LO. it C EDUCATIONAL , /' ' AND COLLEGE TEXT-BOOKS. THIS justly popular Series of Text-Books is noted for its freshnes; pleteii' . oi its manuf >m the simple The Th( tions. UNION ful The s Oi UNION UNION UNION Sir ii PRIM A type /r Th< Series PROGR FIRST TE PROGR MI RuniM PROGK PROGR ARITI- NEW UNIVE EDUCATION DEPT. . Count numerously illustrated. Webster's PRIMARY SCHOOL DICTION- ARY. Webster's COMMON SCHOOL DICTION- ARY. Webster's HIGH SCHOOL DICTIONARY. Webster's ACADEMIC DICTIONARY. Webster's COUNTING-HOUSE AND FAM- ILY DICTIONARY. :er. lustra- beautiful fc .natical i CONIC ' TEGRAL .STRON- ETRY. /EYING, lie and ich are Also: Webster's POCKET DICTIONARY. A pictorial abridgment of the quarto. Webster's ARMY AND NAVY DICTION- ARY. By Captain E. C. Boynton, of West Point Military Academy. Ivison, Blakeman, Taylor & Co.'s Publications. KERL'S STANDARD ENGLISH GRAMMARS. For more of originality, practicality, are recommended over others. KERL'S FIRST LESSONS IN GRAMMAR. KERL'S COMMON SCHOOL GRAMMAR. KERL'S COMPREHENSIVE GRAMMAR. Recently issued ; KERL'S COMPOSITION AND RHETORIC. A simple, concise, progressive, thorough, and practical work on a new plan. KERL'S SHORTER COURSE IN ENGLISH and completeness. KERL'S GRA-IMARS GRAMMAR. Designed for Schools where only one text-book is us -d. We also publish : SILL'S NEW SYNTHESIS ; or, Elementary Grammar. SILL'S BLANK PARSING BOOK. To ac- company above. WELLS' (W. H.) SCHOOL GRAMMAR. WELLS' ELEMENTARY GRAMMAR. GRAY'S BOTANICAL TEXT-BOOKS. These standard text-books are recognized throughout this country and Europe as the most complete and accurate of any similar works published. They are more extensively used than all others combined. Gray's " How PLANTS GROW." Gray's LESSONS IN BOTANY. 302 Draw- ings. Gray's SCHOOL AND FIELD BOOK OF BOTANY. Gray's MANUAL OF BOTANY. 20 Plates. Gray's LESSONS AND MANUAL. Gray's MANUAL WITH MOSSES, &c. Il- lustrated. Gray's FIELD, FOREST AND GARDEN BOTANY. Gray's STRUCTURAL AND SYSTEMATIC BOTANY. FLORA OF THE SOUTHERN STATES. Gray's BOTANIST'S MICROSCOPE. 2 Lenses. WILLSON'S HISTORIES. Famous as being the most perfectly graded of any before the public. PRIMARY AMERICAN HISTORY. HISTORY OF THE UNITED STATES. AMERICAN HISTORY. School Edition. OUTLINES OF GENERAL HISTORY. School Edition. Uni- OUTLINES OF GENERAL HISTORY. versity Edition. WILLSON'S CHART OF AMERICAN HIS- TORY. PARLEY'S UNIVERSAL HISTORY. WELLS' SCIENTIFIC SERIES. NATURAL PHILOSOPHY. PRINCIPLES OF CHEMISTRY. FIRST PRINCIPLES OF GEOLOGY. FASQUELLE'S FRENCH COTJTSE Has had a success unrivaled in this country, having passed through more than fifty editions, and is still the best. Fasquelle's Introductory French Course. Fasquelle's Larger French Course. Revised. Fasquelle's Key to the Above. Fasquelle's Colloquial French Reader. Fasquelle's Telemaque. Fasquelle's Dumas' Napoleon. Fasquelle's Racine. Fasquelle's Manual of French Con- versation. Howard's Aid to French Composi- tion. Talbofs French Pronunciation. Containing the latest researches in Physical science, and their practical i application to every-day life, and is still the best. SCIENCE OF COMMON THINGS. Also: Hitchcock's ANATOMY AND PHYSIOLOGY. Hitchcock's ELEMENTARY GEOLOGY. Eliot &> Storers CHEMISTRY, THE SCIENCE OF COMMON THINGS; FAMILIAK EXPLANATION OF THE FIRST PRINCIPLES OF PHYSICAL SCIENCE. SCHOOLS, FAMILIES, AND YOUNG STUDENTS. Ellustrattfc fcntfc numerous DAVID A. WELLS, A.M. IYISON, BLAKEMAN, TAYLOE & CO. NEW YORK: CHICAGO: 138 & 140 GKAND ST. 183 & 135 STATE ST. Entered according to Act of Congress, In the year 1857, by IVISON & PHINNEY, isv the Clerk's Office of the District Court of the United States for the boutlierm District of New York. CONTENTS. PART I. CHAP-TEE LAWS AND PROPERTIES OF MATTER. P AS I. "What we Know of Matter, and How we Know It . 3 II. Attraction . . 11 III. Weight . 19 IV. Motion 22 PART II. APPLICATION OP THE LAWS AND PROPERTIES OP MATTER TO THE ARTS. I. How we apply Power 31 II. Strength of Materials 36 III. Application of Materials for Architectural and Structural Purposes 38 IV. Principles of Architecture 41 PART III. THE LAWS AND PHENOMENA OF FLUIDS. I. "Water in Motion and at Rest 49 II. Specific Gravity . . 62 III. Capillary Attraction 65 IV. The General Properties of Gaseous and Aeriform Bodies 67 V. The Atmosphere 69 VI. Atmospherical Phenomena 74 VII. The Pump and Barometer 97 VIII. Peculiarities of Climates 104 IV CONTENTS. PART IV. SOUND. I. Origin and Transmission of Sound . . . . 114 II. Vocal arid Musical Sounds . . . . . . 120 in. Reflection of Sounds ,124 PART V. HEAT. I. Nature and Origin of Heat j 129 II. The Sun a Source of Heat 133 III. Other Sources of Heat besides the Sun ... 136 IV. How Heat is Communicated 143 V. The Phenomena of Dew 162 VI. Reflection, Absorption, and Transmission of Heat . 171 VII. Effects of Heat 176 PART VL VENTILATION AND WARMING, COMBUSTION, RESPIRATION, AND NUTRITION. I. "Warming and Ventilation . . . . . . 204 II. Combustion 220 1IL Respiration and Nutrition ... . 233 PART VII. LIGHT, AND HOW WE SEE. I. Nature and Laws of Light 241 II. Structure of the Eye and the Phenomena of Vision . 262 PART VIII. ELECTRICITY, GALVANISM, MAGNETISM, AND ELECTRO- MAGNETISM. I. Electricity 275 II. Galvanism 289 III. Magnetism 295 IV. Electro-Magnetism 299 PART IX. FAMILIAR CHEMISTRY. 303 PREFACE. THE design of the present volume is to furnish for the use of schools and young persons, an elementary text-book on the first principles of science. For this purpose, the system of question and answer, which for certain classes of pupils and for familiar instruction has proved emi- nently popular, has been followed. The advantages of this system are : first, that it affords a most simple and easy method of communicating useful and practical informa- tion : second, the question excites a feeling of curiosity in the mind of the young student, which serves to fix the sub- ject-matter more strongly in the memory : and thirdly, the form of question and answer imparts truth to the mind, in a logical sequence of cause and effect, and by showing how consequents in sciences are deduced from antecedents, unconsciously trains and familiarizes the pupil to think and reason according to the true spirit of inductive philosophy. It is believed that the questions in the. present volume are simple, practical, and expressed in the plainest language that the subject allows. Engravings have also been used to illustrate more clearly the most important topics treated of. As this work has been designed exclusively as an elemen- tary book, the more abstruse and difficult departments of M69927 V PREFACE. physical science hare been passed over, or briefly noticed ; such as the theory and application of the mechanical powers, the polarization of light, crystallography, &c. Those who are desirous of possessing a more complete and elaborate work, arranged in the form of question and answer, em- bracing the whole subjects of Natural Philosophy, Organic and Inorganic Chemistry, the applications of science to the .Industrial Arts, Geology, *fcc., are referred to a work by the 'author of the present volume, entitled " Wells's Familiar Science" and to u Wells's Natural Philosophy," in both of which special reference is made to the application of the principles of physical science to the useful arts and necessi- ties of every-day life. In the preparation of the " Science of Common Things " especial care has been taken to render the facts and prin- ciples given, full, complete, and accurate, and in strict con- formity with the very latest results and researches of modern science. XEW TOEK, May, 1857. SCIENCE OF COMMON THINGS. PAET I LAWS AND PROPERTIES OF MATTER. CHAPTER I. WHAT WE KNOW OF MATTER, AND HOW WE KNOW IT. 1 What is matter t "We apply the term matter to any substance which affects our senses. & How do lee know that anything exists f Because our senses give us evidence of the fact 3 What are the senses t They are the instruments, or means, by which the mind is enabled to know that matter exists and pos- sesses certain properties. 4 How many senses are there f Five ; hearing, seeing, smelling, tasting, and feeling. 5 Wsuld a person deprived of all sensation, be conscious of any mats- rial existence f He would not ; for all knowledge of the material world is derived through the medium of the senses. 6 Is the impression transmitted to the mind by each organ of sensation, different* It is; each organ of sense is adapted to receive a particular influence of matter ; and is designed to con- SCIENCE OF COMMON THINGS. Properties of matter Impenetrability. vey to the mind immediate notice of some peculiar action. This is the more noticeable, when we consider that, however delicate its structure, each organ of sense is wholly insensible to every influence except that to which it is especially adapted ; thus, the eye is never affected by sound, nor the ear by light. 7 What is meant by the term body ? Any distinct portion of matter existing in, and oc- cupying space. 8 What do we mean, when we speak of "he properties or qualities of a body? The powers belonging to the body, which are capa- ble oif^xfeiting* In .'oiii* miad certain sensations. What are the general properties of matter f Tlu- ]a4ftdal ; qualifies of matter are MAGNITUDE or EXTENSION, IMPENETBABiLlTY, DIVISIBILITY, POROSITY, IN- ERTIA, DENSITY, ELASTICITY, DUCTILITY, and MALLEABILITY. 10 What is magnitude f The property of occupying space. It is impossible to conceive of a portion of matter so minute as to have no magnitude. 11 What do we mean by the term size of a body ? The quantity of space a body occupies. 13 What is the surface of a body f The external limits of its magnitude- is What is the area of a body ? The quantity of surface. 14 What is impenetrability f That quality of matter which precludes the possibility of two bodies occupying the same space at the same time. "When bodies are said to be impenetrable, it is therefore meant, that one cannot pass through another without displacing some, or all, of the component parts of that other. There are many instances of apparent penetration ; but in all those, the parts of the body which seem to be penetrated are only displaced. Thus, if a needle be plunged into a vessel of water, all the water which pre- viously filled the space into which the needle enters, will be displaced ; and the level of the water will rise in the vessel to the same height as it SCIENCE OF COMMON THINGS. Divisibility of matter. Atoms. Particles. would by pouring in so much more water as would fill the space occupied by the needle. 15 Why witt water, or any other liquid, poured into a funnel, closely inserted in the mouth of a bottle, or decanter, run over the sides f Because the air filling the bottle, and having no means of escape, prevents the fluid from entering the bottle ; but if the funnel be lifted from the neck of the bottle a little, so as to afford the air an opportunity to escape, the water will then flow into the bottle in an uninterrupted stream. ie What is the figure of a body f Its form or shape, as expressed by its boundaries or terminating extremities. 17 What is meant by the divisibility of matter t Its property, or capability of being divided. 18 Is matter capable of being divided into separate portions infinitely or without limit f So far as we are able to perceive with our senses, all matter is capable of being divided into separate por- tions without limit; yet the recent investigations of chemistry have proved beyond a doubt, that there is a point beyond which matter is no longer divisible. Such a portion of matter as cannot be divided we call an atom. 19 WJiai ffien is an atom of matter f A particle so minute, as to admit of no division. Atoms are conceived to be the first principles or com- ponent parts of all bodies. The extent to which matter can be divided and yet be perceived by the senses, is wonderful. An ounce of gold may be divided into four hundred and thirty-two thousand million parts. Each of these parts will retain all the characters and qualities which are found in the largest masses' of metal. It retains its solidity, texture, and color; it resists the same agents, and enters into combination with the same substances. 20 What is a particle of matter ? The term particle is also used to express^ sraZ com- ponent parts of matter, but is generally applied to those which are not too minute, to be discovered by obser- vation. 1* SCIENCE OF COMMON THINGS. Pores of a body. Compressibility. Density. 31 What are the pores of a body ? No two particles of matter are supposed to be in actual contact with each other; and the openings, or interstitial spaces between these particles, are called pores. 33 What is the reason that a sponge, apiece of tcood or metal, can, by pressure, be made to occupy a smaller space than it did originally f Because the particles of which the sponge, the piece of wood or metal, are composed, are by pressure brought more closely together, diminishing at the same time the pores and the space the body occupies. 33 What then is compressibility ? That quality of matter in virtue of which a body allows its volume or size to be diminished, without diminishing the number of atoms or material particles of which it consists. 34 What reason have we for supposing that no two particles of matter are in absolute contact f Because all known bodies, whatever may be their nature, are capable of having their dimensions reduced without diminishing the amount of matter contained in them ; hence the space by which the volume may be diminished must, before diminution, consist of pores'. 35 What is density f The proportion of the quantity of matter in a body to its magnitude. Thus, if of two substances one contains in a given space twice as much matter as the other, it is said to be twice as dense. 36 What connexion is there between the density of a body and its porosity ? A body will be more or less dense according as its particles are near to or remote from each other ; and hence it is evident that the greater the density the less the porosity, and the greater the porosity the less the density. 37 Why do we caU lead heavy, and feathers light ? Because the amount of matter contained in a quan- tity of lead occupying a given space is much greater than in a quantity of feathers capable of occupying the SCIENCE OF COMMON THINGS. 11 Ductility. Malleability. Attraction. much more dense than the diamond, yet the metal is soft, while the diamond is the hardest body in nature. 56 When is a body said to be ductile ? When it is capable of being drawn into wire. In ductile substances the atoms seem to have no more fixed relation of position than in a liquid, but yet they cohere very strongly. y 57 When is a body said to be malkabk f When it is capable of being hammered or rolled into thin plates. Bodies that are malleable are not always ductile. Lead and tin may be hammered out into very thin plates, but it is 'difficult, or impossible, to draw out these metals into fine wire. CIIAPTEE II.' ATTRACTION. 58 What is attraction ? It is the force manifested by the mutual approach or cohesion of bodies. 59 Is all matter subject to the power of attraction ? All matter is under the influence of attraction in some of its forms. Every particle of matter attracts every other particle, and is in turn itself attracted. 60 What is repulsion ? It is the force manifest in the movement of bodies from each other. Thus, if a piece of glass, having been briskly rubbed, with a silk handkerchief, touch successively two feathers, these feathers, if brought to- gether, will move asunder. 61 What is cohesive attraction f It is the force which holds together the atoms of SCIENCE OF COMMON THINGS. Adhesion. Examples of cohesion^ | bodies. Cohesion acts only between particles of pat- ter of the same kind, and at distances which are not measurable, or, as they are termed, insensible distaaices. 63 What is adhesion ? Adhesion is attraction between particles of matter of different kinds acting at immeasurably small dis- tances only, and uniting the dissimilar particles into one mass. 63 Why is mortar used to fasten bricks together f Because the adhesive attraction between the particles of the brick and the particles of mortar is so strong, that they unite to form one solid mass. j 64 Why is a bar of iron stronger than a bar of wood of the same size ? Because the cohesion existing between the particles of iron is greater than that existing between the par- ticles of wood. 65 Why are the particks of a liquid more easily separated than those of a solid ? Because the cohesive attraction which binds together the particles of a liquid is much less strong than that which binds together the particles of a solid. 66 Why will a small needle, carefully laid upon the surface of water, float f Because its weight is not sufficient to overcome the cohesion of the particles of water constituting the sur- face ; consequently, it cannot pass through them and sink. 6*7 If you drop water and laudanum from the same vessel why wiU sixty drops of the water fill the same measure as one hundred drops of laudanum ? The cohesion between the particles of the two liquids is different, being greatest in the water. Consequently, the number of particles which will adhere together to constitute a drop of water is greater than in the drop of laudanum. 68 Why is the prescription of medicine by drops an unsafe method f Because not only do drops of fluid from the same vessel, and often of the same fluid from different ves- SCIENCE OF COMMON THINGS. 13 Attraction of gravitation. Illustrations of gravitation. jj differ in size, but also drops of the same fluid, to the 'extent of a third, from different parts of the lip of the same vessel. 69 Why is it difficult to pour water from a vessel which has not a pro- jecting lip ? Because, in consequence of the attraction between the water and the sides of the vessel, the fluid has a tendency to run down along the inclined outside of the vessel, and not at once to fall perpendicularly. 7*O | What is the attraction of gravitation ? W<$ apply the term "gravity," or the "attraction of gravitation," to that tendency which every particle of matter in the universe has to approach all other matter. Terrestrial gravitation is the attraction of a body towards the centre of the earth. T'l In what respect does the attraction of gravitation differ from all other attractive forces ? Because it is the common property of all bodies ; since everything to which we can attach the idea of materiality is aftected more or less by gravitation. 7*3 Why does an appk loosened from the tree fall to the ground? Because the earth attracts or draws it to itself. 7*3 Since all bodies are attracted towards the earth, how does it happen that all smoke and some other forms of matter display the contrary pheno- menon of ascending from it ? Because the smoke is lighter than the air, bulk for bulk, and floats upon it. It is unable to advance, how- ever, in the most minute degree, without displacing or thrusting downward portions of the atmosphere equal to its own bulk. 7*4: Why does a cork pressed beneath the water rise and float on the turf ace ? Because the cork is lighter than an equal bulk of water, and is pressed up and sustained by it in the same manner that the particles of smoke are sustained by the particles of air. 7*5 Why does a balloon rise in the air ? Because it is filled with a gas which is lighter, bulk for bulk, than the air. SCIENCE OF COMMON THINGS. All bodies attract each other. Feather and the earth. 76 How long witt smoke continue to float above the surface of the earth f Until its particles, uniting, become heavier than the air, when they descend in the form of small flakes of soot. 77 Why do bubbles in a cup of tea range round the sides of the cup ? Because the cup attracts them. 78 Why do att the little bubbles tend towards the large ones f ^ Because the large bubbles (being the superior masses) attract them. 79 Why do the bubbles of a cup of tea follow a tea-spoon f Because the tea-spoon attracts them. SO Do all bodies attract each other equally f They attract each other with forces proportioned to their masses. 8 1 A feather falls to the ground by the influence of the earth's attraction. Now, as all bodies attract each other, does the feather attract or draw up the earth in any degree towards itself? It does, with a force proportioned to its m-ass / but as the mass of the earth is infinitely greater than the feather, the influence of the feather is infinitely small, and we are unable to perceive it. 83 What would be the consequence if the feather did not attract the earth f If any portion of the earth, however small, failed to attract another portion, and not be itself attracted, the axis of the earth would le immediately changed, involv- ing an alteration of climate, and the place of the ocean in its bed. 83 Why is it more dangerous to fall from, a lofty elevation than from a low one ? As the attraction of the earth varies inversely with the square of the distance, the force with which a fall- ing body will strike the ground will increase in propor- tion to the height from which it has fallen. 84 In what direction does a body, when not supported, endeavor to fall ? In a line drawn from its centre of gravity towards the centre of the earth. 85 Is the attraction of the earth the same at att distances from its sur- face or centre f SCIENCE OF COMMON THINGS. 15 Centre of gravity. Position in which a body can rest. JVb ; the attraction of the earth for a body varies inversely with the square of its distance from the 'centre. 86 How can this be illustrated ? In the following manner : If one body attracts an- other with a certain force at the distance of one mile, it will attract with four times the force at half a mile, nine times the force at one-third of a mile, and so on in like proportion. On the contrary, it will attract with but one-fourth of the force at two miles, one-ninth of the force at three miles, one-sixteenth of the force at four miles, and so on as the distance increases. 87 What do we mean by the centre of gravity ? That point in a body about which, if supported, the whole body will balance itself. 88 When you balance a rod, a stick, or any other body, upon the finger, where is the centre of gravity of the stick or body ? It is the point upon which the body will remain at rest, or upon which it is balanced. 89 In what position only can a body rest ? Only when its centre of gravity is supported ; and until this is accomplished the body will move, and con- tinue to do so, until it settles into a position in which the centre of gravity cannot sink lower. 0O Why does a person carrying a weight upon his back stoop forward ? In order to bring the centre of gravity of his body and the load over his feet. Fig 1. fifr 2. 16 SCIENCE OF COMMON THINGS. Centre of gravity in man and animals. If he carried the load in the position of A, Fig. 1, he would fall back- wards, as the direction of the centre of gravity would fall beyond his heels ; to bring the centre of gravity over his feet, he assumes the posi- tion indicated by B, Fig. 2. 91 When a person carries a load upon his head, why is it necessary to stand perfectly upright ? In order tliat the centre of gravity may be over his feet. i Q& Why does a person in rising from a chair bend forward ? When a person is sitting, the centre of gravity is supported by the seat ; in an erect position, the centre of gravity is supported by the feet / therefore, before rising it is necessary to change the centre of gravity, and by bending forward we transfer it from the chair to a point over the feet. 93 Why does a quadruped, in walking } never raise loth feet on the same side simultaneously f Because, if it did, the centre of gravity would be un- supported, and the animal would tend to fall over. 94 Why is a large turtle placed on its back unable to move f Because the centre of gravity of the turtle is, in this position, at the lowest point, and the animal is unable to change it ; therefore it is obliged to remain at rest. 95 WJiy is it more difficult to overthrow a body Jiaving a broad base than one resting upon a narrow basis f Because a body cannot fall over, so long as a line directed from the centre of gravity vertically towards the surface upon which the body rests, falls within the figure formed by the base of the body in question. SCIENCE OF COMMON THINGS. IT Stability of buildings. Centre of gravity in walking. Hence, tlie broader the base of a body, the more securely it will stand. Thus, in Fig. 3, the line directed vertically from the centre of gravity, G, falls within the base of the body, and it remains standing ; but in Fig. 4 a similar line falls without the base, and the body consequently cannot be maintained in an upright position, and must fall. 96 How long will a watt or tower stand securely ? So long as the perpendicular line drawn through its eentre of gravity falls within its base. The celebrated leaning tower pf Pisa, 315 feet high, which inclines 12 feet from a per- fectly upright position, is an example of this principle. For instance, the line in Fig. 5, falling from the top of the tower to the ground, and pass- ing through the centre of gra- vity, falls within the base, and the tower stands securely. If, however, an attempt had been made to build the tower a lit- tle higher, so that the perpen- dicular line passing through the centre of gravity would have fallen beyond the base, the structure could no longer have supported itself. Fig.5. 7* What is the advantage of turning out the toes when we walk f It increases the breadth of the base supporting the body, and enables us to stand more securely. 98 Why do very fat people throw hack their head and shoulders when they walk ? In order that they may effectually keep the centre of gravity of the body over the base formed by the soles of the feet. 99 W?cy cannot a man, standing with his heels close to a perpendicular watt, bend over sufficiently to pick up any object that lies before him on the ground, without falling ? Because the wall prevents him from throwing part of his body backward, to counterbalance the head and that must project forward. 18 SCIENCE OF COMMON THINGS. Eope-dancing. How we learn to walk. 100 What is the reason that persons walking arm-in-arm shake and jostle each other, unless they make the movements of their feet to correspond, as soldiers do in marching ? When we walk at a moderate rate, the centre of gravity comes alternately over the right and over the left foot. The body advances, therefore, in a waving line; and unless two persons walking together keep step, the waving motion of the two fails to coincide. 101 Where would the centre of gravity be in a wheel made entirely of wood and of a uniform thickness ? In the centre. 1OS Where would the centre of gravity be if a part of the rim of the same wJieel were made of iron f It would be changed to some point aside from the centre of the wheel. 103 In what does the art of balancing or walking upon a rope consist? In keeping the centre of gravity in a line over the base upon which the body rests. 104 What is the base upon which the human body rests or is supported t The two feet and the space included between them. 105 Why is it a very difficult thing for children to learn to walk ? In consequence of the natural upright position of the human body, it is constantly necessary to employ some exertion to keep our balance, or to prevent ourselves from falling, when we place one foot before the other. Children, after they acquire strength to stand, are obliged to acquire this knowledge of preserving the balance by experience. When the art is once acquired, the necessary actions are performed involuntarily. 106 Why do young quadrupeds learn to walk much sooner than chil- dren f Because a body is tottering in proportion to its great altitude and narrow base. A child has a body thus constituted, and learns to walk but slowly because of this difficulty, (perhaps in ten or twelve months,) while the young of quadrupeds, having a broad supporting base, are able to stand and move about almost immedi- ately. 107 Are aU the limbs of a tall tree arranged in such a manner, that tlie SCIENCE OF COMMON THINGS. 10 How trees grow. Weight. * line directed from the centre of gravity is caused to fall within the base of the tree? Nature causes the various limbs to shoot out and grow from the sides with as much exactness, in respect to keeping the centre of gravity within the base, as though they had been all arranged artificially. Each limb growsj in respect to all the others, in such a man- ner as to preserve a due balance between the whole. / CHAPTEK III. "WEIGHT. 1O8 What is weight f Weight is the measure of the attraction of gravita- tion, or, in other words, it is the measure of force with which a body^ is attracted by the earth. Iti an ordi- nary sense it is the quantity of matter contained in a body, as ascertained by the balance. 1O0 To what is the weight of a tody proportional f The weight of a body is always proportional to the quantity of matter contained in it. 110 Why witt a ball of kad weigh more than a baU of cotton of the same size ? Because the quantity of matter contained in the ball of lead is much greater than the quantity of matter contained in the ball of cotton. The attraction of gra- vitation being proportioned to the quantity of matter, it follows that the lead ball will be drawn towards the earth with a greater force (i. e. will weigh more) than the ball of cotton. 111 A man of moderate weight upon the surface of the earth would weigh two tons if transported to the surface of the sun : why would he weigh more upon the surface of the sun than upon the surface of the earth f 20 SCIENCE OF COMMON THINGS. TV hen a body weighs the most Systems of weights. Because the attractive force of the sun, on account of its greater magnitude, far exceeds the attractive force of the earth. 11Q Why witt a mass of iron weigh less on the top of a high mountain than at the level of the sea f Because the force of the earth's attraction is less at the top of the mountain than at the sea-level ; the attrac- tion (and, therefore, the weight of a body) being greatest at the surface of the earth, and decreasing upward, as the square of its distance from the centre of the earth increases. A ball of iron, weighing a thousand pounds at the level of the sea, ~y would be perceived to have lost two pounds of its weight if taken to the top of a mountain four miles high, a spring balance being used. 113 Where witt a body weigh the most on the surface of the earth ? At the poles of the earth, for at these points the attractive power is greatest. It must be remembered that the earth is not a perfect sphere, but flat- tened at the poles : consequently, the poles of the earth are nearer the centre of attraction (i. e. the centre of the earth) than any other point on its surface. 