu, gazelle and chamois; 
 the sheep, goat, ibex, Rocky Mountain goat and others ; the 
 musk ox, the American bison, and the Indian buffalo and the do- 
 mestic ox the sheep and the ox, the horse and hog being the 
 most important and valuable domestic animals ol the temper- 
 ate and warm temperate zones. 
 
 The Proboscidea include the elephants and several extinct 
 animals, all of great size. They are characterized by a long flexi- 
 ble proboscis, which is an organ of touch and of prehension as 
 well. The skin is very thick and sparsely covered with hair, 
 though some of the extinct forms had an abundant coat of hair. 
 They have several toes on each foot furnished with hoofs, but 
 walk on thick pads of integument. The tusks are two upper in- 
 cisors; some extinct forms had lower tusks as well. The grind- 
 ers are seven on each side in each jaw, but they grow forward 
 gradually so that never more than one or parts of two are in 
 service at one time, the earlier ones dropping out and new ones 
 coming in. The grinders of the elephant are considerably longer 
 than wide, and are made up of thin alternate layers of enamel, 
 dentine and cement, showing a flat surface, while the teeth of the 
 mastodon show a tuberculatecl surface. The mammoth and mas- 
 todon seem to have been vegetarians, living in damp shady places, 
 much like the elephants of Africa and Asia of to-day. One extinct 
 form had tusks curving downward from the lower jaw. 
 
312 PRACTICAL LESSONS IN SCIENCE. 
 
 The Eodentia are a numerous group of small animals charac- 
 terized by their chisel-shaped incisor teeth and the broad com- 
 pact skull furnishing attachment and leverage for the powerful 
 muscles used in their work of gnawing. The dental formula is 
 two incisors and six or eight grinders in each jaw. The hares and 
 rabbits having four incisors in the upper jaw, and some Aus- 
 tralian forms have only four grinders. The incisors are enameled 
 on the anterior surface with dentine on the posterior, and as the 
 dentine wears away faster the tooth is always sharp and chisel- 
 shaped. The teeth grow continuously during life about as fast 
 as they wear away, so that they are always the same length. 
 When one incisor is destroyed in any way its opposite unopposed 
 continuing to grow has been known to form a complete ring, 
 sometimes causing the death of the animal by preventing the use 
 of its other teeth. These animals are compactly built, very pro- 
 lific, and often showing great intelligence in the building of homes 
 and the storing of food. Some migrate at the beginning of win- 
 ter; some take a winter sleep. They are vegetarians, feeding on 
 roots, seeds, fruits, etc. The mammals already studied walked 
 on their toes, were in general digitigrada, but the rodentia walk 
 on the palm of the hand or sole of the foot, and are plan tigrada. 
 The digits are freely movable, having claws or nails. In this 
 order belong the hares and rabbits with long ears, powerful hind 
 legs and short tail; the guinea pig and agouti, the porcupine 
 with blunt nose and sharp quills ; the chinchillas and the jumping 
 mice; the true rats and mice and their allies; the voles with their 
 short hairy ears and tail, and the lemming, the beavers, dormice 
 and squirrels. 
 
 The Insectivora are small plantigrade animals whose feet are 
 furnished with strong claws ; the elongated head often ends in a 
 pointed snout and the jaws carry a full set of teeth; the den- 
 tition varies considerably, the most distinctive character being 
 the tubercles or points on the crowns of the grinders and that 
 the canines are not prominent. They feed on small animals, 
 insects and worms. 
 
 The Erinacidae or Hedgehogs with stiff bristles and spines. 
 
LESSONS IN ZOOLOGY. 313 
 
 The Soricidss or Shrews, with a proboscis-like snout and a musty 
 smell. And the Talpidse or Moles with short, powerful digging 
 feet, soft fur and small eyes constitute this order of insect eaters. 
 
 The Pinnipedia are aquatic animals with a somewhat spindle- 
 shaped body, having two pairs of short legs ending in fin-like 
 feet. They are covered with a fine close fur and are carnivorous. 
 This order includes the Phocidse or Seals and the Trichechidae or 
 Walruses. The seals live on fish, have short canines and rough 
 molars. The walrus lives on crustaceae and molluscs, having 
 the upper canines developed into tusks. 
 
 The Carnivora are distinguished by their size, strength and 
 quickness ; by prominent canines and cutting molar teeth; by the 
 massive skull furnishing the attachment and leverage for the 
 powerful muscles moving the sturdy jaws, and they are all armed 
 with strong cutting claws. This order is made up of the Ursidae 
 or Bears. Stout unwieldly plantigrades including the polar 
 and grizzly bears, the black bear, the raccoon and others. Some 
 of the ursidge are omnivorous, eating roots, mast, honey, etc. 
 They have strong non-retractile claws, and some take a winter 
 sleep. 
 
 The Mustelidae or Martens, as the badger, marten, skunk, wea- 
 sel and otter. The Viverridae or Civet-cats. The Canidae or Dogs, 
 which are digitigrades with non-retractile claws, including the 
 dogs, wolves, jackals and foxes. The Hyaenidae or Hyenas ; and 
 lastly the Felidae, the typical family of carnivorous animals. 
 They are digitigrada, of slender but powerful build, with strong 
 retractile claws, with powerful canines and sharp cutting teeth. 
 This family includes the lion, tiger, leopard, panther, jaguar and 
 other cats. 
 
 The Cheiroptera or Bats are characterized by long anterior 
 limbs, with long digits, which are united by a delicate membrane 
 extending from the fore to the hind limbs, and, being attached to 
 the sides of the body, form true organs of flight. They are noc- 
 turnal animals; the eyes are small but the senses of hearing and 
 touch are very acute. Some of the bats live on fruits, some on 
 insects, and some on the blood of warm-blooded vertebrates. 
 
314 PRACTICAL LESSONS IN SCIENCE. 
 
 The Prosimise or the Lemurs. These animals have hand& and 
 prehensile feet; live in trees and feed on insects and small animals, 
 and are generally nocturnal in their habits. 
 
 The Primates or Apes. The apes are vegetarians, generally 
 leading an arboreal life, for which their form, however varied, 
 seems adapted. They are usually of slender build, having hands, 
 prehensile feet and sometimes prehensile tails. 
 
 The jaws are much less prominent than with other animals, 
 which, with the obtuse ear and projecting eyebrow gives the face 
 something of a human appearance. They have two mammary 
 glands situated in the pectoral region, and are covered with a 
 complete coat of hair. The dentition is much like the human, 
 only that the canines are relatively larger and the grinders more 
 tuberculated. The clavicle is always present, and in general the 
 structure is very like the human, differing most widely in the size 
 and structure of the brain and cranium. 
 
 The Hapalidse are South American monkeys of small size with 
 long hairy, non-prehensile tails, and opposable great toes. The 
 Pithecidse have more teeth than the last but are otherwise much 
 the same. 
 
 The Cebidss are South American monkeys with prehensile tails 
 sometimes naked at the end. 
 
 The Cynocephalidse or Baboons. The baboons are of stout 
 build, semiterrestrial in their habits, with a dog-like face. Tail 
 sometimes long, sometimes short, never prehensile. The anterior 
 and posterior limbs sub-equal. The canine teeth are large and 
 the disposition is fierce. They sometimes eat eggs and small 
 birds; in captivity they are omnivorous. There a re several species, 
 but they are all inhabitants of Africa and Arabia. 
 
 The Cercopithecidse are of slender build, having a long tail, 
 with cheek pouches and a short muzzle. They are the common 
 apes of North Africa, Gibraltar, India, and adjacent islands. 
 
 The Semnopithecidse have longer pelvic limbs, no cheek pouches, 
 thumb small, sometimes absent. They are mainly Asiatic. 
 
 The Anthropomorphss have longer anterior limbs and without 
 tail or cheek pouches. In this family are the gibbons, having 
 
LESSONS LV ZOOLOGY. 315 
 
 very long arms; the ourang-outang, a native of Borneo; the go- 
 rilla and chimpanzee of Africa. 
 
 Man. Man, in his physical structure, resembles the anthro- 
 poid apes in innumerable particulars. His hand may be more 
 perfect; his pelvis, legs and feet may fit him for a firm and erect 
 position, and he may differ in every particular detail of physical 
 structure from the apes, yet the difference is only in degree not in 
 kind. And not till we consider the size and development of the 
 brain and cranium and the correlative greater intellectual 
 capacity does the gap between man and other animals reveal 
 itself. 
 
CHAPTER XLI. 
 
 GEOLOGY ASTRONOMICAL . 
 
 GEOLOGY is a general science which has the material world for 
 its subject. It attempts to give a history of the earth, to trace 
 its development from a mass of burning gases to a whirling 
 sphere clothed with verdure and teeming with life. From the 
 study of a manufactured article we may learn how it was made 
 and gain some idea of its history. The geologist studies the 
 earth as a planet in its relation to celestial bodies, he studies the 
 rocky pages of the earth's crust, and the data gathered from 
 these sources interpreted according to the principles of physics, 
 and chemistry, botany and zoology enable him to work out a 
 somewhat complete history of the development of the earth. 
 
 The Earth is a member of the solar system which consists of 
 the Sun, Planets, Planetoids or Asteroids, Moons or Satellites, 
 Comets and Meteors. 
 
 The Sun is the central and controlling member of the solar 
 system. It seems to consist of a central nucleus of molten mat- 
 ter bounded by the photosphere, outside of which is an atmos- 
 phere composed largely of the vapors of iron, nickel, manganese, 
 carbon, calcium, sodium, silicon, aluminium, potassium and sev- 
 eral other substances known upon the earth. This envelope is 
 called the chromosphere. Above this layer of vapors, rise flames 
 and prominences composed largely of hydrogen. And beyond 
 these is the solar corona. At times dark spots maybe seen upon 
 the sun that appear to be deep pits in the photosphere ; they vary 
 in size and in duration. The time of the minimum number of 
 spots occurs every eleven years and the time of the maximum 
 number occurs some four or five years afterwards. We know 
 little about the cause of the spots but they seem in some way to 
 (316) 
 
LESSONS IN GEOLOGY. 317 
 
 disturb the magnetic conditions of the earth, and possibly its 
 climatic conditions as well. 
 
 The gaseous envelopes of the sun are subject to violent dis- 
 turbances or storms, consisting largely of upward and down- 
 ward movements of the gases. It is thought by some that the 
 sun spots are in some way the result of these storms. The quan- 
 tity and intensity of the heat of the sun is beyond comprehension 
 and yet it must be diminishing as there seems to be no adequate 
 means of supplying the enormous and continuous loss of heat by 
 radiation. Others claim that while the sun is continuously send 
 ing out immense quantities of heat, it is actually increasing in 
 temperature through condensation of material due to gravity. 
 The sun is spherical in form and rotates once in about 25 or 26 
 days. Besides rotation, the sun with the whole solar system 
 has a progressive motion in space toward the constellation of 
 Hercules. Its diameter cannot be determined with accuracy, but 
 is given as about 866,000 miles. 
 
 The Planets are spherical bodies which revolve around the sun 
 from west to east in elliptical orbits. Named in their order from 
 the sun the planets are Mercury, Venus, Earth, Mars, Jupiter, 
 Saturn, Uranus and Neptune. Venus, Jupiter, Mars and Saturn 
 appear as brilliant stars. The planets differ in size, time of rev- 
 olution and in density. Mercury is more dense than the earth, 
 but the sun and all the other planets are less dense! Venus seems 
 to have an 'atmosphere, but Mercury is not known to have one. 
 No permanent marks or features have ever been discovered on 
 these planets so that it is not certainly known whether they ro- 
 tate or not. Mars and the earth each has a solid crust, and 
 somewhat similar atmospheric conditions and each rotates from 
 west to east. Jupiter and Saturn seem to be masses of molten 
 matter, each surrounded by a deep dense atmosphere, in which 
 extensive changes and disturbances are known to occur, and 
 somewhat permanent markings can be seen, from which it ap- 
 pears that each of these planets rotates from west to east. But 
 little is known of Uranus or Neptune beyond some idea of their 
 size, density and time of revolution. 
 
31$ PRACTICAL LESSONS IN SCIENCE. 
 
 The Planetoids or asteroids are a group of smaller bodies re- 
 volving around the sun between the orbits of Mars and Jupiter. 
 
 The Moons or satellites are bodies which revolve around some 
 of the planets as these revolve around the sun. The Earth has 
 one moon, Mars two, Jupiter four, Saturn has eight moons and 
 in addition two rings, Uranus has four or more satellites, and 
 Neptune at least one. We can know but little about the moons 
 but they all seem to be spherical bodies and in general to revolve 
 in the same direction as their primaries. The satellite of the 
 Earth, one of the largest of the moons, is nearly a perfect sphere 
 having a diameter of 2,160 miles. It rotates on its axis and re- 
 volves around the earth in about twenty-seven and one-third 
 days, so that the same side is always toward the earth. Seen 
 through a telescope the surface of the moon appears to be very 
 rugged, not from mountain ranges but from great circular de- 
 pressions in which there are sometimes conical elevations. The 
 moon seems to be a great cinder-like body, devoid of air, water 
 and every form of life. It is supposed that the rocky mass may 
 have absorbed the air and water which were formerly abundant 
 on its surface. 
 
 The Comets are interesting, but little known, members of the 
 solar system. They are usually rather small bodies with an ex- 
 tensive atmosphere, revolving in much elongated orbits, moving 
 with great velocity when near the sun. 
 
 Meteors are bodies, which, falling toward the earth, are heated 
 to incandescence by friction in the air, and usually vaporized be- 
 fore reaching the earth. Sometimes they reach the earth as me- 
 teoric stones or meteorites. In general the meteorite is composed 
 mainly of iron, sometimes of a stony substance. 
 
 The Stars are supposed to be bodies like our Sun, many of 
 them, however, much larger than it. The spectroscope shows 
 that many of them contain substances found to exist in the sun 
 and well known on the earth. The stars vary in size, in distance 
 from the earth, in temperature, in color, and apparently in com- 
 position as well. Some appear to be double stars, some revolve 
 about others ; others are variable in appearance, often changing 
 
LESSONS IN GEOLOGY. 310 
 
 rapidly. They are all supposed to be in motion in definite direc- 
 tions but whether they move together as one system or as many 
 distinct systems is not known. 
 
 The Nebulae are cloud-like masses, similar to the milky way, 
 which occur abundantly in different parts of the heavens. Many 
 of these, when examined with a telescope, are shown to consist of 
 distinct stars, others still appearing as clouds when viewed with 
 the most powerful telescopes. Some of these, when examined with 
 the spectroscope are shown to be star clusters, while others are 
 shown to be incandescent gaseous bodies. They differ in size and 
 in distance from the earth ; some are formless masses, some ring- 
 shaped and some spiral, as if the mass were beginning to rotate, 
 but our knowledge of them is very meager. The constitution 
 and conditions of the nebulae and stars ; the motions, conditions 
 and relations of the members of the solar system have given 
 rise to the Nebular Theory, which supposes that the sun was once 
 a mass of burning gases, which filled the orbit of Neptune. The 
 mass had a rotary motion which increased as it cooled and con- 
 tracted, becoming at length so rapid that portions were thrown 
 off, much as water and mud are thrown from rapidly turning 
 carriage wheels, this process continuing until all the planets were 
 formed, each assuming a spherical form, each revolving around 
 the parent mass, some and probably all rotating in the same 
 direction. Some of the planets rotated so rapidly that bodies 
 were thrown off from them and thus the satellites were formed. 
 This theory cannot be demonstrated but it harmonizes with most 
 of the facts known of the solar system. 
 
 The nebulae as burning gas, the sun and stars as molten 
 masses surrounded by intensely heated gases, Jupiter and Sat- 
 urn as molten bodies which have cooled below the point of incan- 
 descence, the Earth and Mars as bodies, over which at least a 
 solid crust has been formed, are each supposed to represent dif- 
 ferent stages through which the earth has passed in developing 
 from the primal fire mist, to its present condition. The moon 
 probably represents a farther stage toward which the earth is 
 approaching. 
 
CHAPTER XLII. 
 
 MINERALS AND ROCKS. 
 
 THE greater part of geological work pertains to rocks. In 
 geology every thing that helps to make up the crust of the earth 
 is rock, whether it be hard and enduring, like the limestone and 
 granite, or loose earthy materials like sand, clay or dust. Rocks 
 are sometimes simple chemical compounds, but generally they 
 are composed of a mixture of several distinct compounds called 
 minerals. There are a great many different kinds of minerals ; all 
 of them are interesting and many are valuable, but only a few 
 are of much importance as rock-forming materials. 
 
 The most abundant and common of the minerals is silica, 
 composed of oxygen and silicon. It crystallizes in six-sided 
 prisms, appearing something like glass. It is hard enough to 
 scratch glass, and this quality distinguishes it from all other 
 minerals having a similar appearance. Silica is sometimes 
 called quartz. It is the chief ingredient of sand, gravel and 
 sandstone. 
 
 The Feldspars, often associated with silica, are a group of in- 
 teresting and abundant minerals. Orthoclase, the most common 
 feldspar, is a silicate of aluminium and potassium. It occurs in 
 all colors from white to a fleshy-red. It sometimes has the ap- 
 pearance of glass, but is readily distinguished from quartz by 
 its inferior hardness, as it will not scratch glass, and may be 
 scratched with a good knife. It crystallizes in rhombic prisms, 
 and splits easily and smoothly in two directions, but it some- 
 times has a massive or granular structure showing no signs of 
 crystallization. Moonstone and sunstone, often used as jewels, 
 are varieties of this feldspar. Sanadine, a glassy variety, is 
 common in many lavas. 
 
 Albite, another species of feldspar, is a silicate of aluminium 
 (320) 
 
LESSONS IN GEOLOGY. 321 
 
 and sodium, while Anorthite is a silicate of aluminium and cal- 
 cium. Several other feldspars are thought to be only mixtures 
 of the ones just mentioned. In general they are very much like 
 orthoclase in appearance, but on a fresh surface their crystals seem 
 like strips of glass on which fine lines may often be found that 
 do not occur in the orthoclase. These are usually called triclinic 
 feldspars. Broken down weathered feldspar is the basis of clays, 
 shales and slate rocks. 
 
 Mica is a silicate of aluminium and potassium or magnesium, 
 with iron and sometimes a little lime. It splits easily into thin 
 flexible leaves, which are nearly transparent, and are frequently 
 used in windows. It often occurs with silica and feldspar as an 
 ingredient of some kinds of granite rock. Sometimes from their 
 glistening appearance .scales of mica are mistaken for gold. 
 
 Hornblende and Pyroxene are silicates of magnesium and cal- 
 cium, containing oxides of iron and manganese. Some varieties 
 contain in addition a little aluminium. They vary in color from 
 white to black, but in general they are greenish-black or black. 
 In general the darker varieties are the ones containing alumin- 
 ium. The fibrous mineral asbestos is a variety of hornblende. 
 The darker varieties are more common, and are easily distin- 
 guished from mica by their hardness and crystalline form, and 
 are not liable to be mistaken for any other mineral. These are 
 common minerals in basalt and lava, in trap and syenite, and 
 sometimes the light-colored varieties occur in limestone. 
 
 Talc is a hydrated silicate of magnesium with a little oxide of 
 iron. It is the softest mineral known, separating easily into 
 thin scales. It has a light green color, a pearly luster and a 
 greasy feel. It is best known as steatite or soapstone. 
 
 Serpentine is much like talc in composition and qualities but 
 is a little harder and has a rich greenish color. 
 
 Chlorite contains more aluminium than talc and is harder 
 than that mineral. It has an olive green color and often a gran- 
 ular structure. 
 
 Calcite, carbonate of calcium, is a mineral that crystallizes in 
 several different forms. When pure it has a pearly luster and is 
 L. s. 21 
 
322 PRACTICAL LESSONS IN SCIENCE. 
 
 nearly transparent. It is the basis of the different kinds of lime- 
 stone and marble, appearing in a great variety of forms. It is 
 easily scratched with a knife, and effervesces vigorously when 
 treated with any acid, even strong vinegar will decompose it. 
 
 Dolomite is a carbonate of calcium and magnesium. It is per- 
 haps a little harder than limestone, and is not as easily affected 
 by acids, but it is often difficult to distinguish between them. 
 
 Gypsum, the hydrated sulphate of calcium, often forms ex- 
 tensive beds of rock. It is easily cut with a knife, is white, some- 
 times variegated, in color and when burned to drive off water of 
 crystallization becomes plaster of Paris. 
 
 Pyrite, the disulphide of iron, is of a pale brassy yellow color, 
 crystallizing in cubes. It is very common in the neighborhood 
 of coal banks, and is the source of the sulphur in the coal. From 
 its color it is often mistaken for gold. Pyrite and the sulphides 
 of copper, lead, zinc, and other metals are often associated with 
 gold, and are abundant minerals. 
 
 Graphite, nearly pure carbon and the various ores of iron are 
 widely disseminated minerals of value and interest. 
 
 Chloride of sodium, common salt; corundum, nearly pure ox- 
 ide of aluminium; apatite, phosphate of lime, etc.; leucite, abun- 
 dant in some lavas ; olivine, a silicate of magnesium and iron, are 
 all important minerals. 
 
 The minerals mentioned, either singly or variously combined, 
 make up the greater part of the rocks which compose the earth's 
 crust. 
 
 Granite is a crystalline rock composed of thoroughly mixed 
 quartz, orthoclase feldspar and mica, the particles being of near- 
 ly uniform size. It is usually hard, light-colored and can gener- 
 ally be identified by the scales of mica. Sometimes the rock is 
 very fine grained, containing large crystals of feldspar scattered 
 through the mass when it is called porphyritic granite. 
 
 Quartz Felsite or Felsite. This rock consists of a fine granular 
 or homogeneous ground mass, through which are disseminated 
 crystals of quartz, feldspar, mica or hornblende. This rock va- 
 ries widely in structure without much modification in composi- 
 
LESSONS IN GEOLOGY. 323 
 
 tion. Felsite consists of the ground mass without the crystals, 
 forming a tough compact rock. 
 
 Liparite has a similar composition but shows more evidence 
 of a former molten or glassy state in its structure. 
 
 Syenite, a rock often associated with granite, is composed of 
 orthoclase mixed with hornblende and occasionally some quartz 
 and mica, and sometimes triclinic feldspar occurs. There is sel- 
 dom any difficulty in identifying this rock after one learns to 
 recognize feldspar and hornblende. 
 
 Trachyte is a volcanic rock composed largely of sanidine, a 
 variety of orthoclase, with some triclinic feldspar, and usually 
 hornblende, mica and iron, and sometimes with pyroxene, apa- 
 tite, etc. It has much the same composition as syenite but has 
 not become fully crystallized. 
 
 Obsidian is a volcanic glass, varying considerably in its com- 
 position, but in general it is rather like trachyte. It shows no 
 trace of crystallization and may represent the first stage in the 
 development of crystalline rocks, trachyte and syenite represent- 
 ing others. 
 
 Diorite, or Green Stone, is composed of triclinic feldspar and 
 hornblende usually with apatite and iron. 
 
 Basalt is a dark-colored volcanic rock, composed of triclinic 
 feldspar, pyroxene, olivine, iron and apatite. It often has a 
 ground mass of glass through which crystals are scattered. 
 
 Schists are crystalline rocks of varied composition in which 
 the materials are arranged in nearly parallel layers. Schist rocks 
 may be composed of but one mineral, but they usually consist of 
 two or more minerals in alternate layers or mingled in the same 
 layer. They are usually named from the principal ingredient, as, 
 mica schist, chlorite schist, and talcose schist, usually containing 
 quartz, feldspar and other minerals besides the one naming the 
 rock. 
 
 Gniess. This rock is composed of quartz, feldspar and mica 
 but the proportions and the arrangements are different from 
 those in granite. It is schistose in structure but coarser than 
 schist. There is a larger proportion of mica than in granite. It 
 
324 PRACTICAL LESSONS IN SCIENCE. 
 
 varies widely in appearance but is usually recognized without 
 difficulty. 
 
 Under the action of atmospheric influences the rocks are gradu- 
 ally pulverized, reduced to boulders, pebbles, gravel, sand and 
 clay. We may find all kinds of rocks represented among the 
 boulders and pebbles, while the gravel and sand are largely of 
 quartz. The clay, dust, etc., making up the soil are from the 
 feldspar, mica and other easily disintegrated materials. Much 
 of the clay, sand and dust are eventually spread out over the sea 
 bed as sediments. Great quantities of rocks are broken down 
 and pulverized by the action of the waves along the sea coast 
 and added to the sediments of the sea. 
 
 Pebbles or gravel, and sometimes boulders, may be cemented 
 together into conglomerate rock, and it is called quartz, lime- 
 stone or granite conglomerate, according to the nature of the 
 material. Conglomerates differ also in the nature of the cement 
 or paste, which may be of quartz, lime, clay or even iron. 
 
 The sand may be cemented into sandstone, which may vary 
 much as the conglomerate varies. The typical sandstone, how- 
 ever, is composed of quartz grains united by a paste of quartz. 
 
 The clays are compacted into shales. They are easily cut with 
 a knife, break into irregular blocks and vary greatly in purity. 
 