114 Where witt a body weigh the least on the earths surface f At the equator, for there the attractive power is less ; the surface at this point being the most distant from the centre of the earth. 115 What would be the weight of a body carried to the centre of the earth f It would have no weight ; for the attraction of gra- vitation acting equally in every direction, no eftect would be produced ; and the body w r ould be fixed as if sustained by a number of magnetic points. 116 What two systems of weights are employed in tlie United States and Great Britain f Troy weight and avoirdupois weight. 117' What is Troy weight used for } and from whence does it derive its name? Troy weight is used for weighing gold and silver. It derives its name from the ancient designation of London, Troy Novant, or from Troyes, in France, where it was first adopted in Europe. It has existed in England from the time of Edward the Confessor. SCIENCE OF COMMON THINGS. 21 Avoirdupois and grain weights. English, American, and French weights. 118 What is avoirdupois weight used for, and from whence does it uerive its name ? Avoirdupois weight is used for the weight of mer- chandise other than the precious metals. It derives its name from the French avoirs (averia\ goods or chat- tels, and poids, weight. 11Q What is a grain weight f A grain weight is the smallest measure of weight made use of in the English system. By a law of Eng- land enacted in 1286, it was ordered that 32 grains of wheat, well dried, should weigh a pennyweight. Hence the name grain applied to this measure of weight. It was afterwards ordered that a pennyweight should be divided into only 24 grains. 150 How do we make a grain weight for practical purposes f By weighing a thin plate of metal of uniform thick- ness, and cutting out, by measurement, such a propor- tion of the whole as should give one grain. In this way, weights may be obtained for chemical purposes, which weigh only lTr Vu1;h part of a grain. 151 What part of an inch is a line f One-twelfth of an inch is designated as a line. 1SS Are tJie standards of weights and measures in the United States tlie same as in Great Britain ? They are essentially the same. 1S3 Where are the standards of weights and measures to be found in the United States ? At Washington, and at the capitals of the several States of the Union ; sets having been furnished to each State by the United States. 124 Are the weights and measures used in France the same as those of the United States and England ? No ; they are entirely different. Within a compa- ratively recent time the French have reconstructed their old system of weights and measures, and formed another on an entirely new plan. The French system is, at present, the best and most accurate system existing. SCIENCE OF COMMON THINGS. Force. Motion. Friction. CHAPTER IYc MOTION. 135 What is force f Force is whatever causes or opposes ike production of motion in matter. 1SS What is motion f It is the term applied to the phenomena of the changing of place among bodies. 13 *7 What would be the state of things if no motion existed f The universe would be dead. There would be no rising and setting of the sun, no flow of water or of air (wind), no sound, light, or animal existence. 128 The surface of the earth at the equator moves at the rate of about a thousand miles in an hour : why are men not sensible of this rapid move- ment of the earth f Because all objects about the observer are moving in common with him. It is the natural uniformity of the undisturbed motion which causes the earth and all the bodies moving together with it upon its surface to ap- pear at rest. 120 How can you easily see that the earth is in motion f By looking at some object that is entirely uncon- nected with it, as the sun or the stars. We are here, however, liable to the mistake that the sun or stars are in motion, and not we ourselves with the earth. ISO Does the sun really rise and set each day ? The sun maintains very nearly a constant position ; but the earth revolves, and is constantly changing its position. Really, therefore, the sun neither rises nor sets. 131 What do we mean by the term friction f In mechanics, it signifies the resistance which a moving body meets with from the surface on which it moves. SCIENCE OF COMMON THINGS. 23 Impossibility of perpetual motion. Centrifugal force. 132 Is it possible to construct any machine, w arrangement of matter^ which will perpetually continue in motion ? It is not / because the operations of gravity, the re- sistance of the medium through which the body moves , or the friction of the surfaces upon which the lody rests, will, in a given time, destroy and terminate all motion. In addition to this, all materials which we employ in construction will, in the course of time, wear out by use, or decay by natural agencies. 133 Do we know of any instances of perpetual motion in nature 1 Yes the various planetary bodies belonging to the solar system have been moving with undiminished velocity for ages past ; and, unless prevented by the agency which governs all nature, will continue to move in the same manner for ages to come. 134 Why are horses obliged to make a much greater exertion to start a carriage than afterwards to keep it in motion ? Because when a carriage is once put in motion upon a level road, with a determinate speed, the only force necessary to sustain the motion is that which is suffi- cient to overcome the friction of the road / but, at starting, a greater expenditure of force is necessary, inasmuch as not only the friction is to be overcome, but the force with which the vehicle is intended to move must be communicated to it. 135 What is centrifugal force? It is that force which causes a revolving body to fly from a centre. 136 Why does a stone, discharged from a sling, move forwards, when the cord which retained it is loosened f Because of the centrifugal force it- has acquired by the whirling of the sling previous to the discharge. 137 Why do grindstones or wheels, in rapid motion, not unfrequenfty 'break and fly to pieces with great violence ? Because the centrifugal force, generated by the rapid revolving motion, overcomes the cohesion of the parti- cles, and thus causes them to separate and fly from the centre. SCIENCE OF COMMON THINGS. Illustrations of centrifugal force. Revolution of the earth. 133 Can almost all revolving bodies be broken by sufficient rotative velocity ? Yes; for the centrifugal force increases with the rapidity of revolution, and finally becomes too strong to be resisted by the cohesive force which binds the particles of the body together. 13Q When a vessel containing water is whirkd rapidly round, why does not the water fall out when the vessel is upside down ? Because the centrifugal force, tending to make the water fly from the centre, overcomes or balances the attraction of gravitation, which tends to cause the water to fall out. In Fig. 6. the water contained in the bucket which is upside down, has no support under it, and if the bucket were kept still in its inverted position for a single moment the water would fall out by its own weight, or, in other words, by the attraction of gravi- tation : but the centrifugal force, which is caused by the whirling of the bucket in the direction of the arrow, tends to drive the water out through the bot- tom and side of the vessel, and as this last force is equal to and balances the other, the water retains its place, and not a drop is spilled. How much faster would the earth be required to revolve in order to make the centrifugal force equal to the attraction of gravitation f /Seventeen times faster, or in eighty- four minutes, instead of twenty-four hours : in this case all bodies at the equator of the earth would be destitute of weight. 141 What would be the consequence if the earth revolved around its axis in less time than eighty-four minutes ? I Gravitation would be completely over- _ powered, and all fluids and loose sub- Fi 6 - stances would fly from the surface. 143 Why does a man or horse, in turning a corner rapidly, incline inwards, or kan towards the corner t Because the centrifugal force, produced by turning SCIENCE OF COMMON" THINGS. 25 Action of centrifugal force in equestrian sports. rapidly, tends to throw him away from, the corner y therefore, he inclines inwards to counteract it. 143 Why does a horse in a circus ring lean towards the centre 1 When the horse moves rapidly around the circular course, the centrifugal force generated, tends to throw him over, outwardly, or away from the centre of the ring ; and this tendency the animal counteracts, by inclining his body in an opposite direction. Fig. 7. In all equestrian feats exhibited in the circus, it will be observed that not only the horse but the rider inclines his body towards the centre, Fig. 7, and according as the speed of the horse round the ring is increased, this inclination becomes more considerable. "When the horse walks slowly round a large ring this inclination of his body is imperceptible ; if he trot there is a visible inclination inwards, and if he gallop he inclines still more, and when urged to full speed he leans very far over on his side, and his feet will be heard to strike against the partition which defines the ring. The explanation of all this is, that the centrifugal force caused by the rapid motion around the ring tends to throw the horse out of, and away from, the circular course, and this he counteracts by leaning inwards. 144 Why do water-dogs give a semi-rotary movement to their skin to free themselves from water ? Because in this way a centrifugal force is generated, which causes the drops of water aaherent to them to fly off. 26 SCIENCE OF COMMON THINGS. Phenomena of jumping. Flying of birds. Flying and leaping. 145 Why does a person who is about to leap over a ditch or chasm first make a run of a little distance ? In order that the impetus he acquires in running may help him in the jump. 140 Why is a standing leap always shorter than a running one f Because in the running leap, in addition to the force acquired by the contraction of the muscles, we have added the force of the motion acquired by running. 147 Why do we kick against the door-post to shake the snow or dust from our shoes ? The forward motion of the foot is arrested by the impact against the post ; but this is not the case with respect to the particles of dust or snow, which are not attached to the foot ; but the motion imparted to them equally with the foot is continued, and causes them to fly off. 148 Why do we beat a coat or carpet to expel the dust f The cause which arrests the motion imparted to the coat or carpet by the blow does not arrest the particles of dust, and their motion being continued, they fly off. 149 Why can birds fly f Because they have the largest bones of all animals in proportion to their weight. Air-vessels also enable them to blow out the hollow parts of their bodies, when they wish to make their descent slower, rise more swiftly, or float in the air. The muscles that move the wings of birds downwards, in many instan- ces, are a sixth part of the weight of the whole body ; whereas those of a man are not, in proportion, one- hundredth part so large. It is an erroneous idea, still taught in many educational works, that the bones of birds are hollow and filled with air. This is not the case. Recent investigations have shown that the bones of birds, as a general thing, are not more hollow than those of other animals, and do not con- tain air. 150 Why does flying differ from leaping 1 Because flying is the continued suspension and pro- gress of the whole body in the air, by the action of the wings. In leaping, the body is equally suspended in SCIENCE OF COMMON THINGS. 27 Action of birds in flying. Action and reaction. the air; but the suspension is only momentary. In flying 3 on the contrary, the body remains in the air and acquires a progressive motion by repeated strokes of the wings on the surrounding fluid. 151 Why do birds stretch out their necks when flying f In order that they may act as a wedge, dividing the air and diminishing the resistance. 152 Why are the strongest feathers of birds in the pinions and tail f Because when the wing is expanded, the pinion- feathers may form, as it were, broad fans, by which the bird is enabled to raise itself in the air and fly; while its tail-feathers direct its course. 153 Why can a person safely skate with great rapidity over ice which would not support his weight if he moved over it more slowly f From the fact that time is required for producing the fracture of the ice : as soon as the weight of the skater begins to act on any point, the ice, supported by the water, bends slowly under him ; but if the skater's Velocity is great, he has passed off from the spot which was loaded before the bending has reached the point which would cause the ice to break. 154 It sometimes happens when persons are knocked down "by carriages that the wheels pass over them with scarcely any injury, though if the weight of the carriage had rested on the body, even for a few seconds, it would have crushed them to death. What explanation can be given of this fact f The wheel moves with such rapidity, that the weight has not time sufficient to exert its full effect. 155 When two equal bodies meet, moving with equal velocities in oppo- site directions, what will be the effect ? They will both come to rest for their motion being equal and contrary, will be mutually destroyed. 150 When two persons strike their heads together, one being in motion and the other at rest, why are both equally hurt f Because, when bodies strike each other, action and reaction are equal ; the head that is at rest returns the blow with equal force to the head that strikes. 157 When an elastic batt is thrown against the side of a house with a certain force, why does it rebound f 28 SCIENCE OF COMMON THINGS. Examples of action and reaction. Laws of falling bodies. Because the side of the house resists the ball with the same force, and the ball, being elastic; rebounds. 158 When the same ball is thrown against a pane of glass with the same force, it goes through, breaking the glass : why does it not rebound as beforef Because the glass has not sufficient power to resist the full force of the ball : it destroys a part of the force of the ball, but the remainder continuing to act, the ball goes through, shattering the "glass. 159 Why did not the man succeed who undertook to make a fair wind for his pleasure boat, by erecting an immense bellows in the stern, and blow- ing against the sails f Because the action of the stream of wind and the reaction of the sails were exactly equal, and, conse- quently, the boat remained at rest 160 If he had blown in a contrary direction from the sails, instead of against them, would the boat have moved ? It would, with the same force that the air issued from the bellows-pipe. 161 Why cannot a man raise himself over a fence by pulling upon the straps of his boots f Because the action of the force exerted to raise him- self, is exactly counteracted by the reaction of the force which tends to keep him down. 163 Does a man, in rowing, drive the water astern with the same fores that he impels the boat forwards t He does : action and reaction being exactly equal. 163 Why is it more dangerous to leap from a, high window than from a low table ? Because the velocity of a falling ~body, and, conse- quently, the force with which it will strike the ground," ^ncrease8 with the distance through which it falls. 164 How far ivitt a, body fall, through the influence of gravity, in one te.cond of time ? Sixteen feet. 165 How far will it fall in two seconds f Four times 16 feet, or 64 feet ; in three seconds it will fall 144 feet ; in four, 256 ; in five seconds, 400 feet, and so on. SCIENCE OF COMMON THINGS. 20 Pendulum. Common clock. 166 Will a mass of iron, weighing one hundred pounds, let fall from an elevation, reach the ground any quicker than a mass weighing only one pound, ktfall at the same time and from the same place f No ; the lighter mass will fall with the same velocity, and reach the ground as soon as the larger one. Before the time of Galileo it was taught and believed, that if two bodies of different weights were let fall from any height at the same mo- ment, the heavier body would reach the ground as much sooner as ita weight was greater than the smaller. Galileo, on the contrary, main- tained that they would both strike the ground at the same time, and, as his doctrine was generally disbelieved, he challenged his opponents to a practical trial. The experiment was made from the top of the celebrated leaning tower of Pisa, in the presence of a great concourse of people, and resulted in the complete triumph of Galileo. 167 What is the rule by which the height from which a body falls may be found, the time consumed in falling being known? Multiply the square of the number of seconds of time consumed in falling, ~by the distance which a body will fall in one second. 168 If a stone is five seconds in falling from the top of a precipice, hoio high is the precipice f The square of five seconds is 25 ; this multiplied by 16, the number of feet a lody will fall in one second, gives 400, the height of the precipice. 169 What is a pendulum ? A pendulum is a heavy body, as a piece of metal, suspended by a wire or cord, so as to swing backwards and forwards. 170 When is a pendulum said to vibrate f When it swings backwards and forwards ; and that part of the circle through which it vibrates, is called its arc. 17*1 What is a common clock f Merely a pendulum, with wheel- work attached to it, to record the number of vibrations, and with a weight or spring, having force sufficient to counteract the re- tarding effects of friction and the resistance of the air. 17S How long must a pendulum be to beat seconds 1 About 39 inches. 178 Why does a common clock go faster in winter than in summer t 2* 30 SCIENCE OF COMMON THINGS. Length of pendulum affects the rate of a clock. Because the pendulum-rod becomes contracted by cold in winter, and lengthened by heat in summer. 174: Why does a change in the length of the pendulum cause a clock to go faster or slower f The number of vibrations which a pendulum makes in a giyen time depends upon its length, because a long pendulum does not perform its journey to and from the corresponding points of its arc so soon as a short one. SCIENCE OF COMMON THINGS. 31 Application of power. What are machines ? PART n. APPLICATION OF THE LAWS AND PROPER TIES OF MATTER TO THE ARTS. CHAPTER I. HOW WE APPLY POWEB. 175 What is a machine f By a machine we understand a combination of me- chanical powers adapted to vary the direction, applica- tion, and intensity of a moving force, so (is to produce a given result. 176 What is the difference between a machine and a tool ? The difference between a machine and a tool is not capable of very precise distinction. A tool is usually 'more simple than a machine : it is generally used by hand, while a machine is generally moved by some vther than human power. 177 Does a machine ever create power, or increase the quantity of power or force applied to it? A machine will enable us to concentrate or divide any kind or quantity of force which we may possess, but it no more increases the quantity of force than a mill-pond increases the quantity of water flowing in the stream. 178 From what sources do we derive advantages by the use of machines and manufactures f From the addition they make to human power ; from the economy they produce of human time ; from the conversion of substances apparently common and worthless into valuable products. 32 SCIENCE OF COMMON THINGS. Object of machinery. Perpetual motion. Sources of power. 179 How do machines make additions to human power f They enable us to use the powers of natural agents, as wind, water, steam; they also enable us to use ani- mal power with greater effect, as when we move an object easily with a lever, which we could not with the unaided hand. ISO How do machines produce economy of human time f They accomplish with rapidity what would require the hand unaided much time to perform. A machine turns a gun-stock in a few minutes ; to shape it by hand would be the work of hours. 181 How do machines convert objects apparently worthless into valuable, products f By their great power, economy, and rapidity of ac- tion, they make it profitable to use objects for manu- facturing purposes which it would be unprofitable or impossible to use if they were to be manufactured by hand. Without machines, iron could not be forged into shafts for gigantic engines ; fibres could not be twisted into cables ; granite, in large masses, could not be transported from me quarries. 182 Why are so many attempts continually made to produce mechani- cal engines which shatt generate perpetual motion f Because the projectors do not understand the great truth, that no form or combination of machinery can, under any circumstances, increase the quantity of power applied. 183 What is the object ef a machine f To receive and distribute motion derived from an external agent, since no machine is capable of generat- ing motion or moving-power within itself. 184 What are the principal sources from whence power is obtained f Men and animals, water, wind, steam, and gunpow- der. The power of all these may be ultimately re- solved into those of muscular energy, gravity, heat, and chemical affinity. 185 Are there any other sources ofpotver ? Yes ; magnetism, electricity, capillary attraction, etc. ; SCIENCE OF COMMON THINGS 33 Muscular energy. Horse-power. Water-power. but none of these are capable of being used practically for the production of motion. 186 How is muscular energy exerted f Through the contraction of the fibres which constitute animal muscles. The bones act as levers to facilitate and direct the application of this force, the muscles operating on them through the medium of tendons, or otherwise. 187 What animals possess the greatest amount of muscular power f Beasts of prey. Some very small creatures, how- ever, possess muscular power in proportion to their bulk, incomparably greater than that of the largest and greatest of the brute creation. Kflea, considered relatively to its size, is far stronger than an elephant or a lion. 188 In what method can a man exert the greatest active strength f In pulling upwards from his feet : because the strong muscles of the back, as well as those of the up- per and lower extremities, are then brought advan- tageously into action. Hence the action of rowing is one of the most advantageous modes of muscular action. 189 What is'the estimate of the uniform strength of an ordinary man for the performance of daily mechanical labor ? That he can raise a weight of 10 pounds to the height of 10 feet once in a second, and continue to labor for 10 hours in the day. 10O What is a " horse-power ?" We say a steam-engine is of a cer- tain horse-power ; what is the meaning of the term ? The measure of a" horse's power" adopted as a standard for estimating the power of steam-engines, is that he can raise a weight of 33,000 pounds to the height of one foot in a minute. 191 What is the strength of a horse compared with that of man f The force of one horse is considered to be equal to that of five men. 193 What do we mean by " water-power f" The power obtained by the action of water, applied generally to the circumference of wheels, which it 34: SCIENCE OF COMMON THINGS. Water- wheels. Power of steam. Gunpowder. causes to revolve, either by its weight^ by its lateral impulse, or "by both conjointly. Fig. 8. Fig 9. The most common forms of water-wheels in use are the under-shot and over-shot, or breast-wheels. In the under-shot wheel, Fig 8, a stream of water strikes against the " float-boards " or paddles, placed so as to receive the impulse of the water at right angles to the radii or spokes of the wheel. In over-shot or breast- wheels, Fig. 9, the water is received in cells or buckets on the top or side. In this case the wheel revolves through the agency of the weight of the water. 103 Upon what does the power of steam depend t Upon the tendency which water possesses to expand into vapor when heated to a certain temperature. 194 What is gunpowder f A solid explosive substance, composed of saltpetre or nitre, sulphur, and charcoal, reduced to powder, and mixed intimately with each other. 105 Upon what does the power of gunpowder depend f When brought in contact with any ignited substance, it explodes with great violence. A vast quantity of gas, or elastic fluid, is emitted, the sudden production of which, at a high temperature, is the cause of the violent effects which this substance produces. 106 Is the power produced in the explosion of powder ever used for propelling machinery regularly f It is not, on account of its expensiveness and the sud- denness and violence of its action. It is chiefly applied to the throwing of shot and other projectiles, and the blasting of rocks. 107' What is (he estimated force of gunpowder when exploded t SCIENCE OF COMMON THINGS. 35 Properties of a gun. Range of cannon. Explosive substances. At least 14,750 pounds upon every square inch of the surface which confines it. 198 What are the essential properties of a gun ? To confine the elastic fluid generated by the explo- sion of the powder as completely as possible, and to direct the course of the ball in a straight or rectilinear path. 199 Why will a rifle send a ball more accurately than a musket, or ordinary gun ? The space produced by the difference of diameter between the tall and the bore of the gun greatly di- minishes the effect of the powder, by allowing a part of the elastic fluid to escape before the ball, and also permits the ball to deviate from a straight line. The advantage of the rifle-barrel is chiefly derived from the more accurate contact of the ball with the sides of its cavity. J3OO To what distance may a ball be thrown by a twenty-four pounder f "With a quantity of powder equal to two-thirds the weight of the ball, it may be thrown about four miles. The effective range of a twenty-four pounder is, however much less than this. SOI How much further would the same ball go, were the resistance of the air removed ? About five times the distance, or twenty miles. 2OS Why is gunpowder always manufactured in little grains f In order to cause it to explode more quickly, by faci' litating the passage of the flame among the particles.* 2O3 By what terms are cannon of different sizes distinguished '? By the weight of the hall which they are capable of discharging. Thus, we have 68-pounders, 24-pounders, 18-pounders, and the lighter field-pieces, from 4 to 12-pounders. J3O4 Are there any more explosive substances than gunpowder f Yery many ; but all of them are too expensive or dangerous for practical use. SO5 By whom was gunpowder supposed to have been discovered f It is generally agreed that gunpowder was used by 36 SCIENCE OF COMMON THINGS. Strength of materials. Hollow tubes. the Chinese many centuries, before the Christian era. In Europe, its composition and properties were dis- covered by Berthold Schwartz, a Prussian monk, ins the twelfth century. It was first used in battle inl 1346. CHAPTEE II. STRENGTH OF MATERIALS. SOQ When materials are employed for mechanical purposes, upon what does their power or strength, apart from the nature of ti*e material, depend for resisting external force? Upon the shape of the material, its hearing, and the nature of the force applied to it. SO7 In what position witt a bar or learn sustain the greatest application of force f When it is strained in the direction of its length. SOS What do we mean by stiffness of a material f It is the resistance to the application of force tending to bend it. 509 How much stiffer is a beam supported at both ends, than one of hall the length firmly faced at only one end? Twice as stiff. 510 In what form can a given quantity of matter be arranged so as to oppose the greatest resistance to a bending force f In the form of a hollow tube or cylinder. 511 Why are the bones of man and animals hollow and cylindrical f Because in this form they can with the least weight of material sustain the greatest force. In man and animals, the hollow part of the bones is filled with an oily substance called marrow. SIS Why are the quills of birds hottow and empty of marrow t SCIENCE OF COMMON THINGS. 37 Stems of grasses hollow. Limit to the size of ships. In order that they may possess the greatest strength, and by their lightness assist in flying. 213 Why are the stems of seeds and grain-bearing plants hollow tube? 1 Because this disposition of matter gives to the stalk its greatest strength, enables it to resist the action of *the wind, and sustain, without breaking, the ripened ear of grain or seed. 314 Is a column with ridges projecting from it, stronger than one that w perfectly smooth f It is. SIS Why is a hoUow tube of metal stronger than tfie same quantity of metal as a solid rod f . Because its substance standing farther from the centre, has a greater power of resisting a bending force. S1G Of two bodies of similar shape, but of different sizes, which is pro- portionably the weaker f The larger. That a large body may have propor- tionate strength to a smaller, it must have a greater proportionate amount of material ; and beyond a cer- tain limit, no proportions whatever will keep it to- gether ; but it will fall in pieces by its own weight. SIT* Why cannot trees attain an unlimited height of trunk f Because, beyond a certain limit, the weight of the material will overcome the supporting strength of the material. 18 Why is it impracticable to build ships beyond a certain size f Because the weight of the timber and other materials contained in them tends to cause them to fall apart. In 1825, two vessels, the largest ever constructed, were built in Ca- nada, of 10,000 tons burden. They were found to be weak from their size alone, and were both lost on their first voyage. SCIENCE OF COMMON THINGS. Ceenta. Quicklime. Whitewash. CHAPTEE III. APPLICATION OF MATERIALS FOB ARCHITECTURAL OR STRUCTURAL PURPOSES. 210 What are cements? Cements are for the most part soft or semi-fluid sub- stances which have the property of becoming hard in time, and cohering with other bodies to which they have been applied. 22O Of what are the ordinary cements which are called mortars com- posed f Of quicklime, sand, and water. {321 What is quicklime? Quicklime is principally pure lime, and is obtained, from the limestone rock, ordinary marble, or shellr, which are composed of carbonate of lime, by calcina tion. The effect of the burning is to drive on the car- bonic acid, leaving the lime pure and uncombined. J3SS What is slacked lime f If quicklime obtained as above described be wet with water, it instantly swells and cracks, becomes exceedingly hot, and at length falls into a white, soft, impalpable powder. This is denominated "slacked lime. 223 What is ordinary whitewash f A mixture of slacked lime with water. 224 Why should slacked lime intended for mortars be excluded from the air, or used soon after it has been prepared f Because if exposed to the air it absorbs carbonic acid, and becomes converted again into its former con- dition of carbonate of lime. 225 Why does mortar become hard after a few days f A portion of the water evaporates, and the lime by a sort of crystallization adheres to the particles of sand SCIENCE OF COMMON THINGS. 39 Mortar. Htucco. Color of bricks. and unites them together. The lime also gradually becomes converted into carbonate of lime. 336 What sand is mest suitable for the formation of mortar f That which is wholly silicious and is sharp / that is, not having its particles rounded by attrition. 337* What are the proportions of lime and sand in good mortar f The proportions are varied in different places : the amount of sand, however, always exceeds that of the lime. The more sand that can be incorporated with the lime the better, provided the necessary degree of plasticity is preserved. 338 What are water, hydraulic, or Roman cements f Those which have the property of hardening under water, and of consolidating almost immediately on be- ing mixed. 330 To what cause do the water-cements owe their property of becoming hard under water f The cause is not satisfactorily known : all water- cements contain a portion of burnt clay, which proba- bly absorbs immediately all superabundant moisture from the lime, and thus expedites its solidification. This explanation is rendered more probable from the fact, that if the clay is burnt sufficient to vitrify it or convert it into brick, it ceases to form a water-cement. 330 What are the constituents of a water-cement f Quicklime, sand or silica, and a proportion of clay. 331 What is stucco f Stucco is composed of various ingredients, generally of "plaster of Paris," sometimes ot white marble pul- verized and mixed with plaster and lime. 333 What is terra-cotta f Literally, baked clay, a name given to statues, archi- tectural ornaments, vases, figures, etc., modelled of potters'-clay and fine colorless sand, and afterwards exposed to a most intense heat. 333 Why are bricks when burned usually of a red color ? Because the iron contained in the clay is converted 4:0 SCIENCE OF COMMON THINGS. Brides with straw. Tiles] Mastic. by the heat into the red oxide of iron, and acts in this state as red coloring material. 334 Why are the bricks manufactured at Chicago, and some other parts of the Western country, of a white or yettow color f Because the clay of which they are formed does not contain sufficient iron to color them. 335 Why did the children of Israel in making bricks desire to mix straw with the clay f j, The bricks of the Egyptians were composed of clay simply baked in the sun, and not burnt. By using straw the clay was held together more firmly and the brick rendered stronger. 336 Why are the Egyptians enabled to dispense with the process of burning the bricks ? The extreme dryness of the climate in which they were used enable them to dispense with the burning. Bricks from Egypt and Babylon, which have remained exposed to the open air uninjured for two thousand years, rapidly fall to pieces when transported to a moist climate. 237 Why do we mix hair with mortar f In order to render it more cohesive and stronger. 338 What are tiles f Plates of burnt clay resembling bricks in composi- tion and manufacture, and used for the coverings of roofs or floors. 339 What is mastich or mastic t The name given to those cements which contain ani- mal or vegetable substances in composition. Mastich used for the external decoration of houses often con- tains oil and a preparation of lead. 340 What is putty? Putty, used by glaziers in setting window-glass and for other purposes, is composed of whiting and linseed- oil, mixed and worked together. "Whiting is simply common chalk ground and purified. SCIENCE OF COMMON THINGS. Principles of architecture. Properties of a good building. CHAPTER PRINCIPLES OF ARCHITECTURE 341 What is architecture ? In its general sense it is the art of erecting buildings. In modern use, this name is often restricted to the ex- ternal forms or styles of building. 343 To what cause do the different varieties of architecture owe their origin ? To the rude structures which the climate or materials of any country obliged its early inhabitants to adopt for temporary shelter. These structures with all their prominent features have been afterwards kept up by their refined and opulent posterity. Thus the Egyptian style of architecture had its origin in the cavern or mound; the Chinese archi- tecture is modelled from the tent; the Grecian is modelled from the wooden cabin ; and the Gothic from the boiver of trees. 343 What kind of shape is it most probable that the fa'st human habi- tations assumed ? We have every reason to believe that huts of a conical form were first constructed. 344 Why? First, on account of their being easily erected, and as easily^ removed ; secondly, because their declivity on all sides would cause the rain to run off; and, thirdly, owing to their breadth at the base and their gradually growing to a point at the top, they were capable of resisting the ordinary force of the wind. 345 Are conical huts anywhere in use at the present time f Yes ; we find them still used by the uncultivated in- habitants of the South Sea Islands, by the American Indians, by the Hottentots, the Kamskatschans, and other uncivilized tribes. 346 What are the three chief properties of a good building f Usefulness, strength, and beauty. 347* Ifrw are they to be attained f SCIENCE OF COMMON THINGS. Essentials for building. Pile. Mortising. The proper arrangement of the respective parts of the building will insure its usefulness. Its strength will principally depend on the walls being laid on a good and firm foundation, of sufficient thickness at the bottom, and standing perfectly perpendicular. And if all the parts of a building correspond with each other, and are handsome in themselves, then the architect may rely on its beauty. S4S What are the essential elementary parts of a "building f Those which contribute to its support, indosure, and covering. J349 What is a pile? A cylinder of wood or metal pointed at one extremity and driven forcibly into the earth, to serve as a support or foundation of some structure. It is generally used in marshy or wet places, where a stable foundation could not otherwise be obtained. 25O Why are long columns supporting great weights made smaller- at the top than at the bottom f Because the lower part of the column must sustain, not only the weight of the superior party but also the weight which presses equally on the ' whole column. Therefore the thickness of the column should gradually decrease from bottom to top. 251 In the construc- tion of buildings various terms are employed to de- signate the method in which the timbers are fitted into each other: what do we mean by mortising ? Mortising is a method of insertion in which the pro- jecting extremity of one timber is received into a perforation in another. (See Jig. 10.) S32 Why are steep roofs, or those constructed with considerable incli- nation, best adapted for houses in cold climates ? In order that the snow may not be retained upon Fig. 10. SCIENCE OF COMMON THINGS. 43 Tenons. Scarfing. Tongueing. Arch. them, which otherwise would be liable to injure the building by its weight. 253 What is a mortise ? The opening or hole cut in one piece of wood to admit the projecting extremity of another piece. 254 What is a tenon? The end of a piece of timber which is reduced in di- mensions so as to be fitted into a mortise for fastening two timbers together. 255 What is scarfing and interlocking t It is that method of insertion in which the ends of pieces overlay each other, and are indented together, so as to resist longitudinal strain by extension, as in tie bearers and the ends of hoops. (See fig. 11.) 256 What is tongueing and rabbeting f It is that method of insertion in which the edges of boards are wholly or partially received by channels in, each other. 257 What is an arch t It is a part of a structure or building suspended over a hollow, and concave towards the area of the hollow. 253 Is it known at what time the arch was invented ? It is not ; it does not appear to have been known to the ancients. 259 Why is an arch capable of resisting a greater amount of pressure than a horizontal or rectangular structure constructed of* the same ma- terials f Because the arrangement of the materials composing 44 SCIENCE OF COMMON THINGS. Dovetailing. Construction of the skull. Egg-shells. the arch is such, that the force which would break a horizontal beam or structure is made to compress all the ^articles of the arch alike, and they are therefore in no danger of being torn or overcome separately. S6O What is meant by dovetailing? It is a method of insertion in which the parts are connected ~by wedge-shaped indentations, which permit them to be sepa- rated only in one direction. (See F. 12. """ ' J 1 ^' *rv SGI What beautiful application of the arch exists in the human struc- ture ? ~ In the skull, protecting the brain. The materials are here so arranged as to present the greatest strength, with the least weight. S6J3 Why is it difficult to break an egg by pressing directly upon its ends ? Because the shell of the egg is constructed on the principle of the arch, and is therefore capable of re- sisting great pressure. SG3 Why is a dished or arched wheel of a carriage much stronger for resisting all kinds of shocks than a flat wheel? In an arched or dished wheel, the extremity of a spoke cannot be displaced inwards, or towards the car- riage, unless the rim of the wheel be enlarged, or all the other spokes yield at the same time ; and it cannot be displaced outwards, unless the rim be diminished, or the other spokes yield in an opposite direction. Now the rim, being strongly bound with a tire of iron, cannot suffer either increase or diminution, and the strength of all the spokee is thus conferred by it on each individually. In a flat wheel, a given degree of displacement, outwards or inwards, of the extremities of a spoke, would less affect the magnitude of the circumference, and therefore the rim of such a wheel secures it much less firmly. S64 Why are the fore wheels of carriages smaller than the hind wheels ? Because they facilitate the turning of the carriage. The advantage of the wheel is proportioned to the mag- SCIENCE OF COMMON THINGS. 45 Arch. Orders in architecture, Gothic structures. nitude ; the smaller wheel having to rise a steeper curve. 365 WJiat is an abutment f The vertical wall which sustains the base, or " spring" of an arch. 366 What is meant by an order in architecture f By an architectural order, we understand a certain mode of arranging and decorating a column, and the adjacent parts of the structure which it supports or adorns. 367 How many orders are recognised? five: the Doric, Ionic, and Corinthian, derived from the Greeks; to these the Romans added two others, known as the Tuscan and Composite. 368 How do pilasters differ from columns f Only in their plan, which is square, as that of columns is round : pilasters are attached to walls. 369 What is a portico f A portico is a continued range of columns covered at the top to shelter from the weather. The portico of the temple at Palmyra was full four thousand feet long. 370 What are balusters? Small columns, or pillars of wood, stone, <&c., used in terraces or tops of buildings for ornament ; also to support railing. When continued for some distance, they form a balustrade. 371 WJieredidthe Gothic order of architecture originate? Among the northern nations of Europe. After the destruction of the Roman empire, it was introduced to the exclusion of the Greek and Roman manner of architecture. It seems particularly adapted to reli- gious edifices. 373 What are the characteristics of the Gothic architecture f Pointed arches, with greater height than breadth in the proportions, with profuse ornament, chiefly de- rived from an imitation of the leaves and flowerg of plants. 4:6 SCIENCE OF COMMON THINGS. Bad taste in architecture. Columns. Capitals. : . .. . ' . . * 373 What is said to have been the model of the aisle of a Gothic cathe- dral? A group of tall trees, meeting at tlie top with, inter- woven branches. 374 Ought architecture to be considered as a fine or a useful art f As a useful art. It is degrading the fine arts to make them entirely subservient to utility. It is out of taste to make a statue of Apollo hold a candle, or a line painting stand as a fireboard. Our houses are for use, and architec- ture is therefore one of the useful arts. In building, we should plan the inside first, and then the outside to cover it. 375 Why is it bad taste to construct a dwelling-house in the form of a Grecian temple f Because a Grecian temple was intended for external worship, not as a habitation or a place of meeting. 370 Had the Goths, who plundered Rome, anything to do with the invention of Gothic architecture f No; the name was introduced abont two hundred years ago as a term of reproach, to stigmatize the edifices of the Middle Ages, which departed from the purity of the antique models. 377 What is the facade of a building t Its front. 278 What is a pedestal f The lower part or base of the column ; a continued base, on which a range of columns is erected, is called a stylobate. 379 What is the base of a column f The lower part, where it is distinct from the shaft. 380 What is the shaft f The middle or longest part of the column. 381 What is the capital f The upper or ornamental part resting on the shaft. The height of a column is measured in diameters of the column itself, always taken at the base. 383 What is the plinth f This term is applied to the lower part of the pedestal, or to any square projecting basis, such as those at the SCIENCE OF COMMON THINGS. Entablaturel Architrave. Frieze. bottom of walls, and under the base of columns. The lower part of the pedestal being called the plinth, the middle part will be termed the die, and the upper part the cornice of the pedestal. (See fig. 13.) r Entablature Column.. Stylobate or Pe- destal.. ... ....Plinth. 283 What is the entablature f The horizontal continuous portion which rests upon the top of a row of columns. S84 What is the architrave f The lower part of the entablature. What is the frieze t 4:8 SCIENCE OF COMMON THINGS. Durability of building materials. Effect of the atmosphere on rocks. The middle part of the entablature. S86 What is the cornice f The upper or projecting part of the entablature^ (For illustration of these different terms, see fig. 13.) 28*7 In selecting a stone for architectural purposes, how may we be able to form an opinion respecting its durability and permanence? By visiting the locality from whence it was obtained, we may judge from the surfaces which have been long exposed to me weather if the rock is liable to yield to atmospheric influences, and the conditions under which it does so. " For example, if the rock be a granite, and it be very uneven and rough, it may be inferred that it is not very durable; that the feldspar, which forms one of its component parts, is more readily decomposed by the action of moisture and frost than the quartz, which is another ingre- dient ; and therefore that it is very unsuitable for building purposes. Moreover, if it possesses an iron-brown or rusty appearance, it may be set down as highly perishable, owing to the attraction which this metal has for oxygen, causing the rock to increase hi bulk, and so disintegrate." 388 Why are the sandstones, termed freestones, ill adapted for the external portions of exposed buildings f Because they readily absorb moisture ; and in coun- tries where frosts occur, the freezing of the water in the wet surface continually peels off the external por- tions, and thus, in time, all ornamental work upon the stone will be defaced or destroyed. 389 Why do some species of rock become harder when taken from the quarry and exposed to the atmosphere f This quality, in some species of stone, arises from the fact that the water contained in it, when forming part of the natural rock, evaporates, and the stone, becoming dryer, becomes harder. 390 Why do some stones, altlwugh hard when first quarried, become friable, and fall to pieces, when exposed to the atmosphere '( Because they contain clay or alumina in such a state as to readily absorb moisture from the atmosphere ; and through the agency of the moisture the particles lose their cohesion and tall apart. SCIENCE OF COMMON THINGS. 49 Laws and phenomena of fluids. Water in motion and at rest. PAET III. THE LAWS AND PHENOMENA OF FLUIDS, S91 Into what two classes may all fluid substances "be divided? Into liquids, as water, oil, molasses, etc. ; and into gases, as common air, carbonic acid gas, oxygen, and others. J393 What designation do we give to those branches of science, which treat of the laws and phenomena of liquids ? Hydrostatics, which considers the laws and pheno- mena of water and other liquids in a state of rest ; and hydraulics, which considers the laws and phenomena of liquids in motion. S93 What designation do we give to that department of science which treats of the laws and phenomena of gases, and other substances resembling air ? We apply the term Pneumatics to that department of science which explains and illustrates those pheno- mena which arise from the weight, pressure, or motion of common air and other gaseous bodies. CHAPTEE I. WATER IN MOTION AND AT REST. S94 When water or any other fluid is at rest, in what condition is its surface ? The surface of water at rest is always perfectly level. 50 SCIENCE OF COMMON THINGS. Velocity of rivers. How we make an aqueduct. 595 Why is the surface of a fluid at rest always kvel ? Because the particles are equally attracted towards the earth ly gravity, and are all equally and perfectly movable among themselves. 596 How slight a declivity is sufficient to give a running motion to water ? Three inches to a mile in a smooth, straight channel, gives a velocity of about three miles per hour. The river Ganges, at a distance of 1800 miles from its mouth, is only 800 feet above the level of the sea. 97 On what principle are we enabkd to conduct water under ground through irregular tubes ? On the principle that water will always rise to an exact level in different tubes, pipes, or vessels communi- cating with each other. If we connect together a series of vessels, no matter how various their shapes and capacities, so that water may rise from the main channel, A B, into them, we shall find upon pouring water into one that it will rise to the same Fig- 14. level in all the vessels. The dependence of all arrangements for conveying water in aqueducts under ground upon the principle, that water in closed tubes or vessels rises to a uniform level, is clearly shown in Fig. 15 : a, a, a, represents the water-level of a pond or reservoir upon elevated ground. From this pond a line of pipe is laid, passing over a bridge or viaduct at d, and Fig. 15. under a river at c. The fountains, at &, 6, show the stream rising to it3 level in the pond, a, at two points of very different elevation. S98 In what part of a river does the water flow most rapidly f In the middle of the stream, at the surface. On the SCIENCE OF COMMON THINGS. 51 Origin of springs. How water collects in wells. sides and bottom the velocity is diminished by the friction of the water against the banks, bars, etc. S99 Wliat is the origin of springs 1 The water falling upon the earth sinks downwards through the sand and porous materials, until an imper- vious bed of clay or rock is reached. Here the water accumulates, and finally bursts out at some point where the impervious bed or strata comes to the surface in consequence of a valley or excavation. Suppose a (Fig. 16) to be a gravel hill, and b a strata of clay or rock, impervious to water. The fluid percolating through the gravel would reach the imper- ~~ " vious strata, along which it would run un- til it found an outlet at c at the foot of the hill, where a spring would be formed. SOO Why does not the water ooze out everywhere along the line of June* tion of the two formations the gravel and the rock or clay so as to form one continuous land soak, instead of a few springs only, and these far distant from one another ? For two reasons : first, on account of rents and fis- sures in the layers of rock, which act as natural drains secondly, the existence of inequalities in the surface of the impermeable stratum, which lead the water, as valleys do on the external surface of a country, into certain low levels and channels. 3O1 Why does the water coUect in an ordinary well f An ordinary well consists of an excavation continued until a stratum or layer of clay or rock is reached that is permanently saturated with water. They are not commonly supplied by springs, but merely by the draining of the , water which exists within the circuit of a few yards into a cavity. SOS Why do wells and springs fail oftentimes in dry weather f Because they are supplied by the water fallina as rain, which percolates from the surface of the earth. 52 SCIENCE OF COMMON THINGS. Artesian wells. SO3 What is an Artesian weU? Water is sometimes obtained by Coring into the earth with a species of auger, until a vein or sheet of water is found, which rises to the surface through the cylindrical excavation. Such excavations are called Artesian wells, because the method was first invented and employed at Artois, in France. /(; 3O4 How do you account for the water rising to the surface in Arte- sian, and sometimes in ordinary wells ? Strata which are pervious frequently alternate with others which are not so ; or may form a basin, the area of which is partially filled with clay, through which water cannot pass ; in such a case it is obvious that the bed of sand beneath the clay, fed by the rain which descends on the uncovered margin of the basin, must form a reservoir where the water will gradually accumulate beneath the central layer of clay, through which it cannot escape. If the bed of clay be pene- trated by natural or artificial means, the water must necessarily rise to the surface, and may even be thrown up in a jet to an altitude which will depend on the level of the fluid in the subterranean reservoir. Fig. 17. Thus, if a sandy stratum, a a (Fig. 17), acting as a filter, occupies an inclined position between two other strata impervious to water, such as clay, the water being absorbed by the superficial parts of the strata, a at a a (which may be of very great extent), will penetrate through its whole depth, and, finding no egress below on account of the basin-like form of the stratum, or from its resting at the lower termination upon a compact rock, will accumulate. The porous strata, therefore, becomes a reservoir tp a greater or less extent, and if, by boring through the super- incumbent mass, we form an opening into the stratum, as at 6, the water SCIENCE OF COMMON THINGS. 53 Effect of drainage upon springs. Pressure of water. will rise in it, and flow over in a jet proportional to the height of the water accumulated in the stratum from whence it flows. 305 What general effect does the cultivation and drainage of a country have upon the springs ? In a well cultivated and improved country the springs are comparatively few in number and not con- stant, While the face of a country is rough, the rain- water remains long among its inequalities, slowly sink- ing into the earth ,to feed the springs, or slowly run- ning away from bogs and marshes towards the rivers ; but in a well drained, country the water runs off quick- ly, often producing dangerous floods. SOS How is the pressure of water exerted? Equally in all directions. SOT* Does ivater, contained in a vessel, press with as great force against t)ie sides and top as against the bottom ? The pressure, in all directions, is the same SOS What is the result if a corked empty bottle be lowered into the ocean for a considerable depth ? The cork is generally forced inwards at a given depth, no matter in what direction the mouth of the bottle may happen to point. SOD Jf the cork is fastened immovably into the bottle, what will be the effect? The bottle will be crushed inwards by the pressure before it reaches a depth of sixty feet. S1O When a ship founders in shallow water, the wreck, on breaking to pieces, generally comes to the surface and is cast upon the shore ; but when a ship sinks in very deep water, it never rises : why is this f The pressure of very deep water forces the water into the pores of the wood, and makes it so heavy that no part of the wreck is enabled to rise again. 311 Can you sink a cork so deep that it will riot rise to the surfact ugain t At a great depth the water forced by pressure into the pores of the cork renders it so heavy that it cannot rise. 313 What is the pressure of water expressed in numbers f The pressure of water at any depth, whether on the 3* SCIENCE OF COMMON THINGS. What is water ? "What is hard water ? sides of a vessel or on its bottom, or on any body im- mersed in it, is nearly one pound on the square inch for every two feet of depth. 313 What is water? Water is a fluid composed of oxygen and hydrogen, in the proportion of eight parts of oxygen to one part of hydrogen. 314 Why is water fluid? Because its particles are kept separate by latent heat ; when a certain quantity of this latent heat is driven out, water becomes solid, and is called ice. By increasing its latent heat, the particles of water are again subdivided into invisible steam. 315 Why is spring water generally called "hard water?", Because it is laden with foreign matters, and will not readily dissolve substances immersed in it. 316 What makes spring or well water geneartty hard ? "When it filters through the earth, it becomes im- pregnated with sulphate of lime, carbonate of lime, carbonic acid, magnesia, and many other impurities, from the earths and minerals with which it comes in contact. 31 7 What is the cause of mineral springs ? "When water trickles through the ground, it dissolves some of the substances with which it comes in contact ; if these substances are retained in solution, the water will partake of their mineral character. 318 When is a mineral water called a chalybeate ? When it contains iron, in some form, dissolved in it. 319 Mineral springs exist in all parts of our country : what is the nature of the substances contained in them ? The great majority of them are only impregnated with iron, salt, or sulphur. Some few, however, con- tain many different substances, as the mineral waters of Saratoga. 3J3O Why are springs containing iron in large quantities beneficial to tome invalids ? Because the iron contained in the water acts as a SCIENCE OF COMMON THINGS. 55 Purity of waters. Air in water. Do fishes breathe air? ionic j that is, it strengthens and invigorates the sys- tem. 331 What quantity of mineral matter is generally contained in com- paratively pure natural waters ? Any water which contains less than fifteen grains of solid mineral matter in a gallon, is considered as com- paratively pure. Some natural waters are known so pure that they contain only gV th of a grain of mineral matter to the gallon, but such instances are very rare. Waters obtained from different sources may be classed as regards com. parative purity as follows : Rain water must be considered as the purest natural water, especially that which falls in districts remote from towns or habitations; then comes river water; next, the water of lakes and ponds; next, spring waters ; and then the waters of mineral springs. Succeeding these, arc the waters of great arms of the ocean into which immense rivers dis- charge their volumes, as the water of the Black Sea, which is only brackish ; then the waters of the ocean itself; then those of the Mediter- ranean and other inland seas ; and last of all, the waters of those lakes which have no outlet, as the Dead Sea, Caspian, Great Salt Lake of Utah, etc. etc. 333 How much solid matter is ordinarily contained in a gallon of sea water f From twenty-two hundred to twenty-eight hundred grains. 333 H line or curve of the wave is broken. 368 What causes the spray of waves f The wind driving the surface of the water from the top of the wave, and scattering the small particles in all directions. 369 What is the surf? When the shore runs out very shallow for a great extent, the breakers are distinguished by the name of surf. SVO What do we know concerning the magnitude and velocity of ocean waves ? On the Atlantic, during a storm, the waves rise to a height of about forty-three feet above the hollow occu- pied by the ship ; the total distance between the crests of two large waves being 559 feet, which distance is passed by the wave in about seventeen seconds of time. 371 With what velocity is it estimated that such storm waves as the above described travel f At the rate of about thirty-two miles per hour. A wave is a /orw, and not a thing ; the form advances, but not the substance of the waves. 3753 If a cock at the extremity of a pipe be suddenly closed while water is running through, why is a noise and shock produced ? Because the forward motion of the whole body of the water contained in the pipe being instantly arrested, and the momentum of a liquid being as great as that of a solid, the water strikes the cock with as much force as if it were a long bar of metal, or a rod of wood hav- ing the same weight and velocity as the water. Then, as a fluid presses equally in all directions, a leaden pipe of great length may be widened, or even burst in the experiment. 