 The finer sands and coarser clays mingle in varying propor- 
 tions so as to form clayey sandstones or sandy shales. 
 
 In deeper water, away from the shore, calcareous sediments 
 are formed from materials furnished mainly by different forms of 
 life; these at length become limestone rocks. Peat and soft coal 
 are sediments. 
 
 The different kinds of sandstone, clay and limestone rocks are 
 formed from sediments, and are known as sedimentary rocks. 
 
 Metamorphic rocks are sedimentary rocks that have been 
 changed by heat, pressure and other agencies into a crystalline 
 form. The sandstones become quartzites ; the mixed sands and 
 clays become gneiss, granites, etc. Limestone becomes crystal- 
 line limestone and marble, and the clays and shales become slate, 
 which is but slightly crystalline. Peat and soft coal become 
 
LESSONS IN GEOLOGY. 325 
 
 bituminous and anthracite. These rocks were formed from sedi- 
 ments that were deposited in layers or strata, and the rocks are 
 often called stratified rocks. 
 
 Obsidian, propylite, trachyte, basalt and other volcanic prod- 
 ucts are called igneous rocks, and are unstratified. Doubtless 
 many of the granites and gneisses had their origin in trachyte or 
 basalt, and are strictly igneous rocks. 
 
 Granite, syenite and other crystalline rocks are the last terms 
 in the series beginning with sediments, as well as in the series be- 
 ginning with obsidian or basalt. 
 
 All rocks are divided by cracks or joints into irregular blocks 
 of various sizes and shapes. In stratified rocks the bedding 
 planes bound the blocks on two sides, and divisions nearly per- 
 pendicular to these and to each other bound the other sides. 
 The last are called joints. In the case of igneous rocks the 
 blocks are bounded on all sides by joints. These blocks vary in 
 form in different rocks ; in limestones they are regular and cu- 
 bical; in basalt regular and columnar; in slate, small and indis- 
 tinct ; in sandstone, large and irregular, etc. The cause of joints 
 is probably the shrinkage of the strata in consolidating frojn 
 sediments. Similar joints or cracks may be seen in the dried mud 
 of ponds that have been drained of water. Joints are confined 
 to individual strata, but fissures are fractures passing through 
 several or many strata, probably caused by movements of the 
 earth's crust. Fissures 30 to 50 feet wide and many miles in 
 length are known. Sometimes the rock on one side of a fissure 
 is forced upward so as to change the relations of the strata, 
 causing what is called a fault. In some cases the displacement is 
 as great as 15,000 or 20,000 feet. Fissures in many cases have 
 been filled with some rock-forming material, when they are known 
 as veins. Much of the gold and silver of the world came origi- 
 nally from veins. In some cases these fissures were filled by an 
 injection of igneous material from below; others are filled by mat- 
 ters deposited from water circulating through them. Joints and 
 fissures are geologically interesting, as they facilitate erosion, 
 determine the course of rivers and the location of valleys. 
 
CHAPTER XLIII. 
 
 EARTHQUAKES AND VOLCANOES. 
 
 IN the geological history of the earth, two sets of forces have 
 been active. Some which may be called plutonic, have been mak- 
 ing the surface of the earth uneven, through them the conti- 
 nents had their origin and the mountains were formed. The 
 others, which are eroding forces, mostly atmospheric, have been 
 equally busy in cutting down the elevations and filling up the 
 depressions, their action tending toward uniformity as the others 
 toward variety. 
 
 The internal condition of the earth is not well understood. As 
 we explore the crust by mines and wells, we find that heat in- 
 creases rapidly with the depth below the surface, so that at a 
 depth of thirty or forty miles, the heat must be intense enough 
 to melt any known substance, if it were only under atmospheric 
 pressure, but under the enormous pressures of such regions, sub- 
 stances would doubtless behave as solids, notwithstanding the 
 great heat. 
 
 In relation to other celestial bodies the earth behaves as a 
 solid, rigid as glass, so that while the interior of the earth is in- 
 tensely hot, it is probably not a liquid. 
 
 In general the irregularities of the surface of the earth are sup- 
 posed to be due to unequal contraction, the interior contracting 
 more rapidly than the crust. This results in enormous horizon- 
 tal pressures under which, along lines of weakness, the crust swells 
 up into wrinkles, folds or corrugations. The lines of weakness are 
 accounted for by supposing an irregular distribution of matter, 
 or that there was more radial contraction, or settling over the 
 area now occupied by the oceans. This idea is strengthened by 
 the fact that the matter underlying the oceans is more dense than 
 that underlying the continents. Whatever may have been the 
 (326) 
 
LESSONS IN GEOLOGY. 327 
 
 origin, when the irregularity was initiated, the pressures due to 
 unequal contraction would continue to intensify them. 
 
 Sometimes under this pressure the crust yields suddenly, is 
 fractured for a great distance, the rocks on one side of the frac- 
 ture being elevated or depressed with reference to the other. Thus 
 an earthquake is caused, a fissure vein is opened and a fault is 
 formed. The fault may be only a few feet at first, but it may in- 
 crease to hundreds of feet as it slowly yields to the continued 
 pressure. Other forces may cause earthquakes, as explosions of 
 superheated water or of gas, possibly in connection with volcanic 
 eruptions. These shocks cause vibrations of the crust, which 
 are often transmitted for immense distances. These waves may 
 be severe enough to overthrow buildings, produce avalanches 
 and land slips, sometimes changing springs and streams of water. 
 Again they cause great waves of the sea, which rush upon the 
 shore with great violence; in fact, the greatest destruction of life 
 by earthquakes has been from the ocean waves which they caused. 
 A wave that destroyed Lisbon in 1755 was nearly sixty feet 
 high. In 1868 an earthquake devastated the coast of Peru. 
 And less than half an hour after the earth wave came several 
 water waves from 50 to 60 feet high, adding greatly to the 
 destruction already begun. These waves reached the Sandwich 
 Islands, 5,580 miles, in 12 hours, and Japan, 10,000 miles dis- 
 tant, the next day. Such waves have been known to move at 
 the rate of 450 miles per hour. An earthquake which occurred 
 near Naples in 1857, by careful examination was shown to have 
 originated in a fissure about nine miles long, through about 
 three miles of rock, the center being about six miles below the 
 surface. The velocity of the earth wave in this case was between 
 nine and ten miles per minute. 
 
 No portion of the earth is free from earthquakes, but they are 
 more common in volcanic regions. 
 
 Again, a fissure is formed as noted above, and from it is poured 
 out vast quantities of molten matter or lava. Such fissure erup- 
 tions were frequent during Tertiary times in the Rocky Mountain 
 region and other localities. At the present time a volcano ia 
 
328 PRACTICAL LESSONS IN SCIENCE. 
 
 usually an opening somewhere on the line of such a fissure, around 
 which a somewhat conical hill has been built up from the ma- 
 terials thrown out. 
 
 In a volcanic eruption gases and vapors are the first materials 
 to appear; they continue during the eruption of other material, 
 and often for centuries after all other evidence of subterranean 
 action has ceased. Aqueous vapor is probably most abundant; 
 it is sometimes given off in such quantities as to result in heavy 
 rainfall. Among the gases the most abundant are hydrochloric 
 acid, sulphuretted hydrogen, sulphurous acid, carbon dioxide, 
 free hydrogen and others. The typical volcanic material is mol- 
 ten rock called lava, which includes material varying considerably 
 in composition and specific gravity. The lighter varieties contain 
 a larger per cent, of silica, and are acid lavas, as trachyte and 
 pumice. Others are basic lavas containing less silica and more 
 iron and pyroxene, as basalt and leudte lava. Others again are 
 intermediate between these groups. Lavas also vary in structure ; 
 some are wholly crystalline, as some liparites ; some show a glassy 
 or stony ground mass, with imbedded crystals, which is, perhaps, 
 the most common structure. Again, others are pure volcanic 
 glass, as obsidian. Then some, as basalt, are dense and compact, 
 while others, as pumice, are vesicular. 
 
 Great quantities, a fine ash-like dust and coarser particles, 
 called sand, usually accompany eruptions. The dust and sand 
 are lava pulverized by escaping vapors and gases. 
 
 The quantity of dust formed and thrown out is sometimes 
 enormous. Dust from volcanoes in Iceland has fallen abundantly 
 in Sweden and Holland, and fell in such quantity at a distance of 
 600 miles as to destroy crops. 
 
 Large blocks of lava are frequently ejected. Water is some- 
 times a volcanic product, which, mingling with the dust and 
 sand, forms a mud stream, and mud itself is a product of some 
 volcanoes. A good idea of the flow of lava, and of the peculiar 
 forms it often assumes, may be obtained by watching the flow of 
 slag at a blast furnace. 
 
 Lavas differ in their fluidity ; those of Kilauea in Hawaii, are 
 
LESSONS IN GEOLOGY. 329 
 
 very liquid, while those of Vesuvius are viscous. The fluidity 
 modifies the flow of the lava. That from Kilauea flows like mol- 
 ten iron; at first white hot, with a temperature of more than 
 2,000 F., it soon becomes red, growing darker till it assumes a 
 black, cinder-like appearance. The viscous lavas of Vesuvius 
 break in rough brown slags, which grind and grate over each 
 other with a metallic sound. Occasionally the lava flows over the 
 edge of the crater, but it often breaks through the side of the 
 mountain, sometimes 2,000 or 3,000 feet below the surface of the 
 lava in the crater, forming fountains of molten rock. Lava that 
 is completely fused when cooled quickly forms volcanic glass 
 obsidian; when cooled slowly crystals are formed and stony lavas 
 result. In most lavas the crystallization is quite complete before 
 the mass becomes solid. 
 
 A volcanic cone is, to a great extent, the work of the volcano, 
 and its composition and form depend on the materials thrown 
 out by eruptions. If the product is fluid lava, as in the case of the 
 Hawaiian volcanoes, the cone will be broad and flat. If the lava 
 is viscid the cone will be steeper and narrower. If the product is 
 chiefly ashes, scoriae and lava, the cone will be steep. The cones 
 formed by successive eruptions have somewhat the structure of 
 an exogenous tree. Sometimes the cone has been ruptured by 
 radiating fissures, and these filled with lava dikes. Secondary 
 cones are frequently formed inside the craters or on the sides of 
 the main cone; there are some 200 such cones on the slopes of 
 Mount Etna. 
 
 Volcanoes are mostly located in the mountain regions along 
 the shores of the Pacific ocean, and many of the islands of that 
 ocean are volcanic. Some are located about the Mediterranean 
 Sea, in the West India islands and elsewhere. 
 
 The causes of volcanic action are not understood, but many 
 theories have been advanced to account for the phenomena. It 
 is generally agreed that the expansive force of steam is the chief 
 force of eruption, but how the water reaches the molten rock is 
 not explained. The source of the volcanic product and of the 
 volcanic energy cannot be deep, as water could scarcely penetrate 
 
330 PRACTICAL LESSONS IN SCIENCE. 
 
 to a depth of more than six or eight miles. Some think the crush- 
 ing of the rocks under the great horizontal pressure develops 
 heat enough to fuse the rocks and produce eruption. Others 
 ascribe the molten matter to chemical action between the unoxi- 
 dized interior and oxidizing agents, as air and water, from the 
 crust ; and again the action must be within reach of surface water. 
 The source must be local, as volcanoes near each other yield dif- 
 ferent kinds of material, and sometimes with lava standing in 
 their craters at widely different levels. And it frequently happens 
 that the same volcano yields different material at different times. 
 We know many things about the effects of earthquakes and vol- 
 canoes but very little about their causes. 
 
 Rocks and lava cool slowly, thick masses retaining high tem- 
 perature for many years. It is said that cigars and sticks might 
 be lighted at fissures in a lava stream from Jorullo, Mexico, 21 
 years after the out-flow. Water percolating through such ma- 
 terial appears again as hot springs, and often with dissolved 
 gases and minerals, as, sulphur springs, iron springs, etc., and 
 doubtless the geysers of Iceland and Yellowstone Park are in 
 a sense secondary volcanic phenomena. 
 
 A geyser appears to be a spring or pool of hot water, but when 
 its depth is measured it is found to be more like a funnel-shaped 
 well of hot water. At somewhat regular intervals eruptions of 
 water and steam occur. The phenomena of an eruption are about 
 as follows : Sounds like cannonading are heard below and bubbles 
 rise through the water, then the water rises a little, overflowing 
 the basin, and immediately afterward the water is thrown out as 
 from a fountain, followed by a great quantity of steam. It is 
 explained by supposing that water toward the bottom of the 
 tube is con verted into steam which throws out the water above it. 
 
CHAPTER XLIV. 
 
 TEMPERATURE, WINDS, WAVES, TIDES AND CURRENTS. 
 
 THE forces active in early geological phenomena, had their 
 origin for the most part in the earth itself. But as the outer 
 portions cooled the initial heat became less effective, and the heat 
 of the sun, causing most of the phenomena of climate, became 
 an efficient geological agent, especially during the later stages of 
 the earth's history. 
 
 The earth revolves around the sun and rotates on its axis. If 
 the axis was perpendicular to the plane of revolution there would 
 be no change in the distribution of heat over the surface of the 
 earth during the year; there would be no zones; no changes of 
 seasons. But the axis is declined from a perpendicular to the 
 plane of revolution about 23 1-2, and to this fact we owe the 
 zones, the long cold winters in the polar regions, the winter and 
 summer of the temperate zones, and the wet season and dry sea>- 
 son of the tropics. 
 
 The crust of the earth is very uneven. The depressions filled 
 with water we call the sea; those portions above the sea we call 
 the land. The sea is divided into oceans and the land is divided 
 into continents, and these into grand divisions. 
 
 Water is not a good absorber nor a good radiator of heat, 
 hence does not gain heat rapidly during the day or the summer, 
 and does not lose heat rapidly during the night or the winter, 
 maintaining quite a uniform temperature during the year. The 
 rough, dense land is a much better absorber and radiator than 
 the water, so that it gets much hotter during the day and sum- 
 mer, and much colder during the night and winter than the water. 
 The water, with its uniform temperature, tends to equalize the 
 varying temperatures of the land, so that climates along the sea- 
 shore are markedly different from inland climates. For this rea- 
 
 (331) 
 
332 PRACTICAL LESSONS IN SCIENCE. 
 
 son the relative extent of land and water areas and the relative 
 positions of the bodies of land and water are important climatic 
 questions. 
 
 At first it seems as if there might have been more land ; but 
 on examination we find that only a portion of the present land 
 surface can get water enough to be productive of plant or animal 
 life. The land extends in two masses almost from pole to pole, 
 and with such general form and irregular outline that very large 
 portions come under the equalizing influence of the sea. 
 
 The land varies in elevation. There are low plains, plateaus 
 and mountains. The important facts to be learned about moun- 
 tains are their location, elevation and direction of extent ; and in 
 regard to plateaus their location, elevation and extent should be 
 known. In general the mountain systems of the Western conti- 
 nent trend north and south, and so do those of South Africa and 
 Australia, while in Europe and Asia the trend is more nearly 
 east and west. The greater mountain systems border closely on 
 the deeper oceans, as the Pacific and Indian. 
 
 The air is an invisible gas surrounding the earth, extending 
 upward some 400 or 500 miles. It is composed mainly of oxygen 
 and nitrogen, with varying quantities of water vapor, carbon 
 dioxide, ammonia, nitric acid, etc. Variation in the temperature 
 of the air is the principal cause of winds, rainfall, dew, frost and 
 other phenomena, which together make up what we call climate, 
 and which is generally discussed under the heads of temperature, 
 winds and rainfall. 
 
 The temperature of the air depends mainly on the temperature 
 of the earth's surface. The heat from the sun passes through the 
 air and warms the earth, and the earth in turn warms the air 
 mainly by convection, partly by radiation and reflection. It is 
 estimated that the air absorbs more than one-third of the heat 
 sent from the sun to the earth, the greater part being taken up 
 by the water-vapor and carbon dioxide, as pure air is nearly dia- 
 thermic. The air absorbs even a larger per cent, of the heat radi- 
 ated from the earth and prevents the surface from cooling as 
 rapidly as it would if the air were diathermic. 
 
LESSONS IN GEOLOGY. 333 
 
 Thus the air serves the surface of the earth as a sun-shade by 
 day and as a blanket by night, tending to equalize its own tem- 
 perature. This effect is greatly increased by the presence of 
 clouds in the air. If it were not for this property of the air it 
 would be so hot in summer, and cold in winter as to destroy all 
 such life as exists on the earth at present. 
 
 As the surface of the earth is the main source of heat for the 
 air, the temperature of the air must decrease from the general 
 surface upward. Mountains and high plateaus usually have a 
 lower mean temperature than the general surface of the earth in 
 the same latitude. 
 
 The difference in temperature between the tropical and polar 
 regions is the chief cause of different pressures in the air, and the 
 unequal pressures cause currents of air or winds. 
 
 Along the equator there is a belt of light pressure ; at about 
 32 north and 25 south there are belts of heavier pressure, and 
 at about 64 north and 70 south there are areas of light pres- 
 sure. The movement of the air is from the heavy pressure toward 
 the light pressure. Currents blow from the belts of light pressure 
 at 32 north and 25 south toward the equator; these form an 
 upward current, which, after rising some distance, spreads out 
 toward the light pressures north and south. 
 
 Owing to the rotation of the earth these currents do not flow 
 directly north and south, but those going toward the equator 
 from 32 north, go southwest as northeast winds, and those 
 from 25 south go northwest as southeast winds. And those 
 toward the north pole go northeasterly as southwest winds; 
 and those toward the south pole, go southeast as northwest 
 winds. In general the winds of the tropics are easterly winds 
 and those of the temperate zones westerly winds. t 
 
 These winds represent the general movements of the air subject 
 to many local exceptions, occurring in each grand division, es- 
 pecially in the coast regions. 
 
 The air always contains water vapor, the amount depending 
 on the temperature of the air and on its distance from large bod- 
 ies of water. The air does not hold the water vapor as the 
 
384 PRACTICAL LESSONS IN SCIENCE. 
 
 sponge holds water, but they are two gases mingled together, 
 each independent and sustained by the same force of heat. When 
 there is mingled with the air as much water vapor as the tem- 
 perature can sustain, the air is said to be saturated with mois- 
 ture, while if it might contain much more it is called dry air. As 
 the temperature of moist air is lowered the water-vapor at length 
 begins to condense into dew, fog or cloud. 
 
 Air in tropical regions, near the sea, contains the most water- 
 vapor. Nature's method of lowering the temperature of the air 
 is by sending it upward or toward the poles. The winds from the 
 equatorial regions are relatively warm and moist winds, and in 
 general are rain-bearing winds. As winds rise over mountain 
 chains their temperature is lowered and the water vapor falls as 
 rain, as they move toward the poles the same thing occurs. The 
 up ward current from the tropical regions rises so high that mois- 
 ture is condensed, forming the copious rains of those regions. 
 
 In South America the easterly winds of the torrid region com- 
 ing from the ocean, leave some moisture on the low mountains 
 near the eastern coast, but the greater part falls as they rise 
 over the giant Andes, giving that region an exceptionally heavy 
 rainfall and one of the most interesting river systems in the 
 world. 
 
 In North America the westerly winds furnish a heavy rainfall 
 for the region west of the mountains and north of San Francisco. 
 And southwesterly winds that come over the regions of Arizona, 
 as upper currents, are the main source of rainfall in the upper 
 Mississippi valley, and westerly winds give Europe an abundant 
 rainfall. 
 
 The eastern plateaus of Asia receive but little moisture on ac- 
 count of their high mountain borders ; their surfaces are barren, 
 and the air is nearly diathermic. During summer they become 
 excessively hot, and the air over them so light that exceptional 
 winds flow in from the east and south, which in rising over the 
 mountains lose their moisture as heavy rainfalls, forming an ex- 
 tensive system of great rivers. 
 
 Africa furnishes a region of exceptional rainfall. The regular 
 
LESSONS IN GEOLOGY. 335 
 
 easterly winds from the Indian Ocean furnish abundance of mois- 
 ture, but during summer the central region becomes so hot 
 and the air so light that exceptional winds from the Atlantic 
 ocean flow into that portion of Africa. These winds both leave 
 abundant moisture on the slopes of the plateau, but the greater 
 part falls after the upward current is formed , condensed by cold 
 from elevation. 
 
 Thus the winds carry the water from the sea to the land, where 
 a portion becomes permanent in the rocks and soil, a portion 
 evaporates and a portion forms springs, brooks and rivers. 
 These inland waters are very efficient geological agents. 
 
 The sea, with waves, tides and currents, is also an important 
 force in geological work. 
 
 Waves are caused by the wind and are common on the sea every- 
 where varying in elevation with the force of the wind. The wave 
 has a forward movement, but the water only moves upward and 
 downward. When waves advancing toward the shore reach shal- 
 low water, the motion is retarded at the bottom by friction, and 
 the top moving on without support breaks over on the shore, thus 
 forming breakers. During storms waves break on the shore with 
 great force. 
 
 Tides are waves caused by the attraction of the sun and moon. 
 There are four tidal waves, two of equal size on opposite sides of 
 the earth caused by the moon, and two much smaller caused by 
 the sun. As the moon revolves around the earth once in about 
 27 days, the waves caused by the moon make the circuit of the 
 earth in the same time. Twice during this circuit the moon waves 
 coincide with the sun waves, making higher or spring tides, and 
 twice the lower part of one coincides with the higher part of the 
 other, and a lower or neap tide is formed. As the earth rotates 
 in the same direction that the moon revolves, a given place 
 passes through the crest of both moon waves once in 24 hours 
 and 52 minutes. In mid ocean the tide does not rise more than 
 three feet, but along some coasts and in narrow bays they rise 
 much higher. At the head of the Persian Gulf the tide rises 
 36 feet; at the Bay of St. Michael, France, 45 feet. In shoal 
 
336 PRACTICAL LESSONS IN SCIENCE. 
 
 water and in narrow bodies of water these waves make strong to 
 and fro currents. 
 
 Ocean currents are as common as the waves, but are not quite 
 as manifest or as easily understood. They are caused mainly by 
 the winds and by the tides. Unequal heating and evaporation 
 would seem to be efficient causes of currents, but a little in- 
 vestigation shows that the effect of one tends to neutralize the 
 effect of the other. The rotation of the earth and the form and 
 arrangement of the land masses help to determine the direction 
 of the currents. In general the currents have the same direction 
 as the winds. The equatorial currents flow westerly with the 
 easterly winds, and the Japan current and the Gulf stream flow 
 northeasterly with the southwest winds, etc. Beside the surface 
 currents there are strong under currents toward the equator. 
 Thus the heat of the sun, the attraction of the earth, causes 
 winds and streams of water, waves and currents in the ocean, 
 and the attraction of the sun and moon cause the tides, all 
 efficient agents active in geological phenomena. 
 
CHAPTEB XLV. 
 
 GEOLOGICAL ACTION OF AIR AND WATER. 
 
 AIR and water; winds, clouds and rain; frost, snow and ice; 
 springs, creeks and rivers ; waves, tides and currents, are the most 
 common objects and phenomena of the material world. They are 
 so common and familiar that most people fail to realize that they 
 are important, efficient, essential agents in nearly all geological 
 phenomena. 
 
 Quiet, dry air of uniform temperature is not an efficient agent, 
 but changes of temperature, which may be mentioned here, are 
 of great importance. The daily variation of temperature in 
 some dry regions is very great. On the southwestern plateaus of 
 North America the temperature varies from 90 F. at mid-day to 
 20 F. during the night, and the same is true of wide regions in 
 Africa and Asia, a variation of 90 F. between day and night be- 
 ing by no means uncommon. The expansion and contraction 
 due to such great and rapid change of temperature soon causes 
 rocks to crack and flake off and rapidly disintegrate into sand. 
 Dr. Livingstone, while in Africa, found that rocks heated up to 
 130 F. during the day, cooled so rapidly during the night that 
 they cracked and split, throwing off angular fragments of all 
 sizes up to those of a hundred pounds weight. In the dry regions 
 the rocks are broken up in this way almost as rapidly as in 
 regions where frost is the active agent. 
 
 The winds carry away the dust and sand formed, and the sur- 
 face of the region is gradually lowered by this dry erosion. The 
 sand carried in this way by the wind acts as a piece of sand- 
 paper, polishing and cutting down the rocks. These natural sand 
 blasts sometimes cut into the base of a cliff, and when under- 
 mined blocks fall, attack them in the same way, continuing the 
 
 L.S.-22 (337) 
 
338 PRACTICAL LESSONS IN SCIENCE. 
 
 process till the cliff is reduced to sand and carried away by the 
 wind. 
 
 The combined action of wide and sudden variation of tem- 
 perature and the wind, has removed a thickness of more than ten 
 thousand feet of strata, from an area of thousands of square 
 miles, of the plateau through which the Colorado river flows. 
 