62 SCIENCE OF COMMON THINGS. Why 1ce floats and iron sinks in water. Platinum and hydrogen. CHAPTER II. SPECIFIC GRAVITY". 373 Why does ice float upon water f Because it is lighter than water. 374 Why does iron sink in water f Because it is heavier than water. 37*5 If we put a piece of ice in alcohol, it sinks ; if we put a piece, of iron upon quicksilver, it floats : why is this f Because the ice is heavier than the alcohol, and the iron is lighter than the quicksilver. 37*6 What do we mean, when we say that ice is lighter than iron ? We mean that, taking equal bulks of each, the former weighs less than the latter ; and when we say that quicksilver is heavier than water, we mean that, in equal volumes, as a pint, for instance, the quicksilver has a greater weight than the water. 377 What, then, is specific gravity f It is the weight of a body compared with the weight of an equal bulk of water. 378 How does it differ from ordinary or absolute weight f In absolute weight no regard is paid to the volume or bulk of substances. In specific weight, a given bulk or volume is compared with an equal volume or bulk of water. 379 What body has the greatest specific weight f Purified platina, which is 22 times heavier than an equal bulk of water. 380 What substance has tlie smallest specific weight f Hydrogen gas, which is 12,000 times lighter than an equal bulk of water. 381 Why will an egg float in strong brine, and not in fresh water f Because the solution of a solid in any liquid increases its density, or its specific gravity : the addition of salt SCIENCE OF COMMON THINGS. 63 Swimming in fresh and salt water. Unskilful swimmers. to the water, renders the specific gravity of the brine greater than that of fresh water, or of the egg. 383 How do cooks sometimes ascertain if their brine be salt enough for pickling f They put an egg into their brine. If the egg sinks, the brine is not strong enough ; if the egg floats, it is. 383 Why witt an egg sink, if the brine be not strong enough for pick- ling f Because an egg will be the heavier ; but if as much salt be added as the water can dissolve, an egg will be lighter than the strong brine, and consequently float on the surface. 384 Why is it more easy to swim in the sea than in a river ? Because the specific gravity of salt water is greater than that of fresh ; and, therefore, it buoys up the swimmer better. 385 Why do persons sink in water when they are unskilful swimmers? Because they struggle to keep their head out of water. 386 Explain how this is f When our head is thrown back boldly into the water, our mouth is kept above the surface, and we are able to breathe ; but when the head is kept above the sur- face of the water, the chin and mouth sink beneath it, and the swimmer is suffocated. This may be illustrated thus : If a piece of wood be of such specific gravity that only two square inches can float out of water, it is manifest, that if two other inches are raised out, the two former inches must be plunged in. The body (in floating) resembles this piece of wood. If two square inches of our face float out of the water, we can breathe; but if part of the back and crown of the head are raised above the water, the lower part of the face will be depressed beneath it. 387 Why can quadrupeds swim more easily than man f 1. Because the trunk of quadrupeds is lighter than water, and this is the greater part of them ; and 2. The position of a beast (when swimming) is a na- tural one. 388 Why is it more difficult for a man to swim than for a beast f 1. Because his body is more heavy in proportion than that of a beast ; and 64: SCIENCE OF COMMON THINGS. How fishes ascend and descend in water. Life boats. Cream on milk. 2. The position and muscular action of a man (when swimming) differ greatly from his ordinary habits ; but beasts swim in their ordinary position. 389 Why can fat men swim more easily than spare men? Because fat is lighter than water / and the fatter a man is, the more buoyant will he be. 390 How are fishes able to ascend to the surface of water f I Fishes have an air-bladder near the abdomen ; when this air-vessel is distended, the fish increases in size and (being lighter) ascends through the water to its surface. 391 How are fishes able to dive in a minute to the bottom of a stream f They compress the air in their air-bladder ; in conse- quence of which their size is diminished, and they sink instantly. 393 Why does the body of a drowned person rise and float upon the surface several days after death ? Because, from the accumulation of gas within the body (caused by incipient putrefaction), the body be- comes specifically lighter than water, and rises and floats upon the surface. 393 How are life-boats prevented from sinking ? They contain in their sides air-tight cells, or boxes filled with air, w T hich by their buoyancy prevent the boat from sinking even when it is filled with water. 394 The slaves of the West Indies have a plan of stealing rum from a cask, by inserting the long neck of a bottle, full of water, through the bung. How are they enabled in this manner to obtain the rum ? The rum is very much lighter than the water / and as the heavy water falls out of the bottle into the cask, the lighter rum rises to take its place. 395 Why does cream rise upon milk ? Because it is composed of particles of oily or fatty matter, which are lighter than the watery particles of the milk. 396 Why do stale eggs fioat upon water? Because, by keeping, air is substituted for a portion of the water of the egg, which escapes. SCIENCE OF COMMON THINGS. 65 Iron ships. Movement Of stores in water. Capillary attraction. SOT* Why does not a vessel constructed of iron sink, as the iron is much heavier than the water ? Because the vessel is constructed in a concave form, and is thus rendered buoyant. Every substance be- comes lighter in water, in proportion to the amount of water displaced. This is a law of nature: if it dis- places less water than its weight in air, it sinks; if more, it floats. The ship, being concave, displaces a greater weight of water than the weight of the iron of which it is composed in the air. A thick piece of iron, weighing half an ounce, loses in water nearly one-eighth jf its weight ; but if it is hammered out into a plate or vessel, of such a size that it occupies eight times as much space as before, it then loses its whole weight in water, and will float, sinking just to the brim. If made twice as large, it will displace one ounce of water, consequently, twice its own weight ; it will then sink to the middle, and can be loaded with half an ounce weight before sinking entirely. 398 Why are stones, gravel, and sand so easily moved by waves and currents ? Because the moving water has only to overcome about half the weight of the stone. 399 Why can a stone which, on land, requires the strength of two men to lift it, be lifted and carried in water by one man f Because the water holds up the stone with a force equal to the weight of the volume of water it displaces. CHAPTER III. CAPILLARY ATTRACTION. 400 Why does water melt salt ? Because very minute particles of water insinuate themselves into the pores of the salt by capillary at- traction, and force the crystals apart from each other. 401 Why does water melt sugar f Because very minute particles of water insinuate 66 SCIENCE OF COMMON THINGS. "Watering plants. Cotton lamp-wick. Blotting paper absorbs ink. fig. 18. themselves into the pores of the sugar by capillary attraction* and force the crystals apart from each other. 4OS What is capillary attraction ? The power which very minute tubes possess of causing liquid to rise in them above its level. " Capillary," from the Latin word, " capil- laris" (like a hair) ; the tubes referred to are almost as fine and delicate as a hair. Water ascends through a lump of sugar or pieee of sponge r by capillary attraction. N. B. The smaller the tube, the higher will the liquid be attracted by it. Fig. 18 illus- trates the manner in which water will rise in tubes of different diameters. 403 Why is vegetation on the margin of a river more luxuriant than in an open field ? Because the porous earth on the bank draws up too-. ter to the roots of the plants by capillary attraction. 404 Why do persons who water plants very often pour the water into the saucer, and not over the plants ? Because the water in the saucer is drawn up by the mould (through the hole at the bottom of the flower- pot), and is transferred to the stem and leaves of the plant by capillary attraction. 405 Why is cotton best adapted for lamp-wicks f Because the arrangement of the fibres of the cotton- wick is such, that the whole forms a bundle of minute tubes, in which the oil ascends and supplies the flame by capillary attraction. 406 Why does blotting-paper absorb ink f The ink is drawn up between the minute fibres of the paper by capillary attraction. 407 Why will not writing or sized paper absorb ink f Because the sizing, being a species of glue into which writing papers are dipped, fills up the little in' terstices or spaces between the fibres, ana in this way prevents all capillary attraction. 408 How does a sponge absorb water t SCIENCE OF COMMON THINGS. 67 Dry wood swells in water. Solution of substances. Liquids and gases. The pores of the sponge constitute minute tubes in which the water rises by capillary attraction. 409 Why does dry wood, immersed in water, swell 1 Because the water enters the pores of wood by capil- lary attraction, and forces the particles further apart from each other. 41 Why does sugar or salt give a flavor to water f Because the sugar or salt (being separated into very minute particles) floats about the water, and mixes with it intimately. 411 Why does hot water dissolve sugar and salt more readily than cold water f Because the heat of the water assists its solvent ac- tion, and opens for the water a passage through the particles of the substance. CHAPTEK IT. THE GENERAL PROPERTIES OF AERIFORM OR GASEOUS BODIES. 413 What is the difference between a liquid and a gas? The distinction between liquids and those more elas- tic fluids which w r e term air, gas, vapor, steam, etc., depends principally on heat and pressure. Thus, wa- ter, according to the addition or subtraction of heat, may exist as a solid, ice ; as a liquid, w r ater ; or as a vapor, steam. 413 Under what pressure of the atmosphere is water converted into steam ? Tinder the ordinary pressure of the atmosphere, wa- ter is converted into steam at 212 degrees, Fahrenheit's thermometer ; if this pressure is increased, it requires 68 SCIENCE OF COMMON THINGS. Varieties of gaseous bodies. Composition of the atmosphere. Air porous. a proportionally higher temperature ; if this pressure is diminished, the amount of heat required is propor- tionably less. 414 How many kinds of aeriform or gaseous bodies exist in nature f Those which, under common circumstances of tem- perature and pressure, are always in a gaseous state, as common air ; and those which become gases chiefly at high temperature, as steam, or vapor of water. 415 Are all gases invisible or colorless like atmospheric air f Some gases possess color, but the greater number are colorless and invisible. 416 Of what is atmospheric air composed f Principally of two gases, oxygen and nitrogen, mixed together in the following proportion : viz. one volume of oxygen to four of nitrogen. It must not be forgotten that the air contains small quantities of other gaseous substances also, as vapor of water, carbonic acid, and ammonia. 41 7* Do the particles of which atmospheric air and other gaseous bodies are composed, appear to have any cohesion between themselves f The ultimate particles of which air and other gases are composed appear to be destitute of cohesion ; hence air has a disposition not only to sink down and spread out laterally, like liquids when unconfined, but also to expand and rise upwards. 418 Is the air porous f Yes ; in a very high degree. 419 How do we know this fact ? Because air readily yields to pressure, and a great bulk of it may be forced to occupy a very small space. 4SO Is air also impenetrable f Yes ; beyond a certain limit it cannot be compressed. 431 How much lighter is steam than ordinary air f Steam has but little more than half the weight of atmospheric air ; and hence it rises and floats in the air as a cork rises and floats in water. SCIENCE OF COMMON THINGS. 69 What is the atmosphere ? Why mountains appear blue. CHAPTEE Y. THE ATMOSPHERE. 433 What do we understand by the atmosphere f The thin transparent fluid which surrounds the earth to a considerable height above its surface, and which, by its peculiar constitution, supports animal life by respiration, and is also necessary for the due exercise of the vegetable functions. 433 Is the atmosphere invisible f It is generally, but erroneously, so regarded. The atmosphere is not invisible. 434 How can you prove that the atmosphere is not invisible f Because when we look upwards into the firmament on a clear day, the space appears of an azure or clear color. This color belongs not to anything which occupies the space in which the stars or other celestial objects are placed, but to the mass of .air through which the bodies are seen. 435 Why do distant mountains appear Hue f "Not because it is their color, but because it is the color of the air through which they are seen. -36 Has air weight f It has / as well as lead, stone, or any other material substance. 437 How can this be readily proved? By weighing a vessel filled with air, and the same vessel after the air has been exhausted from it. 438 Can the existence of air be known by the sense of touch or feeling f It can ; since it opposes resistance when acted upon, and strikes with a force proportionate to the speed of its motion. 438 Why do we always feel a breeze on the deck of a steamboat in motion, even upon the calmest day t Because our bodies forcibly displace the air as w$ are carried through it, 4 70 SCIENCE OF COMMON THINGS. Height of the atmosphere. Weight of the atmosphere. 430 How are waves of the ocean produced ? By the force of the air in motion, or wind striking upon the surface of the water. 431 Could a bird fly in a space devoid of air, even if it could exist without respiration ? It could not ; as the bird rises simply by the resist- ance of the particles of air to the beating of its wings. / 432 How do we know that air is elastic f Because a volume of compressed air, the pressure being removed, immediately restores itself to its origi- nal bulk. 433 When is air said to be rarefied f When a given quantity of air is caused to expand and occupy a greater space, it is said to be rarefied. "When a part of the air inclosed in any vessel is withdrawn, that which remains, expanding by its elastic property, always tills the dimensions of the vessel as completely as before. If nine-tenths were withdrawn, the remaining one-teiith would occupy the same space that the whole did formerly. 434 What is the height of the atmosphere above the surface of the earth f It is supposed to be about 45 miles ; the zone or shell of air which surrounds the earth to the height of nearly 21 miles from its surface, contains one-half of the atmosphere ; and the remaining half being relieved of this superincumbent pressure, expands into another zone or belt of the thickness of 41 or 42 miles. Some authorities suppose this last zone to have a much greater area. 435 What is the weight of air compared with that of water f Water is about 840 times the weight of air, taken l>ulkfor bulk. 430 What is the estimated weight of the whole atmosphere enveloping tJie globe f To the weight of a globe of lead sixty miles in dia- meter. 437' As air has weight, and as the mass of it extends at least 45 miles above the earths surface, what amount of pressure does it exert ? At the level of the ocean the atmosphere exerts a pressure of about 1 5 pounds for every square inch of surface. SCIENCE OF COMMON THINGS. 71 Pressure of air. Vacuum. 438 If the air were condensed, so as to occupy no more space than the same weight of water, to how great an tkvation above the earth would it extend ? To an elevation of thirty-four feet. 439 In what direction is the pressure of the atmosphere exerted f It is the nature of a fluid to transmit pressure in every direction equally ; therefore the air presses upwards, downwards, laterally, and obliquely, with the same force. 440 How great a pressure is exerted by the air upon the body of a man or animal having a surface of 2000 square inches f Not less than 30,000 pounds, or about 15 tons. 441 Why is not the individual crushed beneath so enormous a load? Because the atmosphere presses equally in all direc- tions^ and our bodies are filled with liquids capable of sustaining pressure, or with air of the same density as the external air ; so that the external pressure is met and counteracted by the internal resistance. 44S What would be- the effect upon a man or animal if at once relieved of all atmospheric pressure ? All the blood and fluids of the body would be forced ~by expansion to the surface, and the animal would burst. 443 What do we mean by a vacuum? A space devoid of all matter ; in general, we mean by a vacuum, a space devoid of air. 444 Can a perfect vacuum be produced artificially f No ; but confined spaces may be deprived of air sufficiently for all experimental or practical purposes. 445 Are there any instances of a vacuum in nature? There is no positive certainty that the spaces which exist between the various planets and other hea- venly bodies, are occupied with any material sub- stance. 446 Is the existence of air necessary to the production of sound? It is ; in a vacuum there can be no sound ; and on the top of high mountains, where the air is greatly rarefied, as on Mont Blanc, the report of a pistol can hardly be heard. 72 SCIENCE OF COMMON THINGS. How flies walk on the ceiling. How we breathe. 447* Why is it often painful and difficult to breathe on a mountain-top f Because, owing to the extreme rarity of the air on the top of the mountain, a person, although expanding his chest as much as usual, really takes in only half as much air as he does when at the foot of the moun- tain. 448 If the lips be applied to the back of the hand, and the breath drawn in so as to produce a partial vacuum in the mouth, why will the skin be drawn or sucked in f Not from any force resident in the lips or the mouth drawing the skin in, but from the fact that the usual external pressure of air is removed, and that the pres- sure from within the skin is suffered to prevail. 449 How is a boy enabled to lift a stone by means of the common sucker ? The sucker consists of a disk of moistened leather, with a string by which it may be suspended with any weight attached to it. If its smooth moist surface be pressed so closely against the flat side of a stone or other body that the air cannot enter between them, the weight of the atmosphere pressing upon the upper sur- face of the leather makes it adhere so strongly, that a stone of weight proportioned to the extent of the disk of leather may be raised by lifting the string. 450 How are flies and other small insects enabled to walk on ceilings and surfaces presented downwards, or upon smooth panes of glass in an upright position ? Their feet are formed in such a manner that they act as small air-pumps or suckers, excluding the air between them and the surface with which they are in contact ; and the atmospheric pressure keeps the animal in position. 451 Why in breathing do we first draw in the breath, as it is termed? Because by so doing we make an enlarged space in the chest, and the pressure of the external atmosphere forces the air in to fill it. The air enters the lungs, not because they draw it in, but by the weight of the atmosphere forcing it into an empty space. 453 How is the air caused to escape from the lungs f Simply by means of its elasticity ; the lungs by SCIENCE OF COMMON THINGS. 73 Why a jug gurgles. Air in water. muscular action compress the air contained in them, and give to it by compression a greater elasticity than the air without. By the excess of the elasticity it is propelled, and escapes by the mouth and nose. 453 Why does a bottle or jug gurgle when liquid is freely poured from it ? On account of the pressure of the atmosphere forcing air into the interior of the bottle. In the first instance, the neck of the bottle is filled with liquid, so as to stop the admission of air. When a part has flowed out, and an empty space is formed within the bottle, the atmo- spheric pressure forces in a bubble of air through the liquid in the neck, which, by rushing suddenly into the interior of the bottle, produces the sound. . 454 How long will a lottle continue to gurgle ? /So long as the neck continues to be choked with liquid. But as the contents of the bottle are discharged, the - liquid, in flowing out, only partially fills the neck ; and, while a stream passes out through the lower half of the neck, a stream of air passes in through the upper part. The flow being now continued and uninterrupted, no sound takes place. 455 Does air exist in water f Water, and most liquids exposed to the air, absorb a greater or less quantity r , which is maintained in them by the pressure of the atmosphere acting on the surface. 456 Why is boiled water flat and insipid f Because the agency of the heat expels the &ir which the water previously contained. 457* Could fishes and other marine animals live in water deprived of air ? They could not, as they breathe the air contained in the water. 458 Why do ale, porter, and cider froth, and champagne sparkle, when uncorked and poured into an open vessel f When these liquors are bottled, the air confined under the cork is condensed, and exerts upon the sur- face a pressure greater than that of the atmosphere. SCIENCE OF COMMON THINGS. Frothing of ale. Sparkling of champagne. Meteorology. This has the effect of holding, in combination with the liquor, air or gas which, under the atmospheric pressure only, would escape. If any air or gas rise from the liquor after being bottled, it causes a still greater con- densation, and an increased pressure above its surface. When the cork is drawn from a bottle containing liquor of this kind, the air fixed in the liquid, being released from the pressure of the air which was condensed under the cork, instantly makes its escape, and, rising in bubbles, produces effervescence and froth. 459 Why do bottles containing ale, cider, porter, &c., frequently burst f It is the nature of these liquids to produce gas or air in considerable quantities, the elastic force of which sometimes becomes greater than the cohesive strength of the particles of matter composing the bottle, which then necessarily gives way, or bursts. 460 Why does one kind of liquor froth, and another kind only sparkle, f Those liquors only which are viscid, glutinous, or thick, froth, because they retain the little bubbles of air as they rise ; while a thin liquor, like champagne, suffers the bubbles to escape readily. CIIAPTEK VI. ATMOSPHERICAL PHENOMENA. 461 What designation do we give to that department of science which treats of the various phenomena of the atmosphere? Meteorology. 463 How is the air heated f In two ways ; either by the rays of the sun passing through it, or by the heat communicated to it by the earth. SCIENCE OF COMMON THINGS; 75" Air, how heated and cooled. Origin of winds. 463 In what manner is the air heated by the earth ? The sun heats the earth, and the earth heats the air resting upon it ; the air thus heated rises, and is suc- ceeded by other air, which is heated in a similar way, till the whole volume is warmed, 464 How is the air made cold? The air resting on the earth is made cold by contact / this cold air makes the air above it cold / and cold cur- rents (or winds) cause the whole to mix together, until all becomes of one temperature. 465 What effect is produced upon air "by cold f It is condensed or compacted into a smaller compass ; in consequence of which it becomes heavier, and de- scends towards the ground. 466 Prove that the air is condensed ly cold. Lay a bladder half full of air before a fire, till it has become inflated ; if it be now removed from the fire$ the bladder will collapse again, because the air con- denses into its former bulk. 467 What effects has heat upon air f Heat rarefies or makes it lighter ; that is, a quantity of air heated will occupy more space than the same quantity which has been cooled. 468 What is wind f "Wind is air put in motion. 460 What occasions- those movements of the air which we call wind? The principal cause is the variation of temperature produced by the alternation of day and night and the succession of the seasons. 4"7O How can winds originate through variations of temperature f { "When through the agency of the sun a particular portion of the earth's surface is heated to a greater degree than the remainder, the air resting upon it becomes rarefied and ascends, while a current of cold air rushes in to supply the vacancy. Two currents, the one of warm air flowing out, and the other of cold air flowing in, are thus continually produced ; and to these 76 SCIENCE OF COMMON THINGS. "Wind always blows. Effect of mountains on winds. movements of the atmosphere we apply the designation of wind. 471 Does the wind always blow f Yes ; there is always some motion in the air ; but the violence of the motion is perpetually varying. 473 Does the rotation of the earth upon its axis affect the motion of the air f 1 Yes, in two ways : 1. As the earth moves round its axis, the thin movable air is left somewhat behind, and therefore seems (to a stationary object) to be blowing in the opposite direction to the earth's motion ; and 2. As the earth revolves, different portions of its sur- face are continually passing under the vertical rays of the sun. 473 When are the rays of the sun called vertical rays ? When the sun is in a direct line above any place, his rays are said to be "vertical " to that place. 474 When the sun is vertical, or nearly over head at any place, what time of day is it at that place ? Noon. 475 How does a change in the heat of air produce wind f The air always seeks to preserve an equilibrium so cold air rushes into the void made by the upward cur- rent of warm air. 470 Why does not the wind always blow one way, following the direc- tion of the sun f Because the direction of the wind is subject to per- petual interruption from kills and valleys, deserts, seas, &c. 477 How can hills or mountains affect or change the direction and course of the wind ? If a current of air, blowing from a particular direc- tion, strike against the side of a mountain, it will neces- sarily be deflected from a straight line, and must either ascend the mountain, turn back, or assume a lateral direction. 478 Why are those winds which llow over large continents or tracts of land generally dry ? SCIENCE OF COMMON THINGS. 7< Velocity of winda. Force of winds. Because in their passage they absorb very little water, as they do not blow over large oceans. 479 Why do our "hands and lips chap in frosty and windy weather 1 Because a cold, dry wind absorbs moisture from the surface of the skin ; and this action, in turn, causes the skin to crack and inflame. 480 Would the wind blow regularly from east to west if all obstructions were removed ? Without doubt. If the whole earth were covered with water, the winds would always follow the sun, and blow uniformly in one direction. 481 Do winds ever blow regularly f Yes, in those parts of the world which present a large surface of water, as in the Atlantic and Pacific Oceans. 483 With what velocity do winds move f Every graduation exists in the speed of winds, from the mildest zephyr to the most violent hurricane. 483 With what velocity does a wind which is hardly perceptible move f With a velocity of about one mile per hour, and with a perpendicular force on one square foot of *005 Ibs. avoirdupois. 484 In a gentle wind, what is the velocity and estimated pressure f 'From four to Jive miles per hour, and a force of "079 to 123 Ibs.* 485 In a very brisk wind, what is the velocity and pressure ? From twenty to twenty -free miles per hour / force 1*9 to 3-07 Ibs. 4SQ What is the velocity and pressure of the wind in a storm t From fifty to sixty miles per hour, with a pressure of 7 to 12 Ibs. 487 In a hurricane, what is the estimated velocity and pressure f From eighty to one hundred miles per hour> with a varying force of 31 to 50 Ibs. * In these estimates the pressure is computed per square foot in pounds avoirdupois. 78 SCIENCE OF COMMON THINGS. Movements of clouds. Trade winds and their location. 488 Why do we sometimes see clouds at one elevation moving in one direction, and at anotfier elevation, at the same time, others moving in a contrary direction ? Because different currents of air exist at different elevations, moving in different airections, with different velocities. In 1839, an English aeronaut, at the height of 14,000 feet, encountered a current that bore him along at the rate of five miles per hour ; but, upon descending to the altitude of 12,000 feet, he met with a contrary- wind, blowing with a velocity of eighty miles per hour. 489 How is the force of the wind ascertained ? By observing the amount of pressure that it exerts upon a given plane surface perpendicular to its own direction. If the pressure plate acts freely upon spiral springs, the power of the wind is denoted by the extent of their compression, and that weight will be a measure of their force, the same as in weighing by the ordinary spring-balance. 09 O What is an instrument for measuring the force of the wind called f An Anemometer. 491 What are the constant winds which bloiv over the Atlantic and Pacific Oceans called f They are called " trade-winds" 493 Why are they called trade-winds f Because they are very convenient to navigators who have to cross the ocean, inasmuch as they always blow in one direction. 493 In what direction do the trade-winds blow f That in the northern hemisphere blows from the north-east ; that in the southern hemisphere from the south-east. 494 Do trade-winds blow from the north-east and south-east all Hie year round 1 Yes, in the open sea; that is in the Atlantic and Pacific oceans, for about 25 each side of the equator. 495 Where do the trade-winds blow with uniform force and constancy f In many parts of the Pacific embraced within the region of the trade-winds, a vessel may sail for a week without altering the position of a sail or rope. SCIENCE OF COMMON THINGS. 79 Cause of sea breezes. North and south winds. 406 Why does a sea breeze feel cool f Because the sun cannot make the surface of the sea so hot as the land ; therefore the air which blows from the sea is cooler than the air of the land. 407 Why is there generally a fresh breeze from the sea during ihe summer and autumn mornings f Because land is more heated by the sun than the sea is ; and the land air becomes hotter than that over the sea ; in consequence of which the cooler sea air glides inland to restore the equilibrium. 408 Why are ihe west winds in the Atlantic States generally dry? Because they come over large tracts of land, and therefore absorb very little water ; and being* thirsty, they readily imbibe moisture from the air and clouds, and therefore bring dry weather. 400 Why is the north wind generally coldf Because it comes from the polar regions, over moun- tains of snow and seas of ice. 500 Why are north winds generally dry ? Because they come from colder regions, and being warmed by the heat of our climate, absorb moisture from everything they touch ; in consequence of which they are generally dry. 501 Why are south winds generally warm f Because they come over countries warmer than our own, where they are much heated. SOS Why are winds which blow over a vast body of water generally rainy f Because they come laden with vapor ; if, therefore, they meet with the least chill, some of the vapor is deposited as rain. SOS Why is there often an evening breeze during the summer months 9 Because the earth radiates heat at sunset, and the air is rapidly cooled down by contact; this conden- sation causes a motion in the air, called the evening breeze. SO4 Why do south winds often bring rain f Because, coming from the torrid zone, they are much 80 SCIENCE OF COMMON THINGS. Effect of the winds on the weather. Hurricanes. heated, and absorb water very plentifully as they pass over the ocean. SOS How does this account for the rainy character of south winds f As soon as they reach a cold climate they hecome chilled, and can no longer hold all their vapor in sus- pension ; in consequence of which some of it is deposited as rain. SOG Why are dry winds in the spring montJis desirable and advan* tageous for agricultural operations f They dry the soil saturated with the moisture ot winter, 'break up the heavy clods, and fit the land for the seed committed to it. SOT* Why is a fine clear day sometimes overcast in a few minutes ? Because some sudden change of temperature has condensed the vapor of the air into clouds. SO 8 Why are clouds sometimes dissipated very suddenly ? Because some dry wind (blowing over the clouds) imbibes their moisture, and carries it off in invisible vapor. O9 Why does wind sometimes Iring rain, and sometimes fine weather f If the wind be colder than the clouds, it will condense their vapor into rain / but if the wind is warmer than the clouds, it will dissolve them and cause them to dis- appear. 510 What is a hurricane f The hurricane is a remarkable storm wind, peculiar to certain portions of the world. It rarely takes its rise beyond the tropics, and it is the only storm to dread within the region of the trade-winds. 511 How are hurricanes especially distinguished from other kinds of tempests f By their extent, irresistible power, and the sudden changes that occur in the direction of the wind. S1J3 Do any particular portions of the tropics appear to be especially visited with hurricanes ? In the northern hemisphere, the hurricane most fre- quently occurs in the regions of the West Indies ; in SCIENCE OF COMMON THINGS. 81 What are hurricanes ? Breadth and velocity of hurricanes. the southern hemisphere, it occurs in. the neighborhood of the Mauritius. 513 Do the hurricanes occur at particular seasons f The West Indian occur from August to October / the Mauritian from February to April. 514 What have recent investigations shown the hurricanes to be? Extensive storms of wind, which revolve round an axis either upright or inclined to the horizon ; while at the same time the body of the storm has a progres- sive motion over the surface of the ocean. 515 Illustrate more clearly the manner in which a hurricane moves f It is the nature of a hurricane to travel round and round as well as forward, much as a corkscrew tra- vels through a cork, only the circles are all^^, and de- scribed by a rotatory wind upon the surface of the water. 516 In ivhat direction would a ship revolving in the circles of a hurri- cane find the wind ? As the ship revolved, she w r ould in turn find the wind blowing from every point of the compass. 517 What is known concerning the distance travelled by hurricanes f The distance traversed by these terrible tempests is immense. The great gale of August, 1830, which oc- curred at St. Thomas on the 12th, reached the Banks of Newfoundland on the 19th, having travelled more than three thousand nautical miles in seven days / the track of the Cuba hurricane of 1844: was but little infe- rior in length. 518 What is known of their progressive and rotary velocity f Their progressive velocity is from seventeen to forty miles per hour but distinct from the progressive velo- city is the rotary, which increases from the exterior boundary to the centre of the storm, near which point the force of the tempest is greatest, the wind sometimes blowing at the rate of one hundred miles per hour. 519 How great is the breadth of the hurricane $ The surface simultaneously swept by these tremen- dous whirlwinds is a vast circle varying from one hun- dred to Jive hundred miles in diameter. 82 SCIENCE OF COMMON THINGS. Tornadoes-~cause of. Eddies in water. 520 How great is the surface over whicJi they prevail ? Mr. Redfield, of New York, lias estimated the great Cuba hurricane of 1844 to have been not less than eight hundred miles in breadth, and the area over which it prevailed during its whole length was com- puted to be two million four hundred thousand square 'miles an extent of surface equal to two-thirds of that of all Europe. 521 What curious fact have mariners noticed when in the centre or vortex of the hurricane ? An awful calm prevails, described as the lull of the tempest, in which it seems to have rested only to gather strength for greater efforts. 522 In what respect does a tornado differ from a hurricane f Tornadoes may be regarded as hurricanes, differing chiefly in respect to their continuance and extent. 523 How long do they usually last f From fifteen to seventy seconds. 524 What is their extent f Their breadth varies from &few rods to several hun- dred yards, and the length of their course rarely ex- ceeds twenty miles. 525 What phenomena generally attend them f The tornado is generally preceded by a calm and sultry state of the atmosphere, when suddenly the whirlwind appears, prostrating everything before it. Tornadoes are usually accompanied with thunder and lightning, and sometimes showers of hail. 526 What is supposed to be the origin of tornadoes f They are supposed to be generally produced by the lateral action of an opposing wind, or the influence of a brisk gale upon a portion of the atmosphere in repose. 527 How are the eddies or whirlpools produced which occur in water, and which in their formation resemble some tornadoes f Eddies or whirlpools are most frequently formed in water when two streams flowing unequally meet, They may be seen at the junction of two brooks or rivers. SCIENCE OF COMMON THINGS. 83 Waterspouts. Why winds feel cool. What are clouds? 535 How are the whirlwinds which we frequently see at the corners of streets in cities produced f They are caused by a gust of wind sweeping round a corner of a building, and striking the calm air be- yond it. 530 What is a waterspout f A waterspout is a whirlwind over the surface of water, and differs from a whirlwind on land in the fact that water is subjected to the action of the wind, instead of objects on the surface of the earth. 530 Why does wind generally feel cold f Because a constantly-changing surface comes in con- tact with our body to draw off its heat. 531 What are the effects of wind noticed in the Arctic regions f Arctic explorers inform us that in those regions, when the thermometer ranges from 40 to 60 below zero, the cold of the external air is easily endurable, provided the air is calm and the individual exercises freely / but if a wind arises at this temperature, the severity of the cold becomes too great for human endurance. 533 If the winds should cease to blow over the ocean, what would be the e/ectf The water would undoubtedly become stagnant. Tempests and hurricanes also exercise a beneficial effect by agitating and purifying the atmosphere, and sweep- ing from it the seeds of pestilence and contagion. 533 What are clouds f Moisture evaporated from the earth^ and again par- tially condensed in the upper regions of the air. 534 What is the difference between a fog and a cloud ? Clouds and fogs differ only in one respect. Clouds are elevated above our heads, but fogs come in contact with the surface of the earth. 635 Why are clouds higher on a fine day f Because they are lighter and more buoyant. 536 Why are clouds lighter on a fine day f 1. Because the vapor of the clouds is less condensed; and 84: SCIENCE OF COMMON THINGS. Why clouds float in the air. Height of clouds. Size of clouds. 2. The air itself (on a fine day) retains much of its vapor in an invisible form. 537* Why do clouds float so readily in the air f Because they are composed of very minute globules (called vesicles), which (being lighter than air) float like soap-bubbles. 538 Are att clouds alike f No ; they vary greatly in density, height, and color. 530 What is the chief cause of fog and clouds f During the daily process of evaporation from the surface of the earth, warm, humid currents of air are continually ascending ; the higher they ascend, the colder is the atmosphere into which they enter ; and, as they continue to rise, a point will at length be attained where, in union with the colder air, their original humidity can no longer be retained : a cloud will then appear, which increases in bulk with the upward pro- gress of the current into colder regions. 540 How do changes in the wind produce clouds f If a cold current of wind blows suddenly over any region, it condenses the invisible vapor of the air into cloud or rain j but if a warm current of wind blows over any region, it disperses the clouds by absorbing their vapor. 541 What distance are the clouds from the earth f Some thin, light clouds are elevated above the high- est mountain-top ; some heavy ones touch the steeples, trees, and even the earth ; but the average height ia between one and two miles. Streaky, curling clouds, like hair, are often five or six miles high. 542 What is the size of the clouds f Some clouds are many square miles in surface, and above a mile in thickness / while others are only a few yards or inches. 543 How can persons ascertain the thickness of a cloud f As the tops of high mountains are generally above the clouds, travellers may pass quite through them into SCIENCE OF COMMON THINGS. 85 Cause of the appearance of clouds. Color of clouds. a clear blue firmament, when the clouds will be seen beneath their feet. 544 Why do clouds, when not continuous over the whole surface of the sky, appear jagged, rough, and uneven ? The rays of the sun, falling upon different surfaces at different angles, melt away one set of elevations, and create another set of depressions ; the heat also which is liberated from below in the process of condensation, the currents of warm air escaping from the earth, and of cold air descending from above, all tend to keep the clouds in a state of agitation, upheaval, and depression. Under their various influences the masses of vapor composing the clouds are caused to assume all manner of grotesque and fanciful shapes. 545 What effect have winds on the shape of clouds f They sometimes absorb them entirely ; sometimes increase their volume and density ; and sometimes change the position of their parts. 546 How can winds absorb clouds altogether ? Warm, dry winds will convert the substance of clouds into invisible vapor, which they will carry away in their own current. 54*7 How can winds increase the bulk and density of clouds f Cold currents of wind w r ill condense the invisible vapor of the air, and add it to the clouds with which, they come in contact. 54S Why is not the color of clouds always alike f Because their size, density, and situation in regard to the sun are perpetually varying, so that sometimes one color is reflected and sometimes another. 549 Why do the clouds after sunset about the western horizon often exhibit a beautiful crimson appearance ? Because the red rays, of which the sun's light is in part composed, are less refrangible than any of the other colors. In consequence of this, they are not bent out of their course so much as the blue and yellow rays, and are the last to disappear. For the same reason they are the first to appear in 86 SCIENCE OF COMMON" THINGS. Eeft uigibility of light Red clouds at sunrise and sunset. the morning when the sun rises, and impart to the morning clouds red or crimson colors. Fig. 19. Let us suppose, as in^. 19, a ray oflight, proceeding from the sun, S, to enter the earth's atmosphere at the point P. The red rays, which compose in part the solar beam, being the least refrangible, or the least deviated from their course, will reach the eye of a spectator at the point A ; while the yellow and blue rays, being refracted to a greater degree, will reach the surface of the earth at the intermediate points B and C. They will, consequently, be quite invisible from the point A. 550 What, is meant by being " less refrongiblef' 1 Being less able to be bent. Blue and yellow rays are more easily bent below the horizon through the action of the atmosphere, but red rays are not so much bent down, and therefore we see them later in the evening. 551 What is the cause of a red sunset f The vapor of the air not being actually condensed into clouds, but only on ihe point of being condensed. In the same manner, if light be transmitted through steam mingled with air, and therefore on the verge of condensation, it assumes a deep orange or red color. 552 Why is a red and lowering sky at sunrise an indication of a wet day f The red and lowering appearance of the morning sky ? which indicates foul weather, probably depends upon such an excess of vapor being present in the whole atmosphere that clouds are actually forming in the SCIENCE OF COMMON THINGS. 87 Haziness of the Indian summer. When vapor forms clouds and fogs. higher regions, or upon the point of condensation, which the rising sun cannot disperse. Hence our Lord's observation " In the morning ye say, It will be foui weather to-day, for the sky is red and lowering." (Matt. xvi. 3.) 553 Which is the most transparent, dry or moist air ? Air moderately moist is more transparent than very dry air. 554 What is the cause of the haziness of the atmosphere during that portion of the autumn known as the " Indian Summer f " It is undoubtedly due to several causes ; partially to an excessive dryness of the atmosphere, and, in some degree, to the prevalence of smoke in the air arising from burning forests. But it is also a fact, ascertained within a few years, that the constitution of the atmo- sphere is changed in the autumn, and that solar light at that season has less chemical influence than at any other portion of the year. 555 Why does the sun seen through a fog appear red? Because the red rays of light have a greater power to pass through a thick, dense atmosphere than any of the other colored rays. 556 Why does vapor sometimes form into clouds, and sometimes rest upon the earth as mist or fog? This depends on the temperature of the air. "When the surface of the earth is warmer than the lower air, the vapor of the earth (being condensed by the chill air) becomes mist or fog. But when the lower air is warmer than the earth, the vapor rises through the air, and becomes cloud. 557* Why do clouds often hover around mountain peaks, when the atmosphere elsewhere is clear and free from clouds 1 It is caused by the wind impelling up the sides of the mountains the warm humid air of the valleys, which in its ascent gradually becomes condensed by the cold, and its excess of moisture becomes visible, and appears as a cloud. 558 Why are windoios at night often covered with thick mist, and the frames wet with standing water ? Because the temperature of the external air always 88 SCIENCE OF COMMON THINGS. Mist on windows. Insensible perspiration. falls at sunset, and chills the window-glass with which it comes in contact. 559 How does this account for the mist and water on a window f As the warm vapor of the room touches the cold glass it is chilled and condensed into mist, and the mist (collecting into drops) rolls down the window-frame in little streams of water. 560 Does the glass of a ivindow cool down more rapidly than the air of the room itself f Yes ; because the air is kept warm by fires and by the animal heat of the people in the room ; in conse- quence of which the air of a room suffers very little diminution of heat from the setting of the sun. 561 Whence arises the vapor of a room f The air of the room always contains vapor ; vapor also arises from the breath and insensible perspiration of the inmates, from cooking and the evaporation of water. 563 What is meant by " the insensible perspiration f " From every part of the human body an insensible and invisible perspiration issues all night and day, not only in the hot weather of summer, but also in the coldest days of winter. 563 If the perspiration be both insensible and invisible, hoiu is it known that there is any such perspiration ? If you put your naked arm into a clean, dry glass tube, the perspiration will condense on the glass like mist. 564 Why is a tumbler of cold water made quite dull with mist, when brought into a warm room ? Because the hot vapor of the room is condensed upon the cold tumbler, with which it comes in contact, and changes its invisible and gaseous form into that of dew. 565 Why does breathing on a glass make it quite dull f Because the cold glass condenses the invisible vapor contained in warm breath, and converts it into dew. 566 Why are the walls of a house covered with damp in a sudden thaw? Because the walls (being thick) cannot change their SCIENCE OF COMMON THINGS. 89 Breath visible in cold weather. Difference between mist and fog. temperature as fast as the air ; in consequence of which they retain their cold after the thaw lias set in. 567 How does "retaining their cold" account for their being so wet? As the vapor of the warm air touches the cold walls, it is chilled and condensed into water, which either sticks to the walls or trickles down in little streams. 568 Why is our breath visible in winter, and not in summer ? Because the intense cold condenses its moisture into visible vapor, but in summer the air is not cold enough to do so. 569 Why are our hair and the brim of our hat often covered with lit- tle drops of pearly dew in ivinter-time f Because the vapor of the breath condenses as it comes in contact with our cold hair or hat, and hangs there in little dew-drops. 570 What are fogs f Fogs are visible vapors that float in the atmosphere near the surface of the earth. 571 What is the cause of fogs 1 They originate in the same causes as rain the union of a cool body of air with one that is warm and humid ; when the precipitation of moisture is slight, fogs are produced ; when it is copious, rains are the result. 573 What distinction is to be made between a mist and a fog ? Mist is generally considered to be a fine rain, while fog is vapor not sufficiently condensed to allow of its precipitation in drops. The term mist is also generally applied to vapors condensed on marshes, rivers, and lakes, while the name fog is often applied to vapors condensed on land, especially if those vapors are laden with smoke. 573 Why does not the fog become dew ? Because the chill of the air is so rapid that vapor is condensed faster than it can be deposited, and covering the earth in a fog) prevents any further radiation of heat from the earth. 574 When the earth can no longer radiate heat upwards, does it con- tinue to condense the vapor of the air ? Ko ; the air (in contact with the earth) becomes 90 SCIENCE OF COMMON THINGS. When fogs occur. When vapor forms clouds and when fogs. about equal in temperature with the surface of the earth itself; for which reason the fog is not condensed into dew, but remains floating above the earth as a thick cloud. 57*5 This fog seems to rise higher and higher, and yet remains quite as dense below as at first : explain the cause of this ? The air resting on the earth is first chilled, and chills the air resting on it ; the air which touches this new layer of fog being also condensed, layer is added' to, layer ; and thus the fog seems to be rising, when (in fact) it is only deepening. 57*B Why are there not fogs every night f Because the air will always hold in solution a cer- tain quantity of vapor (which varies according to its temperature) ; and, when the air is not saturated, it may be cooled without parting with its vapor. 57"? Wften do fogs occur at night f When the air is saturated with vapor during the day. When this is the case, it deposits some of its superabundant moisture in the form of dew or fog as soon as its capacity for holding vapor is lessened by the cold night. 578 Why is there very often a fog over marshes and rivers at night- time ? Because the air of marshes is almost always near saturation and therefore the least depression of tem- perature will compel it to relinquish some of its moist- ure in the form of dew or fog. 57*9 Why does vapor sometimes form into clouds, and sometimes rest upon the earth as mist or fog 1 This depends on the temperature of the air. "When the surface of the earth is warmer than the air, the vapor of the earth (being condensed by the chill air) becomes mist or fog. But, when the air is warmer than the earth, the vapor rises through the air, and be- comes cloud. 58O If cold air produces fog, why is it not foggy on a frosty morning f 1, Because less vapor is formed on a, frosty day ; SCIENCE OF COMMON THINGS. 91 What is rain ? Why falls in drops. and 2. The vapor is frozen upon the ground before it ean rise from the earth, and becomes hoar-frost. 581 What is rain? Rain is the vapor of the clouds or air condensed and precipitated to the earth. 58J3 In what manner is the vapor of the air condensed so as to form rain ? i When two or more volumes of humid air differing considerably in temperature unite, the several portions in union are incapable of absorbing the same amount of moisture that each could retain if they had not united. The excess of moisture, if very great, is pre- cipitated as rain ; if in slight amount, it appears as clouds, fogs, or mists. 583 Upon what law does this condensation of vapor and formation of rain depend f Upon the law that the capacity of the air for moist- ure decreases in a greater ratio than the temperature. 58*4 Why does rainfall in drops ? Because the vapory particles in their descent attract each other ; and those which are sufficiently near unite and form into drops. The size of the rain-drop is increased according to the rapidity with which the vapors are condensed. 585 Why does not the cold of night always cause ram f Because the air is not always near saturation ; and unless this be the case, it will be able to hold its vapor in solution, even after it is condensed by the chilly night. 580 Why does a passing cloud often drop rain ? Because the cloud (travelling about on the wind) comes into contact with something that chills it; and its vapor being condensed, falls to the earth as 58 T Can the air absorb moisture at all temperatures, and retain it in an invisible state f It can ; and this power of the air is termed its capacity of absorption. 92 SCIENCE OF COMMON THINGS. What is snow ? Cause of sleet. 588 How much moisture can a volume of air at 32 F. absorb f An amount equal to the hundred and sixtieth part of its own weight. 589 How does the capacity of air for moisture increase with the tem- perature ? Eor every 27 additional degrees of heat, the quantity of moisture it can absorb at 32 is doubled. Thus a body of air at 32 F. absorbs the 160th part of its own weight; at 59 F. the 80th; at 86 F. the 40th; at 113 F. the 20th part of its own moisture. It follows from this that, while the temperature advances in an arithmetical series, the capacity is accelerated in geo- metrical series. , 590 In what situations is the air always saturated f Over the ocean and upon the adjacent coasts. 591 Where is the absolute humidity of the atmosphere the greatest f In the tropics, where the temperature of the air, and its consequent capacity for moisture, is the greatest. 593 What is snow ? The condensed vapor of the air frozen and precipi- tated to the earth. 593 What is the cause of snow f When the air is nearly saturated with vapor, and is acted on by a current of air l>elow the freezing point, some of the vapor is condensed, and frozen into snow. A few years ago, some fishermen (who wintered at Nova Zembla), after they had been shut up in a hut for several days, opened the window, and the cold external air rushing in, instantly condensed the air of the hut, and its vapor fell on the floor in a shower of*now. 594 What is the cause of sleet ? "When flakes of snow (in their descent) pass through a bed of air above the freezing point, they partially melt, and fall to the earth as half-melted snow, or sleet. 595 How does snow prove beneficial to the earth in the cold season f It keeps the surface of the earth warm, protects vege- tation to a considerable extent from the cold, and acts as a fertilizer. SCIENCE OF COMMON THINGS. 93 How snow keeps the earth warm. Why snow is white. 596 Does snow Jceep the earth warm f Yes, because it is a very bad conductor j in conse- quence of which, when the earth is covered with snow, its temperature very rarely descends below the freezing point, even when the air is fifteen or twenty degrees colder. 59 7 Why is snow a lad conductor of heat and cold f Because air is confined among the crystals, and air is a very bad conductor ; when, therefore, the earth is covered with snow, it cannot throw off its heat by radiation. Why is there no snow in summer-time f Because the heat of the air adjacent to the earth melts it in its descent, and prevents it from reaching the surface of the earth. 590 Why is snow white f Because it is formed of an infinite number of very minute crystals and prisms, which reflect all the colors of the ravs of light from different points, and these colors, uniting before they meet the eye, cause snow to appear white. The same answer applies to salt, loaf-sugar, etc. GOO Under what circumstances does snow fall in large flakes, and when in small f The largest flakes are formed when the air abounds with vapor, and the temperature is about 32 F. ; but as the moisture diminishes, and the cold increases, the snow becomes finer. 6O1 What is the snow flake composed off Regular and symmetrical crystals, having a great diversity of forms. 6 OS Do we see the same crystals in ice f They exist in ice, but are so blended together that their symmetry is lost in the compact mass. 6O3 How much more bulky is snow than water ? The bulk of recently-fallen snow is ten or twelve times greater than that of the water obtained by melting it fi 94: SCIENCE OF COMMON THINGS. Red and green snow. "What is hail ? Meteorites. GO4 Does snow ever occur of any other appearance than white? Yes ; in the Arctic regions and on some mountains it is red, and occasionally green. 6O5 What is the cause of these appearances 1 These singular hues are occasioned by little micro- scopic plants, which germinate and live in the snow. They consist of little globules from TT f To - of an inch to 3-500 f an inch. Each globule is divided into seven or eight cells filled with a liquid, which gives a color to the snow, and is sometimes green and sometimes red. eoe What is 'hail? Rain, which has passed in its descent through some cold bed of air, and has been frozen into drops of ice. GOT* What makes one bed of air colder than another f It is frequently caused by electricity unequally dis- tributed in the air. 60S How can electricity make air cold ? Air, when electrified, is expanded, and expansion produces cold. 6O9 Why does hail fall generally in summer and autumn f Because the air is more highly electrified in summer and autumn than in winter and- spring; and the vapors in summer and autumn (being rarefied) ascend to more elevated regions, which are colder than those nearer the earth. G1O Is the occurrence and formation of hail clearly understood? It is not ; much information exists upon the subject, but no theory has yet been formed which satisfactorily accounts for all the facts which have been observed. Gil What are meteorites f Meteorites are solid, luminous bodies, which from time to time visit the earth, moving with immense velocity, and remaining visible but for a few moments. They are generally accompanied by a luminous train, and during their progress explosions are often heard. 61Q What is an aerolite f The term aerolite is given to those stony masses of SCIENCE OF COMMON THINGS. 95 Aerolites. Appearance. Composition. matter which are sometimes seen to fall from the atmosphere. It is derived from the Greek words, acp (atmosphere), and Xi0<>? (a stone). A meteor is distinguished from an aerolite by the fact that it bursts in the atmosphere, but leaves no residuum except a vapor-like smoke ; while the aerolite, which is supposed to be a fragment of a meteor, comes to the ground. 613 What is the weight of those aerolites which have been known to fall from the atmosphere ? Their weights vary from a few ounces to several hun- dred pounds, or even tons. 614 At what height in the atmosphere are meteors supposed to appear f Their height above the earth has been estimated to vary from eighteen to eighty miles. 