 The sand and dust eroded by the wind from one locality is de- 
 posited in another. The dust is widely disseminated, and settling 
 quietly is constantly adding to the growth of soil. In this way 
 dust from the high plateaus of Asia has built up a formation of 
 loess from 1,000 to 2,000 feet thick over regions between the 
 plateaus and the ocean. The loess is unstratified, fine yellow cal- 
 careous clay, containing abundance of land shells and remains of 
 vegetation. Other loess seems to have been formed with the aid 
 of water, and is called lake loess or river loess. It is said in some 
 places in Asia dust enough falls to serve as a fertilizer for the soil. 
 This dust, which pervades the air everywhere, is of interest in the 
 matter of rain-fall, for it seems that water-vapor condenses only 
 on free surfaces, and the cloud and mist is formed by the conden- 
 sation of moisture on the particles of cosmic dust. 
 
 The sand may be carried into rivers or lakes or into the sea, or 
 may form sand hills or dunes on the margin of the dessicated 
 region, as in northern Africa, Arabia and western United States. 
 But the most interesting sand dunes are those formed along the 
 margin of large bodies of water. When the prevailing winds are 
 from the water toward the land they carry sand from the beach 
 over the land till, meeting some obstruction, a dune is formed. It 
 may be ridge-like or somewhat conical in form; the seaward 
 slope is long and gentle, the other as steep as loose sand will 
 stand. 
 
 The wind not only carries or rolls sand from the beach, up the 
 gentle slope to the crest, but is continually carrying sand from 
 the slope itself to the crest and letting it fall on the landward 
 side, so that the dune travels inland, destroy ing forests and crops, 
 covering buildings, filling ponds, damming up streams, etc. In 
 time another dune forms between the first and the beach, which 
 
LESSONS IN GEOLOGY. 339 
 
 follows the leader as waves follow each other. Where there is 
 abundance of moisture not much sand can be moved during the 
 year, and vegetation soon begins to grow on the dunes, and may 
 in time so cover them as to stop the action of the wind and the 
 dune becomes permanent. Sometimes these dunes interfere with 
 drainage forming lakes, ponds, and marshes, as alongthe eastern 
 shore of Lake Michigan and western coast of France. Dunes 
 sometimes serve as barriers against the sea and sometimes as 
 wind brakes. This action of the wind in moving sand can be 
 studied almost anywhere on windy days, even in the street or 
 schoolhouse yard. 
 
 Of the rain and snow that falls on the earth some is soon 
 evaporated, some is taken up by the soil, some by plants, some 
 sinks into the ground to reappear as springs, and some from 
 25 per cent, to 30 per cent. flows into the ponds, brooks and riv- 
 ers. Water acts on the soils and rocks chemically and mechanic- 
 ally. Water, when it reaches the soil, contains a little air and 
 carbon dioxide, dust, living germs, etc., so that one effect is to 
 fertilize the soil as well as to moisten it. Pure water usually pro- 
 tects the rock it covers, but water in conjunction with air is an 
 active oxidizing agent. 
 
 A thin pellicle of the oxide is formed on the surface, which if not 
 washed away thickens from the inside until a thick crust covers 
 the rock. The oxidation of iron and iron compounds is the most 
 interesting and important. Sulphide of iron is widely dissemi- 
 nated through nearly all kinds of rock, and under the influence of 
 air and water both the sulphur and iron are oxidized, sometimes 
 forming ferrous sulphate; and sometimes other bases take the 
 acid, leaving the iron free to become the ferric oxide. Thus 
 many kinds of rocks are entirely broken up, some parts passing 
 away in solution, allowing the whole to disintegrate rapidly. 
 Carbonate of iron is also acted on in much the same way, the iron 
 changing to the ferric oxide, allowing the rocks containing it to 
 decay rapidly. 
 
 Water dissolves salt, sodium chloride, without aid, but in 
 most cases of solution water is aided by carbon dioxide or 
 
340 PRACTICAL LESSONS IN SCIENCE. 
 
 some other re-agent. In this way limestones, and feldspathic 
 rocks, carbonates and silicates of calcium, potassium, and sodium , 
 are disintegrated, the calcium and alkalies, becoming carbonates, 
 are removed by solution and the rocks crumble down into sand 
 and clay. 
 
 In this connection may be mentioned the action of freezing 
 water. In northern latitudes the soils and rocks become satu- 
 rated with moisture during the autumn. During winter the water 
 in all the cracks, joints and interstices freezes, and by its expan- 
 sion increases all these spaces, and so on from year to year till 
 as the ice melts in the spring some of the outer particles becom- 
 ing loosened are washed away ; thus soils and rocks are broken 
 up and pulverized in some cases with great rapidity. The work 
 of water is somewhat increased by the mechanical action of fall- 
 ing rain. 
 
 The general effect of air and water aided by heat, frost, grav- 
 ity, and vegetable acids on rocks is called weathering. This ac- 
 tion varies with different rocks and in different climates ; by this 
 process nature transforms rocks into soil and carves out many 
 strange and interesting forms on the rocky surfaces of the earth. 
 
 Soil is formed in various ways, but on level or gently sloping 
 surfaces, much soil is formed by the decomposition of rock in situ 
 by the process of weathering. Perhaps most of the work is done 
 by carbonated water, but other agencies have more or less effect. 
 
 Nearly all rocks are more or less jointed or fissured, so that 
 water charged with carbon dioxide from the air or decaying veg- 
 etation, readily finds its way deep into the rocky strata, reappear- 
 ing at lower levels as springs. During its underground journey the 
 water dissolves more or less material from the rocks over which 
 it passes, so that the water of springs is seldom pure water. 
 Sometimes the water may have passed over insoluble rocks, and 
 issue from the earth as pure, soft water. Or it may have passed 
 over limestone rocks, and loaded with calcium carbonate form a 
 calcareous spring, supplying " hard " water. And according to 
 the nature of the rocks through which the water flows, a spring 
 will be ferruginous, sulphur, saline, alkaline, etc. 
 
LESSONS IN GEOLOGY. 341 
 
 The effect on the rocks of this underground water is much the 
 same as the effect of air and water on the surface rocks. Solu- 
 tion and disintegration are usually more rapid in limestone rocks, 
 large channels and caves being common in such formations. 
 Sometimes the roof of the cave falls in and the cave or under- 
 ground channel becomes a gorge or narrow valley. The caves of 
 Southern Indiana, Kentucky and Tennessee are remarkable for 
 their size and the beauty of their stalactitic architecture. In 
 these caves there are often interesting examples of reparative 
 action. In cases where the bed of the stream has been lowered so 
 as to leave some rooms practically dry, the dripping from thereof 
 at length forms pillars, supporting the roof, and in time perhaps 
 fills the room. Again, where quantities of rock have fallen, the 
 drippings from above fill the spaces between the fallen rocks with 
 stalagmitic material and at length build supporting columns, 
 finally closing the cavity. 
 
 Sometimes the underground water, on sloping surfaces, dis- 
 solves away the union between large masses of rocks and the 
 mountain side, causing land slips, rock avalanches, etc. 
 
CHAPTER XLVI. 
 
 RIVER AND MARINE EROSION. 
 
 THE rain falling upon the uneven surface of the earth, forms 
 little rivulets, which, uniting with others, form larger, and so on, 
 till the brooks and creeks are formed ; which together constitute 
 the river that receives all these little streamlets each with its 
 burden of sediment and conveys them, at length, to the great 
 and wide sea. Beside this surface water, the rivers receive the 
 water from thousands of springs, spring water, in many cases, 
 forming the greater part of the supply during the year. The re- 
 gion of country drained by a river is called the river valley, or 
 basin, and is usually considerably longer than wide. The char- 
 acter of a river will depend on the nature of the rocks of its val- 
 ley ; on the character of the climate of the valley and on the rap- 
 idity of its slope. Rivers vary in the amount of water and other 
 material they carry. Nearly all rivers have an annual flood, and 
 many are subject to change from exceptionally wet or dry seasons. 
 
 The Mississippi river, draining a wide valley embracing a va- 
 riety of climate, is somewhat uniform in its flow, subject to its 
 annual spring flood, and sometimes an exceptionally wet season 
 will give a summer flood. 
 
 The Nile river depends for its water supply on seasonal rains 
 in the upper part of its valley, and is very uniform in all its phe- 
 nomena from year to year. In regions subject to great irregu- 
 larities of rain-fall, the change from low water to flood is often 
 very great, as rivers in south-east Australia, or even in the south- 
 western part of the United States. 
 
 In general a river has three parts the mountain portion, 
 where formed by mountain torrents, it rushes noisily over its steep, 
 rocky bed to the lower ground that forms its middle or valley 
 course. In this part of its course the river flows through a more 
 varied country, lower mountains, wide valleys, narrow gorges, 
 (342) 
 
LESSONS IN GEOLOGY. 343 
 
 and sometimes spreading out into lakes, and in this region the 
 largest tributaries are received. From this undulating country 
 it passes into a broad alluvial plain, mostly deposited from its 
 own waters, and winds sluggishly onward, and finally, amid 
 marshes and banks of mud and sand, it empties into the sea. 
 The great rivers of the globe probably have an average slope of 
 less than 24 inches per mile. The Volga from source to sea has a 
 slope of less than 4 inches per mile, while the Missouri has a 
 slope of about 28 inches per mile. The water next the bottom 
 and sides of the river channel is retarded by friction, so that 
 water in the center and upper part of the river flows most rap- 
 idly. The fact that rivers flow more rapidly when in flood is 
 explained on the theory of less friction and increased slope from 
 high water in the upper courses. 
 
 Each little rivulet, each spring in the whole valley, brings to 
 the river products of terranean and subterranean weathering, 
 which the river carries out to sea with materials gathered up by 
 erosion along its course. The amount of material carried by riv- 
 ers in this way varies greatly; rivers flowing through cultivated 
 regions usually carry great quantities of sediments. The Mis- 
 souri river, flowing through recent, partially consolidated strata, 
 is loaded with sediment, and so are the rivers of China that flow 
 through the loess deposits; while the St. Lawrence system, with 
 its rocky valley and lake basins, is nearly always clear and free 
 from sediment. The water of rivers doubtless has some chemical 
 effect on the materials over which it flows, but the chief work of 
 flowing streams is mechanical. The matter carried by streams 
 is partly in solution and partly in suspension, and partly coarse 
 material pushed along the bottom. Of the substances in solu- 
 tion, calcium carbonate is most abundant, then calcium sul- 
 phate, sodium chloride, magnesium carbonate, and sulphate, etc. 
 It is estimated that the quantity of calcium carbonate removed 
 from the limestone areas of the Thames amounts to 140 tons 
 per square mile annually. 
 
 The power of a stream to transport suspended matter is said 
 to increase as the sixth power of the velocity of the current, so 
 
344 PRACTICAL LESSONS IN SCIENCE. 
 
 that the power of the current is increased 64 times by doubling- 
 its velocity. A current of three inches per second will begin to 
 work on fine clay, one of six inches per second will lift fine sand, 
 and one of eight inches per second will move coarse sand, and one 
 of one foot per second will move fine gravel; while a current of 
 two feet per second, or a mile and a third per hour, will roll along 
 pebbles an inch in diameter, while a current of two miles per hour 
 will move stones the size of an egg. These figures are given for 
 the bottom velocity, and it should be remembered s'tones are not 
 more than two-thirds as heavy in the water as in the air, so that 
 they are more easily transported. 
 
 In the upper course of the stream large angular blocks of rock, 
 loosened by the frost, are urged down the steep slope by the 
 rushing torrent ; these, gradually abrading each other and the 
 bed of the stream, in time reach the sea as gravel, sand or mud. 
 Some fragments may have reached the sea within a year after 
 leaving their mountain bed, while the last particles of some of the 
 blocks may be thousands of years in reaching their final destina- 
 tion in the bed of the ocean. 
 
 The amount of solid matter conveyed by a large river to the 
 sea each year is almost beyond comprehension. Many investi- 
 gations have been made, but the most extensive and reliable are 
 those made by Humphrey and Abbott, on the Mississippi river. 
 They estimated that the amount pushed along the bottom of the 
 river into the Gulf, was 750,000,000 cubic feet annually, and the 
 amount in suspension was about 4,368,280,000 cubic feet, a to- 
 tal of 5,116,280,000 cubic feet per year, equal to a prism 268 
 feet high, with a base of one square mile. This means that the 
 Mississippi moves about one foot from the surface of its valley 
 in 6,000 years. Other rivers erode more rapidly, and some less 
 rapidly, but the above, as an average rate, would carry North 
 America into the sea within 4,000,000 years. 
 
 Rivers erode their channels, but clear water erodes very slowly, 
 as shown in the case of the Niagara and St. Lawrence rivers, 
 which have had very little effect on the glaciated rocks in their 
 beds, during the 3,000 or 4,000 years since glacial times. The 
 
LESSONS IN GEOLOGY. 345 
 
 work of erosion seems to be done by sand and gravel carried or 
 pushed along the bed of the river. The rate of erosion will de- 
 pend on the strength of the current, the amount and kind of sed- 
 iment carried, and the nature of the rock through which the 
 channel was located. In the Missouri river, in many places, 
 there are from 40 to 50 feet of sand and mud between the bed 
 rock and the water. When the river is low, or at a medium stage, 
 this bed of mud and sand is quiet, and there is no erosion of the 
 rock-bed; but when the river is in flood, the whole mass is in 
 motion, sliding along like a rasp over the bottom of the rocky 
 channel. Limestone rocks erode more easily than some others, 
 and they are more easily soluble. Sometimes flint nodules in 
 limestone rocks hasten erosive action. The limestone eroding, 
 more rapidly, leaves the nodule as a projection; a piece of 
 floating ice or a log strikes the nodule, knocking it from its bed, 
 leaving a hollow. Sand and gravel collect in the hollow and, kept 
 in motion by the water, soon forma pot-hole, which is an interest- 
 ing and effective mode of erosion in rocks, where in any way little 
 cavities are formed. 
 
 Another special form of erosion, is by water-falls, which are 
 formed in various ways. The falling water splashing against the 
 foot of the cliff gradually undermines the upper portions, which 
 at length break down, and thus the falls recede and a gorge is 
 formed. If the lower portions are easily eroded, the action is 
 more rapid. At the Niagara Falls, the upper stratum is hard lime- 
 stone, the lower shale -which are favorable conditions for rapid 
 work. It is estimated that at the present time the falls are reced- 
 ing at the rate of about 2.4 feet per year. The Grand Canon of 
 the Colorado river about 300 miles long, and in some places 
 6,000 feet deep, is the work of the erosive forces of the river. 
 Sometimes a fissure determines the course of a river, and helps to 
 form its channel; but such cases are not as common as was for- 
 merly supposed. Ice in streams often adds considerably to their 
 erosive power. Land ice, or glaciers, are efficient geological 
 agents, which will be discussed in another place. 
 
 A stream of water carrying sediment begins to drop it when- 
 
346 PRACTICAL LESSONS IN SCIENCE. 
 
 ever the current is checked. When a mountain torrent, with its 
 burden of sediment, flows out upon a plain, it drops the greater 
 part in a fan-shaped mass, the apex pointing up the stream ; lit- 
 tle streams flowing into ponds deposit sediments in the same 
 shape ; and the delta of the Mississippi is an enormous mass of 
 sediment of the same form, and deposited in the same way, the 
 current slackened by the waters of the Gulf. 
 
 A river seldom deposits any sediments along its mountain 
 course, but when it enters its middle course the current is lessened 
 and the sediments deposited sometimes raise the bed of the river 
 above the level of the adjacent land. The same thing occurs fre- 
 quently in rivers flowing through low plains or deltas. Some 
 rivers in Northern Italy illustrate the first and the Mississippi 
 river the second. During floods rivers often spread out over 
 adjacent low lands which are covered with vegetation ; the rough 
 ground and the vegetation check the current and a layer of sedi- 
 ment results. Turbid rivers flowing into lakes drop their sedi- 
 ments, the water at the outlet being clear. In this way lakes 
 are sometimes obliterated, entirely filled by the sediments of their 
 inlets. The course of a stream consists of a system of irregular 
 curves or bends, with occasional stretches of nearly straight 
 channel. On the convex side of a curve the current is strong 
 and erosive, while on the concave side it is weaker and depos- 
 iting sediments. In this way streams change their channels, 
 wandering about their valleys, eroding old sediments and depos- 
 iting new, so that a bit of gravel may form a portion of scores 
 of different gravel beds before it reaches the ocean. The whole 
 matter of the geological work of streams can be studied in almost 
 every phase along any little brook or creek in the country. 
 
 Marine erosion is very extensive, but is not as rapid or exten- 
 sive as river erosion. The waves with their burden of sand or 
 gravel gradually undermine the rocks so that they fall within 
 reach of the waves ; the smaller fragments are rolled backward 
 and forward by the waves, hurled against the larger ones till at 
 length they are broken up, and the fragments abrading each 
 other become pebbles that slide up and down the beach with 
 
LESSONS IN GEOLOGY. 847 
 
 every wave, and are soon worn to sand and mud. In the river 
 the pieces of rock move forward, and are more nearly spherical 
 in form, while on the beach they move backward and forward 
 and soon become flattened, and are sometimes called shingle. 
 The sand resulting may form sand bars parallel with the shore, 
 or may be transported to other localities by ocean currents, or 
 may be built into dunes by the winds. 
 
 The different forms of life often are of great importance as 
 geological agents. Plants, as mosses and liverworts, by keeping 
 the surface of rocks moist, promote their decay, and in the decay 
 of their leaves and stems organic acids are formed which are 
 active oxidizing agents. These acids, for the most part, become 
 carbon dioxide, and in one form or the other are the great sol- 
 vents of the mineral world, often penetrating rocks to a great 
 depth. Plants and trees also aid erosion in a mechanical way, 
 as their growing roots open cracks and seams in the rocks. 
 
 Turf and trees protect from erosion. Forests protect hillsides 
 and sand dunes; the sand-grass and other plants also protect 
 the same from the wind. Mangrove swamps along the seashore 
 are especially effective in reclaiming and making land. While 
 live plants protect, dead and decaying plants often open the soil 
 to the erosive action of wind and rain. Decaying vegetation en- 
 riches soils, forms muck beds, peat bogs, etc., from which all the 
 coal and much of the rock oil and natural gas were formed. 
 
 Burrowing animals of all kinds, earth worms, cray-fish, open 
 the soil to the action of oxidizing agents, and often to the action 
 of erosive agents as well. Beavers build dams, making ponds 
 and swamps, while cray-fish, rats, etc., open holes through banks 
 which lead to destructive erosion. Some mollusca bore holes in 
 rocks and wood, thus promoting their disintegration. The shells 
 of the mollusca, the framework of corals and other animal 
 organisms have made up most of the calcareous or limestone 
 rocks. And the coral polype, in the tropical sea, is building 
 islands and reefs of coral limestone, while diatoms, and some 
 forms of animal life, are furnishing material for silicious deposits 
 of great extent. 
 
CHAPTER XLVII. 
 
 THE ARCHAEAN AND ALGONKIAN ERAS. 
 
 ASTRONOMICAL studies lead us to suppose that our earth was 
 once a sphere of glowing gas, and that as it gradually cooled, por- 
 tions were condensed, forming a molten nucleus surrounded by 
 intensely heated gases. That as the cooling process continued, 
 the nucleus gradually increased in size and the temperature of the 
 surrounding gases diminished until the mass ceased to be lumi- 
 nous. At length a solid crust began to form over the heated in- 
 terior. It was doubtless broken up, remelted and reformed many 
 times, but at last a continuous slag-like crust became permanent. 
 From what we know of the composition of the rocks, this crust 
 was composed mainly of the silicates of aluminium, calcium, 
 potassium, sodium and magnesium, with iron manganese and 
 other substances. 
 
 All the water of the present oceans, lakes, and rivers, all the 
 mercury, sulphur, chlorine and other volatile matters with the 
 air formed an atmosphere of dense, poisonous vapors. In time, 
 portions of these vapors condensed, covering the crust with 
 broad, shallow oceans of hot, acid water. As the earth continued 
 to cool, the interior contracted more rapidly than the solid crust, 
 and as the crust settled down with the inner mass broad, low 
 swells and wide, shallow depressions were developed . These grad- 
 ually increased in elevation and depth until the continents ap- 
 peared, and the ocean boundaries were defined. Portions of 
 these ancient continents may have been submerged from time to 
 time for many hundreds of feet, but at no time have the conti- 
 nents and oceans changed places ; their relative positions have 
 probably always been substantially the same. 
 
 The reactions between the acid waters and the basic rocks re- 
 (348) 
 
LESSONS IN GEOLOGY. 349 
 
 suited in adding many soluble chlorides and sulphates to the 
 sea-water and in the formation of sediments as silica, silicates 
 of aluminium, potassium, calcium and sodium. These materials 
 with the original crust make up a system of granites, gneisses 
 and crystalline schists, which represent the oldest rocks of the 
 earth. These rocks are doubtless of a mixed origin partly igne- 
 ous, partly sedimentary, but they have been so completely 
 changed by metamorphic agencies that all trace of lava, slag, 
 and sediment has been obliterated. 
 
 These rocks, sometimes called the " Basement Complex," are 
 found in Arizona, Nevada, and Texas, in the regions of Lake 
 Superior and Hudson's Bay, including the greater part of theLau- 
 rentian rocks of Canada. These rocks were subjected to the 
 folding, crumpling and faulting incident to mountain formation 
 and to atmospheric erosion, and have been covered extensively 
 by later rocks so that we can know little of their original form 
 and extent. The time from the beginning of the crust to the time 
 when rocks that are distinctly sedimentary began to be formed 
 is called the Archaean or beginning era, and the rocks belong to 
 the Basement Complex, or Laurentian Age. 
 
 The AlgonkianEra. Under the action of erosive agencies large 
 portions of the Archaean rocks were broken down and distributed 
 over adjacent sea bottoms as sediments, which afterward were 
 changed into conglomerates, quartzites, quartz, mica and iron 
 schists and limestones. These rocks vary considerably, pass- 
 ing from quartzite to quartz-schist; from conglomerate to con- 
 glomerate schist ; from pure limestone almost like marble, to lime- 
 stone containing great quantities of chert; and with the iron 
 schists there are cherts and jaspers in abundance. These rocks are 
 called the Lower Huronian. At the end of Lower Huronian time 
 this region was raised above the sea, crumpled and folded, and 
 subjected to erosive agencies, which in some instances carried 
 away the whole series. After this period of erosion the surface 
 was depressed and sediments were deposited on the eroded sur- 
 faces that afterward were changed into the conglomerates, quartz- 
 ites, shales, schists, iron schists and slates, chert, jasper, etc., 
 
350 PRACTICAL LESSONS IN SCIENCE. 
 
 which make up a group of rocks known as the Upper Huronian. 
 The exposed area of these rocks is much greater than that of the 
 Lower Huronian, and they include the most of the rich iron ore 
 deposits of the Lake Superior region. 
 
 These rocks in some places are as much as 13,000 feet in thick- 
 ness. In general these rocks are not as highly metamorphic as 
 the Lower Huronian. At the close of Upper Huronian time 
 the surface was raised above the sea and exposed to erosive 
 agencies again. After some time great floods of volcanic mate- 
 rials were poured out over this region. Later the region was cov- 
 ered by the sea and sediments were deposited which afterwards 
 became conglomerates and sandstones. These volcanic and 
 sedimentary rocks make up the Keweenawan group or series. In 
 some cases the volcanic rocks are in terst ratified with the sediment- 
 ary rocks, which seems to indicate a subaqueous flow of lava. This 
 series is very extensive, and in some places is estimated to have 
 a thickness of 50,000 feet. These rocks include most of the rich 
 copper deposits of the Lake Superior region. Rocks to the east ot 
 Lake Superior belonging to this or an earlier series contain thick 
 beds of graphite as well as iron. 
 
 The reactions between the air, water, and land so purified the 
 air and water that low forms of aquatic life began to appear, 
 and soon became abundant, even acquiring new characters and 
 spreading out over the rocks. Great quantities of insoluble iron 
 ore were disseminated throughout the slag-like crust. Water 
 containing carbon dioxide derived from decaying organic matter 
 changed this insoluble peroxide into the soluble protoxide and 
 carried it down to the ponds, lakes and marshes, where taking 
 oxygen from the air, it again became insoluble, and settling to the 
 bottom helped to form sediments which afterward became thick 
 beds of iron ore. The immense beds of iron ore and graphite, 
 indicate that some forms of life must have been very abundant ; 
 but there is no positive evidence as to its character, as all 
 organic remains were destroyed when the sediments were changed 
 to rocks. 
 
 Granitic, gneissoid, schistose and slate rocks make up the 
 
LESSONS IN GEOLOGY. 351 
 
 Laurentian tableland extending from Labrador southwestward 
 to the region of Lake Superior, thence north westerly to the Arctic 
 Ocean. They occur in the Adirondack and White mountain re- 
 gions, at many localities in the Western mountain regions 
 in the Alleghanies, in Arkansas and Missouri and in other 
 places, but only in the region of Lake Superior and some western 
 localities have the rocks of the two eras been clearly separated. 
 
 These rocks as exposed in the Laurentian tableland are from 
 40,000 to 50,000 feet in thickness. Their formation and their ele- 
 vation into mountains is explained as follows : The area now oc- 
 cupied by these rocks was a shallow sea, adjacent to an extensive 
 land surface, probably on the north in the region of Hudson's 
 Bay. The sediments derived from the land were spread out over 
 this sea bottom. For some reason this area of the crust was 
 weak, so that it settled gradually, as the sediments were depos- 
 ited, till they became more than 50,000 feet deep. At length the 
 settlement was so great that the rocky masses underneath be- 
 came softened by the internal heat, and the whole mass became 
 so weak that it yielded to the lateral pressure of the sinking 
 crust and the sediments were mashed together, the crumpled, 
 folded strata slowly swelling up into mountains. 
 
 Under this great pressure, through the agency of heat and 
 water, the organic matter of the sediments was destroyed and 
 they were changed into met amor phic rocks. 
 
 Originally the substances which make up the earth's crust 
 were widely disseminated, and the great bulk of the Archaean rocks 
 were formed from a mixture of a wide variety of substances ; but 
 the assorting tendency of nature's operations is manifest in the 
 beds of quartzite, slate, limestone, iron ore, and graphite. 
 
 The Laurentian tableland is the oldest portion of North Amer- 
 ica; it seems never to have been submerged. It has been subject 
 to eroding agencies for untold ages; it has furnished materials for 
 the rocks of all subsequent ages; yet rising by intervals or con- 
 tinuously, it has always kept pace with the degrading effects of 
 the eroding forces. 
 
CHAPTER XLVIII. 
 
 THE PALCEOZOIC ERA. 
 
 THE next period of the earth's history is called the Palceozoic 
 , or era of old life. This era includes the Silurian age, the 
 Devonian age, and the Carboniferous age. 
 
 At the beginning of this era, besides the Lauren tian tableland, 
 there seems to have been a large body of land occupying the 
 region of the Atlantic coast plain ; and another in the region now 
 occupied by the Rocky Mountains. Between these bodies of land 
 there was a broad, shallow sea, called by some the Paloeozoic sea. 
 The earliest rocks of this era are sandstones and slates, composed 
 of materials that accumulated on the beach of this ancient sea, 
 over a region extending from Canada to Georgia. They are 
 known as the Cambrian rocks. In them we find the earliest re- 
 mains of life, representing protozoans, coelenterates,echinoderms, 
 worms, and crustaceans, nearly all the invertebrate forms of life, 
 besides several species of plants. 
 
 This abundance of the various forms of life, calls attention to 
 the nature of the geological record. We know nothing about how 
 much time elapsed between the formation of the primal crust and 
 the formation of the Algonkian rocks, with their evidences of 
 beginning life, and we know very little of what events transpired 
 during the period. 
 
 The life of the Algonkian era must have consisted mainly of low 
 forms of vegetation with some protozoans, as no other forms 
 could exist under the conditions of those times; and yet in the 
 next higher rocks that have been found there is evidence of an 
 abundance of life of well-advanced forms. The early rocks had 
 been strongly folded and deeply eroded before the later rocks were 
 deposited. Thus the relations of the rocks and the forms of life 
 show that after the formation of the Algonkian rocks there is an 
 (352) 
 
LESSONS IN GEOLOGY. 353 
 
 immense period of the earth's history, of which no record can be 
 found. Erosive forces were active; sediments inclosing remains 
 of various forms of life were deposited and changed to rocks, and 
 the whole submerged and covered from view by later rocks. The 
 rocks of that era which we can examine seem to be mere remnants 
 of great continents of rocks that have been cut away by erosion 
 and submerged. They stand between great unknown periods in 
 the history of the earth. Breaks in the geological record are 
 numerous, but perhaps no other is as well marked as this one. 
 
 During the balance of the Silurian age thick beds of rock were 
 deposited over a wide portion of the continent, as the Trenton, 
 Niagara and Galena limestones, the Utica and Niagara shales 
 and the Medina sandstones ; the limestone largely exceeding the 
 others in some regions, so that it is mentioned as the characteristic 
 rock of the age. 
 
 All classes of invertebrate life were abundantly represented, but 
 mollusks were most numerous and varied, so that this period is 
 often called the Age of Mollusks. Some fossil fishes have been 
 discovered in European rocks. More than 10,000 species of fos- 
 sils have been described from the Silurian rocks ; remains of sea- 
 weeds and of plants that were terrestrial, as ground pines and 
 others, some like the yew and pine. 
 
 The area of Silurian rocks extends from Newfoundland to Mis- 
 souri, from Lake Superior to Georgia, but they are thickest in the 
 Appalachian region. In the west the limestones are most abund- 
 ant, while in the Appalachians they only make up about one-half 
 of the beds. The limestones were formed in quiet waters, largely 
 from the shells of mollusks, the stems of crinoids, the framework 
 of corals, etc. The sandstones and shales were generally beach 
 deposits, sand bars, mud flats, etc. Some clayey iron ores and 
 salt deposits indicate the existence of marshes and shallow salt 
 lakes. The frequently alternating beds show many upward and 
 downward movements of the crust. It takes but a few moments 
 to make these statements of the events of this age, but they were 
 the work of millions on millions of years. And in this study we 
 need to keep constantly in mind that geological time units are 
 
 L. S. 23 
 
354 PRACTICAL LESSONS IN SCIENCE. 
 
 very, very long. It is said that no group of strata has been 
 traced over a wider area of the earth's surf ace, and none are more 
 uniform and well marked in their composition and in the charac- 
 ter of their fossil remains than are the Silurian. 
 
 Following the Silurian age came the Devonian age, character- 
 ized by the " old red sandstone beds " of Great Britain. In North 
 America the lowest formation is the corniferous limestone, one of 
 the great limestones of the continent; the later strata were 
 mainly sandstones and shales in the east, with shales and 
 thin limestones in the west. The corniferous limestone is distin- 
 guished by seams of horns tone or flint and occurs in New York, 
 Ohio, Michigan, Iowa, Missouri, Kentucky and adjacent regions. 
 The Hamilton shales of New York and the black shales of Ohio 
 and neighboring regions belong to this age. 
 
 During the Devonian age the different classes of invertebrate 
 life were abundantly represented, but in general by different spe- 
 cies from those of the silurian age. Fishes, however, were the 
 characteristic and dominant life of the age. They were like the 
 sharks and skates, garfish and sturgeons of the present, repre- 
 senting the lower orders of vertebrate life. They existed in great 
 variety, and often attained a large size. 
 
 Plants were represented by seaweeds and other aquatic forms, 
 but terrestrial forms, as equisetaB, ferns, lycopods, and the lower 
 gymnosperms were abundant and characteristic, often attaining 
 the size of trees, forming forests. The corniferous limestone 
 indicates a quiet sea for a long time, but the later rocks were 
 largely the products of erosion deposited on the sea bottom near 
 the coasts. And the vegetation suggests extensive swamps and 
 marshes. The character and relations of the rocks indicate no 
 marked distinction or gap between the Silurian and Devonian 
 ages, but the marked difference between the life forms of the two 
 ages does suggest an interval of time not shown by the rocks. 
 
 The Devonian passed without violent changes into the carbon- 
 iferous age. The rocks in many localities show changes of level and 
 crumpling of strata indicating some difference of conditions be- 
 tween the Devonian and the following Carboniferous age; but the 
 
LESSONS IN GEOLOGY. 355 
 
 difference is not very great. This age is divided into three parts, 
 the sub-carboniferous, carboniferous and permian. The sub-car- 
 boniferous rocks are mainly limestone, but in Ohio, Michigan and 
 Pennsylvania there are more sandstones and shales, all of marine 
 formation. The lowest strata of the Carboniferous is a coarse 
 sandstone called the Millstone grit. The other strata are thin 
 beds of coal, shale, limestone, sandstone, clay, iron, stone and 
 under clay. The permian rocks are an ill-defined group of sand- 
 stones, limestones, gypsum beds and shales, that mark a transi- 
 tion period from the palaeozoic to mesozoic eras. 
 
 Coal occurs in separate areas or basins, as the Appalachian 
 coal field, the greatest in the world, extending from Pennsylvania 
 to middle Alabama, with an area of about 60,000 square miles 
 of work able coal; the central field, covering the greater part of 
 Illinois, part of Indiana and Kentucky, about 47,000 square miles. 
 The western field includes southern Iowa, and portions of Missouri, 
 Kansas, Arkansas and Texas, about 80,000 square miles. Then 
 about 6,000 square miles in Michigan, about 500 in Rhode 
 Island and about 18,000 in the region of the Bay of Fundy. 
 The carboniferous and sub-carboniferous rocks have a much 
 more extended area than the coal proper, as given above. 
 
 As in the two previous ages, the invertebrates were well repre- 
 sented, and in addition to the marine forms there were many ter- 
 restrial and fresh- water mollusks, and some spiders and insects. 
 Fish were as large, abundant and varied as during the Devonian 
 age, and toward the close some amphibians appeared. But the 
 notable, the characteristic life of this age was its plants. Only 
 the cycads, a group of gymnosperms, were added to those known 
 in the Devonian age; but in general the plants of the carbonifer- 
 ous age were larger, more abundant and more varied in form; as 
 many as 500 species have been described from American rocks, 
 besides a large number of different ones from European rocks. 
 
 It is generally believed that coal is of vegetable origin, and 
 that coal and its associated rocks were, in general, deposited 
 under the following circumstances : A large, nearly level, some- 
 what basin-shaped area of land has been covered with a bed of 
 
356 PRACTICAL LESSONS IN SCIENCE. 
 
 fine clay thick enough to hold water and support a growth of 
 vegetation ; a slight elevation makes shallow, stagnant or slow- 
 moving water, in which springs up a dense growth of mosses, 
 ferns, equisetse, lycopodia, sigillaria, calamites, etc., forming 
 a swamp. The stems and leaves of these plants, preserved from 
 complete decay by the water, accumulate as peat. After a time 
 the area is slightly depressed and currents of water flow over the 
 peat, depositing on it sediments of clay or sand, and perhaps the 
 depression may be enough to allow the sea to invade the region 
 and deposit lime sediments. Again the region is elevated, a de- 
 posit of fine clay is made and the cycle of deposits begins anew. 
 In Belgium, Nova Scotia and other localities there are more than 
 eighty seams of coal, and as at least two strata of other material 
 separate each seam from the next, we can form some idea of how 
 many upward and downward movements, how many changes of 
 condition have occurred in the for mat ion of a group of coal strata. 
 The layers of peat are changed by heat and pressure into bitu- 
 minous coal, and the pressure and heat maybe enough to change 
 the beds of peat to anthracite coal, or even to graphite. 
 
 Iron in some form always occurs with coal. Nearly all the iron 
 of England, and much of the iron of America, comes from the 
 coal measures. It often occurs as the sulphide, which is of no 
 value for iron, and is a damage to the coal ; but it occurs most 
 abundantly as clay iron stone, or kidney iron ore, which is a car- 
 bonate of iron. In some manner, not well understood, vegetation 
 gathers up the iron from adjacent rocks, and concentrates it into 
 these forms. Sand rocks and shales near coal seams are white or 
 gray, not red their coloring matter has become iron ore. 
 
 Besides coal, we find in the rocks of different ages, quantities 
 of asphalt and bitumen, petroleum oil and natural gas. They 
 are supposed to be of organic origin, as similar substances may 
 be derived from coal by distillation ; and while they might origi- 
 nate from any accumulation of organic matter, it is probable that, 
 for the most part, they were the products of the carboniferous 
 age, although they may have accumulated in cavities of rocks of 
 other ages. 
 
LESSONS IN GEOLOGY. 357 
 
 During the Algonkian era, the Lauren tian tableland was raised 
 above the sea level, as a permanent feature of the continent. 
 During the Silurian age, the Green Mountains were formed; and 
 the paloeozoic era closed with the elevation of the Appalachians, 
 extending the land surface of the continent westward to the region 
 of the Missouri, and southward to the Tennessee. The elevation 
 was doubtless slow, and possibly there were oscillations, but this 
 area seems never to have been below the sea level since the car- 
 boniferous age. 
 
 The heat and pressure attending the elevation of the Appal- 
 achians, changed sediments to metamorphic rocks, as clays to 
 slates, sands to quartzite, limestones to marbles, peat beds to 
 anthracite coal, etc., the forces, the elevation and the metamor- 
 phism diminishing from the east toward the west. It is interest- 
 ing to note the similarity of events in North America and in 
 Europe ; the practical identity of the Algonkian rocks, the occur- 
 rence of evidences of a lost period, the similarity of the Silurian 
 and Devonian rocks, the identity of the millstone grit, the marshy 
 areas and other conditions for the formation of coal, with sim- 
 ilar forms of life, from beginning to end, including multitudes of 
 identical species ; and the eras of crumpling strata and mountain 
 formation seem to have been coincident. 
 
CHAPTER XLIX. 
 
 THE MESOZOIC OR SECONDARY ERA, AND THE TERTIARY AGE. 
 
 THE Mesozoic Era in Europe'shows three well-marked divisions, 
 which are known as the Triassic, Jurassic, and Cretaceous periods. 
 
 The triassic and Jurassic are not as distinct in North America, 
 but the three periods are recognized. The triassic rocks are 
 mainly red sandstones, with some conglomerates, shales, and im- 
 pure limestones. They occur in Nova Scotia, Connecticut, enn- 
 sylvania, and North Carolina, and over wide areas in the Rocky 
 Mountain region, extending far north into the Canadian prov- 
 inces. Some quarries furnish a brown sandstone, much prized for 
 ornamental building ; but in general the rocks of this period are 
 not of much economic value. The rocks seem to have been 
 formed in shallow water, and the abundance of mud cracks, rain- 
 drop impressions, and tracks of animals show that the sediments 
 were often half-emerged sand flats. 
 
 Jurassic rocks are found near the Black Hills, and in the 
 Uintah, Wasatch and Sierra Nevada mountains, usually sand- 
 stones, sandy limestones, etc. 
 
 The cretaceous rocks are beds of sand, clay, shells, green sand, 
 limestone ; all these beds usually loose, easily crumbled, but occa- 
 sionally compact beds are found. They occur in detached areas 
 along the Atlantic and the Gulf coasts, and north along the 
 Mississippi almost to the Ohio river; along the slopes of the 
 Rocky Mountains from Texas into Canadian territory quite to 
 the Arctic ocean, the thickest beds being in Colorado, Utah, and 
 Wyoming, where the rocks are fully 9,000 feet thick. The life 
 forms were abundant. Among plants there were equisetae, ferns, 
 conifers, and others known during the coal period. The cycads, 
 having the appearance of palms, with leaves that unrolled like 
 ferns and wood like the pine, were characteristic and peculiar. In 
 (358) 
 
LESSONS IN GEOLOGY. 359 
 
 thecretaceous the first dicotyledons appeared, as the oak, willow, 
 maple, and sassafras, and became numerous, as many as 100 
 species having been discovered. And leaves of the redwood and 
 of the palm have also been discovered. 
 
 The characteristic life of the age was reptilian, so that it is 
 often called the Age of Reptiles. They practically appeared with 
 the age, reached their culmination and passed into a decline. 
 They were very large and very numerous, they dominated the 
 water and the land, and some were furnished with wings for ex- 
 cursions in the air. Invertebrate life was abundant, and so were 
 ganoid fishes and amphibians. In the cretaceous the teleosts, or 
 bony fishes, and birds of different kinds appeared, and remains 
 of mammals have been found in the triassic rocks. 
 
 The famous chalk cliffs of England, and the cretaceous beds of 
 eastern North America, were doubtless formed at the same time, 
 and were continuous. These localities were raised above the sea 
 level, while chalk is still being formed in the ocean between. 
 
 At the close of the Jurassic, there were some igneous eruptions 
 in the Connecticut Valley, and other slight disturbances on the 
 Atlantic coast; but the great revolution was the swelling up of 
 the then marginal sea bottoms into the Sierra Nevada and Coast 
 Range mountains, and doubtless theUintah and Wasatch ranges 
 began to rise about the same time. 
 
 At the close of the cretaceous, or soon afterward, the whole 
 western half of the continent was elevated, the interior cretaceous 
 sea disappeared, the Rocky Mountain region joined the tableland 
 and the Appalachian region, completing the continent. 
 
 The Cenozoic Era, or Age of Mammals, is divided into the Ter- 
 tiary and Quaternary Ages. 
 
 The Tertiary Age is divided into the Eocene, or lower, Miocene, 
 or middle, and Pliocene, or upper tertiary. 
 
 The tertiary deposits constitute the Atlantic and Gulf coast 
 plains, and extend from the Gulf up the Mississippi river to the 
 mouth of the Ohio river. These are marine deposits of a some- 
 what varied character. In the Rocky Mountain region there 
 are numerous basins of fresh-water deposits belonging to this 
 
360 PRACTICAL LESSONS IN SCIENCE. 
 
 age, as the Green river and Uintah basins of the eocene ; basins 
 in Nebraska and Oregon belonging to the miocene; the Nio- 
 brara and White river basins and others containing pliocene 
 deposits. 
 
 The rocks of the tertiary consist of beds of sand and clay, 
 shell beds and marls, compact sandstones, calcareous sandstones 
 and limestones. On the Pacific slope some metamorphic rocks 
 are found, metamorphic agencies having been in force in that 
 region after some of the tertiary sediments had been deposited. 
 Some coal in the Western mountain system is referred to this 
 period . 
 
 Among plants, the genera of the dicotyledons, palms and 
 grasses were about the same as now, but most of the species were 
 different from those of the present. Magnolias, palms and other 
 sub-tropical plants grew in the extreme north of Europe and 
 North America, indicating a much warmer climate than now pre- 
 vails in those regions. Immense deposits of infusorial earth, 
 composed largely of diatom shells, indicate an abundance of 
 microscopic life. 
 
 Among animals, mollusks, insects, worms and fish were abun- 
 dant ; reptiles and birds were numerous, but mammals were the 
 characteristic and dominant form of life. Herbivorous animals, 
 like the rhinoceros, mastodon, elephant, camel, giraffe, tapir, 
 antelope, hog and horse were common. From the Green river 
 and adjacent basins more than 150 species of vertebrates have 
 been described. Carnivorous animals, like the tiger, panther, 
 wolf, fox and hyena were abundant, and remains of animals like 
 the beaver and porcupine have been found. 
 
 Quite a series of the ancestors of the modern horse have 
 been found in these rocks, beginning with one having four 
 toes, and gradually diminishing till the present form, with one 
 toe, is reached. The horse and camel seem to have originated on 
 this continent; and the number of old-world forms found in the 
 rocks of North America would indicate free communication be- 
 tween the continents through long periods of time. The nearly 
 common forest vegetation prevailing through the northern 
 
LESSONS IN GEOLOGY. 361 
 
 parts of Asia, Europe, and North America, testifies in the same 
 direction. 
 
 The tertiary was the great mountain-forming period, and in 
 connection with this work the continents were elevated and 
 extended to their present limits ; in fact, the boundary lines be- 
 tween the land and the sea were laid during the tertiary period. 
 
 The whole western mountain system of North America was 
 elevated more or less, some of the eastern chains rising as much 
 as 10, 000 feet, and thecoast ranges were formed at this timealso. 
 
 Long cracks or fissures were opened and immense sheets of lava 
 poured out; one sheet, cut through by the Columbia river, is 
 over 3,000 feet thick and 150,000 square miles in extent. Eleva- 
 tions in the south-east exposed recent sediments and extended 
 the continent to its present limits, except a portion of the Penin- 
 sula of Florida. ' ; Throughout the old world, from the Pyrenees 
 to Japan, the bed of the early tertiary sea was upheaved into a 
 succession of giant mountains, some portions of that sea floor 
 now standing at a height of at least 16,500 feet above the level 
 of the sea" on the Himalayas. Along with these elevations of 
 the land, there were doubtless depressions in the ocean beds, of 
 which there are some indications in the Pacific ocean. 
 
 The movements of the crust of the earth during the tertiary, 
 are among the most extensive of which we have any record, yet 
 they were doubtless quiet and slow, in fact, rivers in the Rocky 
 Mountains and in the Himalayas have deepened their rocky 
 channels as rapidly as the mountains rose. 
 
CHAPTER L. 
 
 GLACIAL PERIOD. 
 
 THE Quaternary Age is divided into the Glacial, the Champlain, 
 and the Terrace periods. 
 
 The glacial, or ice period, like other geological phenomena, seems 
 to have come on gradually. In the early part of the tertiary, the 
 climate of Central Europe and North America was sub-tropical, 
 and flowering plants and shrubs were growing within the Arctic 
 circle. During the extensive changes in the crust of the earth 
 which occurred in the tertiary, the northern parts of the conti- 
 nents seem to have been gradually elevated to a height of some 
 1,000 to 2,000 feet above the present level. With this elevation 
 the climate gradually became more severe, until the ice and snow 
 had crowded the shrubs and flowering plants far toward the 
 south, and were occupying the greater part of North America, 
 north of the Ohio river, and the northern and central portions of 
 Europe, and parts of Asia and the glacial period was in full 
 progress. 
 
 Then followed periods when the ice seems to have retreated 
 and advanced several times, as if the climate were alternately 
 warmer and colder. One retreat was so great, that many speak 
 of the next advance as a second glacier. But at length the ice 
 retreated to the confines of the polar zone, and temperate climates 
 prevailed over Central Europe and North America. 
 
 The glaciers of the Alps and the Pyrenees, those that linger in 
 Norway and cover Greenland, the glaciers of Alaska and the 
 Rocky Mountains, are but the remnants of the great ice sheet 
 that dominated the northern part of both continents for untold 
 centuries. 
 
 From a study of these existing remnants, and the work they 
 do, we may gain some idea of what were the conditions of our 
 (362) 
 
LESSONS IN GEOLOGY. 363 
 
 country during the glacial period; and may find some rational 
 explanation of the interesting and peculiar surface features which 
 were determined wholly, or in part, by glacial ice. 
 
 The study of surface features is somewhat complicated by the 
 fact that coincident with the final retreat of the ice, the whole 
 region sank slowly down almost to sea level, and was cov- 
 ered with the broad, shallow lakes, or seas, of the Champlain 
 period, which greatly modified the surface left by the ice sheet. 
 Then the surface rose to about its present level, the lakes drained 
 away, still further modifying the old glacial surface, as the coun- 
 try gradually attained its present condition. 
 
 Ice seems to be a brittle solid, but as it accumulates in the 
 mountains of Switzerland, it flows down those valleys like rivers, 
 slowly but surely following every change in direction, every vari- 
 ation in slope, and every irregularity of surface almost as per- 
 fectly as water does. 
 
 As the ice moves down the valley loose fragments of rock are 
 pushed forward, abrading each other as they roll along; sharp 
 angles of rock are broken off, which, with rocks falling from cliffs 
 above, jostle along between the ice and the sides of the valley 
 abrading each other, till in time the whole mass of ice is filled 
 with sand, gravel, pebbles and fragments of rock. Those along 
 the bottom and sides, held firmly in the frozen grasp, make the ice 
 a gigantic rasp scratching, striating and grooving its rocky bed, 
 and smoothing out its sharper irregularities. Thus the ice river, 
 like the river of water, flows toward the sea with its burden of 
 mud, sand, pebbles, etc. At the end of the glacier the melting ice 
 forms a stream which carries away much of the fine dust from 
 the glacial mill ; but the pebbles, boulders and rocks, with much 
 of the finer materials accumulate, forming what is called a mo- 
 raine. A few hotter seasons cause the ice to retreat from the 
 moraine, covering the ground with clay, pebbles and boulders, 
 which otherwise would have been heaped on the moraine. A few 
 colder seasons and the ice advances again, pushing before it the 
 loose material it dropped on its retreat, until it again reaches 
 the moraine and perhaps crowds it forward. 
 
364 PRACTICAL LESSONS IN SCIENCE. 
 
 As the continental ice sheet retreated, it left the whole country 
 covered with clay that was so filled with pebbles and boulders 
 that it has received the name of boulder clay, sometimes known 
 as bard pan ; it is so hard, and resists erosion so well that it is 
 often mistaken for rock. The margin of the ice sheet can be 
 traced across the United States with some degree of accuracy, 
 but in many cases the location is doubtful, as the original de- 
 posits, doubtless thin toward the margin, have been so washed 
 away and commingled with other material that the limit of the 
 ice cannot be denned. 
 
 The line that marks in a general way the southern limit of the 
 ice and drift, runs from Cape Cod along the south shore of Long 
 Island to New Jersey, then northwesterly to near the headwaters 
 of the Alleghany river, not far from Salamanca, thence south- 
 westerly through New Lisbon, Danville and Winchester, Ohio, 
 crossing the Ohio river near Cincinnati to Madison, Indiana, 
 thence northwesterly a little beyond Martinsville, thence south- 
 westerly through New Harmony to the Mississippi river near the 
 mouth of the Big Muddy, thence up the river crossing to the Mis- 
 souri below St. Louis, thence up the Missouri to the Osage, then 
 up the Osage for a short distance, then westerly and northwest- 
 erly in a course generally parallel with the Missouri river to the 
 Rocky Mountains, thence southerly nearly to the head waters of 
 the Red river, thence across the mountains and northerly to 
 about the Columbia river, thence southerly including most of 
 the Sierra Nevada Mountains and the northern part of the Coast 
 ranges. The mountain region was hardly covered by an ice 
 sheet, but was rather the seat of numerous local glaciers, much 
 as Alaska and Switzerland are to-day. 
 