615 With what velocity do they move ? The velocity of these bodies is somewhat more than three hundred miles per minute, though one meteor of immense size, w r hich is supposed to have passed within twenty-five miles of the earth, moved at the rate of twelve hundred miles per minute. 616 What is the value of such estimates ? Owing to the short time the meteor is visible and its great velocity, accurate observations cannot be made upon it ; and all estimates respecting their distance, size, etc., must be considered as only approximations to the truth. 617 What is the general appearance of aerolites f Most of them are covered with a Hack shining crust, as if the body had been coated with pitch. When broken their color is ash-grey, inclining to black. Very many of the meteorites which have fallen at different times and m different parts of the globe, resemble eacli other so closely, that they would seem to have been broken from the same piece or mass of matter. 618 What is their composition ? Great numbers of aerolites have been analysed, and found to contain nineteen or twenty different elementary substances. But for the most part they consist of malle- able iron and niokel. 96 SCIENCE OF COMMON THINGS. Meteoric iron. Origin of meteors. Shooting stars. 619 Do tJie aerolites resemUe in composition any other bodies upon the surface of the earth f They do not : malleable iron is rarely if ever found in terrestrial substances / and metallic nickel does not occur upon the surface of the earth naturally. 620 What is peculiar to the composition of meteoric iron t It has a highly crystalline arrangement, so peculiar that it is especially distinguished by it. This arrange- ment .of its particles enables us to decide upon the meteoric origin of masses of iron which are occasionally found scattered up and down the surface of the earth. 621 Where have such masses been found? In the south of Africa, in Mexico, /Siberia, and on the route overland to California. Some of these masses are of immense weight, and undoubtedly fell from the atmosphere. 622 How are meteorites supposed to originate ? four hypotheses have been advanced to account for the origin of these extraordinary bodies : 1. That they are thrown up from terrestrial volcanoes. 2. That they are produced in the atmosphere from vapors and gases exhaled from the earth. 3. That they are thrown from lunar volcanoes. 4. That they are of the same nature as the planets, either derived from them, or existing independently. 623 Which of these hypotheses is regarded as most probabk ? The fourth most fully explains the facts connected with the appearance of meteorites, and the third like- wise has some strong evidence in its favor. 624 In what respect do shooting stars differ from meteors ? Their altitude and velocity are greater, they are far more numerous and frequent, and are unaccompanied by any sound or explosion. Their brilliancy is also much inferior to that of the meteor / and no portion of their substance is ever known to have reached the earth. 625 What do we know concerning their altitude f Owing to their great number and frequency of occur- rence, many careful observations have been made upon SCIENCE OF COMMON THINGS. 97 Origin of shooting stars. Zodiacal light. them ; their altitude is supposed to vary from six to four hundred and sixty miles, the greatest number appearing at a height of about seventy mites. 636 What is their supposed velocity ? It is supposed to range from sixty to fifteen hundred miles per minute. 637* Are meteors and shooting stars at all times equally abundant f They are not some may be seen every clear night, but they appear to return at certain periodical epochs, when they descend literally in showers. 638 What are the periods when they may be noticed most abundantly f On the 9tk and Wth of August, and the 12^A and 13t/t of November. They have also been noticed in unusual abundance on the 18th of Octo- ber, the- 6th and 7th of December, the 2d of January, the 23d and 24th of April, and from the 18th to the 20th of June. 639 Do the shooting stars appear to emanate from any particular part of the heavens ? The majority seem to start from a point in the con- stellation Perseus, and undoubtedly far beyond the limits of our atmosphere. 63O What is the zodiacal light f It is a singular luminous appearance seen in the horizon before sunrise and after sunset, most conspicu- ously in the months of April and May. Observations made during the year 1855 seem to conclusively prove that the appearance known as the " zodiacal light " is occasioned by a ring of nebulous matter encircling and pertaining to the earth. CHAPTER YII. THE PUMP AND BAROMETER. 631 Why, when we suck up a liquid with a tube or straiv, does th& liquid rise to the mouth 1 One end of the tube being placed between the lips, SCIENCE OF COMMON THINGS. The common pump. How constructed. Pump valves. the air is removed from the tube by the ordinary pro- cess of inhaling, when the pressure of the atmosphere compels the liquid to fill the space deserted by the air. 633 Through how great a length of tube could tve raise a liquid by suction ? About thirty-two feet. 633 Why can we not raise it above thirty-two feet f Because the atmospheric pressure will only support or balance a column of water or similar liquid of that height. 634 How is the common pump constructed ? The common pump consists of a hollow tube, the lower part of which, descending into the water, is called the siiction-pipe, and the upper part, b (Fig. 20), the barrel or cylinder of a spout, s, at the top of the cylinder ; of an air-tight piston, which works up and down in the cylinder ; and of two valves, both opening upwards, one of which, g, is placed at the top of the suction-pipe, and the other, p, in the piston. 635 How does the common pump operate f When the piston is raised from the bottom of the cylinder, the air above it is drawn uj?, leaving a vacuum be- low the piston ; the water in the well then rushes up through the valve, g, and fills the cylinder ; the piston is then forced down, shutting the valve, g, and causing the water to rise through the piston-valve, p ; the piston is then raised, closing its valve, and raising the water above it, which flows out of the spout, s. 636 What is a valve f A valve, in general, is a contrivance by which water or other fluid, flowing through a tube or^ aperture, is allowed free passage in one direction, but is stopped in Fig. 20. SCIENCE OF COMMON THINGS. 99 Common suction-pump. Height water rises in common pump. the other. Its structure is such, that, while the pressure of fluid on one side has a tendency to close it, the pressure on the other side has a tendency to open it. /tys. 21, 22, and 23 represent the various forms of valves used in pumps, water-engines, etc. Fig. at. Fig. 22. Fig. 53. 637 How can water be raised by the common suction-pump ? As the action of this pump depends upon the pressure of the atmosphere, water cannot be raised by it from a depth of more than 34 feet below the upper valve, and in practice a much shorter limit is usually assigned. 633 A tinman of Seville, in Spain, ignorant of the principles of science, undertook to construct a suction-pump to raise water from a well sixty feet deep ; when the machine was finished, he was confounded at discovering that it had no power to raise water at all, and enraged at his disappoint- ment, while some one was working the pump, he struck the suction pipe with a hammer or axe so forcibly as to crack it, when, to his surprise and delight, the water almost immediately began to flow, and he found he had attained his purpose. How is this result to be accounted for ? The explanation is as follows : the air pressed in through the slit, or aperture of the suction-pipe, and becoming mixed with the water in its ascent, formed a compound fluid far lighter than water alone, and there- fore acted upon more readily by the atmospheric pres- sure ; and thus produced the phenomenon described. 639 How high can water be raised in the suction-pump by resorting t* Hie expedient above described ? About fifty-five feet, instead of thirty to thirty-four. 6*1O To whom is the invention oftJie common pump attributed ? To Ctesibius, an Athenian engineer, who lived at Alexandria, in Egypt, about the middle of the second century before the Christian era. 100 SCIENCE OF COMMON THINGS. Forcing-pump. Construction of chain-pump. Fig. 24. 641 When it is desired to raise ivater above thirty -four feet, as in fire- engines, etc., how is it accomplished ? By means of tliQ forcing-pump. 643 In what manner is the forcing-pump con- structed ? In the forcing-pump atmospheric pressure plays but a small part. There is no valve in the piston c (fig. 24), but the water raised through the suc- tion-pipe #, and the valve ad radiator, and parts w r ith its heat very slowly. 1O81 Is that the reason why grass is saturated with dew, and the gra- vel is not f Yes. When the vapor of warm air comes in contact with the cold grass, it is instantly chilled into dew ; but 168 SCIENCE OF COMMON THINGS. Dew on rocky and on fertile Boils. Dew most abundant after a hot day. it is not so freely condensed as it passes over gravel, because gravel is not so cold as the grass. 1O8S Why does dew rarely fall upon hard rocks and barren lands ? Because rocks and barren lands are so compact and hard, that they can neither absorb, nor radiate much heat / and (as their temperature varies but very -little) very little dew deposits upon them. 1O83 Why does dew fall more abundantly on cultivated soils than on barren lands f Because cultivated soils (being loose and porous) very freely radiate by night the heat which they ab- sorb by day ; in consequence of which they are much cooled down, and plentifully condense the vapor of the passing air into dew. 1OS4 Show the wisdom of the Creator in this arrangement f Every plant and inch of land which needs the moist- ure of dew is adapted to collect it ; but not a single drop is wasted where its refreshing moisture is not required. 1O85 When is dew most copiously distilled t After a hot day in summer or autumn, especially if the wind blows over a body of water. 1OSG Why is dew distilled most copiously after a hot day ? Because the surface of the hot earth radiates heat very freely at sunset, and (being made much colder than the air) chills the passing vapor and condenses it into dew. 108*7 Why is there less dew when the wind blows across the land, than when it blows over a body of water ? Because the winds which blow across the.Zan^ are dry and arid / but those which cross the water are moist and full of vapor. 1088 How does the dryness of the wind prevent dew-falls? As winds (currents of air) which blow over the land are very dry, they imbibe the moisture of the air ; in consequence of which there is very little left to be con- densed into dew. 1089 Why is meal very subject to faint on a moonlight niyhtt SCIENCE OF COMMON THINGS. 167 Protection against frost. Cause of fog and mist. Because it radiates heat very freely in a bright moon- light night ; in consequence of which it is soon covered with dew, which produces rapid decomposition. 1O0 O How do moonlight nights conduce to the rapid growth of plants f Radiation is carried on very rapidly on bright moon- light nights ; in consequence of which dew is very plentifully deposited on young plants, which conduces much to their growth and vigor. 1O91 Why is the air in immediate contact with the earth, on a clear night, cooler than tlie air at a little distance from the surface f Because it parts with its heat to the earth, which in turn loses it by radiation. 1O93 How can a thin covering of bass, or even muslin, protect trees from frost ? Because any covering prevents the radiation of heat from the tree ; and if trees are not cooled down by radi- ation, the vapor of the air will not fe frozen as it comes in contact with them. Bass a kind of matting used by gardeners. 1093 Why is the bass or canvas itself (which covers the tree) ahvays drenched with deiv ? Because it radiates heat both upwards and down- wards j in consequence of which it is so cooled down that it readily chills the vapor of the air into dew. 1094 What is the cause of mist or earth-fog ? If the night has been very calm, the radiation of heat from the earth has been very abundant ; in consequence of which the air (resting on the earth) has been chilled, and its vapor condensed into a thick mist. 1095 Why does not the mist become devj ? Because the chill of the air is so rapid, that vapor is condensedy^site/' than it can be deposited and (covering the earth as a mist) prevents any farther radiation of heat from the earth. 1096 When the earth can no longer radiate heat upwards, does it con- tinue to condense the vapor of the air ? No ; the air (in contact with the earth) becomes about equal in temperature with the surface of the earth itself; 168 SCIENCE OF COMMON THINGS. Mist and dew vanish at sunrise. No dew in cities. for which reason the mist is not condensed into dew^ but remains floating above the earth as a thick cloud. 1097* This mitt seems to rise higher and higher, and yet remains quite as dense below as at first : explain the cause of this. The air resting on the earth is first chilled, and chills the air resting on it ; the air which touches this new layer of mist being also condensed, layer is added to layer ; and thus the mist seems to be rising, when (in fact) it is only deepening. 1O08 Why do mist and dew vanish as the sun rises f Because the air becomes warmer at sunrise, and ab- sorbs the vapor. 1OS9 Can the dew properly be said to "fall?" Kow ; dew is a\w&ys formed upon the surface of the material upon which it is found, and does not fall from the atmosphere. 1100 Does the color of an object influence the deposition of dew f It does to a considerable extent. 1101 How can this be sliown f If we take pieces of red, black, green, and yellow glass, and expose them when the dew is condensing, we shall find that moisture will show itself first on the yellow and then on the green glass, but that none will appear on the red or black glass. The same thing will take place if we expose colored fluids in white glass bottles. 11O3 Why is the deposition of dew rarely observed in the close and sheltered streets of cities f Because there the objects are necessarily exposed to each other's radiation, and an interchange of heat takes place, which maintains them at a temperature uniform with the air. 1103 When is dew converted into frost f \ If the temperature of the earth, or of the vessel, sink to the freezing point or below, the moisture will be de- posited as before ; but by freezing, it assumes the solid Ibrm, and is called frost. 1104 Why is a deiv-drop round f SCIENCE OF COMMON THINGS. 169 Why a dew-drop is round. AVhy a duck is not wet with water. Because every part of it is equally balanced ; and therefore there is no cause why one part of the drop should be farther from the centre than another. 11O5 Why will dew-drops roll about cabbage plants, poppies, &c., with- out wetting the surface ? Because the leaves of cabbages and poppies are covered with a very fine waxen powder, over which the dew-drop rolls without wetting the surface, as a drop of rain would over dust. HO 6 Why does not a drop of rain wet the dust over which it rottsf Because dust has no affinity for w^ater, and therefore repels it. HOT* Why can swans and ducks dive under water vnthout being wetted 1 Because their feathers are covered with an oily secre- tion, which has no affinity for water, and therefore re- pels it. 11O8 WJiat is tlie figure which water always assumes when unsupported, or supported on a surface having little attraction for it? The figure of a sphere. This figure becomes more or less globular or spheroidal in its shape, as the attraction of the substances upon which it is received increases or diminishes ? 11O0 What is the form of a drop of rain when descending in the air? A sphere. 11O Why should drops of water, resting upon surfaces which have no affinity for them, assume a spheroidal shape? Because such surfaces not having so great an attrac- tion for the drops of water as the particles of water have for each other, the drops tend to preserve, as nearly as possible, the spheroidal form which they would have if entirely unsupported, as when falling as drops of rain. 1111 Is dew ever formed upon the surface of water ? The formation of dew upon ships which traverse the vast solitudes of the ocean has never been noticed ; and it has been ascertained by experiment that even a small quantity of water gains no weight by exposure during a single night. 170 SCIENCE OF COMMON THINGS. No dew on the ocean. No dew falls on the human body. Although dew dcx s not appear upon ships at a great distance from land, it is freely deposited on the same vessels arriving in the vicinity of terra firma. Thus, navigators who proceed from the Straits of Sunda to the Coromandel coast, know that they are near the end of the voyage when they perceive the ropes, sails, and other objects placed on the deck become moistened with dew during the night. 1112 Why does not dew form upon the surface of water ? Because whenever the aqueous particles at the sur- face are cooled, they become heavier than those below uiein, and sink, while warmer arid lighter particles rise to the top. These, in their turn, become heavier, and descend; and the process, continuing throughout the night, maintains the surface of the water and the air at nearly the same temperature. 1113 Is the temperature at which dew is deposited from the air always the same ? No ; when the air is saturated with moisture, a slight reduction of temperature occasions a deposition of dew; but when the air is very dry, a greater reduction of temperature is necessary to condense its vapor. 1114 Why are the exposed parts of the human body never covered with deiv? Because the vital heat, varying from 96 to 98 Fah- renheit, effectually prevents such a loss of warmth as is necessary to its production. 1115 In what countries are the dews most copious and abundant ? In tropical climates. 1116 What is the reason of this f Because in those countries there is the greatest dif- ference between the temperature of the day and that of the night. The development of vegetation is greatest in tropical countries, and a great part of the nocturnal cooling is due to the leaves, which present to the sky ?.T\ immense number of thin bodies, having large surface, well adapted to -radiate heat. SCIENCE OF COMMON THINGS. 171 Reflection of heat. What are rays of heat f CHAPTER YI REFLECTION, ABSORPTION, AND TRANSMISSION OF HEAT. 1117 What is meant by the reflection of heat f Heat is said to be reflected when it is caused to re- "bound or be thrown back from the surface of a reflect- ing body. 1118 What are the best reflectors of heat f All bright surfaces and light colors. 1119 Are good absorbers of heat good reflectors also ? No ; those things which absorb heat best reflect heat worst and those which reflect heat worst absorb it best. 1130 Why are those things which absorb heat unable to reflect it f Because if anything sucks in heat, as a sponge does water, it cannot throw it off from its surface ; and if anything throws off heat from its surface, it cannot drink it in. 1131 Why are reflectors always made of light-colored and highly- polished metal f Because light-colored and highly-polished metal makes the best of all reflectors. If metal be such an excellent conductor of heat, how can it reflect heat, or throw it off? Polished metal is a conductor of heat only when that heat is communicated by actual contact; but when- ever heat falls upon bright metal in rays* it is reflected back again, and the metal remains cool,. 1133 What is meant " by heat falling upon metal in rays" and not " by contact ?" If a piece of metal were thrust into a fire, it would be in actual contact with the fire ; but if it were held before a flre^ the heat of the fire would fall upon it in rays. 1134 Why will a kettle be slower in boiling if the bottom and sides are clean and bright f 172 SCIENCE OF COMMON THINGS. Use of white dresses in summer. Coldness of high mountains. Because bright metal does not absorb heat, but re- flects it ; and (as the heat is thrown off from the sur- face of 'bright metal by reflection) therefore a new ket- tle takes a longer time to boil. Reflects heat that is, throws it off. 1135 Why do persons wear white dresses in summer-time f Because white throws off the heat of the sun by re- flection, and is a very bad absorbent of heat ; in con- sequence of which w r hite dresses never become so hot from the scorching sun as dark colors do. 1136 Why do persons not wear white dresses in winter-time ? Because white will not absorb heat like black and other dark colors ; and therefore white dresses are not so warm as dark ones. Why are shoes hotter for being dusty f Because dull, dusty shoes will absorb heat from the sun, earth, and air ; but shoes brightly polished throw off the heat of the sun by reflection. 1138 Why do not the solar rays, even in the hottest day, melt the snow upon the tops of high mountains, which are nearer to the sun than tlie kvel portions of the earth ? Because they only heat those bodies which can alt- sorb their warmth, as the rough surface of the earth. The snow is indeed struck by the rays of the sun, but being a white and shining body, it reflects them, and remains cold. 1139 Why does it always freeze on the top of a high mountain ? 1. Because air is heated by contact with the earth's surface more than by solar rays which pass through it : as a mountain-top affords very small surface for such contact, it remains intensely cold ; and 2. When air flows up the side of a mountain, it ex- pands from diminished pressure ; and consequently absorbs heat from surrounding objects. Karefied air can hold more latent heat than dense air can. 11SO What is the difference between conducting heat and absorbing heat? To conduct heat is to transmit it from one body to SCIENCE OF COMMON THINGS. 173 Conduction of heat. How fanning cools. another through a conducting medium. To absorb heat is to suck it up, as a sponge sucks up water. 1131 Give me an example ? Black cloth absorbs, but does not conduct heat / thus, if black cloth be laid in the sun, it will absorb the rays very rapidly ; but if one end of the black cloth be made hot, it w r ould not conduct the heat to the other end. 113S Are good conductors of heat good absorbers also f No ; every good conductor of heat is a lad absorber of it ; and no good absorber of heat can be a good con- ductor also. 1133 Is iron a good absorber of heat f No ; iron is a good conductor, but a very bad ab- sorber of heat. 1134 If a piece of brown paper be submitted to the action of a burning- glass it will catch fire much sooner than a piece of white paper would : ex- plain the reason. Because white paper reflects the rays of the sun. or throws them back ; in consequence of which it appears more luminous, but is not so much heated as dark brown paper, which absorbs the rays, and readily be- comes heated to ignition. 1135 How does the ceaseless change of air tend to decrease the warmth of a naked body ? The air (which cases the body) absorbs as much heat from it as it can, while it remains in contact ; bein^ then blown away, it makes room for a fresh coat of air, which readily absorbs more heat. Use Does the air which encases a naked body become (by contact) as warm as the body itself? It would do so, if it remained motionless ; but, as it remains only a very short time, it absorbs as much heat as it can in the time, and passes on. 1137* Why does fanning the face in summer make it cool f Because the fan puts the air in motion, and makes it pass more rapidly over the face ; and (as the tem- perature of the air is usually lower than that of the 8* 174 SCIENCE OF COMMON THINGS. Wind generally feels cool Utility of black kettles. liumtmface) each volume of air carries off some portion of its heat. 1138 Does a fan cool the air f No ; it makes the air hotter by imparting to it the heat out of our face / but it cools our face by transfer- ring its heat to the air. 1139 How does fanning the face increase the heat of the air f By driving the air more rapidly over the human body, and causing it, consequently, to absorb more heat. 1140 If fanning makes the air hotter, why can it make a person feel cooler f Because it takes the heat out of the face, and gives it to the air. Why does wind generally feel cool f Because it drives the air more rapidly over our body, and this rapid change of air draws off a large quantity of heat. 114S Why does air absorb heat more quickly by being set in motion f Because every fresh gust of air absorbs a fresh por- tion of heat ; and the more rapid the succession of gusts, the greater will be the quantity of heat absorbed. 1143 If the air were hotter than our body would the wind feel cool f No ; the air would feel insufferably hot, if it were hotter than our body. 1144 Why would the air feel intensely hot, if it were warmer than our body f Because it would add to the heat of our body, instead of diminishing it. 1145 Is the air ever as hot as the human body f In the extreme of summer the temperature of the air sometimes exceeds the natural temperature of the body ; and when that is the case, the heat is almost insupportable. 1146 Why does a kettle boil faster when the bottom and sides are fovered wiih soot f Because the black soot absorbs heat very quickly from the fire, and the metal conducts it to the water. SCIENCE OF COMMON THINGS. 175 Colors most suitable for dresses. Why a negro never sunburns. 1147* Why do we wear white linen and a black outer dress, if we want to be warm f Because the black outer dress quickly absorbs heat from the sun ; and the white linen (being a bad absorb- ent) abstracts no heat from the warm body. 1148 What colors are warmest for dresses? For outside garments black is the warmest, and then such colors as approach nearest to black (as dark blue and green). White is the coldest color for external clothing. 1149 Why are dark colors (for external wear) so much warmer than light ones f Because dark colors absorb heat from the sun more abundantly than light ones. 1150 How can you prove that dark colors are warmer than light ones ? If a piece of black and a piece of white cloth were laid upon snow, in a few hours the black cloth will have melted the snow beneath / whereas the white cloth will have produced little or no effect upon it at all. The darker any color is, the warmer it is, because it is a better absorb- ent of heat. The order may be thus arranged : 1, black (warmest of all) ; 2, violet ; 3, indigo ; 4, blue ; 5, green ; 6, red ; 7, yellow ; and 8, white (coldest of all). 1151 Why does the black skin of a negro never sunburn or blister with Hie hot sun? Because the black color absorbs the heat, conveys it below the surface of the skin, and converts it into sen- sible heat and perspiration. 1153 Why does the white European skin blister and burn when exposed to the hot sun f Because white will not absorb heat ; and therefore the hot sun rests on the surface of the skin^. and burns it. 1153 Why do most of the animals inhabiting the frigid zones have white fur, hair, or feathers? Because white radiates and absorbs but little heat. 1154 What relation exists between the power of bodies to absorb and communicate heat? Those bodies which absorb heat freely, also part with it most rapidly / that is, they are sooner heated and more speedily cooled than other bodies. 176 SCIENCE OF COMMON THINGS. Temperature of scalding water. General effects of heat. 1155 At what temperature do metals burn when handled f Metals cannot be handled when raised to a tempe- ratnre of more than one hundred and twenty degrees. 1156 At what temperature does water scald 7 At one hundred and fifty degrees. 1157 To what extent can the human system sustain the influence of heated air f Workmen enter ovens, in the manufacture of moulds of plaster of Paris, in which the thermometer stands 100 above the temperature of boiling water, and sustain no injury. If the person so entering a heated oven should hold next to his skin a piece of metal, the latter would absorb heat with sufficient rapidity to burn the surface with which it was in contact. 1158 Why is there so great a difference between the burning tempera- ture of 'metals and air f The metals absorb heat quickly, and part with it freely ; the air absorbs heat very slowly, and does not readily part with it. 1159 What class of bodies allow heat to pass freely through them,? Transparent bodies of little density, as the air, the various gases, etc., etc. CHAPTEE VII. EFFECT OF HEAT. 116 O What effect has heat upon substances generally f It expands them, or enlarges their dimensions. 1161 Are the dimensions of every kind of matter regulated by heatf They are; its increase, with few exceptions, separates the particles of bodies to a greater distance from each other, producing expansion, so that the same quantity SCIENCE OF COMMON THINGS. 177 Form of bodies dependent on heat. Heat expands all matter. of matter is thus made to occupy a larger space ; the diminution of heat has an opposite effect. The expansion of solids by heat is clearly shown by the following experi- ment, Fig. 40 : m represents a ring of metal, through which, at the ordinary temperature, a small iron or copper ball, a, will pass freely, this ball being a little less than the diameter of the ring. If this ball be now heated by the flame of an alcohol lamp, it will become so far expanded by heat as no longer to pass through the ring. 116J3 Is Hie form of bodies depend- ent on heat ? It is. 1163 Sow is this shown ? By the increase of heat, solids are converted into liquids, and liquids are dissipated into vapor ; by its decrease, vapors are condensed into liquids, and these become solid. 1164 If matter ceased to be influenced by heat, what would be the effect? All liquids, vapors, and doubtless even gases, would become permanently solid, and all motion on the sur- face of the earth would be arrested. 1165 What are the three most apparent effects of heat, so far as relates to the form and dimensions of bodies ? Expansion, liquefaction, and vaporisation. 1166 Does heat expand air f Yes ; if a bladder (partially filled with air) be tied up at the neck, and laid before the fire, the air will expand till the bladder bursts. 1167 Why will the air swell if the bladder be Md before the fire f Because the heat of the fire will drive the particles of air apart from each other, and cause them to occupy more room than they did before. 