 The greater part of this region had been above the sea and 
 subject to erosion since Devonian times, and was deeply scored 
 by drainage channels that in great measure determined the direc- 
 tion of the ice flow, tongues or lobes of ice flowing along the val- 
 leys in advance of the ice sheet ; and these are sometimes called 
 glaciers, as the Green Bay lobe or gla,cier, the Lake Michigan 
 glacier, the Saginaw glacier, the Maumee glacier and several les- 
 
LESSONS IN GEOLOGY. 365 
 
 ser ones farther east. During the time of most extensive glacia- 
 tion these doubtless were all united into one broad sheet of ice 
 that extended nearly or quite to the line already traced across 
 the country ; but for the most part they were separate bodies of 
 ice. The moraines in many places are very distinct; they are 
 readily traced on Long Island, across Pennsylvania, Ohio and 
 Indiana. The moraine bounding the Lake Michigan glacier has 
 been traced, the common portion between the Lake Michigan and 
 the Saginaw glaciers being well marked, extending north and 
 south just west of the center of Michigan. And the one between 
 the Saginaw and Maumee glaciers is also well marked in the 
 eastern part of Michigan. And the peculiar relation of the St. 
 Mary's and St. Joseph rivers to the Maumee is due to a terminal 
 moraine of the Maumee glacier along which these rivers flow to 
 a common opening through the ridge. In Minnesota and Dakota 
 there are numerous moraines, forming two systems of lobes or 
 loops, the arrangement being more complicated than farther east. 
 
 At places over this area where bed rocks are exposed, they 
 show marks of glaciation, as at Put-in-Bay in Northern Ohio, Ni- 
 agara Falls, and other places, the striae indicating the direction 
 of ice flow ; sometimes two or more systems of striae occur on the 
 same surface, indicating two or -more invasions of ice flowing in 
 different directions. 
 
 Boulders from the hard pan are often glaciated ; sometimes 
 specimens are found that have been striated in a dozen different 
 directions, as they have turned in the loosening grasp of the ice. 
 Many of the boulders and much other glacial material came from 
 limestone and sandstone rocks whose original bed is not far 
 away, but for the most part glacial debris came from the Lauren- 
 tian tableland. 
 
 It is interesting to trace these boulders back to the native 
 quarry, selecting well-marked varieties, so that there shall be no 
 doubt as to the identity of specimen and quarry or ledge. In 
 this way it is shown that the "drift" material of Iowa, in 
 general, came from the northeast, of Indiana and Ohio from the 
 north, of New England from the northwest. In Indiana, Ohio 
 
366 PRACTICAL LESSONS IN SCIENCE. 
 
 and Michigan nearly all the varieties of granitic rocks may be 
 found among the boulders of the hard pan. Large quantities of 
 drift have been transported from 300 to 500 miles, but for the 
 most part the transportation has seldom been more than 100 
 miles. But little is known about the thickness of the ice ; it seems 
 to have covered the mountains of New England, but was doubt- 
 less much thinner west and south, for in southwestern Wisconsin 
 and vicinity there is a large area over which no glacial ice ever 
 flowed; it is a "driftless area." The flow of ice over such low 
 gradients as seemed to prevail during the glacial period is not 
 well explained. It flows over similar gradients in Greenland, so 
 that it is not impossible, only difficult to understand. It is also 
 difficult to understand how the ice became so loaded through and 
 through with rocks, boulders, etc. 
 
 The Laurentian tableland includes the oldest mountains, and 
 the great lakes occupy the oldest valleys on the continent. 
 Their great depth, some of them reaching two or three hun- 
 dred feet below the level of the sea, is not only evidence of 
 great erosion, but of the fact that the whole region for ages stood 
 at least from 1,000 to 1,500 feet higher than now ; for those old 
 channels must have had outlets to the sea. The glacier smoothed 
 up these old channels, perhaps changing their form somewhat, 
 but not materially; and when it retreated, its load of clay and 
 rocks filled many of them, and parts of many more, result- 
 ing in the formation of thousands of lakes, great and small, over 
 some parts of the glaciated area. 
 
 The rocky bed of the Cuyahoga river, at Cleveland, is about 
 225 feet below the present level of Lake Erie. The beds of other 
 tributaries of Lake Erie are at about the same distance below its 
 level, which seems to indicate that the lake occupies an old valley, 
 which formerly had an outlet to the sea at a much lower level. 
 There is evidence of such a channel, now filled with glacial mate- 
 terial, extending from Lake Erie to the head of Lake Ontario. 
 The filling up of this old channel changed a portion of a river 
 valley into a lake, and the waters of this lake, finding an outlet 
 across the divide to Lake Ontario, formed the Niagara river, with 
 
LESSONS IN GEOLOGY. 367 
 
 its famous rapids, gorge, and cataract. Some think the old out- 
 let of the Ontario valley was by the Mohawk and Hudson river 
 valleys, and that the St. Lawrence flows in a recent channel, at 
 least for a portion of its course. Lakes Huron and Superior are 
 supposed to have had their outlet by the Ontario valley, but 
 many suppose Lake Michigan flowed toward the Gulf. 
 
 The glacier as it advanced southward drove before it all the 
 plant and animal life of the region, carried away all the soil, and 
 in many respects changed and modified the surface features of the 
 country. Then retreating, it deposited material for a new soil, 
 obliterated many old channels and changed many others, formed 
 ridges, hills, and lakes, in fact changing the whole face of the 
 country. 
 
 The cause of the climate of the glacial period is one of the 
 questions which geologists have not satisfactorily answered. 
 The elevation of northern regions with the advance of the ice, 
 and their depression as the ice retreated, seems to connect the 
 events in the relation of cause and effect. Such elevation might 
 have closed Bering strait, and shut the Gulf stream from the 
 Arctic ocean, and yet it does not seem to geologists generally as 
 if such elevation was adequate to the effect. Some have at- 
 tempted to find a cause in the changes in the eccentricity of the 
 earth's orbit, combined with other astronomical causes, but this 
 idea does not appear satisfactory. Others have supposed a de- 
 pression of the Isthmus of Panama, allowing the Gulf stream to 
 pass into the Pacific ocean, as an adequate cause; but there is 
 no evidence of such depression during glacial times, and nothing 
 to show that it would have affected the climate if there had been. 
 Other theories have been advanced, but have not been received 
 with favor. At present it can only be said that most geologists 
 acknowledge elevation as a cause, but think that some other as 
 yet unexplained cause must have acted in connection with eleva- 
 tion to have produced the results. 
 
 When did the glacial period begin, how long did it continue, 
 and how many years has it been since the ice retreated? are 
 questions often asked of the geologist. No very definite answer 
 
368 PRACTICAL LESSONS IN SCIENCE. 
 
 can be given to the first or the second questions, but many at- 
 tempts have been made to answer the third. 
 
 It is generally supposed that the gorge of the Niagara has 
 been formed since the retreat of the ice, and that if we knew the 
 age of the gorge we would know how long it has been since the 
 glacier. Early estimates of the age of the gorge varied from 
 35,000 to 100,000 years, but later ones vary from 4,000 to 
 10,000 years. The river at the present time is cutting back at 
 the rate of about 2.4 feet per year, or a mile in about 2,200 years, 
 and the gorge in about 15, 400 years. But there are evidences 
 that the river found considerable work already done on the 
 gorge when it began to flow, so that perhaps 7,000 years would 
 be a safe estimate for the age of the Niagara gorge, and for the 
 time that has elapsed since the ice retreated from the St. Law- 
 rence valley. 
 
 The glacier was a very effective erosive agent, but whether 
 more effective or rapid than air and water is very doubtful. 
 
CHAPTER LI. 
 
 THE CHAMPLAIN AND TERRACE PERIODS. 
 
 AFTER a long period of elevation the northern portions of 
 Europe and North America were slowly depressed and the ice be- 
 gan to retreat. The floods from the melting glacier opened many 
 old drainage channels that had long been closed by glacial debris. 
 But as the depression continued, the streams became sluggish 
 and began to silt up their channels with clay, sand, gravel, etc. 
 At length over great areas drainage almost ceased, and wide, 
 shallow lakes and marshes and ponds were formed, their surplus 
 waters carried away by broad, sluggish streams. The waters and 
 waves of these shallow lakes dissolved and broke down much of 
 the hard pan and assorted it into beds of sand and clay. There 
 were several slight oscillations of the crust, giving rise to differ- 
 ent conditions, so that in some localities there are as many as 
 six or seven layers of different kinds of material lying over the 
 boulder clay. 
 
 The Orange sand or bluff gravel, a thick deposit of glacial 
 material along the Mississippi river as far south as Louisiana, 
 may have been transported by glacial floods early in this period. 
 Later the Erie, Champlain and other clays were deposited, and 
 later still, over much of the glaciated area, reaching far down the 
 Mississippi, thick beds of fine clay or loess were formed. 
 
 The ice seems to have retreated more rapidly in the west than 
 in the east, so that when the region now occupied by the great 
 lakes was free from ice, the natural outlet of the Ontario basin 
 was still closed by the glacier. These valleys, filled with water 
 from the melting ice, formed a great inland sea with shores of 
 ice on the east and north, discharging its surplus waters toward 
 the Gulf. An old beach ridge, nearly parallel with the shores of 
 Lake Erie, shows the level of this old lake to have been at one 
 
 L. 8.-5K 
 
370 PRACTICAL LESSONS IN SCIENCE. 
 
 time at least 200 feet above the present level of Lake Erie. Other 
 beaches, at lower levels, seem to indicate that the barrier was cut 
 down at an irregular rate. 
 
 Icebergs were doubtless common on this inland sea, and per- 
 haps on other lakes of this period. It is thought by many that 
 they had much to do with distributing glacial material near the 
 margin of the drift area in the southwest, as there is often no evi- 
 dence of glacial ice having reached that region. 
 
 The Champlain period of Europe was much the same as in 
 North America, and is often called the era of fresh water for- 
 mations. 
 
 The glacial period merged gradually into the Champlain, and 
 the Champlain as gradually into the terrace period. The north- 
 ern regions began to rise again, sluggish rivers became narrower 
 and more rapid, other rivers were formed, lakes and inland seas 
 were drained away, carrying along great quantities of fine silts 
 and sands ; and at length the slender, rapid rivers began cutting 
 out channels in the sediments that filled the older, deeper, 
 wider valley. In this way bluffs and terraces were formed which 
 gave name to the period. Sometimes several terraces have been 
 formed, which are often known in common language as first bot- 
 tom, second bottom, etc. 
 
 Where the drainage was not complete, extensive marshes or 
 wet prairies and multitudes of little ponds or lakes are the only 
 remains of wider bodies of water. 
 
 The life of the quaternary was interesting as being the culmi- 
 nation of the mammalian type. 
 
 The plants and marine mollusca that during the glacial period 
 lived in what are now temperate regions, are represented at the 
 present time by species living in polar or sub-polar climates. As 
 the ice retreated both plants and mollusca migrated northward. 
 Very little is known about the birds, fishes and reptiles of the 
 period, but it is supposed that there was not much change, sim- 
 ply a migration southward as the ice advanced and a migration 
 northward as the ice retreated. 
 
 The mammalia of this period were abundant, varied in form 
 
LESSONS IN GEOLOGY. 371 
 
 and often of enormous size. Their remains are found in caves, in 
 marshes, and sometimes in the drift and silt of streams. In Eu- 
 rope more have been found in caves, while in North America more 
 have been found in swamps and bogs. 
 
 The mastodon, two species of elephants, two great bisons, a 
 giant stag, large horses and beavers, the megalonyx and the tapir 
 were the most interesting among the herbivorous animals; there 
 were one lion and two bears to represent the carnivora. In South 
 America there were several large edentates, a mastodon, with 
 wolves, panthers and others. But Europe and Asia had the 
 richest variety of species, especially among the carnivora. In the 
 bone caves of Europe they have found remains of the cave bear, 
 cave hyena, cave lion and two tigers, all of remarkably large 
 size. Several elephants, a rhinoceros, a hippopotamus, horses, 
 oxen, the great Irish elk and others represent the herbivora. The 
 mammoth, a species of elephant, was over twice the bulk and 
 weight of modern elephants. Some have been found frozen in the 
 ice of Siberian swamps; they were covered with hair and wool, 
 and the flesh, preserved by cold, was eaten with relish by dogs. 
 In one cave the remains of 800 bears were found, and one con- 
 tained the remains of at least 300 cave hyenas. 
 
 The difference between the plant life of the quaternary and the 
 present was not great, neither was the difference between the 
 lower animals of that time and the recent period, and while, at 
 first, the difference between the mammalia seems great, yet the 
 type is still the same; many species of mammals, some birds 
 and others, have become extinct, but in general the change has 
 been slight. There is no definite event that marks the close of 
 the quaternary and the opening of the recent age, or age of 
 man. The country rose out of the waters of theChamplain 
 period, formed a soil, was clothed with vegetation, and entered 
 upon the various lines of activity now in progress. 
 
 The Mississippi river is silting up its channel, which indicates 
 that the region of its upper course is slowly settling. Old beach 
 lines along the shores of Lake Ontario, that, when made, were 
 level, have been raised considerably toward the east, so that the 
 
372 PRACTICAL LESSONS IN SCIENCE. 
 
 two portions now differ in level. There are upward and down- 
 ward movements in Norway and Sweden and along the Mediter- 
 ranean sea. There are volcanoes and occasional earthquakes, 
 showing that one group of geological forces is still in operation. 
 The formation of sediments along river beds and at their 
 mouths, along the shores of lakes and of the sea, the formation 
 of sand dunes, of bog iron ore, and bog limestone, and the action 
 of rain and frost, etc., in furnishing the materials for the sedi- 
 ments, shows another set of forces at work also. The geological 
 agencies are doubtless working just as vigorously at the present 
 as ever in the history of the earth; but one set works so slowly 
 that we do not notice them, and the others are so common that 
 we do not think of them as geological. 
 
 The large and fierce animals that dominated the Quaternary 
 age passed away, and those of a smaller size and more tractable 
 disposition appeared in their stead. And the earth, with pure 
 air and water, with temperate climate, with useful plants and 
 animals, after ages of preparation at last became a fit place for 
 the home of man. 
 
 Man has doubtless lived on the earth for many centuries, was 
 contemporary with many of the large mammals, and with the 
 later events of the Glacial and Champlain periods, but does not 
 seem to have become the dominant type of life until quite recent 
 times. Remains of man are found in caverns, lake beds, peat 
 bogs and similar places, and we find the tools of bone, wood 
 and stone which he used ; and we may know something of how 
 he lived from finding fragments of bones and shells with tools, 
 etc., in caves, and at particular places along the shores of lakes 
 and seas. But the story told by these remains is very fragmen- 
 tary and not easily interpreted, but seems to indicate at least a 
 low stage of culture for primitive man. 
 
 Considered as an animal, man's appearance on the earth was 
 abrupt, as abrupt as the appearance of vertebrates in the Dev- 
 onian, and this idea is intensified when we consider man's intelli- 
 gence. 
 
 What is th ag of the earth? This is an interesting question, 
 
LESSONS IN OEOLOOY. 373 
 
 often asked, but seldom answered with any degree of satisfaction. 
 The matter of geologic time bears on so many important ques- 
 tions that much time has been given to the investigation of all 
 available data on tl^ subject, and many estimates have been 
 made. The early estimates in general were large. Sir Charles 
 Lyell considered that the earth was at least 240,000,000 of years 
 old. Dr. Charles Darwin thought that 200,000,000 of years 
 could hardly be sufficient for the evolution of organic forms. Dr. 
 A. Winchell, 1883, estimates the time since the crust was formed 
 at 3,000,000 years. Mr. W. J. McGee, 1892, estimated the age 
 of the earth at 15,000,000, and Prof. Warren Upham, 1893. 
 thinks the time necessary for building up the stratified rocks and 
 developing the plant and animal life of the world must be about 
 100,000,000 of years. These results would seem to indicate that 
 the data were not satisfactory, or else that they were not cor- 
 rectly interpreted. Mr. Charles D. Waleott, Aug. 17, 1893, in an 
 elaborate paper reviews the whole question, working out an esti- 
 mate that seems conservative when compared with those given 
 by other investigators. Confining his investigations mainly to 
 the cordilleran region of North America, he shows that erosion 
 and deposition of mechanical and chemical sediments have al- 
 ways been going on at substantially the same rate. While one 
 foot in 3,000 years is usually considered an average rate of denu- 
 dation, he assumes a rate of one foot in 200 years for the region 
 under consideration. Then, carefully estimating the area of ero- 
 sion, the area of deposition, and the thickness of sediments, both 
 mechanical and chemical, he estimates the cenozoic, including gla- 
 cial or pleistocene, at 2,900,000 years; mesozoic at 7,240,000 
 years; paleozoic at 17,500,000 years; algonkian at 17,500,000 
 years and archsean at 10,000,000 years, a total of 55,140,000 
 years. He concludes that the time since the archaean age lies be- 
 tween 25,000,000 or 30,000,000 of years as a minimum and 
 60,000,000 or 70,000,000 as a maximum time. 
 
 The physicist, calculating on the time necessary for the earth 
 to cool to its present condition, limits the time to from 10,- 
 000,000 to 30,000,000 of years. These estimates may not be very 
 
374 
 
 PRACTICAL LESSONS IN SCIENCE. 
 
 
 
 00 
 
 
 
 
 
 
 
 M *-* 
 
 4) * 
 
 
 
 |l 
 
 . . 
 
 
 
 S rrt 
 
 
 
 > OD 
 
 11 
 
 
 s 
 
 H s 
 
 42 * 
 
 ^ 
 
 ^ 3 
 
 bQ O 
 
 
 
 
 on ja 
 
 "S 
 
 O> OQ 00 
 
 G O 
 
 Is ^ 
 
 
 1 
 
 >" ^ 
 
 r< 4-s 
 S 
 
 rf^5"3 
 
 -2 H 
 
 S-& 
 
 
 9 
 
 r " H r rf 
 
 a> 
 
 x* o ^ o 
 
 r t> 
 
 C^^-^ 
 
 
 S 
 
 'd 
 
 5. :| 
 
 a) a G aT 
 
 11 
 
 'S'S 
 
 iRAM. 
 
 
 .& 
 
 Ill 
 il? 
 
 o3 ^ O 
 
 "3 73-5* 
 
 S * SS 
 1 ^^ 
 
 I | l| 
 
 Shales, lignit 
 Sandstones a 
 Limestones a 
 Conglomeratl 
 
 Limestones, 
 Silicious and 
 
 Limestones a 
 Quartzites an 
 
 (!) 
 
 
 
 ^) O O 
 
 
 tc 
 
 
 ^ 
 
 
 
 C C G fl 
 
 
 Q 
 
 
 5 
 
 & 
 
 : oj 
 
 ; C 
 
 tlllll 
 
 
 1 
 
 
 
 S9 
 
 V u 
 
 cj p, i *^ ^^ JD 
 
 
 K^* 
 
 
 j 
 
 5 
 
 T3 
 
 a 
 
 O X 
 
 OS 4J 
 
 & .22 
 o3 5 
 
 x^V-^ ^N^^ v-^ 
 
 
 2 
 
 03 
 
 i 
 
 > 
 
 
 
 03 
 
 
 1 
 
 H c S 
 b.S fa 
 
 83 o 
 
 J4 * O 
 
 " J5 ' 
 
 i| 
 
 o 
 
 ^* 
 
 3 /^ 
 
 (D 
 
 
 1 
 
 s 
 
 111 
 
 0X3 -S 
 
 tfOO 
 
 
 ti Q'O 3 
 
 .3 o^ 
 
 S J 
 
 ! 
 
 at 
 
 Sw 
 
 
 
 
 v v 
 
 v ^ . / 
 
 
 
 
 
 ^^^~v^^^> 
 
 V 
 
 v L 
 
 ~*~ y ^* h- * 
 
 *_* t"^" 
 
 
 
 u 
 
 1 
 
 - *1 
 BtlBUI 
 
 JBTC PUB 
 ta^H jo a3y 
 
 wmd 
 
 an jo e3v 
 
 
 
 
 
 
 ; 
 
 
 
 
 
 
 fe 
 
 
 3 
 
 
 
 
 1 
 
 a 
 M 
 
 J 
 
 
 
 'S3 
 
 .H 
 
 
 
 I 
 
 5 
 
 "i 
 
 
 
 J 
 
 
 
 
 
 0) 
 
 M 
 
 3 
 
 'C 
 
 
 
 O* 
 
 H 
 
 O 
 
 
 H 
 
 
 
 
 
 
 
 
 
 
 
 O 
 
 
 O 
 O 
 
 
 
 S 
 
 
 I 
 
 
 H 
 
 
LJ&tiONS IN GEOLOGY. 
 
 375 
 
 A 
 
 
 
 
 
 I 3 5 
 
 
 
 c 
 
 
 
 
 00 'f' 
 
 
 2 
 
 
 
 
 
 
 0} QJ 
 
 ^2 S 
 
 00 
 
 
 
 
 
 o o 
 
 GJ wT O 
 
 0) 
 
 
 
 
 
 
 
 ** o> 
 
 c 
 
 . s 
 
 o> S 
 
 
 
 00 
 
 'S 
 
 be 
 
 Is 
 
 CD r+ 
 
 If 
 
 i sandston 
 limestone 
 
 iPi 
 
 sip 
 
 s 
 
 || 
 
 lii 
 
 Ta 03 cs 
 
 -G QQ OD 
 
 s ^ s 
 
 fl * 00 
 
 1 j-fl 
 
 granites, 
 
 itB. 
 
 rO H 
 Sw '2 
 
 S S 
 22 
 
 W 00 """H 
 
 1111 
 
 S g 
 
 O 3 
 
 * 
 
 00 OJ <JJ 
 
 III 
 
 ^ S ^ o ^ 
 
 fl) ^ di c rt) 
 4J >4J tC*J OQ 
 
 || 
 
 bO 
 
 C o3 0) 
 
 r 
 
 <D o> 
 
 a S 
 
 . . X CD 
 
 C G C C 
 
 OD rt 00 
 
 $ s 
 
 c 3 fl 
 
 T3 oo" 
 
 SiS 
 
 S&S'gsl 
 
 |l 
 
 1-sj 
 
 il"3 
 
 3o 
 
 Limesto 
 Sandstoi 
 
 03 c3^ 
 
 B-3 
 
 02 >-. CD 
 HJr-'O) 
 
 s^s 
 
 2 S3 
 
 5 ".3 
 
 CO 00 OQ 
 2^^ 
 
 52 
 
 h^OQGQ 
 
 ttji= 
 
 ?s 
 
 
 
 
 
 
 : 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 d d 
 
 '^ /H 
 
 o3 c3 
 
 
 
 
 
 
 rt C3 
 
 
 Permian 
 Coal Measures 
 Conglomerates 
 
 a a 
 
 22 
 
 *i ^ 
 
 r Chemung .... 
 Hamilton .... 
 Corniferous . 
 !>. Oriskany 
 
 Helderberg. . 
 Salina 
 Niagara 
 
 Trenton 
 Canadian 
 Primordial. . . 
 
 'Keweenawan 
 Upper Huroni 
 Lower Huroni 
 
 Upper Laureni 
 Lower Laurent 
 
 ^- v- -^- 
 
 
 
 
 
 V 
 
 
 
 Id 
 
 wqsjj 
 
 
 . 
 
 >w 
 
 Sati 
 
 {BOO JO 
 
 
 J09SV 
 
 pu 
 
 B ajn I9AVC 
 
 )1 jo 83y 
 
 
 a 
 
 00 
 
 a 
 
 
 
 c 
 
 03 fl 
 
 
 
 
 
 o 
 
 
 
 C 03 
 
 
 
 Upper 
 Carbonifer 
 
 Lower 
 Carbonifer 
 
 i 
 
 1 
 
 1 
 
 Silurian . . 
 
 Lower Silu 
 or Cambri 
 
 1 
 
 1 
 
 3 
 
 Archaean.. 
 
 
 
 
 
 
 
 
 
 
 . 
 
 j > 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 *T 
 
 o 
 
 
 
 o 
 
 
 
 
 | 
 
 
 
 o 
 
 
 
 
 4 
 
 
 
 N 
 
 
 
 
 q 
 
 
 
 O 
 
 
 
 f 
 
 M 
 
 
 
 
7 PRACTICAL LESSONS IN SCIENCE, 
 
 satisfactory, but they give us some idea of how difficult it is to 
 say how old the earth is. Geological time is divided into eras, 
 ages, and periods, and the rocks into systems and groups. And 
 once there were primary, secondary, tertiary, and quaternary 
 systems or ages. The primary and secondary have been subdi- 
 vided, and the names dropped, while the terms tertiary and quat- 
 ernary have been retained. 
 