116S Does heat expand all matter ? Yes ; every thing (that man is acquainted with) is expanded by heat. 1169 How can we prove that solids expand with heat f 178 SCIENCE OF COMMON THINGS. Force of expansion. Ice, why lighter than water. If we take the exact dimensions in length, breadth, and thickness of any substance when cold, and measure it again when strongly heated, it will be found to have increased in every direction. 117*O Do bodies expand with the increase of heat, and contract upon its withdrawal, with any degree of force f Yes ; the force with which bodies contract and ex- pand under the influence of heat is apparently iwesist- ible, and is recognised as one of the greatest forces in nature. 117*1 What peculiarity exists in the effect of heat upon the bulk of so^* fluids ? That at a certain temperature increase of heat causes them to contract, and its diminution makes them ex- pand. 117*3 What classes of liquids exhibit this peculiarity f Those only which increase in bulk in passing from the liquid to the solid state^ and this change is remarked only within a few degrees of temperature above their point of congelation. 117*3 What is a noted example of this exception to the general laios of Jieat? Water / ice swims upon the surface of water, and therefore must be lighter, a convincing proof that wa- ter in the act of freezing must expand. 117*4 Why is the ice produced ly the freezing of sea water ahvays fresh and free from salt ? Because water, in freezing, if in sufficient quantity to allow freedom of motion to its particles, expels all impurities and coloring matters. 117*5 If a solution of indigo be frozen, why will the ice formed be clear and colorless f Because the water in which the indigo was dissolved expels all the blue coloring matter while freezing. 117*6 Why are blocks of ice generally filled with air-bubbles f Because the water, during the act of freezing, expels the air contained in it, and many of the liberated bub- bles become lodged and imbedded in the thickening fluid. SCIENCE OP COMMON THINGS. 179 Cause of wcuthcr-worn rocks. Cause of icicles. "What is ice f IIT* 7 Is the force created by the expansion of water in the act of freezing very great? Yes ; as an illustration the following experiment may be quoted : Cast-iron bomb-shells, thirteen inches in diameter and two inches thick, were filled with wa- ter, and their apertures or fuse-holes firmly plugged with iron bolts. Thus prepared, upon exposure to the severe cold of a Canadian winter, about 19 below " zero," at the moment the water froze, the iron plugs were violently thrust out, and the ice protruded, and in some instances the shells burst asunder, thus demon- strating the enormous interior pressure to which they were subjected by water assuming the solid state. 117*8 What is the principal cause of the rounded and weather-worn aspect of some rocks, especially the limestone and sandstone rocks ? The expansion of freezing water : water is absorbed into their fissures and pores by capillary attraction, and when it freezes during winter, it expands and de- taches successive fragments, so that the original sharp and abrupt outline is gradually rounded and softened down. 117*9 Why, in the winter, do we let the water run to prevent its freezing in the service pipe ? Because the motion of the water prevents the crys- tals of ice from forming or attaching themselves to the sides of the pipe. 1180 Can a lens be made of ice capable of concentrating the rays of the sun with sufficient intensity to inflame substances ? Yes ; a burning-lens can be formed of transparent ice, of power sufficient to produce effects nearly equal to those of the glass lens. 1181 What is " ground ice," or " anchor ice ?" Ice formed at the bottom of streams or rivers. 1183 Upon what does the formation of icicles depend ? Upon the successive congelation of drops or slender streams of water. 1183 What is ice t Frozen water. "When the temperature of water un- 180 SCIENCE OF COMMON THINGS. Expansion of water in freezing. der ordinary circumstances is reduced to 32 of heat, water will no longer remain in a fluid state. 118-4 Can water be cooled below 32, under any circumstances, without freezing f If pure, recently-boiled water, be cooled very slowly and kept very tranquil, its temperature may be low- ered to 21 without the formation of ice ; but the least motion causes it to congeal suddenly, and its tempera- ture rises to 32. 1185 Why is solid ice lighter than water ? Because water expands by freezing ; and as its bulk is increased, its specific gravity must be less. Nine cubic inches of water become ten when frozen. 118S Why are earthen or porcelain water vessels apt to break in a frosty night ? Because the water in them freezes, and (expanding by frost) bursts the vessels to make room for its increas- ed volume. 1187 Why does it not expand upwards (like boiling water) and run over? Because the surface is frozen first ; and the frozen surface acts as a plug , which is more difficult to burst than the earthen vessel itself. 1188 Why do tiles, stones, and rocks often split in winter f Because the moisture in them freezes, and (expand- ing by frost) splits the solid mass. 1180 In winter-time, footmarks and wheel-ruts are often covered with an icy netivork, through the interstices of which the soil is clearly seen : why does the water freeze in the form of network f Because it freezes first at the sides of the footprints ; other crystals gradually shoot across, and would cover the whole surface, if the earth did not absorb the water before it had time to freeze. 110 O In winter-time, these footmarks and wheel-ruts are sometimes covered with a perfect sheet of ice, and not an icy network : why is this f Because the air is colder and the earth harder than in the former case ; in consequence of which the entire surface of the footprint is frozen over before the earth has had time to absorb the water. SCIENCE OF COMMON THINGS. 181 Water-pipes often burst in winter. Bottom of a river rarely frozen. 1191 Why is not the ice solid in these ruts ? why is there only a very thin film or network of ice ? Because the earth absorbs most of the water, and leaves only the icy film behind. 1193 Why do water-pipes frequently burst in frosty weather? Because the water in them freezes, and (expanding by frost) bursts the pipes to make room for its increased volume. 1193 Why does the earth crack in intense cold weather ? The moisture in the soil in the act of freezing ex- pands^ and forces the particles asunder. The disrup- tion of the earth is frequently accompanied with a loud sound. 1194 Does not water expand by heat as well as ly coldf Yes ; it expands as soon as it is more than 42, till it boils / after which time it flies off in steam. 1195 When does water begin to expand from cold? Yv r hen it is reduced to 40. Water is wisely ordained to be an exception to a very general rule : it contracts till it is reduced to 40, and then it expands till it freezes. The general rule is this : That cold condenses and contracts the volume of nearly everything; but .water is not contracted by cold when it freezes (which it does at 32). 1196 Why does water expand when it freezes $ The expansion of water at the moment of freezing is attributed to a new and peculiar arrangement of its particles. Ice is, in reality, crystallized water, and dur- ing its formation the particles arrange themselves in ranks and lines which cross each other at angles of 60 and 120, and consequently occupy more space than when liquid. This may be seen by examining the sur- face of water in a saucer while freezing. 1197' Why is the bottom of a river rarely frozen f Because water ascends to the surface as soon as it be- comes colder than 42, aad (if it freezes) floats there till it is melted. 1198 Show the wisdom of the Creator in this wonderful exception to a general law. 182 SCIENCE OF COMMON THINGS. Why -water freezes first at the surface. Why running water freezes slowly. If ice were heavier than water it would sink, and a river w^ould soon become a solid Hock of ice, which could never be dissolved. The general rule is, that all substances become heavier from condensa- tion ; but ice is lighter than water. 1199 Why does not the ice on the surface of a river chill the water beneath, and make it freeze f 1. Because water is a very bad conductor ', and is heated or chilled by convection only ; 2. If the ice on the surface were to communicate its coldness to the water beneath, the water beneath would communicate its heat to the, ice. and the ice would in- stantly melt / and 3. The ice on the surface acts as a shield, to prevent the cold from penetrating through the river to freeze the water below the surface. 1500 Why does water freeze at the surface first? Because the surface is in contact with the air, and the ftir carries away its heat. 1501 Why does the coat of ice grow tiiicker and thicker if the frost continues f Because the heat of the water (immediately below the frozen surface) passes through the ice into the cold air. 1SOS Why are not whole rivers frozen (layer ly layer) till they be- come solid icef Because water is so slow a conductor, that our frosts never continue long enough to convert a whole river into a solid mass of ice. 12O3 Why does not running water freeze as fast as still water f 1. Because the motion of the current disturbs the crystals, and prevents their 'forming into a continuous surface ; and 2. The heat of the under surface is communicated to the upper surface by the motion of the water. 1SO4 When running water is frozen, why is the ice generally very rough f Because little flakes of ice are first formed and carried down the stream, till they meet some obstacle to stop SCIENCE OF COMMON THINGS. 183 Sea water is rarely frozen. How the depth of water influences freezing. them ; other flakes of ice (impinging against them) are arrested in like manner ; and the edges of the different flakes overlapping each other, make the surface rough. 13O5 Why do some parts of a river freeze less tlian others ? Because springs issue from the bottom, and (as they bubble upwards) thaw the ice, or make it thin. 13O0 When persons fall into a river in winter-time, why does the water feel remarkably warm 1 Because the frosty air is at least ten or twelve de- grees colder than the water is. The water below the surface is at least 42, but the air 32, or even less. ' 1207 Why is sea water rarely frozen 1 1. Because the mass of water is so great, that it re- quires a very long time to cool the whole volume down to forty degrees ; 2. The ebb and flow of the sea interfere with the cooling influence of the air ; and 3. Salt water never freezes till the surface is cooled down to twenty-seven degrees, or five degrees below the freezing point of fresh water. 13O3 Why do some lakes rarely (if ever) freeze? f 1. Because they are very deep ; and 2. Because their water is supplied by springs which bubble from the bottom. ISO 9 How does the depth of water influence its freezing 1 It is necessary that the whole volume of water should be reduced to forty degrees before the surface will begin to freeze ; and the deeper the water, the longer it will be before the whole volume is thus reduced. 1310 Why do springs at the bottom of a lake prevent its freezing ? Because they keep continually sending forth water having a temperature above that of the mass of the water, which prevents the lake from being reduced to the necessary degree of coldness. 1311 It is more chilly in a thaw than in a frost : explain the reason of this. When froz3n water is thawed, it absorbs heat from 184 SCIENCE OF COMMON THINGS. Why it is chilly during a thaw. Cause of hoar-frost. the air, etc., to melt the ice ; in consequence of which the heat of the air is greatly reduced. 1212 To what extent can the temperature be reduced by the liquefaction of a mixture of the two solids, snow and salt ? By means of a mixture of equal weights of common salt and fresh snow (or pounded ice), a steady temper- ature of nearly 40 below the freezing point of water can be maintained for hours. 1213 How much heat is required to melt ice f The conversion of a cube of ice, three feet on the side, into water at 32, would absorb all the heat pro- duced by the combustion of a bushel of coal. 1214 Why does the frost of winter make the earth in spring loose and friable f Because the water absorbed by the earth in warm weather, expanding by the frost, thrusts the particles of earth apart from each other, and leaves a chink or crack between. 1215 Show the wisdom of the Creator in this arrangement. These cracks in the earth let in air, dew, rain, and many gases favorable to vegetation. 1216 Why are delicate trees covered with straw in winter f Because straw (being a non-conductor) prevents the sap of the tree from being frozen. 1217 What is hoarfrost f There are two sorts of hoarfrost : 1. Frozen dew ; and 2. Frozen fog. 1218 What is the cause of the ground hoarfrost, or frozen dew ? Yery rapid radiation of heat from the earth ; in consequence of which the surface is so cooled down, that \\, freezes the dew condensed upon it. 1219 Why is hoarfrost seen only after a very clear night ? Because the earth will not have thrown off heat enough by radiation io freeze the vapor condensed upon its surface, unless the night be very clear indeed. 1220 What is the cause of that hoarfrost which arises from frozen fog f SCIENCE OF COMMON THINGS. 185 Where hoar-frost does not accumulate. Frostwork on windows. The thick fog which invested the earth during the night (being condensed by the cold frost of early morn- ing) is congealed upon every object with which it comes in contact. 1221 Why is there little or no hoarfrost under shrubs and shady trees f 1. Because the leafy top arrests the process of radi- ation from the earth ; and 2. Shrubs and trees radiate heat towards the earth ; and therefore the ground beneath is rarely cold enough to congeal the little dew which rests upon it. 1SSS Why does hoarfrost very often cover the ground and trees, when the water of rivers is not frozen ? Because it is not the eifect of cold in the air, but cold on the surface of the earth (produced by excessive radiation), which freezes the dew condensed upon it. 1223 Why is the hoarfrost upon grass and vegetables much thicker than that upon lofty trees ? Because the air (resting on the surface of the ground) is much colder after sunset than the air higher up in consequence of which more vapor is condensed and frozen there. 1224 What is the cause of the pretty frostwork seen on bedroom win- dows in winter-time? The breath and insensible perspiration of the sleeper (coming in contact w T ith the ice-cold window) 2x0, frozen by the cold glass, and, crystallizing, form those beautiful appearances seen on a winter morning. 1225 Are all the figures of frostwork formed in accordance ivith certain fixed laws ? All these figures are limited ~by certain laws, and the lines which bound them form among themselves no angles but those of 30, 60, and 120. 1226 If you fracture thin ice by allowing a pole or weighi to fall upon it, will the lines of the fracture have anything of regularity ? Yes ; the fracture will generally present a star with six equidistant radii, or angles of 60. 122 7 Why is a glass or earthen vessel apt to break when hot water is poured into itf Because the inside of the glass is expanded by the 186 SCIENCE OF COMMON THINGS. Why glass breaks when placed in hot water. "Why a stove snaps. hot water, and not the outside / so tlie glass snaps in consequence of this unequal expansion. 1338 Why is not the outside of the glass expanded by the hot water as well as the inside ? Because glass is a bad conductor of heat, and breaks before the heat of the inner surface is conducted to the outside. 1339 Why does a glass snap because the inner surface is hotter than the outer ? Because the inner surface is expanded, and not the outer ; in consequence of which an opposing force is created which breaks the glass. 1330 Why does a cooper heat his hoops red hot when he puts them on a tub? 1. As iron expands by heat, the hoops will be larger when they are red hot ; in consequence of which they w T ill fit on the tub more easily ; and 2. As iron contracts by cold, the hoops w r ill shrink as they cool down, and girt the tub with a tighter grasp. 1331 Why does a wheelwright make the tire red hot which he fixes on a wheel f 1. That it may^ on more easily and 2. That it may girt the wheel more tightly. 1333 Why will the wheelwrights tire Jit the wheel more easily for beiny made red hot f Because it will be expanded by the heat, and (being larger) will go on the wheel more easily. 1333 Why will the tire which has been put on hot girt the wheel more. firmly ? Because it will shrink when it cools down, and therefore girt the wheel with a tighter grasp. 1334 Why does a stove make a crackling noise when afire is very hot? Because it expands from the heat ; and the parts of the stove rulbing against each other, or driving against the bricks, produce a crackling noise. 1335 Why does a stove make a similar crackling noise when a large fire is put out f SCIENCE OF COMMON THINGS. 187 Why clocks go faster in summer than in winter. Because the metal of the stove contracts, by reason of a reduction of temperature, when the fire is extin- guished. 1336 Why are the nails in almost all old houses loose and easily drawn out ? Because the iron expands in the summer, and con- tracts in the winter, more than the stone or wood, and thus the opening is gradually enlarged after a lapse of time. 133*7 Why does a piano give a higher tone in a cold than in a warm room f Because in a cold room the strings are contracted and tighter. 1333 Why do clocks go slower in summer and faster in winter? Because the pendulums elongate in summer through the effects of heat, and consequently vibrate slower ; while in winter they contract, become shorter, and vibrate more rapidly. 1339 Hoiu is this inequality in the rate of motion in timepieces obviated f By what is called a compensating pendulum / that is, one constructed of two metals, possessing different expansive powers, in such a manner that the greater expansion of one bar in one direction equals the less expansion of other bars in a different direction, and thus maintain an invariable length of the pendulum. 1340 Does wood expand under the influence of heat differently from metal ? Yes ; an iron bar expands and contracts equally in all directions, but wood expands and contracts more in breadth than in length. 134:1 Why will a person, buying oil, molasses, spirits, etc., by the mea- sure, get a greater weight of the same material in the same measure in the winter tiian in the summer ? Because these liquids contract and occupy less space in the winter than in summer ; consequently it requires more of the same kind to fill the same space in winter than in summer. 1343 How can heat be measured f Only by its effects : since the magnitude of any body 188 SCIENCE OF COMMON THING?. What is temperature ? Thermometers and pyrometers. changes with the heat to which it is exposed ; and since, when subject to the same calorific influences, it always has the same magnitude, these dilatations and contrac- tions, which are the constant effects of heat, may be taken as the measure of the physical cause that pro- duced them. 1343 What is the temperature of a body ? It is the actual state of a body at any moment, deter- mined by a comparison of its magnitude with the heat to which it is exposed. 1344 What is a change of temperature f The change in magnitude which a body suffers by changes in the heat to which it is exposed. 1345 What are the instruments for measuring lieat called? Thermometers and pyrometers. 1346 What is the difference between them f A thermometer is used for measuring moderate tem- peratures ; w r hile the pyrometer is chiefly applied to de- termine the more elevated degrees of heat. 1347* What substances are best adapted for measuring the effects of heat by their expansion and contraction f Liquids, above all other substances. 1348 Why are liquids best adapted for this purpose f Because in solids the direct expansion by heat is so small as to be seen or measured with difficulty ; in air or gases it is too extensive and too liable to be affected by atmospheric pressure ; but liquids are free from both disadvantages. 1349 What liquid is generally used for the construction of ordinary thermometers f Mercury or quicksilver. 035 O What metal is distinguished from aU others by its fluidity at ordinary temperatures f Mercury or quicksilver. 1351 Does mercury, like other metals, expand by heatf It readily expands or contracts with every variation of temperature. SCIENCE OF COMMON THINGS. 189 Use of mercury in thermometers. How thermometers are constructed. 1353 Why is mercury preferable to all other liquids for the purposes of the thermometer f Because it 'boils at a higher temperature than, any other liquid, except certain oils ; and, on the other hand, it freezes at a lower temperature than all other liquids, except some of the most volatile, such as ether and alcohoL Thus, a mercurial thermometer will have a wider range than any other liquid thermometer. It is also attended with this convenience, that the extant of temperature included between melting ice and boiling water- stands at a considerable distance from the limits of its range, or its freezing and boiling points. 1253 Of what does the mercurial thermometer consist f The mercurial thermometer consists essentially of a glass tube with a bulb at one extremity, and which, having been filled with mercury at a certain tempera- ture, introduced through the open end, has been her- metically sealed while full, so that no air can after- wards enter it. As the tube and mercury in it gradually become cooled, the inclosed fluid contracts, and consequently sinks, leaving above it a vacant space or vacuum, through which it may again expand on the application of heat. 1354 As thermometers are constructed of different dimensions and capacities, how are they graduated to indicate the same temperature under the same circumstances, as the freezing point, for example? The thermometers are first immersed in melting snow or ice. The mercury will be observed to stop in each thermometer-tube at a certain height ; these heights are then marked upon the tubes. Now it has been ascertained that at whatever time and place the instru- ments may be afterwards immersed in melting snow or ice, the mercury contained in them will always fix itself at the point thus marked. This point is called the freezing point of water. 1355 How is the boiling point ascertained ? It has been found that at whatever time or place the instruments are immersed in pure water, when boiling, provided the barometer stands at the height of thirty inches, the mercury will always rise in each to a certain 9 190 SCIENCE OF COMMON THINGS. Determination of the boiling and freezing points. height. This, therefore, forms another fixed point on the geometric scale, and is called the boiling voint. 1356 How are the intermediate points determined ? In Fahrenheit's thermometer, the intervals on the scale, between the freezing and boiling points, are divided into 180 equal parts. This division is similarly continued below the freezing point to the place 0, and each division upwards from that is marked with the suc- cessive number 1, 2, 3, etc. The freezing point will now be the 32d division, and the boiling point will be the 212th division. These divisions are called degrees, and the boiling point will therefore be 212, and the freezing temperature, 32. 1557 When and by wham was the thermometer invented ? The thermometer was invented about the year 1600; but, like many other inventions, the merit of its dis- covery is not to be ascribed to one person, but to be distributed among many. 1558 Why is the thermometer in general use in the United States, England, and Holland, called Fahrenheit's thermometer '? Because thermometers having a like graduation were first manufactured by Fahrenheit, a Dutch philoso- phical instrument-maker. The employment of mercury as the most suitable fluid for the thermometer is also usually attributed to him. IS 5 9 How many kinds of tliermorneters are in general use ? Three : Fahrenheit's, Reau- mur's, and the Centigrade ther- mometer, or thermometer of Celsius. 126O What constitutes the di/erence letween these instruments f The differences of graduation between the freezing and boiling points of water. Reaumur is divided into eighty degrees, the Centigrade into one hundred, Fig 4L and Fahrenheit's into one hun* SCIENCE OF COMMON THINGS. 191 Different varieties of thermometers. Construction of pyrometers. dred and eighty. According to Reaumur, water freezes at 0, and boils at 80 ; according to Centigrade, it freezes at 0, and boils at 100 ; and according to Fah- renheit, it freezes at 32, and boils at 212; the last, very singularly, commences counting not at the freezing point, but 32 below it. The differences between these instruments can be easily seen by refer- ence to Fig. 41. 1261 In what countries are the Reaumur and Centigrade thermometers generally used ? fieaumur is in general use in Germany, and the Centigrade in France / but for scientific purposes the Centigrade is almost universally adopted. 12362 At what temperature does mercury freeze ? At about 39 below the zero of Fahrenheit's thermo- meter. 1263 How are degrees of cold more intense than this measured f By using a thermometer filled with alcohol colored red, as this fluid when pure does not congeal at 100 Fahrenheit below zero. 1264 At what temperature does mercury boil f At 660 Fahrenheit. 1265 How are temperatures greater than this determined f By means of the expansion of solids and instru- ments founded upon this principle are commonly called pyrometers. Fig. 42. Ihe construction of the pyrometer is represented in Fig. 42. A repre- 192 SCIENCE OF COMMON THINGS. What is liquefaction 1 Why ice is melted by heat. senta a metallic bar, fixed at one end, B, but left free at the other, and in contact with the end of a pointer, K, moving freely over a graduated scale. If the bar be heated by the flame of alcohol, the metal expands, and pressing upon the end of the pointer moves it, in a greater or less degree. 13 GQ On what principle have pyrometers generally been constructed f On the relative expansion of bars of iron, or some other metal. 12Q7 Does a thermometer inform us how much heat any body con- tains ? No ; it merely points out a difference in the tem- perature of two or more substances. All we learn by the thermometer is whether the temperature of one body is greater or less than that of another ; and if there is a difference it is expressed numerically namely, by the degrees of the thermometer. It must be remembered that these degrees are parts of an arbitrary scale, selected for convenience, without any reference whatever to the actual quantity of heat present in bodies. 1368 After the expansion of solids, when acted upon by heat, what other effect is next observed ? They change their original state, become liquid, or melt. Many of them become soft before melting, so that they may be kneaded ; for instance, wax, glass, and iron ; in this condition, glass can be bent and moulded like wax, and iron can be forged or welded. 13 B9 What is meant by liquefaction ? The conversion of a solid into a liquid by the agency of heat, as solid ice is converted into water by the heat of the sun. 137O Why is ice melted by the heat of the sun f Because, when the heat of the sun enters the solid ice, it forces its particles asunder, till their attraction of cohesion is sufficiently overcome to convert the solid ice into a liquid. 13*71 Why are metals melted by the heat of fire f Because, when the heat of the fire enters the solid metal, it forces its particles asunder, till their attraction of cohesion is sufficiently overcome to convert the solid metal into a liquid. SCIENCE OF COMMON THINGS. 193 What is a solution ? Why water dissolves sugar. IS 7*3 When salt is mixed with water and disappears in the liquid, what is said to have taken place ? The salt is said to have dissolved in the water, and .the liquid is now a solution of salt. IS 73 What, then, w a solution f A solution is the result of an attraction or affinity between a solid and a fluid ; and when a solid disap- pears in a liquid, if the compound exhibits perfect transparency, we have an example of a perfect solution. 1374 When is a solution said to be saturated f When the fluid has dissolved as much of the solid as it is capable of doing, it is said to be saturated ; or, in other words, the affinity or attraction of the fluid for the solid continues to operate to a certain point, where it is overbalanced by the cohesion of the solid ; it then ceases, and the fluid, is said to be saturated. 1S75 What is the difference between a solution and a mixture f A solution is a chemical union / a mixture is a mere mechanical union of bodies. IS 70 Why will water dissolve sugar f Because there is attraction or affinity between the particles of the water and the particles of the sugar. 1S77 What do we mean by affinity f Affinity is that kind of attraction in virtue of which bodies of a dissimilar character combine together into a whole, which appears perfectly uniform to the senses, even when assisted by powerful magnifying instruments. 1S7S Why will not water dissolve granite or metallic iron f Because there is not sufficient affinity or attraction between the particles of the water and those of the iron or granite. 1379 Are there any liquids that have sufficient affinity to dissolve iron and granite ? Yes ; certain acids have so great an affinity for the iron and granite that they are enabled to dissolve them. 1S8O Why will not water dissolve oil? Because there is no affinity or attraction between the particles of the two substances. 194: SCIENCE OF COMMON THINGS. Vaporization. Why heat converts water into eteam. IS 81 Why will alcohol and ether dissolve oil f Because the attraction or affinity between the alco- hol or ether and the oil is sufficient to enable them to effect a solution. 1S8S What effect has heat upon the dissolving power of liquids! In most cases the addition of heat to a liquid greatly increases its solvent properties. Hot water will dissolve much more sugar than cold water, and hot water will also dissolve many things which cold water is unable to affect. 