 Geological studies began in Europe, and the names were de- 
 rived from localities, as Devonian, from the town of Devon, and 
 Silurian from the town of Silures, in England, Jurassic from the 
 Jura mountains, etc. The first important geological work done 
 in this country was in New York. Some European names were 
 retained, but many local names were adopted, as Niagara, Ham- 
 ilton, Chemung, and other states have followed the same custom, 
 so that we have Knoxville, St. Louis, Keokuk, limestones, etc. 
 The period or group names for the Mesozoic and early Cenozoic 
 eras in this country are derived mainly from localities in the 
 western mountain region, where those rocks are most abundant. 
 With increasing investigation and knowledge the nomenclature 
 and classification will change, but the diagram on two preceding 
 pages represents in a general way the present condition of the 
 subject. 
 
CHAPTER LII. 
 
 THE THEORY OF ORGANIC DEVELOPMENT. 
 
 WE have learned something about the different kinds of matter, 
 and of the forms under which they appear; and we have studied 
 the forces acting upon matter, and the laws in accordance with 
 which they are supposed to act. In this study we have learned 
 that the molecular or atomic theory of matter, the law of defi- 
 nite proportions in chemical combinations, the undulatory the- 
 ory of light and heat, the conservation of energy, and the theory 
 of universal gravitation, are the great propositions or theories 
 which determine the lines of scientific thought, and around which 
 all the varied phenomena of the material world cluster for corre- 
 lation and explanation. These theories may not stand the test 
 of future investigation; they may prove inadequate, may be 
 modified, may give place to others; but at present they are the 
 best the only working theories we have and through them 
 most of the activities of nature around us may be explained ; 
 hence, some knowledge of them is valuable in any system of 
 education. 
 
 We have studied the different forms of life which occur on the 
 earth. In them we found matter under the influence of a new 
 force, displaying quite a different cycle of events. A group of 
 molecules, endowed with life, comes into existence, is developed to 
 maturity , reproduces its kind, and dies. The history of life forms, 
 as individuals, is simply this and nothing more all their en- 
 ergies are directed toward growth and reproduction. Primarily, 
 their relations are to parents on the one side, and to offspring on 
 the other; incidentally, they have a wide range of relations with 
 other forms of life, and with the inorganic world. Living beings 
 differ widely in form, structure, and intelligence, and in many re- 
 spects the phenomena of life are more interesting than those of 
 
 (877) 
 
78 PRACTICAL LESSONS IN SCIENCE. 
 
 the inorganic world; and the question is often asked, how do 
 you account for, and explain this bewildering variety of life 
 forms and the complex phenomena incident to their existence? 
 
 Until quite recent times, most people believed that the sun, 
 moon and stars, the earth, with all its varied forms of life, and 
 all material things, were created out of nothing. No one could 
 comprehend the idea, but few doubted its truth. But as man be- 
 came more intelligent, the idea of the creation of matter from 
 nothing began to be questioned, not irreverently, but simply 
 from a desire for the truth. This inquiry brought out the fact 
 that the word creation, as used, had different meanings, and the 
 idea began to grow that perhaps matter in its essence is eternal, 
 was not created from nothing, but was moulded or shaped over 
 into its present forms, something as the potter moulds the clay, 
 or the workman makes a watch. And it was believed that every 
 particular form of life was the result of a special act of creation. 
 But a careful study of the phenomena of life has led students of 
 botany, zoology and geology to the conclusion that special crea- 
 tion was not God's method in nature, but that some form of 
 evolution or development was most probably the method 
 employed. Organic development, then, is the great proposi- 
 tion or theory around which the facts and phenomena of the 
 vegetable and animal kingdoms gather for correlation and 
 explanation. 
 
 This theory may prove inadequate ; may not stand the test of 
 future investigation; but it is the only one now recognized by 
 scientific men. No other theory ever promulgated has been as 
 prolific of good results. It has stimulated thought in every de- 
 partment of human endeavor, not only in all lines of scientific 
 work, but in all lines of social and historical work. Thus, whether 
 true or false, every intelligent person should know at least some- 
 thing of the grounds for its existence. Evolution in its present 
 form is a modern theory which required for its elaboration an 
 amount of knowledge whick could only be acquired gradually 
 through years of scientific research. But the idea of evolution is 
 by no means recent; some of its problems have been considered 
 
LESSONS IN QEOLOGI. 379 
 
 in almost every system of philosophy. They were matters of 
 speculation among the East Indians, the Arabs, the Jews, the 
 Greeks and the Schoolmen, and they have been discussed by later 
 philosophers, as Hobbs, Descartes, Locke, Kant, Hegel and 
 others. But the honor of bringing the doctrine before the world 
 in such a clear and forcible way as to command universal atten- 
 tion belongs to Charles Darwin and Russel Wallace, whose first 
 publications were in 1858 and 1859. 
 
 One of the first steps toward this theory is the observed unity 
 of all forms of life, as shown by the fact that plants and animals 
 have about the same chemical composition; that plant and ani- 
 mal protoplasm appear to be identical; that the germinal vesicle 
 and sexual reproduction are similar in each; the difficulty in dis- 
 tinguishing between the lower forms of animals and plants; that 
 plants and animals are cellular in structure; that plants and an- 
 imals, as individuals, develop from a bit of structureless proto- 
 plasm to a complicated organism, each growing by the simple 
 multiplication of cells; and the fact that animals and plants are 
 affected in much the same way by physical environment all of 
 which with many other things point toward the unity, the con- 
 tinuity of life on the earth; plants and animals possibly develop- 
 ing from a common germinal stock, plants through fixed forms, 
 animals through motile forms. 
 
 Another is the fact that offspring inherit some of the charac- 
 teristics of the parents, but not all. A number of children may 
 be similar to their parents and to each other in many respects, 
 the family features and traits may be well marked, yet each has 
 his pecmliarities, differing from all the others in some particulars. 
 This fact is expressed in the phrase, " heredity, or descent with 
 variation." Variation in size and activity is common among 
 men and domestic animals, and among wild animals as well, va- 
 riations in size sometimes amounting to as much as one fourth 
 of the average size of the species. There may be variations in 
 the length of legs, breadth of wings, size of fins and in other respects. 
 
 Then the fact that a pair of the slowest breeding animals, or 
 plants if unchecked, would stock the earth to repletion within 
 
S80 PRACTICAL LESSONS IN SCIENCE. 
 
 1,200 or 1,500 years. Thus with the great numbers of different 
 kinds of animals and plants there must be a continued struggle 
 for existence, animals of the same kind struggling with each 
 other, and with other kinds of animals and with plants, and 
 plants struggling with each other and with animals, and all per- 
 haps struggling against unfavorable climatic conditions. In 
 this conflict many in fact, most perish, the few only survive. 
 The strongest, the most active, the most intelligent, those that 
 are in some way superior, survive and produce offspring. This 
 process Darwin called " natural selection," Spencer calls" survival 
 of the fittest." In this way Mr. Darwin believed new species were 
 formed instead of by special creation, and that animals were de- 
 scendants from at most only four or five progenitors, and plants 
 from an equal or lesser number. Thus, he says, "From the war of 
 nature, from famine and death, the most exalted object which we 
 are capable of conceiving, namely, the production of the higher 
 animals, directly follows." " There is grandeur in this view of life 
 with its several powers, breathed by the Creator into a few forms, 
 or into one; and that from so simple a beginning endless forms 
 most beautiful and most wonderful, have been and are being 
 evolved." 
 
 Many things seem to point toward the probable truth of the 
 theory. There is no doubt about the fact of individual develop- 
 ment; we are all descended from Adam by natural processes; 
 each individual a complex organism, developed from structureless 
 protoplasm. If evolution is God's method with the individual, 
 there seems to be no reason why it may not be His method with 
 the species, genus, etc. 
 
 In horses, the bone above the fetlock joint corresponds to the 
 middle bone of the hand. On each side of this bone there is a 
 little bone called a splint bone. These splint bones seem to be 
 of no use 01 value to the horse, and on the theory of special crea- 
 tion they cannot be explained, but on the theory of descent they 
 represent the second and fourth digits of some three or five-toed 
 ancestor, and thegeological record shows that thehorsehad such 
 ancestors. Many similar cases might be mentioned. Most ani- 
 
LESSONS IN GEOLOGY. 381 
 
 raals are able to move their ears freely and many can move por- 
 tions of the skin ; in general, man can move neither the ears nor skin 
 and yet muscles for moving the ears and scalp exist in an aborted 
 form, and occasionally individuals can use them. The presence 
 of these muscles is not explained by special creation, but on the 
 theory of descent with variation they indicate that some ances- 
 tor of man had use for such muscles. 
 
 The embryos of the higher animals in their development simu- 
 late the forms of lower animals; the embryo of the chick shows 
 the gill slit of fishes and the teeth of reptiles, and it is not till 
 quite late in its embryonic life that the human embryo takes on 
 or begins to develop human characteristics. These phenomena, 
 utterly unexplained on one theory, are at least partially elucidated 
 under the other. According to the theory of evolution, the devel- 
 opmental history of the individual appears to be a short recapitu- 
 lation of the course of development of the species. There seems 
 to be a correspondence between the individual development of the 
 higher animals and the progressive advance of organization 
 in the whole animal series. The geological record gives interest- 
 ing evidence in the case; it is necessarily an imperfect record, for, 
 as a rule, only the hard parts of aquatic life would regularly be 
 preserved, and only a small part of the record has been or can be 
 examined. When the crust was first formed, no life of any kind 
 could exist; but as the earth cooled water and other substances 
 were condensed from the atmosphere, and the inter-actions be- 
 tween the atmosphere, water and crust removed impurities from 
 the air and water, and put them away in permanent form, leav- 
 ing the water and air in a. condition favorable for the lower forms 
 of life. And such forms of life appeared in great abundance, as 
 the thick beds of iron ore and graphite in the older rocks are 
 supposed to show. The life must have been of low form, as none 
 other could have existed under the conditions which probably 
 prevailed. As these chemical reactions continued, the plant and 
 animal life also removing impurities, the air and water gradually 
 became fitted for higher and higher types of life. The early forms 
 of life seem to have been flexible and abundant, so that they 
 
382 PRACTICAL LESSONS IN SCIENCE. 
 
 adapted themselves to changing conditions and crowded into 
 every new addition to the domain of life. As conditions changed 
 some forms could not adapt themselves, and, overcome in the 
 struggle, passed away and others took their places. It is esti- 
 mated that there were more than thirty complete changes of 
 species during the paleozoic time. So that the principle of the 
 " survival of the fittest " seems to have prevailed from the very 
 beginning of life on the earth. 
 
 The graphite of the early ages, the limestones of the Silurian 
 and later ages, the coal of the carboniferous, all represent impuri- 
 ties removed from air and water by different forms of life. It is 
 interesting to note that each form of life has helped to prepare 
 the way for other and higher forms, generally lessening the op- 
 portunities for their own existence. The coal plants not only ren- 
 dered the air more pure, but so changed it as to allow the sunshine 
 to reach the surface of the earth with vigor enough to promote 
 the growth of flowering plants. 
 
 Every step in the history of the earth prior to the advent of life 
 was in preparation for life, and every step afterward was in prep- 
 aration for higher forms of life. 
 
 But the geological record at present is by no means contin- 
 uous; the Wank between the archaean and the Cambrian equals 
 nearly one third of the whole record, leaving the origin of the 
 protozoa, coelenterata, arthropoda, echinodermata, mollusca, 
 molluscoida and tunicata without record. Some of the rocks of 
 this period have been found, and some fossils have been discov- 
 ered, but the rocks are so highly metamorphic that there is little 
 hope of ever finding anything like a complete record of the period. 
 In this period the protophyta, zygophyta, oophyta, and carpo- 
 phyta had their origin, of which no trace has been found in the 
 rocks. 
 
 Fishes, the first of the vertebrates, appeared somewhat ab- 
 ruptly in the later part of the Silurian age. It is claimed that 
 the first so-called fiiJies were of a comprehensive type, from which 
 both fishes and reptiles were derived, but transitional forms are 
 not numerous. And so on, the geological record inageneral way 
 
LESSONS IN GEOLOGY. 383 
 
 sustaining the development theory, new discoveries as a rule 
 being favorable to that idea. 
 
 While the testimony is fragmentary, and the evidence incom- 
 plete, yet there is scarcely a botanist, zoologist or geologist of 
 note, who does not believe that some form of development was 
 God's method of creation. Progress means the laying aside of 
 ideas which are the result of limited knowledge, and the accept- 
 ance of other ideas, the result of wider information. The world 
 had to give up the Ptolemaic theory, had to accept the theory of 
 universal attraction, had to give up the idea that the earth was 
 not more than 8,000 or 10,000 years old, had to give up the 
 corpuscular theory of light, had to accept the theory of conserva- 
 tion of energy, had to change its theory as to the treatment of 
 the insane. These and many other changes hare been ma^e, as 
 the result of wider knowledge, and these changes were made with- 
 out detriment to any, but rather resulted in benefit to all. So if 
 we have to give up the idea of special creations, and accept the 
 idea of development, no damage will be done. 
 
 Some persons object to the theory of evolution as atheistical. 
 Dr. Asa Gray, a strict Presbyterian, Prof. Joseph Le Conte, an 
 earnest Christian, Dr. Alexander Winchell, a Methodist, and hosts 
 of others equally prominent as believers in God, would unite with 
 Prof. John Fiske in saying, " The doctrine of evolution asserts as 
 the widest and deepest truth, which the study of nature can dis- 
 close to us, that there exists a Power to which no limit in time or 
 space is conceivable, and that all the phenomena of the universe, 
 whether what we call material, or what we call spiritual, are 
 manifestations of this infinite and eternal Power." 
 
CHAPTER Lin. 
 
 SUGGESTIONS AS TO LINES OF STUDY. 
 
 THE first and perhaps the most important work to do in be- 
 ginning the study of the geology of any locality is topographic. 
 The topography of a place includes its actual location, its rela- 
 tive position as to mountains, hills, valleys and plains; as to 
 lakes, ponds, swamps, marshes, rivers and other streams. It 
 also includes a study of the soil and vegetation, and as these and 
 other topographic features depend largely on climatic conditions, 
 temperature, winds and rainfall need to be considered in topo- 
 graphic work. 
 
 This work is not only an important introduction to geological 
 investigation, but the items considered in topography constitute 
 the environment of the various forms of life, and need to be un- 
 derstood and considered in any good botanical or zoological 
 work. Topographic work is not only important, but easy and 
 interesting. 
 
 Actual location is readily ascertained in all those states where 
 the rectangular system of survey was used. Under this system 
 principal meridians were located with great accuracy, and the 
 country on each side was divided into ranges six miles wide by 
 secondary meridians, as nearly parallel with the primary merid- 
 ian as the spherical form of the earth would permit. The first 
 principal meridian is the boundary between Ohio and Indiana in 
 longitude 84 51' west; the second runs through Indiana in 
 longitnde 86 28' west; the third through Illinois in longitude 
 89 10' 30" west; the fourth is in longitude 90 29' 56" west,- 
 the fifth is in longitude 90 58' west; the sixth in longitude 97 
 22' west, and the Michigan meridian in longitude 84 19' 9 // 
 west. Others were located as occasion required. A base line 
 (384) 
 
LESSONS IN GEOLOGY. 
 
 385 
 
 was also run with great care perpendicular to the principal me- 
 ridian, and then lines were run parallel to the base line at inter- 
 vals of six miles on either side, dividing the ranges into townships 
 about six miles square. 
 
 On account of the form of the earth it was necessary to estab- 
 lish correction, or secondary base lines at certain intervals. The 
 base line for Indiana and Illinois is in 38 58' 12" north latitude. 
 
 
 N 
 
 
 1 
 
 
 
 
 
 (3) 
 
 (2) 
 
 (1) 
 
 
 
 3 
 
 
 
 
 w 
 
 13 
 (4) 
 
 (5) 
 
 (6) 
 
 E 
 
 
 
 
 
 
 
 
 
 Base. 
 
 Line. 
 
 
 
 i 
 
 1 
 
 2 
 
 
 
 (9) I 
 
 (8) 
 
 (7) 
 
 
 
 s 
 
 fl) Township 2 north of range 2 east. 
 
 (2) Township 2 north of range 1 east. 
 
 (3) Township 2 north of range 1 west. 
 
 (4) Township 1 north of range 1 west. 
 
 (5) Township 1 north of range 1 east. 
 
 (6) Township 1 north of range 2 east. 
 
 (7) Township 1 south of range 2 east. 
 
 (8) Township 1 south of range 1 east. 
 
 (9) Township 1 south of range 1 west. 
 
 The ranges are designated by number east or west of the 
 principal meridian and the townships by number north or south 
 of the base line; as shown in the above diagram. 
 
 A township is six miles square and is divided into thirty-six 
 
 L. S. 25 
 
386 
 
 PRACTICAL LESSONS IN SCIENCE. 
 
 square miles, or sections, which are numbered from 1 to 36, 
 inclusive; as shown in the diagram below. 
 
 The township is not perfect in form, neither is the section, but 
 the township is so divided as to throw most of the irregularity 
 into the north and west tiers of sections which are often frac- 
 tional, and there are fractional sections along lakes and large 
 streams of water. 
 
 6 
 
 5 
 
 4 
 
 3 
 
 2 
 
 1 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 18 
 
 17 
 
 16 
 
 15 
 
 14 
 
 13 
 
 19 
 
 20 
 
 21 
 
 22 
 
 23 
 
 24 
 
 30 
 
 29 
 
 28 
 
 27 . 
 
 26 
 
 25 
 
 31 
 
 32 
 
 33 
 
 34 
 
 35 
 
 36 
 
 A section contains about 640 acres. It is divided by lines 
 through the center, parallel to its sides, into quarter sections of 
 160 acres each, and these into quarter quarters of 40 acres each, 
 and so on as far as desirable. 
 
 A section is one mile, 80 chains, 320 rods, or 5,280 ft. square, 
 the quarter section is one-half mile, 40 chains, 160 rods or 2,640 
 ft. square, and the quarter quarter is 80 rods or 1,320 ft. 
 
LESSONS IN GEOLOGY. 387 
 
 square. The system is simply the application of latitude and 
 longitude to land measurement, and was first used in Ohio. 
 
 The following sample description will show the practical work- 
 ing of the system : Five acres being the south half of the north- 
 west quarter of the northeast quarter of the southeast quarter 
 of section twelve (12), township ten (10), north of range nine (9), 
 west of the second principal meridian. From the foregoing one 
 can easily interpret the description of an ordinary deed. If you 
 wish to locate a certain tract of land, hill, stream, or ledge of 
 rock, borrow a deed of the land or of some in the immediate 
 neighborhood; make a diagram of a township and locate the 
 land described in the deed on the diagram. Sometimes the one 
 description solves the whole question of location; sometimes one 
 may have to consult several deeds, and may need to ask some one 
 to point out a few section lines and corners before a given locality 
 is fixed satisfactorily. 
 
 After locating a few prominent points, find out by measure- 
 ment where the streams you wish to locate cross the section lines, 
 and if very crooked, where they cross the quarter-section lines 
 also, then map in the stream across the section as accurately as 
 possible. In this work a pocket compass is useful. For measur- 
 ing use the surveyor's chain or tape measure, if possible, but for 
 much of such work many people can learn to step off the distance 
 with sufficient accuracy. A little practice in walking over a meas- 
 ured distance, as 100 feet will enable one to walk with 2-foot 
 step. The field work for some of the finest geological maps I ever 
 saw was done with a pocket compass and step measurement. The 
 elevations were taken with an aneroid barometer. But the eleva- 
 tion of a moderately steep hill can be determined quite closely 
 without instruments. Measure accurately the height of the eye 
 from the ground, then practice in "standing straight" and 
 ''looking level " will soon enable one to stand at the foot of a hill 
 and note on its side a point on the level of his eye, then advanc- 
 ing to that point, note another, and so on until the summit is 
 reached, when the product of the number of stations by the 
 elevation of the eye gives the approximate elevation of the hill. 
 
388 PRACTICAL LESSONS IN SCIENCE. 
 
 Locate and map the streams, hills, outcrops of rock, and other 
 prominent physical features, also the roads, farm lines, and 
 houses of the neighborhood or district you are intending to 
 study. In this work school children and their parents can ren- 
 der material aid. The children should make maps for themselves; 
 in no way can map drawing be made more interesting and prac- 
 tical than when familiar ground is made the subject of study. 
 While the map is in process of construction other work may be in 
 progress. Perhaps the most important group of material phe- 
 nomena affecting man is the one called the weather or climate. 
 Many of these phenomena and their relations can be observed, 
 and some idea of future manifestations can be derived, from an 
 intelligent knowledge of the present. It is one of the latest deduc- 
 tions of science that it pays to collect and study " weather saws,'* 
 to observe and note the relations of sunshine and cloud, wind, 
 rain, etc. We have in the barometer an artificial weather glass, 
 but among plants and animals there are many natural barome- 
 ters or weather indicators. Cultivate the powers of observation 
 by noting the aspects of the weather, and requiring the children to 
 do the same; observe which way the wind blows, morning, noon 
 and night; whether the day was clear, cloudy or rainy; any 
 marked changes of temperature during the day or night should 
 be noted, and the observations of each day should be made a 
 matter of record. Collect " weather saws " and study them, some 
 may be fanciful, but many will be found to stand on a scientific 
 basis. In connection with this work note the habits of plants 
 and animals that appear to relate to climate, also study the 
 weather predictions from Washington and compare them with 
 your own observations. 
 
 In winter corn and beans may be grown and each studied in dif- 
 ferent stages, gaining ideas of the seed embryo, cotyledons, ordi- 
 nary leaves, etc., and noting the distinctions between the great 
 classes of exogenous and endogenous plants. Much also may be 
 learned from the study of the various house plants so common 
 everywhere. Make a list of the different trees and shrubs of the 
 neighborhood, studying carefully the peculiarities that distin- 
 
LESSONS TN GEOLOGY. 389 
 
 guish them in winter. Get specimens of the wood of different 
 trees and learn to distinguish them by the character of the wood. 
 
 Most insects die in autumn, being represented during the winter 
 by eggs, larvae, or some imperfect form, but a large number live 
 through the winter, usually in a torpid state. They are perhaps 
 more commonly found under decaying logs, in rotten wood, or 
 between the bark and wood and similar places. A collection of 
 such insects with notes of the circumstances under which they 
 were found would be interesting and valuable. Whilelooking for 
 insects one may find salamanders, mice, snail shells and other 
 things of interest. In every locality a number of birds, as owls, 
 hawks, woodpeckers, shrikes, chickadees, blue jays and others are 
 found during the winter; make a list of these winter birds, and 
 note their habits, the food they eat, and the places in which they 
 are found. 
 
 As spring approaches watch for signs of life in the trees and 
 plants; note which trees and shrubs blossom before putting out 
 their leaves, and the plants that send up the first flowers; study 
 the trees and shrubs in their spring and summer vegetation, and 
 note the colors the leaves of different plants and trees assume in 
 autumn. Note the soil and surroundings in which the different 
 plants and trees seem to thrive best; some will be found to have 
 a wide range, others will be confined to narrow limits. 
 
 Observe, also, the returning summer birds, which come first, and 
 when they come, and how soon after the first one is seen do the 
 birds of its kind become common. Study the feeding and nesting 
 habits of the birds, and note the localities the different kinds 
 seem to prefer. Notice how completely the opening flowers and 
 returning birds depend on the weather. At certain times in the 
 spring birds visit us for a few days on their journey to more 
 northern regions, and again in autumn on their return to the 
 warmer regions. Make notes of these dates and of the birds 
 passing. 
 
 The study of the smaller mammals, as mice, moles, shrews, 
 ground squirrels, etc., is an interesting and neglected field of ob- 
 servation. The study of reptiles, batraehians, crustaceans, mol- 
 
390 PRACTICAL LESSONS IN SCIENCE. 
 
 lusks and other forms of life well repays the time spent in making 
 the investigations. 
 
 In connection with the topographic work make notes of geo- 
 logical features, the kinds of rock, thickness of beds, the effects 
 of weathering upon them, and their relations to each other. 
 Study water sheds and divides; you can find as typical examples 
 of each in every township as you could find in the Rocky moun- 
 tains. Study the valleys of the streams, the upper, middle and 
 lower course. Notice the work done by the streams, eroding 
 here, building up there busy everywhere. Observe in how many 
 different ways during the year material is removed from an 
 eroding bank. Where the stream is making ground note the 
 order in which different forms of vegetation occupy the new-made 
 land. The study of fish and other life of the streams is interest- 
 ing and profitable. Much of this study should be general, en- 
 gaged in by the whole school, and a little time should be set 
 apart each day for report of observations. Other work may be 
 delegated to certain pupils according to their liking or aptitude. 
 Do as much work as you can and do it as well as you can, and 
 you will be astonished at the amount accomplished during a 
 season. 
 
INDEX. 
 
 PAGE 
 
 Abdomen of Grasshopper 280 
 
 Abdomen of Insects 276 
 
 Absolute Zero 42 
 
 Acids defined 118 
 
 Acids named 119 
 
 Acetylene, how formed 134 
 
 Acetic Acid, composition 177 
 
 Acid of Lemons, etc 180 
 
 Acorn, the parts of 228 
 
 Acarina, Mites and Ticks 272 
 
 Adhesion defined 21 
 
 Adaptation illustrated 246, 302 
 
 Adductor Muscles 286 
 
 Age of the Earth 372 
 
 Air, properties of 115 
 
 Air, composition of 116 
 
 Air, pressure of 39 
 
 Air Plants described 246 
 
 Aluminium described 161 
 
 Aluminium, compounds of 161 
 
 Alumus, different kinds 161 
 
 Albumen, composition of 176 
 
 Alcohol, composition of 177 
 
 Alternation of generations 201 
 
 Allantois, purpose of 298 
 
 Algonkian Era described 349 
 
 Ammonia, composition of 116 
 
 Ammonium , a compound 117, 153 
 
 Ammonium, chloride 117, 153 
 
 Ammon mm, nitrate 118 
 
 Ammonium sulphide 153 
 
 Amphibia described 296 
 
 Amoeba, description of 259 
 
 Amnion, a membrane 298 
 
 Aniline and Aniline Colors 169 
 
 Antheridia described 200 
 
 Anthophyta defined 207 
 
 Andro2cium defined 224 
 
 Annuals defined 233 
 
 Annelida described 265 
 
 Autenuse defined (crayfish) 270 
 
 Antennulse defined 270 
 
 Ants, communities of 282 
 
 Anthropomorphse 314 
 
 Annuals as geological agents 347 
 
 Aphidse, Plant Lice 281 
 
 Apidse or Bees described 283 
 
 Apoda, description of 297 
 
 Aristotle, theories of 14 
 
 Arsenic and its compounds 144 
 
 Arsenical Colors 145 
 
 Arsenic, tests for 145 
 
 Archegonia described 200 
 
 Arthropoda described 258, 267 
 
 Arachnida described 272 
 
 Araneida, true spiders 272 
 
 Artiodactyla described 
 
 Archsean Era described 
 
 Archaean Rocks, kinds of 
 
 Assimilation defined 
 
 Astronomical Geology 
 
 Atoms and Atomic Theory. . 
 Attraction defined... 
 
 PAGE 
 
 ...348 
 ...349 
 ...188 
 ... 316 
 .17,104 
 . 19 
 
 Attractive Forces, effect of 25 
 
 Auditory hairs and sac 270 
 
 Avogadro's Law stated 123 
 
 Aves or Birds described 300 
 
 Avalanches of Rock, etc 341 
 
 40 
 95 
 99 
 118 
 156 
 
 Barometer, principle of 
 Batteries, Electrical, described 
 Batteries, Storage, described 
 Base, definition and composition. 
 Barium and its compounds ..... .. 
 
 Bacteria, description of ............. 191 
 
 Bark, manner of growth ............. 217 
 
 Banana Family described ........... 226 
 
 Barnacles described ................ 271 
 
 Batrachia described ................ 297 
 
 Basalt, composition of .............. 323 
 
 Base lines and correction lines ... .384 
 
 Benzole, composition of ............ 169 
 
 Bees or Apidse described ........... 288 
 
 Bismuth and its compounds ....... 166 
 
 Biennials defined .................... 233 
 
 Bivalve Shells described ............ 286 
 
 Birds, description and study of ..... 301 
 
 Birds, development of ............... 302 
 
 Botany, treats of what ............... 12 
 
 Boiling Point explained ............. 29 
 
 Boron and its compounds ........... 136 
 
 Botany, general statement .......... 182 
 
 Botany in winter ..................... 388 
 
 Bony Tissue described .............. 253 
 
 Boulders, from the drift ............. 364 
 
 Boulder Clay or Till ................. 364 
 
 Brittleness defined .......... ........ 32 
 
 Breezes, Land and Sea ............... 49 
 
 Bromine described ............ ...... 124 
 
 Brick, made of what ................. 161 
 
 Bread making explained ............ 178 
 
 Bryophyta described ................ 200 
 
 Brittle Stars described ............. 262 
 
 Bryozoa described ................... 289 
 
 Brachioppda described .............. 289 
 
 Bunsen Burner described ........... 133 
 
 Butterflies, description of ........... 281 
 
 Buckwheat Family described ....... 229 
 
 Capil lary Attraction denned ........ 22 
 
 Capstan described ................... 66 
 
392 
 
 INDEX. 
 
 Camera described 
 
 Carbon, different forms of 
 
 Carbon, Oxides of 
 
 Calcium and its compounds . . . 
 
 Carbolic Acid, source of 
 
 Camphor described 
 
 Caoutchouc, properties of 
 
 Cambium Layer described 
 
 Canning, process explained 
 
 Carpophyta described 
 
 Calyx and Sepals defined 
 
 Catkin, description of 
 
 Cactus Family described 
 
 Cartilage described 
 
 Carapace, formed how 
 
 Cavicornia described 
 
 Carnivora, description of 
 
 Canidse or Dogs described 
 
 Calcite, composition of 
 
 Carbon Dioxide and Water 
 
 Caves, how formed 
 
 Cambrian Rocks, kinds 
 
 Cambrian Life, nature of 
 
 Carboniferous Age and Life 
 
 Cellulose, composition of 
 
 Cells of Plants described . . . . \ 
 Cells of Animals described 
 
 Cells, Products of 
 
 Celery described 
 
 Cestoda described 
 
 Cephalothorax described 
 
 Centipede, description of 
 
 Cephalopoda described 
 
 Cetacea or Whales described . . 
 Cervidae or Deer described 
 
 Cenozoic Era described 
 
 Chemistry, deals with what 
 
 Chemical Attraction denned. . 
 
 Chemistry, history of 
 
 Chemical Combinations 
 
 Chlorine Properties, etc 
 
 Chlorine Disenfectant, etc 
 
 Chloric and other Acids 
 
 Charcoal, properties of 
 
 Chromium described 
 
 Chlorophyll described 
 
 Characese described 
 
 Chickweeds, universal 
 
 Chelonia or Turtles described 
 Cheiroptera or Bats described. 
 
 Champlain Period, cause 
 
 Circulatory System, general . . 
 
 Circulatory Organs, Insects 
 
 Cicadidse or Cicadia 
 
 Clay, composition and use 
 
 Clover Crop, depends on 
 
 Classification of Animals 
 
 Cohesion defined 
 
 Cold, what is it 
 
 Conduction defined 
 
 Conductors, good and poor 
 
 Colors, what the cause 
 
 Coil, primary and secondary. . 
 
 Combustion explained 
 
 Composition by volume 
 
 Coal and Cake described 
 
 Copper and its compounds 
 
 Copper and its alloys 
 
 Corolla and Petals defined .... 
 
 Cotyledons described 
 
 Cones, Bracts, Scales, etc 
 
 PAGE 
 
 .... 127 
 .130, 132 
 .... 155 
 .... 170 
 .... 172 
 .... 173 
 .... 185 
 ..... 192 
 .... 196 
 .... 211 
 .... 227 
 .... 238 
 .... 253 
 .... 268 
 .... 311 
 .... 313 
 
 .. 313 
 .... 321 
 .... 339 
 .... 341 
 .... 352 
 .... 352 
 .... 355 
 .... 173 
 .... 183 
 .... 251 
 
 .. 184 
 
 .... 267 
 
 .... 274 
 
 .... 288 
 
 .... 308 
 
 .... 310 
 
 .... 359 
 
 .... 11 
 
 .... 23 
 
 .... 102 
 .. .103 
 
 .... 120 
 
 .... 121 
 
 .... 122 
 
 128 
 
 .... 166 
 .184, 192 
 
 197 
 
 .... 230 
 
 300 
 
 .. 313 
 
 255 
 277 
 281 
 161 
 247 
 258 
 21 
 
 85 
 
 96 
 
 .103, 109 
 .122, 124 
 
 129 
 
 158 
 
 ..... 159 
 
 211 
 
 .213, 215 
 .. 218 
 
 PAGE 
 
 Coniferae Family 219 
 
 Cotton Plant described 235 
 
 Collection of Plants 249 
 
 Connective Tissue described 232 
 
 Correlation of Organs 254 
 
 Coelenterata described 260 
 
 Coral Polyps described 261 
 
 Cockroaches described 2Hi 
 
 Coccus Cacti described 281 
 
 Coleoptera, number and description 281 
 
 Collection of Specimens 284 
 
 Colubriformia described 299 
 
 Compositae Family described 242 
 
 Columbines or Pigeons 303 
 
 Comets described 318 
 
 Conglomerate Rocks :'>2i 
 
 Colorado Canon, The 345 
 
 Continents, permanence of 348 
 
 Coal, how found 355 
 
 Coal Strata, number of 356 
 
 Comprehensive Type 382 
 
 Crystals, what and how found 88 
 
 Crowfoot Family described 230 
 
 Cruciferae Family described 232 
 
 Crotalidse, description of 300 
 
 Crinoids, description of 262 
 
 Crustacea, description of 268 
 
 Crayfish, a study of 268 
 
 Crickets, description of 280 
 
 Crocodilia, description of 300 
 
 Crush of the Earth 348 
 
 Cretaceous Rocks, kinds 358 
 
 Cuttle Fish described 289 
 
 Cursores, description of 304 
 
 Cyanogen described 134, 165 
 
 Cyanide Bottle, how made 284 
 
 Cynocephalidse or Baboons 314 
 
 Development, Theory of 
 
 Density defined and "illustrated. . . . 
 
 Dextrine, composition of 
 
 Desmids and Diatoms 
 
 Development of Insects 
 
 Dentirostres, Fissirostres, etc 
 
 Devonian Age, Rocks 
 
 Devonian Age, Life 
 
 Descent, with variation 
 
 Divisibility defined 
 
 Diathermancy illustrated 
 
 Diamond, description of 
 
 Diastase, how formed 
 
 Diseases caused by plants 
 
 Dicotyledons described 
 
 Dioecious explained 
 
 Digestive Apparatus, general 
 
 Dissection under water 
 
 Digestive Organs, crayfish 
 
 Digestive Organs, insects 
 
 Diptera (flies) described 
 
 Division of Labor, Bees 
 
 Dipnoi, description of 
 
 Digitigrada and Plantigrada 
 
 Diorite or Greenstone described. . . 
 
 Dolomite, composition of 
 
 Dragon Flies described 
 
 Drift, sources of 
 
 Driftless Area, cause 
 
 Ductility defined and illustrated. . 
 
 Dynamo, Electric Machine 
 
 Dynamo, extensive use of 
 
 14 
 21 
 175 
 195 
 278 
 304 
 354 
 854 
 379 
 17 
 31 
 127 
 176 
 198 
 227 
 227 
 254 
 270 
 271 
 277 
 
 295 
 312 
 
JNUEX. 
 
 393 
 
 Dyeing, the process of 170, 171 
 
 Dynamite, how made 179 
 
 Earwigs (Forficulidae) described ... 280 
 
 Earth, internal condition of 326 
 
 Earthquakes, causes of 327 
 
 Earthquakes, effects of ^ . . 327 
 
 Earth Surface, irregular 326 
 
 Echo, cause of, in rooms 56 
 
 Echinodermata described 262 
 
 Edentata, description of 307 
 
 Elements defined 17 
 
 Electrical Attraction defined 23 
 
 Elasticity defined 34 
 
 Electricity, kinds of 87 
 
 Electricity, how shown 87 
 
 Electricity, frictional 88 
 
 Electrical Conductors, good and 
 
 poor : 95, 98 
 
 Electricity, dynamical 93 
 
 Electrical Circuit 94 
 
 Electrical Current 94 
 
 Electrical Batteries described 95 
 
 Electro Magnets described 95 
 
 Electric Telegraph 95 
 
 Electric Lightning 98 
 
 Electrical Units 100 
 
 Elements, most important 105 
 
 Elements, symbols of, etc 105 
 
 Elm Family described 229 
 
 Embryo of the Plant, etc 213 
 
 Embryonic Life (animals) 381 
 
 Energy defined and illustrated 58 
 
 Energy, kinetic and potential 58 
 
 Energy, changes form 62 
 
 Entomastracea described 271 
 
 Epidermal System (plants) 186 
 
 Epithelial Tissue 252 
 
 Equi'setaceae, described. . , 206 
 
 Equidse or Horses , 309 
 
 Ergot of Rye, what is it ? 197 
 
 Erinacidae or Hedgehogs 312 
 
 Evaporation, explained 29 
 
 Events of the Silurial Age 353 
 
 Evolution, history of 378 
 
 Evolution and Geology 381 
 
 Evolution not atheistic 383 
 
 Extension, definition of 16 
 
 Expansion of Bodies explained 29 
 
 Excretory Organs, general 255 
 
 Experiments showing : 
 Impenetrability of solids and 
 
 liquids 16 
 
 Impenetrability of liquids and 
 
 gases, etc 16 
 
 Divisibility of Matter, etc 17 
 
 Adhesive Attraction , etc ; . . 22 
 
 Capillary Attraction 22 
 
 Conduction of Heat 28 
 
 Convection of Heat 31 
 
 Specific Gravity of Solids, etc 37 
 
 Specific Gravity and Elasticity of 
 
 Gases 39 
 
 The Laws of Vibrating Cords 53 
 
 Frictional Electricity, etc 87 
 
 Physical Mixture and Chemical 
 
 Combination 103 
 
 The Composition of the Air 115 
 
 Bleaching by Chloride of Lime ... 121 
 Blue Color with Iodine and Starch 125 
 
 Experiments showing : PAGE 
 Carbon Dioxide to be non-combus- 
 tible 130 
 
 A flame to consist of parts 132 
 
 Combustion, Potassium, Chlorate 
 
 and Sugar 148 
 
 Decomposition of Sugar Solution. 190 
 Bacteria in Infusions 191 
 
 Falls of Niagara described 345 
 
 Falling Bodies, Laws of 44 
 
 Feldspars, different kinds 161, 320 
 
 Ferns, description and study of 202 
 
 Feathers and Quills described 301 
 
 Felidae or Cats described 313 
 
 Fibrous Tissue described 185 
 
 Fibro Vascular System 186 
 
 Figwort Family described 241 
 
 Fibro Cartilage described 253 
 
 Field work, how done 387 
 
 Fish, dissection of 292, 293 
 
 Fish, economic value of 285 
 
 Fish, preservation of 295 
 
 Fish, first appearance of 382 
 
 Fissures and Faults 325 
 
 Fluorine, preparation of 126 
 
 Flame, parts of, shown 132 
 
 Flint, composition and use 135 
 
 Floridese (seaweeds) described 196 
 
 Flax Family described 236 
 
 Force defined and illustrated 18 
 
 Force constant and impulsive 43 
 
 Forces, composition of 45 
 
 Forces, resolution of 45 
 
 Force, Centripetal and Centrifugal. 46 
 
 Fog horns, their value, etc 56 
 
 Foot Pounds defined 60 
 
 Food Group of Plants 226 
 
 Foraminiferse described 259 
 
 Formicidse or Ants described 282 
 
 Foot of Mollusca described 287 
 
 Forces, Plutonic, effect of 326 
 
 Forces, Erosive, effect of 326 
 
 Friction, cause and use 61 
 
 Franklin Dr., a Discoverer 90 
 
 Frond and Stipe described 202 
 
 Fruit of Different Kinds 213 
 
 Fundamental System in Plants 187 
 
 Fungi or Moulds described 194 
 
 Fucus, Seaweeds, described 196 
 
 Galvani and the Telephone 11, 93 
 
 Galvanometer described 96 
 
 Gas, relation of forces in 25 
 
 Gas, properties of, etc 39 
 
 Gases, diffusion of 40 
 
 Gases, volume of, varies how 41 
 
 Gas Carbon, where formed 129 
 
 Gas, Illuminating, how made 169 
 
 Ganglion, formed of what 254 
 
 Gasteropoda described 288 
 
 Ganoidei (fishes) described 291 
 
 Gallinacese described 303 
 
 Germs, removed by filtering 191 
 
 Gemmae, purpose of 200 
 
 Geyser explained 330 
 
 Geological Agents 337 
 
 Geological Record Imperfect 353 
 
 Geological Work of the Present 371 
 
 Geological Diagram 374, 375 
 
394 
 
 INDEX. 
 
 FAGE 
 
 Geological Names 876 
 
 Geological Periods 876 
 
 Geological Studies 889 
 
 Gills of Crayfish described 269 
 
 Gills of Fish described 298 
 
 Glass, composition of 156 
 
 Glucose or Grape Sugar 175 
 
 Glyoerine, how made 178 
 
 Glumes described 221 
 
 Glands, how formed 252 
 
 Glacial Period : . 862 
 
 Glacial Climate 362, 367 
 
 Glacier, effect on plants 362 
 
 Glacier, the work of 363 
 
 Glacial Striae, direction 365 
 
 Gneiss, structure of 323 
 
 Gold, properties of, and uses 167 
 
 Golden Rod described 243 
 
 Gourd Family described 242 
 
 Gravitation or Gravity defined 19 
 
 Gravity, laws of, shown 19 
 
 Gravity, center of, how found 20 
 
 Graphite, where found 127, 350 
 
 Grass Family, extent 221 
 
 Grass Crop, value of 223 
 
 Grasshopper, study of 280 
 
 Grallatores or Wading Birds 303 
 
 Granite, composition of 322 
 
 Gunpowder, manufacture of 149 
 
 Gunpowder, expansive force of 152 
 
 Gunpowder, gases of explosion 150 
 
 Gum Resins described 172 
 
 Gutta Perch a, properties of 173 
 
 Gun Cotton, composition of 174 
 
 Gum Acacia, description of 240 
 
 Gypsum, composition of 155 
 
 Gyncecium defined 224 
 
 Hardness defined 32 
 
 Harmonics or Overtones 54 
 
 Haemoglobin described 252 
 
 Hairs and Scales of Animals 252 
 
 Hapalidse (monkeys) described 314 
 
 Heart uf a Crayfish 270 
 
 Heart of Mussel 287 
 
 Heat and Light, Theory of 14, 27 
 
 Heat, effects of 25 
 
 Heat, Sensible and Latent 28 
 
 Heat, specific standard of 29 
 
 Heat, absorption and reflection of . . 30 
 Heat, convection and radiation of, 27, 31 
 Heat, conduction and conductors . . 28 
 
 Heat, mechanical equivalent of 69 
 
 Heat, sources of 27 
 
 Heaih Fainilv described 241 
 
 Hermaphrodite Animals 256 
 
 Hemiptera described 281 
 
 Hilum described 225 
 
 Hinge Ligament 286 
 
 Hibiscus, description of 235 
 
 Horse Power denned 61 
 
 Holothurians described 263 
 
 Hornblende and Pyroxene 321 
 
 Honey Locust described 240 
 
 Huronian, Lower Rocks of 849 
 
 Huronian, Upper Rocks of 350 
 
 Hydrometer, principle of 87 
 
 Hydraulic Press, principle of 38 
 
 Hydrogen, how prepared Ill 
 
 Hydroxides denned , 119 
 
 PAGE 
 
 Hydrochloric Acid 120 
 
 Hydrocarbons defined 134 
 
 Hydrogen Sulphide 141 
 
 Hymenoptera, Bees, etc 282 
 
 Hysenidse or Hysenas 313 
 
 Ice, why it floats 33 
 
 Ice Lobes or Glaciers 364 
 
 Ice Sheet, extent of 864 
 
 Igneous Rocks 825 
 
 Illuminating Gas 185 
 
 Images in a Convex Lens 80 
 
 Images in a Curved Mirror 75 
 
 Images in a Plane Mirror 75 
 
 Impenetrability defined 16 
 
 Inclined Plane, equation of 66 
 
 Indig9 described 170, 240 
 
 Individual, development of 880 
 
 Indusium described 205 
 
 Inertia defined and illustrated 19 
 
 Infusions, how made 191 
 
 Infusoria described 260 
 
 Insect, fauna of 279 
 
 Tnsecta, description of 275 
 
 Insectivora described 312 
 
 Insectivorous Plants 234 
 
 Insects, diseases of 279 
 
 Insects in winter 389 
 
 Iodides of Mercury 125 
 
 Iodine, properties and use 125 
 
 Iron and Decay of Rocks 889 
 
 Iron, Cast and Wrought 164 
 
 Iron, compounds of 165 
 
 Iron, distribution of 168 
 
 Iron, reduction of 163 
 
 Iron in Algoukian Rocks 350 
 
 Jelly Fish described 261 
 
 Joints in Rocks, cause of 825 
 
 Jurassic Period, etc 358, 859 
 
 Kinetic Energy 58 
 
 Keweenawan Rocks 350 
 
 Lamellibranchiata described 285 
 
 Laughing Gas described 118 
 
 Law as used in Science 13 
 
 Law of Falling Bodies 44 
 
 Laws of Radiant Heat 27 
 
 Lava, different kinds 829 
 
 Land, surface uneven 382 
 
 Lakes, settling basins 846 
 
 Laurentian Tableland 351 
 
 Lake Erie, how formed 366 
 
 Lever defined and illustrated 64 
 
 Lever, principle and equation of 64 
 
 Lever, compound equation of 65 
 
 Lens, different kinds of 78 
 
 Lenses, convex effect of 79 
 
 Lenses, concave effect of 79 
 
 Leyden Jar described 89 
 
 Lead and its compounds 166 
 
 Leaves, different forms of 187, 208 
 
 Leaf, the parts of 207 
 
 Leaves, mode of veining 207 
 
 Leaves, form of base and apex 208 
 
 Leaves, lobed and cleft 208 
 
 Leaves, simple and compound 209 
 
INDEX. 
 
 395 
 
 PAGE 
 
 Leaves, arrangement of, on stem. . . 210 
 
 Leech (medical) described 265 
 
 Lepidoptera described 281 
 
 Leptocj.rdii described 290 
 
 Liquids, properties of 34 
 
 Light, the sources of, etc 70 
 
 Light, phosphorescent 70 
 
 Light, velocity and intensity of . . . . 71 
 
 Light, reflected and absorbed 71, 73 
 
 Light, refraction of 76 
 
 Lightning explained 89 
 
 Lightning rods described 90 
 
 Litmus paper, use of 118 
 
 Lithium, where found 154 
 
 Linseed oil, properties of 179 
 
 Lichens described 197 
 
 Lily Family described 223 
 
 Linden Family described 234 
 
 Liuen Fiber, value of 236 
 
 Lizards described 299 
 
 Limestone rocks described 324 
 
 Life of the early eras 350 
 
 Life of Silurian Age 353 
 
 Location, how found 387 
 
 Loess, of different origin 338 
 
 Lost Period in Geology 352 
 
 Lycopodium or club-moss 206 
 
 Lycosedse (spiders) described 273 
 
 Matter, some properties of 15 
 
 Mass defined and illustrated 21 
 
 Magnetic attraction defined 23 
 
 Malleability defined 82 
 
 Mariotte's Law stated 42 
 
 Machines, principle of 63 
 
 Magic Lantern defined 82 
 
 Magnetism and Magnets 91 
 
 Magnetic needle and poles 91, 92 
 
 Mariners' compass 92 
 
 Magnetic variation 92 
 
 Matches, how made 142 
 
 Magnesium and its compounds 157 
 
 Manganese and its compounds 165 
 
 Malt, how formed 177 
 
 Marchantia described 200 
 
 Magnolia Family described 231 
 
 Mallow Family described 234 
 
 Maple Family described 236 
 
 Maxilla and Mandibles 270 
 
 Mav Flies described 280 
 
 Mantle of a Mussel 286 
 
 Mammalia, description of 805 
 
 Margipobranchia 291 
 
 Mammal, skeleton and organs 306 
 
 Marsupialia described 307 
 
 Man and animals 315 
 
 Marine erosion 346 
 
 Man's appearance on earth 372 
 
 Map drawing, etc 388 
 
 Melting points explained 29 
 
 Methane or Marsh Gas 134 
 
 Metastasis or Metabolism 188 
 
 Mercury, chlorides of 159 
 
 Mercury-amalgams 159 
 
 Medullary rays 217 
 
 Meteors described 318 
 
 Metamorphic Rocks 324 
 
 Mesozoic Era and Life 358 
 
 Method of the Creation 878 
 
 Mirrors, plane, effect of 73 
 
 PAGE 
 
 Mirrors, concave, effect of 74 
 
 Mirrors, convex, effect of 75 
 
 Microscope, simple, compound. . .80, 81 
 
 Mirrors, how made 159 
 
 Mimosa, or sensitive plant 240 
 
 Mint Family described 241 
 
 Milkweed Family 242 
 
 Minerals defined 820 
 
 Mica, composition of 321 
 
 Mississippi Rivej 344 
 
 Mixture and Combinations 104 
 
 Molecular theory of Matter 14 
 
 Molecules defined 17 
 
 Molecular Forces 25, 34 
 
 Mobility explained 35 
 
 Motion, varying or uniform 43 
 
 Motion, Laws of 43 
 
 Motion in Curved Lines 46 
 
 Mortar, how made 156 
 
 Mordants, use of 161, 165 
 
 Mosses described 201 
 
 Monocotyledons described 220 
 
 Mono3cious Flowers 227 
 
 Monadelphous Stamens 239 
 
 Mouth Parts of Insects 276 
 
 Mollusca, description of 285 
 
 Molluscoidea 258, 289 
 
 Moon, condition of 318 
 
 Monotremata described 806 
 
 Mountains 332, 351, 357 
 
 Mountains of the Tertiary 361 
 
 Moraines explained 365 
 
 Musical Tones and Scale 52, 54 
 
 Musical Pitch Standard 64 
 
 Musical Instruments 55 
 
 Multiple Proportions 104 
 
 Mushrooms described 197 
 
 Muscular Tissue 253 
 
 Muscular System of Insects 277 
 
 Mussel, study of 286 
 
 Mustelidse or Martens 813 
 
 Mycelium described 194 
 
 Mygalidse, Spiders 272 
 
 Myriopoda described 274 
 
 Nascent state explained 124 
 
 Nails, Hoofs, and Claws 252 
 
 Natochord described 290 
 
 Natatores or Swimming Birdg 303 
 
 Natural Gas. source of 356 
 
 Natural Selection 380 
 
 Newton , Sir Isaac 10 
 
 Nelumbium (water lily) 231 
 
 Nervous Tissue 253 
 
 Nerve Cells described 253 
 
 Nerve Fibers, different kinds 253 
 
 Nerves, their structure and use. ... 254 
 
 Nematoda described 264 
 
 Nervous System of Crayfish 271 
 
 Nervous System of Insects . . 277 
 
 Nebulae described 319 
 
 Nebular Theory 819 
 
 Neuroptera described 281 
 
 Niagara River Gorge 368 
 
 Nickel, alloys of 165 
 
 Nitrogen, properties of 116 
 
 Nitric Acid described 117 
 
 Nitroglycerin, properties of 179 
 
 Nitrobenzole described . 160 
 
 Nodes and Internodes 2*4 
 
396 
 
 JNDEX. 
 
 Oak Family described 
 
 Oak, different kinds 
 
 Oak Timber, value of 
 
 Obesa or Hippopotami 
 
 Obsidian, volcanic glass 
 
 Ocellus, Ocelli, eyes 
 
 Octopus, Devilfish 
 
 Ocean Currents, causes 
 
 CEdogonium described 
 
 Oils, composition of 
 
 Oil of Bergamot, etc 
 
 Oidium Tucheri (fungi) 
 
 Olefiant Gas Composition 
 
 Olive Family described 
 
 Olfactory cells, etc 
 
 Oligocb.se ta (worms) ? 
 
 Oldest laud in America 
 
 One-celled organisms 
 
 Oophyta, characteristic of 
 
 Oospore, a spore case 
 
 Opaque bodies defined 
 
 Opera Glass described 
 
 Opium, source and use 
 
 Opercle, Subapercle, etc 
 
 Ophidia or Snakes 
 
 Orchid Family described 
 
 Orange, Lemon, etc 
 
 Organs, systems of 
 
 Organs of Locomotion 
 
 Organisms, Complex 
 
 Organs, developed from 
 
 Organic Development 
 
 Orbitelse (wheel-spinners) 
 
 Orthoptera described 
 
 Oscillaria, blue-green scum . . . 
 
 Osseous or Bony Tissues 
 
 Ostridse or Oysters 
 
 Oscillations of the Crust 
 
 Overtones or Harmonics 
 
 Ovule described 
 
 Ovum or Egg-cell 
 
 Ovum, development of 
 
 Oxygen, discovery of 
 
 Oxygen, preparation of 
 
 Oxygen, properties of 
 
 Oxides defined 
 
 Oxides of nitrogen 
 
 Oxyhydrogen flame 
 
 Oxalic and other acids 
 
 Oysters, development of 
 
 Palets and awns 
 
 Palm Family described 
 
 Paloeozoic Era and Sea 
 
 Panicle described 
 
 Pancreas described 
 
 Parsley Family described 
 
 Pappus described 
 
 Parasites, plants 
 
 Passeres or Passerine buds . . . 
 
 Pendulum, use of 
 
 Petroleum, gases of 
 
 Petroleum oil, source of 
 
 Perennials defined 
 
 Pediculidse or lice 
 
 Perissodactvla described 
 
 Physics deals with what 1 
 
 Physics and chemistry distin- 
 guished 
 
 Photometry explained 
 
 PAGE 
 .. 227 
 
 228 
 310 
 
 275 
 
 .... 195 
 .... 178 
 .... 172 
 . ..196 
 .... 134 
 .... 242 
 .... 256 
 .... 265 
 .... 351 
 .... 254 
 .... 195 
 .... 195 
 .... 71 
 .... 82 
 .... 232 
 .... 293 
 ... 299 
 .... 225 
 .... 235 
 .... 251 
 .. . 256 
 .... 254 
 .... 257 
 .... 377 
 
 273 
 
 279 
 
 .... 193 
 .... 253 
 ....288 
 .356, 369 
 
 54 
 
 ... 213 
 
 256 
 
 .... 257 
 .102, 106 
 .... 106 
 
 108 
 
 110 
 
 .... 118 
 
 112 
 
 .. 180 
 
 .... 221 
 
 .... 225 
 
 .... 352 
 
 222, 237 
 
 ... 255 
 
 ... 237 
 
 .... 243 
 
 .188, 198 
 
 304 
 
 50 
 
 134 
 
 .172, 356 
 
 .... 233 
 
 .. 281 
 
 ..11, 15 
 
 . 15 
 .... 72 
 
 PAGE 
 
 Phosphorus, source of 141 
 
 Phosphorus, different forms of 142 
 
 Phosphorus, uses of 144 
 
 Photography, principle of 160 
 
 Phocidse or seals 313 
 
 Pistil, stigma, style, and ovary.... 212 
 
 Pine, a study of 215 
 
 Pine, the growth of 218 
 
 Pink Family described 230 
 
 Pitcher plant described 2;>4 
 
 Pisces or fishes described 290 
 
 Pithecidse described 314 
 
 Plants fertilized by insects 242 
 
 Plaster of Paris, how made 155 
 
 Platinum, properties of 168 
 
 Plants, composition of 182 
 
 Plants as geological agents 347 
 
 Placenta, purpose of 212 
 
 Plumule described 213 
 
 Pleurite, sternite, etc., 269 
 
 Planets named in their order 317 
 
 Planetoids or asteroids 318 
 
 Porosity explained 18 
 
 Potential energy 58 
 
 Power, loss of, in use 67 
 
 Potential, high and low 94 
 
 Potential energy in coal HO 
 
 Poles, positive and negative 94 
 
 Potassium, properties of 146 
 
 Potassium, compounds of 147, 148 
 
 Pottery ware, how made 162 
 
 Porcelain ware, how made 162 
 
 Potassium per mangauate 165 
 
 Pot holes, how formed 345 
 
 Poppy Family descri bed 232 
 
 Proboscidea described 311 
 
 Prisms described 83 
 
 Projectiles, trajectory, etc 47 
 
 Prosimioe or Lemurs 314 
 
 Primates or apes 314 
 
 Principal meridians 384 
 
 Progress means what 383 
 
 Processes of life 190 
 
 Protoplasm described 183 
 
 Protophyta described 190 
 
 Protococcus, green scum 102 
 
 Protonema in Mosses 201 
 
 Prothalium in Ferns 203 
 
 Proembryo, embryo, etc 213 
 
 Protection, means of, in plants 248 
 
 Preservation specimens of plants.. 249 
 
 Pronucleus, male and female 257 
 
 Protozoa described 258 
 
 Pseudopodia described 259 
 
 Ptolemy, theories of 14 
 
 Pump, principles of 41 
 
 Pulley, equation of 66 
 
 Pulque plant and pulque 238 
 
 Pulse or Pea Family 239 
 
 Pyrometer, made of what ? 27 
 
 Pyroxene and Hornblende 321 
 
 Pyrites of iron described 322 
 
 Quartz or Silica 135, 320 
 
 Quaternary Age 362 
 
 Quaternary plants and animals 370 
 
 Radiation explained 27 
 
 Radiators, good and poor 30 
 
 Rainbow explained 85 
 
INDEX. 
 
 397 
 
 PAGE 
 
 Rachis, midvein and stipe 203 
 
 Raspberries described 239 
 
 Radiolaria described 260 
 
 Raptores, birds of prey 304 
 
 Rain, explanation of :-i34, 338 
 
 Rainfall, exceptional 334 
 
 Rainwater, where does it go ? 339 
 
 Rest and motion defined 18 
 
 Reflection defined 30 
 
 Reflectors, good and poor 30 
 
 Refraction, laws of 76 
 
 Refraction, cause of 77 
 
 Refraction, index of 77 
 
 Reactions and Reagents 119 
 
 Reindeer Moss 197 
 
 Resin ducts 217 
 
 Receptacle defined 224 
 
 Respiratory organs 255 
 
 Reproductive process 250 
 
 Respiration in insects 277 
 
 Reptilia, description of 298 
 
 Recent Geological Period 372 
 
 Reproduction, rapidity of 379 
 
 Relations of life forms 382 
 
 Rectangular system of survey 384 
 
 Rhizoma or rootstock 202 
 
 Rhubarb, uses of 230 
 
 Rhinocerotidse described 308 
 
 Rivers, how formed 342 
 
 Rivers vary how 342 
 
 River valley, parts of 342 
 
 River, carrying power 344 
 
 Rivers, eroding agents 344 
 
 Rivers deposit sediments 346 
 
 Rosin and resins 172 
 
 Roots, uses of 188 
 
 Rose Family described 239 
 
 Rotifera described 266 
 
 Rodentia described 312 
 
 Rocks, composition of 320 
 
 Rocks, disintegration of 324 
 
 Rocks, first formed 349 
 
 Rocks of Silurian Age 353 
 
 Rocky Mountains formed 359 
 
 Rue Family described 236 
 
 Ruminants, stomach of 310 
 
 Salt, composition and definition 119 
 
 Salts, how named 119 
 
 Safety lamp, principle of 133 
 
 Saltpeter, how made 147 
 
 Samara or wing fruit 229, 236 
 
 Sargassum, seaweed 196 
 
 Saxifrage Family 238 
 
 Saprophytes 189, 198 
 
 Saltigradse (spiders) 273 
 
 Satellites or moons 318 
 
 Sandstone rocks 324 
 
 Sand dunes formed 338 
 
 Sand bars in rivers 346 
 
 Sand bars in the sea 347 
 
 Sample descriptions 387 
 
 Science age and growth 9 
 
 Science considers what 10 
 
 Science, opposed by whom 9 
 
 Science attempts what 10 
 
 Scientific work 10 
 
 Scientific meti^d 11 
 
 Science, educational value 12 
 
 Screw described 67 
 
 Scorpions described 
 
 Scales of a fish 
 
 Scansorial or Climbing Birds. 
 
 Schists, structure of 
 
 Sepals and calyx 
 
 Sedge Family described 
 
 Sensitive plant 
 
 Seeds, dispersal of 
 
 PAGE 
 
 .. 274 
 
 303 
 323 
 211 
 223 
 240 
 247 
 
 Sea urchins ........................... 262 
 
 Sense organs, insects ................ 278 
 
 Selachii described ................... 291 
 
 Semnopithecidse, monkeys .......... 314 
 
 Serpentine, composition of ........ 321 
 
 Sediments deposited ................ 346 
 
 Section, size, divisions .............. 386 
 
 Siphon explained .................... 40 
 
 Silicon, properties of ................ 135 
 
 Silica, forms of ........... ^ .......... 135 
 
 Silicates, abundance of ............. 135 
 
 Silver, properties of .................. 159 
 
 Silver nitrate ......................... 160 
 
 Silver chloride and bromide ........ 160 
 
 Silique and silicle (pods) ............ 232 
 
 Siphons of a mussel .................. 287 
 
 Skin of the insect ..................... 267 
 
 Slime moulds ........................ 183 
 
 Snails and slugs ...................... 288 
 
 Snakes described ..................... 299 
 
 Solids described ...................... 25 
 
 Sounds, how caused .................. 52 
 
 Sound, report, noise ................. 52 
 
 Sound, transmission of .............. 55 
 
 Solar spectrum ....................... 83 
 
 Sodium, source of .................... 157 
 
 Sodium compounds .................. 152 
 
 Sodium silicate ...................... 153 
 
 Soap, how made ...................... 179 
 
 Solonacese (potato) .................. 241 
 
 Soricidse or shrews ................... 313 
 
 Soil, composition of. ................. 324 
 
 Soil, how formed .................... 340 
 
 Specific gravity defined .............. 36 
 
 Specific gravity, how found ......... 36 
 
 Specific gravity, uses of .............. 36 
 
 Spectrum of iron 
 Spectrum of stars 
 Space and motion 
 Spirogyra (green scum) 
 Sporocarp described 
 Sporogonium described 
 Sphagnum, Moss 
 Sporangia 
 
 84 
 84 
 43 
 193 
 196 
 200 
 202 
 203, 205 
 
 Spike and spikelet ............... 217, 222 
 
 Spurge Family ........................ 237 
 
 Sperm cell and egg cell .............. 256 
 
 Sponge described. ................... 260 
 
 Spider, study of ..................... 272 
 
 Spiders ballooning .................. 274 
 
 Springs, how formed. . . ............ 340 
 
 Springs, soft and hard water ....... 340 
 
 Springs, mineral, etc ................ 340 
 
 Spring studies ...................... 389 
 
 Study of nature, importance of .... 3 
 
 Steam engine, parts of .............. 69 
 
 Strontium, properties of ............. 157 
 
 Steel, composition of ................ 164 
 
 Steel , how made ...................... 164 
 
 Strawberry, what is it? .............. 239 
 
 Starch, source, use .......... . ........ 175 
 
 Stearin, properties of ................ 178 
 
 Stomato described ................... 186 
 
898 
 
 PAGE 
 
 Stems, forms of 187 
 
 Stamens, filament and anther 211 
 
 Struggle among plants 248 
 
 Star fish described 262 
 
 Stigmata insects 277 
 
 Stars described 318 
 
 Streams, study of 390 
 
 Struggle for existence 380 
 
 Study of Marchautia 200 
 
 Study of Mosses 201 
 
 Study of Ferns 204 
 
 Study of the Pine 217 
 
 Study of growing corn 
 
 Study of the Oat 
 
 Study of the Trillium 
 
 Study of the Oak 
 
 Study of the Bean 
 
 Study of the Crayfish 
 
 Study of a Spider 
 
 Study of the Giasshopper 
 
 Study of a Mussel 
 
 Study of a Fish 
 
 Study of a Bird 
 
 Study of a Mammal 
 
 Surface Tension 
 
 Sunlight, its effects 
 
 Sulphur, forms of 
 
 Sulphur, compounds of 
 
 Sulphuric acid, how made.. . . 
 
 Sulphuric acid, its uses jay 
 
 Sugar from cane and beet 175 
 
 Sugar, manufactured 176 
 
 Sundew Family 233 
 
 Succession of plants 249 
 
 Sun, description of 316 
 
 Sun spots, effect 816 
 
 Sun, size and motions 317 
 
 Suidse or Swine Family 309 
 
 Survival of the fittest 380 
 
 Swimmerets, crayfish 269 
 
 Syenite composition 323 
 
 Syngenesious 211, 242 
 
 .. 221 
 
 .. 223 
 
 ,.228 
 
 .. 240 
 
 .. 268 
 
 ... 272 
 
 .. 280 
 
 .. 286 
 
 .. 292 
 
 .. 301 
 
 .. 305 
 
 .. 21 
 
 . .. 70 
 
 .. 137 
 
 .. 138 
 
 Tallow, source and use 
 
 Tannic acid 
 
 Tanning, process of 
 
 Tape Worms described 
 
 Tapirs described 
 
 Talpidse, or Moles 
 
 Talc, composition of 
 
 Temperature defined 
 
 Tenacity and toughness 
 
 Telescope, refracting 
 
 Telescope, reflecting 
 
 Telescope, terrestrial and Galilean 
 
 Telephone bells 
 
 Telautograph, Gray's 
 
 Temperature for plants 
 
 Tergite, sternite, pleurite 
 
 Telson, the parts of 
 
 Termites, or white ants 
 
 Teleostei described 
 
 Temperature modified by land 
 
 Temperatmre modified by water . . . 
 Temperature. great variation of 
 
 Tertiary Age, divisions of 
 
 Tertiary deposits, where ? 
 
 Tertiary Rocks and Life 
 
 Tertiary Lava flows 
 
 Tertiary Mountains formed 
 
 178 
 
 180 
 
 180 
 
 264 
 
 308 
 
 313 
 
 321 
 
 26 
 
 32 
 
 81 
 
 82 
 
 82 
 
 99 
 
 100 
 
 280 
 
 331 
 337 
 359 
 359 
 360 
 861 
 861 
 
 Terrace Period defined 
 
 Thermometer, principle of 
 
 Thallophytes mentioned ...... 
 
 Thorax of Arthropoda 
 
 Thysanura, or Spring Tails 
 
 The Earth, motions of 
 
 The Air, how warmed 
 
 The Air modifies temperature. 
 
 The Air varies in density 
 
 The Air and winds * 
 
 Theories of Matter 
 
 Theories of Heat and Light . . . 
 
 The Sea first formed 
 
 Time, importance of 
 
 Time, an element in work 
 
 Tin, properties and use 
 
 Tissues of plants 
 
 Tissue systems 
 
 Tides, how formed 
 
 Torulse described 
 
 Tobacco, its relations 
 
 Topographic work 
 
 Townships and Ranges 
 
 Townships, how divided 
 
 Transparent bodies 
 
 Trematoda described 
 
 Tragacanth, a germ 
 
 Trichina described 
 
 Trichomes named 
 
 Trilobites, abundant when ? . 
 
 Trap-door spider 
 
 Tracheae of insects 
 
 Trichechidse, or Walruses 
 
 Trachyte Rock described 
 
 Turbine wheels : 
 
 Turpentine, etc 
 
 Tubellaria described 
 
 Tulip Tree mentioned 
 
 Tubicolse described 
 
 Tubitelse, spiders 
 
 Tunicata described 
 
 Turtles, description of 
 
 Turf and trees, protect 
 
 PAGE 
 .. 370 
 .. 26 
 .. 197 
 .. 267 
 .. 279 
 .. 331 
 .. 332 
 .. 333 
 .. 333 
 .. 333 
 .. 377 
 .. 877 
 .. 348 
 .. 13 
 .. 61 
 .. 167 
 .. 184 
 
 Umbels described 
 
 Umbo of a shell 
 
 Undulatory, theory of heat. . . 
 
 Unit of Time 
 
 Unity in Plant Structure 
 
 Univalve Shells 
 
 Unity of Plants and Animals. 
 Ursidse or Bears 
 
 191 
 241 
 384 
 384 
 886 
 71 
 263 
 240 
 265 
 188 
 271 
 272 
 277 
 
 68 
 172 
 263 
 231 
 265 
 273 
 289 
 300 
 347 
 
 238 
 
 286 
 
 14 
 
 43 
 
 244 
 
 288 
 
 379 
 
 313 
 
 Vaporization explained 29 
 
 Valence explained 128 
 
 Vascular Plants 190 
 
 Vaucheria described 195 
 
 Valvate explained 235 
 
 Variation in Form 244 
 
 Valleys, Preglacial 366 
 
 Velocity defined 43 
 
 Vegetable Parchment 174 
 
 Venus Fly Trap 234 
 
 Vermes or Worms 2G3 
 
 Vespidse or Wasps 283 
 
 Vertebrata, characteristics of 290 
 
 Vertebral column 290 
 
 Veins and Fissures 826 
 
 Vibrations of the Pendulum 50 
 
INDEX. 
 
 399 
 
 PAGE 
 
 Vibrations of the Air 52 
 
 Vibrations of Cords 53 
 
 Vibrations, vary how 53 
 
 Vibrations, velocity of 56 
 
 Vinegar, how made 177 
 
 Victoria Regia 232 
 
 Violet Family 237 
 
 Violet, hidden flowers 2:33 
 
 Vine Family 237 
 
 Virginia Creeper 237 
 
 Viverridse or Civet cats 313 
 
 Von Humboldt 12 
 
 Volume defined 20 
 
 Volume of irregular bodies 36 
 
 Voices, peculiarities of 65 
 
 Volta, Professor 93 
 
 Volvox globater 260 
 
 Volcano, description of 328 
 
 Volcano, products of 329 
 
 Volcano, causes of 329 
 
 Volcanic Action, depth of 829 
 
 Water, weight of 35 
 
 Waves caused by Wind 47 
 
 Waves or Vibrations in Air 52 
 
 Water Wheels 68 
 
 Waves of Light 83 
 
 Water, composition of 110 
 
 Water, decomposition of Ill 
 
 Water, properties of 113 
 
 Water a cinder 130 
 
 \Vater in plants 188 
 
 Water Net described 194 
 
 Walnut Family 227 
 
 Water Lily Family 231 
 
 Watermelon, gourd, etc 242 
 
 Walking Sticks, insects 280 
 
 Water Vapor in the Air 333 
 
 PAGE 
 
 Water and Frost 840 
 
 Waves, how formed 335 
 
 Weight defined 20 
 
 Weight, modified how 20 
 
 Wedge defined 67 
 
 Weathering explained . 340 
 
 Weather, observation of 888 
 
 " Weather saws," collect 388 
 
 W T heel and Axle 65 
 
 White Water Lily 231 
 
 Whales, different kinds 308 
 
 Winds, cause of 48 
 
 Winds, direction of 48 
 
 Winds explained 333 
 
 Willow Family 227 
 
 Wings of Insects 276 
 
 Wind and Sand, action of 337 
 
 Winter Birds, study of 889 
 
 Work defined 58 
 
 Work, formula of 58 
 
 Work, how measured 60 
 
 Work wasted 61 
 
 Woods, differ how 174 
 
 Wood, distillation of 171 
 
 Worms or Vermes 268 
 
 Yeast, what is it 177 
 
 Yucca, fertilized how 247 
 
 Yuccasella, the insect 247 
 
 Zero, absolute 42 
 
 Zinc, properties of 157 
 
 Zinc, compounds of 157 
 
 Zoology, treats of what 12, 251 
 
 Zygnema, green scum 193 
 
 Zygospore described 193 
 
 Zygophyta described 195 
 
THE WORKING TEACHERS' LIBRARY 
 
 COMPRISES 
 
 Five Standard, Reliable and Comparatively Inexpensive Volumes, 
 
 covering in the most successful manner the whole field of 
 
 the actual needs of the Public School Teacher: 
 
 I. The Complete Writings Of David P. Page, edited by J. M. Greenwood, Superintendent 
 Kansas City Schools, contains a new life with portrait of this great educator, and includes 
 the Theory and Practice of Teaching, thoroughly revised and modernized. The Mutual 
 Duties of Parents and Teachers and the "Schoolmaster" a Dialogue, to which are added 
 the Legal Status of the Teacher, also Reading Outlines the latter for reading circles, for 
 reviews and as an aid to individual study. 
 
 II. The Teacher in Literature is a publication of exceptional merit, containing selection!. 
 from ASCIIAM, MOI.IHRE, ROUSSEAU, SHENSTONE, PESTALOZZI, COWPER, GOETHE, IRVING, 
 MITFORD, BRONTE, THACKERAY, DICKENS, and others, who have written on educational 
 subjects, from the reign of Queen Elizabeth to the present time. It is a pleasing presentation 
 of the " schools of literature," and illustrates in an exceedingly practical manner the gradual 
 development of the public school system. 
 
 III. Practical Lessons in Science, by Dr. J. T. Scovell, for ten years professor of Natural 
 Science, Indiana State Normal School, is designed to cultivate observation and perception, 
 as it deals with the common everyday facts and phenomena which are the familiar events 
 of our lives. It crystallizes the facts and laws of the various sciences and presents an 
 abundance oi easy experiments suited to the ordinary school-room conveniences, making 
 it a work of inestimable value to teachers of all grades. 
 
 IV. Practical Lessons in Psychology, by Prof. ^. O. Krohn, of the University of Illinois, 
 is a book on tact and "common sense" in teaching. One of the most important requisite^ 
 of the teacher is a knowledge of at least the elementary principles of the Science of the 
 Mind. Before he can enter intelligently upon his work, he must know something of his 
 own mental powers and have some idea of how to measure the intellectual needs and 
 capabilities of the children under his charge. In no other publication is this subject sj 
 comprehensively, so interestingly and so instructively treated,. 
 
 V. The Manual Of Useful Information, with an Introduction by F. A. Fitzpatrick, Superin. 
 tendent Omaha City Schools contains more than 100,000 facts, figures and fancies drawi 
 from every land and language, and carefully classified for the ready reference of the student, 
 the teacher and the home circle. It is a compendium of the most important facts of gener 
 interest, and so arranged as to supply the teacher with more food for reflection, mon 
 subjects for discussion, more curious and helpful suggestions, and more general exercise 
 material than was ever before published in such convenient and practical form. 
 
 These Five Volumes are handsomely printed on heavy paper 
 and elegantly bound in uniform style. Price for the Library complete, 
 $6 50. For further information, address the Publishers. 
 
 THE WERNER COMPANY, 160-174 Adams Street, CHICAGO. 
 

 
 543:159 
 
 
 
 UNIVERSITY OF CALIFORNIA LIBRARY