1583 Why does not wood melt like metal ? Because the heat of the fire decomposes the wood into gas, smoke, and ashes, and the different parts separate from each other. 1584 What is meant by vaporization? The conversion of a solid or liquid into vapor / as snow or water is converted into vapor by the heat of the sun. IS 85 Why is water converted into steam by the heat of the fire f Because, when the heat of the fire enters the water, it separates its substance into very minute particles, which (being lighter than air) fly off from the surface in the form of steam. 1S86 Why do doors swell in rainy weather ? Because the air is filled with vapor, w r hich (pene- trating into the pores of the wood) forces its particles farther apart, and swells the door. 1SS7 Why do doors shrink in dry weather? Because the moisture is absorbed from the wood, and, as the particles are brought closer together, the size of the door is lessened / in other words, the wood shrinks. 1SSS Why does a drop of water sometimes roll along a piece of hot iron without leaving the least trace f Because the bottom of the drop is changed into vapor, which buoys the drop up, without allowing it to touch the iron. 1SS9 Whydoesitrott? SCIENCE OF COMMON THINGS. 195 Volatile substances. What is distillation ? Because the current of air (which is always passing over a heated surface) drives it along. 1290 Why does a laundress put a little saliva on aflat-iron to know if it be hot enough ? Because when the saliva sticks to the iron and is evaporated, she knows it is not sufficiently hot ; but when it runs along the iron, it is. 1291 Why is the flat-iron hotter if the saliva runs along it, than if it adheres till it is evaporated? Because when the saliva runs along the iron, the heat is sufficient to convert the bottom q the drop into vapor but if the saliva will not roll, the iron is not sufficiently hot to convert the bottom of the drop into vapor. 1292 To what substances do we apply the term " volatile ?" To those which have a great tendency to assume the gaseous form. 1293 To what substances do we apply the term "fixed," or "non-vola- tile?" To those in which the tendency to assume the gaseous" form is small. 1294 Do vapors occupy much more space tlian the substances from which they were produced f They occupy a much greater space ; water, in passing from its point of greatest density into vapor, expands to sixteen hundred and ninety-six times its volume. 1295 Under what two heads does the subject of vaporization divide itself? Into ebullition and evaporation 1296 What is distillation? A process by which one body is separated from an- other by means of heat, in cases where one of the bodies assumes the form of vapor at a lower temperature than the other ; this first rises in the form of vapor, which is received and condensed in a separate vessel. 1297* How is the process of simple distillation effected ? A peculiar-shaped vessel called a retort (Fig. 43) is half filled with a volatile liquid and heated ; the steam, as it forms, passes through the neck of the retort into a 196 SCIENCE OF COMMON THINGS. "Why distilled water Is Tery pure. Construction of a still. glass receiver contained in a vessel filled with cold water y and is then condensed. Fig. 43. 1298 Why is water obtained in this manner by distillation purer than spring water f Because the non-volatile, earthy, and saline portions contained in all spring waters do not ascend with the vapor, but remain in the retort. By this means very volatile bodies can be easily separated from less volatile ones ; as brandy and alcohol from the less volatile water which may be mixed with them. 1J390 When the vessel used for generating the vapor is very large, what is it called f A "still ;" and, for con- densing the vapor, vats are constructed, holding ser- pentine pipes or " worms" which present a greater condensing surface than if the pipe had passed di- rectly through the vat. To keep the coil of pipe cool, the vats are kept filled with cold water. Fig (See Fig. 44.) In this figure a is a furnace, in which is fixed a copper vessel to contain the fluid. Heat being applied, the steam rises in the head 6, and passes through the worm d, which is placed in a vessel of water, the refrigerator. The vapor thus generated is condensed in its passage, and passes out as a liquid by the external pipe into a receiver. 13OO What is the difference between drying by heat and distil'tmg f SCIENCE OP COMMON THINGS. 197 What is evaporation ? Danger of wearing wet clothes. In the one case, the substance vaporized, being of no use, is allowed to escape or become dissipated in the atmosphere ; while in the other, being the valuable part, it is caught and condensed into the liquid form. 13O1 What is the vapor from damp linen ? The vapor from damp linen, if caught, would be dis- tilled water. 13OS What is evaporation 1 The conversion of a fluid into vapor. "When vaporization takes place only from the surface of a body, either because the heat has access to that part, or because the evolution of vapor takes place through the medium of a gas or air already present, the action can only be recognised by the diminution of the bulk of the body : this phenomenon is called evaporation. 1303 What effects are produced by evaporation f The substance vaporized absorbs heat from the body whence it issues ; and the body, deprived of a portion of its substance by evaporation, loses heat. 1304 If you wet your finger in your mouth, and hold it up in the air, why does it feel cold ? Because the saliva quickly evaporates, and (as it evaporates) absorbs heat from the finger, making it feel cold. 1305 If you lathe your temples ivith ether, cologne water, spirits, etc., why does it allay inflammation and feverish heat? Because these liquids very rapidly evaporate, and (as they evaporate) absorb heat from the burning head, producing a sensation of cold. 1306 Why do we feel cold when we have wet feet or clothes f Because the wet of our shoes or clothes rapidly eva- porates, and (as it evaporates) absorbs -heat from our body, which makes us feel cold. ISO? Why do wet feet or clothes give us " cold?" Because the evaporation absorbs heat so abundantly from the surface of our body, that its temperature is lowered below its natural standard ; in consequence of which health is injured. 13O8 Why is it dangerous to skep in a damp bed? Because the heat is continually absorbed from the 9* 198 SCIENCE OF COMMON THINGS. Health injured by reducing the temperature of the body. surface of our body to convert the damp of the sheets into vapor ; in consequence of which our animal heat is reduced 'below the healthy standard. 1309 Why is health injured when the temperature of the body is reduced below its natural standard f Because the balance of the circulation is destroyed. Blood is driven away from the external surface by the chill, and thrown upon the internal organs, which are oppressed by this increase of Hood. 1310 Why do we not feel the same sensation of cold if we throw a waterproof coat over our wet clothes f Because water-proof coats (being air-tight) prevent evaporation, and (as the wet cannot evaporate) no heat is absorbed from our bodies. 1311 Why does sprinkling a hot room with water cool it f Because the heat of the room causes a rapid evapora- tion of the sprinkled water, and as the water evaporates, it absorbs heat from the room, which cools it. 131J3 Why does watering the streets and roads cool them f Because they part with their heat to promote the eva- poration of the water spi^inkled on them. 1313 Why does a shower of rain cool the air in summer-time ? Because the wet earth parts with its heat to promote evaporation y and when the earth is cooled, it cools the air also. 1314 Why is linen dried by being exposed to the wind f Because the wind accelerates evaporation by removing the vapor from the surface of the wet linen as fast as it is formed. 1315 Why does draining land promote warmth, Because abstracting water diminishes evaporation ; in consequence of which less heat is withdrawn from the earth. 1310 Why does cultivation increase'the warmth of a country f A cultivated country is better drained, and laid open to the rays of the sun. The forests being cut down, the snow quickly disappears in the spring, and the earth soon becomes dry. SCIENCE OF COMMON THINGS. 199 Air cool after a rain. Production and nature of steam. 131V Why does bread after the lapse of a few days become dry and stale f Because the moisture contained in it evaporates ; the particles then shrink, and the whole mass becomes hard. 1318 Why is not the vapor of the sea salt f Because the salt is always left behind in the process of evaporation. 131O " AH the rivers run into the sea :" why is not the sea full f Because the quantity of water evaporated from the surface of the sea is equal to the quantity poured into it by the rivers ; therefore the sea is never full. 13J3O Why is it frequently cooler after a rain f Because water which falls from the atmosphere soon returns to it in the form of vapor, carrying with it, in the latent form, a large amount of heat taken from every object, thus moderating the temperature of the earth, and refreshing the animal and vegetable creations. 1331 Does evaporation take place from the surface of snow and ice f Yes, to a very considerable extent, even when the temperature of the air is below the freezing point. 13SS What is steam? The vapor of boiling water. 1323 Is steam visible or invisible f Steam is invisible; but when it comes in contact with the air (being condensed into small drops) it in- stantly becomes visible. 13S4 How do you know that steam is invisible f If you look at the spout of a boiling, kettle, you will find that the steam (which issues from the spout) is always invisible for about half an inch, after which it becomes visible. 1325 Why is the steam invisible for half an inch t Because the air is not able to condense it, as it first issues from the spout ; but when it spreads and comes in contact with a larger volume of air, the invisible steam is readily condensed into visible drops* 200 SCIENCE OF COMMON THINGS. Vapor of water always exists in air. White appearance of steam. 1336 Does air ever exist without steam or vapor of water ? Air without steam (theoretically called dry air) is not ~known to exist in nature, and is probably not pro- ducible by art. 1337* Is the visible matter, popularly called steam, really true steam ? By no means, and should be carefully distinguished from steam proper, or the aeriform state of water. The cloud or smoke-like matter alluded to is really not an air or vapor at all, but a dust-like cloud of minute bodies of liquid water, wafted by a current either of true steam, or, more frequently, of mere moist air. 1338 Is it necessary to the production of steam that water should be raised to the boiling temperature f It is not / the surface of any watery liquid, about 20 warmer than any superincumbent air (however warm or cold that may be), rapidly gives off true steam, which is invisible, but which no sooner mixes with colder air than it is recondensed into water, and assumes the forms of minute globules. 1339 What causes the visible white appearance of condensed steam f The myriads of minute globules of water into which the steam is condensed are separately invisible to the naked eye, but each, nevertheless, reflects a minute ray of white light. The multitudes of these reflecting points, therefore, make the space through which they are diffused appear like a cloudy body, more or less white, according to their abundance. 1330 In what manner is the production of steam in boiling water first manifested ? , When steam begins to be produced, as in the process of making water boil, and the heat overcomes the atmospheric pressure on the surface, small bubbles are formed, adhering slightly to the sides of the vessel. 1331 In what parts of the boiler will its development be most conspicu- ous? The bubbles are formed most rapidly at those points against which the flame is most strongly directed. 1333 How much lighter is steam than water f SCIENCE OF COMMON THINGS. Different spaces occupied by steam and water. Pressure of steam. About 1700 times ; because a quantity of water yields nearly 1700 measures of steam at 212 F. Fig. 45 represents the comparative volume of water and of steam. 1333 How much steam will a cubic inch of water furnish 1 A cubic inch of water ex- pands into about a cubic foot of steam at 212 F., under the ordinary atmospheric pres- sure. 1334 Upon what does the power of .. steam depend f On the tendency which water possesses to expand into vapor when heated to a certain temperature. 1335 What is the most important property of steam ? Its elasticity or pressure. By virtue of this property, when freed from the limits which confine it, steam will dilate into any space to which it may have access. 133S Jf a quantity of pure steam be confined in a close vessel, in what manner will its pressure be exerted ? It will exert on every part of the interior of the vessel a certain pressure directed outwards, and having a ten- dency to burst the vessel. 1337* How great a pressure does steam, formed under ordinary cir- cumstances, have to overcome before it can rise from the surface of the water ? That of one atmosphere -fifteen pounds on eveiy square inch, or one ton on every square foot a force equivalent to the strength of six hundred horses. 1338 What happens when the temperature of 'steam generated under ordinary pressures is reduced below 212 f 1 . f It is immediately condensed into water. 1339 As steam sustains and elevates a weight occasioned by the pressure of the atmosphere, of fifteen pounds per square inch, what takes place when a column of steam is immediately condensed ? The atmospheric weight will immediately fall w r ith a force equal to that with which it was raised. 1340 How can steam be used to advantage for cooking vegetables, etc. f 202 SCIENCE OF COMMON THINGS. "What is high-pressure steam ? What is a steam-engine ? In cookery, if steam raised from boiling water be allowed to pass through meat and vegetables, it will be condensed upon their surfaces, imparting to them the latent heat which it contained before its condensation, thus cooking them as effectually as if they were im- mersed in boiling water. 1341 What do we mean when we speak of high-pressure steam f High-pressure steam is merely steam condensed, not by withdrawal of heat, but by pressure, just as high- pressure air is merely condensed air. To obtain a double, triple, or greater pressure of steam, we must have twice, thrice, or more steam under the same vo- lume. 1343 Is high-pressure steam, escaping from a boikr heated to 300 or more, hotter than low-pressure steam escaping from a boiler at 212 ? No ; for the instant that high-pressure or condensed steam escapes into the air, it immediately expands and becomes low-pressure steam, and is greatly cooled down by its expansion. 1343 Does high-pressure steam, acting in a boiler at a high tempera- ture, exert a greater mechanical and chemical power than low-pressure steam f It does f high-pressure steam acting upon bones, breaks up and dissolves the whole mass, extracting all the glue and fat, when ordinary steam would dissolve nothing. In the Western States, where large quantities of lard are manufactured, the whole hog is exposed to high-pressure steam, and the carcass reduced in a short tune to a fat fluid mass. 1344 Can high-pressure steam be raised to a very elevated degree of heat? It can / in some of the methods lately introduced for purifying oils, etc., the temperature of the steam, before its application, is required to be sufficiently elevated to enable it to melt lead. 1345 What is the steam-engine f The steam-engine is a mechanical contrivance by which coal, wood, or other fuel is rendered capable of executing any kind of labor. SCIENCE OF COMMON THINGS. 203 Mechanical force of steam. Comparison of steam power and animal power. 1346 What substance furnishes the means of calling the powers of coal into activity ? Water. 1347* How much water will two ounces of coal evaporate t About a pint. 1348 How much steam will this produce f Two hundred and sixteen gallons. 1340 How much mechanical force can this steam exert t It can raise a weight of thirty-seven tons to the height of one foot. 1350 What amount of force can a man exert when applying his strength to the best advantage through the help of machinery f It has been found by experiment, that a man work- ing on a tread-mill continuously for eight hours, will elevate one and a half millions of pounds to the height of one foot. 1351 With how much coal will a well constructed steam-engine perform the same labor ? With the expenditure of a pound and a half. 1352 How much coal then would be equivalent to the average power of an able-bodied man during his active life, supposing him to work for twenty years at Hie rate of eight hours per day ? The consumption of about four tons of coal would evolve in a steam-engine fully as much power. 1353 The great pyramid of Egypt is five hundred feet high, and weighs twelve thousand seven hundred and sixty millions of pounds. Herodotus states that in constructing it one hundred thousand men were constantly employed for twenty years. With how much coal could all the materials of this pyramid be raised to their present position from the ground ? With the expenditure of four hundred and eighty tons of coal. 204: SCIENCE OF COMMON THINGS. What Is ventilation ? Warming and ventilation of buildings. PART VI. .VENTILATION AND WARMING, COMBUSTION, RESPIRATION, AND NUTRITION. CHAPTEK I. WARMING AND VENTILATION. 1354 What is ventilation f Ventilation is the act or operation of causing air to pass through any place, for the purpose of expelling impure air and dissipating noxious vapors. 1355 What is the theoretical perfection of ventilation ? To render it impossible for any portion of air to be breathed twice in the same building. 1356 Upon what principle does the whole process of warming and ven- tilating buildings depend ? Upon the expansion and contraction of air, or, in other words, upon the fact that air which has been heated and expanded ascends, and air w r hich has been deprived of heat, or has become contracted, descends. 1357 f Is there an upward current of air always rising from heated substances f There is ; air made lighter by heat ascends through colder strata, as a cork (put at the bottom of a basin of water) rises to the surface. 135S What simple experiment shows the exist* ence of this upward current in an ordinary stove f If we attach to the side of a heated stovepipe a wire on which a piece of paper cut in the form of a spiral may SCIENCE OF COMMON THINGS. 205 Why a fire balloon rises. Where ventilation is perfect. Oxygen. be suspended, as is represented in Fig. 46, the upward current of hot air will immediately put the paper in motion, and make it revolve rapidly around the wire. 1359 When a boy makes a fire-battoon, and sets fire to the cotton or sponge (which has been steeped in spirits of wine), why is the balloon inflated f Because the air of the balloon is expanded by the heat of the flame, and fills the balloon to its utmost capacity. 1360 Why does the balloon rise after it has been inflated by the expanded air? Because the same quantity of air is expanded to three or four times its orig^nal volume ; and made so much lighter, that even when all the paper, wire, and cotton are added, it is still lighter than common air. 1361 In what situation is ventilation perfect ? In the open air, because the breath, as it leaves the body, is warmer and lighter than the surrounding fresh air, and ascending is immediately replaced by an in- gress of fresh air ready to be received by the next respiration. 1363 Why is it desirable to avoid breathing the same air twice ? Air which has been once respired, is unwholesome, and not suited to supply the wants of the animal system. 1363 What are the elements of atmospheric air? Oxygen and nitrogen mixed together, in the propor- tion of seventy-nine parts of nitrogen and twenty-one of oxygen. 1364 What is oxygen f A gas, colorless, tasteless, and odorless ; it is heavier than atmospheric air, and is a non-conductor of elec- tricity. 1365 Is oxygen a substance existing in great abundance ? Oxygen is the most abundant of all known substances ; it constitutes at least one third of the solid mass of the globe, eight-ninths of all water, and nearly one-fourth part of the atmosphere ; it also exists in most organic substances. 1366 Is oxygen ever found in a liquid or solid state f 206 SCIENCE OF COMMON THINGS. Use of oxygen in the air. Nitrogen, its properties and uss. ~No ; when pure it is only known in the gaseous state ; all efforts to reduce it to a liquid or solid condition by cold or pressure have completely failed. 1367 Of what use is oxygen in the atmosphere ? It sustains animal life and supports combustion. 1368 If an animal were immersed in oxygen gas, would it continue to live for a time? It would ; at the same time animal life could not be sustained for any great length of time in an atmosphere of pure oxygen. 1369 What is meant when it is said that oxygen " sustains life f " It means this : if a person could not inhale oxygen, he would die. 1370 What good does this inspiration of oxygen do f 1. It gives vitality to the blood ; and 2. It is the cause of animal heat. 1371 What is nitrogen f An invisible gas existing largely in atmospheric air, and in most animal and vegetable substances. 1372 What are its principal characteristics f 1. It is not combustible / 2. It does not support animal life ; and 3. It is the principal ingredient in the composition of atmospheric air. 1373 What proportion of the air we breathe is composed of nitrogen f About four -fifths of the air is nitrogen / the other one-fifth is oxygen. 1374 Why is there so much nitrogen in the air f The uses of nitrogen are in a great measure unknown. It has been supposed to act as a diluent to the oxygen, but it most probably serves some useful purpose in the economy of animals and vegetables, the exact nature of which has not been discovered. 1375 What would be the effect if the proportion of oxygen in the atmo- sphere were increased f The inflammability of most substances would be in- creased, fires would burn out very quickly, and the SCIENCE OF COMMON THINGS. 207 Carbonic acM gas. The composition of the air never varies. functions of life would be called into such rapid action as to soon exhaust the powers of the system. 1370 Are the two gases, oxygen and nitrogen, existing in tlie atmo- sphere, chemically combined, or merely intermingled ? They are merely mixed, and not combined with each other. 1377' Does thv atmosphere always contain any other ingredients besides oxygen and nitrogen f There is always in the air, at all places, carbonic acid gas, in variable proportions, and watery vapor, besides the odoriferous matter of flowers and other volatile substances. 1378 What is carbonic acid gas f A gas formed by the union of carbon and oxygen ; it used to be called fixed air. Its chemical com- position is one atom of carbon united to two of oxygen. 1379 Is the air collected on the tops of high mountains, over marshes in hospitals, and over deserts, the same in character and composition f It is not found to vary, but is the same in all regions of the earth and at all altitudes. 1380 Are the component parts of air, oxygen, nitrogen, carbonic acid, and watery vapors, of different specific gravities, or do they all differ in weight ? They are all different, carbonic acid gas being the heaviest. 1381 Then, as we have before stated that they are merely mixed, and not combined, why do they not arrange themselves in the order of their densi- ties, and float one upon the other, as oil and water do when mingled f Because of a wonderful principle or law of nature, that when two gases of different weights or specific gravities are mixed together, they cannot remain sepa- rate, as fluids of different densities do, but diffuse them- selves uniformly throughout the whole space which both occupy. 1383 Carbonic acid is tiventy times heavier than hydrogen gas ; if we fill the lower part of a tatt jar with carbonic acid, and the upper part with kydrogen, will the two gases mix ? After a few hours the two gases will be found equally 208 SCIENCE OF COMMON THINGS. Carbonic acid gas in the atmosphere. mingled, as much carbonic acid being at the top of the jar as at the bottom. 13 S3 Does this law appear to be opposed to the principles of the law of gravitation ? It appears to be opposed to it ; the only exception we are acquainted with in the natural world. 1384 How much carbonic acid is estimated to exist in the atmosphere f I About one part in two thousand, by volume. 1335 If this were all collected in one layer over the surface of the earth, how great a thickness would this layer or stratum have ? About thirteen feet. 138Q Can we breathe carbonic acid? No the animal immersed in it dies instantly. 1387* If, then, this singular law of the diffusion of gases did not prevail, would the surface of the earth be habitable ? It would not; carbonic gas would fill up all the valleys and lower levels, separating every hill and ele- vation by an invisible ocean of poisonous gas, as im- passable as the barrier between the dead and the living. 1388 Is it owing to this law that we are enabled to enjoy and perceive at a distance the odor of a flower-garden, or the perfume which has been opened in an apartment f It is by this law that a vapor, arising by its own elasticity from a volatile substance, is caused to extend its influence and mingle with the surrounding atmo- sphere, until its effects become so enfeebled by dilution as to be imperceptible to the senses. 138Q If the oxygen and nitrogen of which our atmosphere is composed were combined together, instead of being merely mingled, what would the compound be ? A most deadly poison. 1390 What gas is generated by a lighted candle or lamp ? Carbonic acid gas formed by the union of the carbon of the oil or tallow with the oxygen of the air. 1391 Under what circumstances does carbon most readily unite with oxygen ? 1. When its temperature is raised : thus, if carbon be red hot, oxygen will most readily unite with it ; SCIENCE OF COMMON THINGS. 209 Carbonic acid a poison. Crowded room unhealthy. 2. Carbon in. the Hood unites readily -with oxygen during respiration ; and 3. Carbonic acid is formed in large quantities during the chemical changes which we call fermentation. 1302 Js carbonic acid in any degree wholesome f No / it is fatal to animal life, and (whenever it is inhaled) acts like a narcotic* poison, producing drowsi- ness, which sometimes ends in death. 1303 When persons commit suicide by building a charcoal fire in a closed room, what occasions their death ? The inhalation of carbonic acid, which is generated by the combustion of the charcoal. 1304 How can any one know if a place be infested with carbonic acid gasf If a pit or well contain carbonic acid, a lighted candle (let down into it) will be instantly extinguished. The rule, therefore, is this : where a candle will burn, a man can live / but what will extinguish a candle, will also destroy life. 1305 Why does a crowded room produce headache? Because we breathe air vitiated by the crowd. 1306 Why is the air of a room vitiated by a crowd ? Because it is deprived of its due proportion of oxy- gen, and loaded with carbonic acid. 1307* How is the air of a room affected thus by a crowd ? The elements of the air inhaled are separated in the lungs ; the oxygen, incorporated in the blood, forms carbonic acid ; and the carbonic acid (together with the nitrogen) is thrown back again by the breath into the room, 1308 Is all the nitrogen rejected by the lungs f Yes ; all the nitrogen of the air is always expired. 1300 How much oxygen does afull-groivn person consume per hourf It is calculated that an adult of average size absorbs * A narcotic is a substance which, when used as a medicine, relieves pain and produces sleep, but in poisonous doses produces death. Opium, laudanum, tobacco, etc,, are narcotics. 210 SCIENCE OF COMMON THINGS Air consumed by a person in an heur. Vegetation purifies the air. about a cubic foot of oxygen per hour by respiration, and consequently renders five cubic feet of air unfit for breathing, since every five cubic feet of air contain one cubic foot of oxygen. It is also calculated that two wax or sperm candles absorb as much oxygen as an adult. 1400 To keep tJie air of a room pure, how much fresh air should be allowed to pass in per hour f Five cubic feet for each person, and two and a half cubic feet for each candle, should be allowed to pass in, and an equal quantity to pass out. 1401 Why do persons in a crowded church feel drowsy f 1. Because the crowded congregation inhale a large portion of the oxygen of the air, which alone can sus- tain vitality and healthy action ; and 2. The air of the church is impregnated with carbonic acid gas, which (being a strong narcotic) produces drowsiness in those who inhale it. 14OS Why do persons who are much in the open air enjoy the best health f Because the air they inhale is much more pure than the air of close and confined rooms. 1403 How does vegetation (trees and flowers] serve to purify the airf 1. Because trees and flowers absorb the carbonic acid generated by the lungs of animals, putrid sub- stances, and other obnoxious exhalations ; and 2. Trees and flowers restore to the air the oxygen which man and other animals inhale. 1404 Why is the air of cities generally less pure than the air of the open country f 1. Because there are more inhabitants to vitiate the air; 2. The sewers, drains, bins, and filth of a city very greatly vitiate the air ; 3. The streets and alleys prevent a free circulation ; and 4. There are fewer trees to absorb the excess of car- bonic acid gas, and restore the equilibrium. SCIENCE OF COMMON THINGS. 211 * ,. Close rooms unhealthy. Carbon thrown off by the lungs. 1405 Why are persons who live in close rooms and crowded' cities generally sickly f Because the air they breathe is not pure, but is (in the first place) defective in oxygen, and (in the second) is impregnated with carbonic acid gas. 1406 Where does the carbonic acid of close rooms and cities com* from ? From the lungs of the inhabitants, the sewers, drains, and other like places, in which organic substances are undergoing decomposition. 1407 What becomes of the carbonic acid generated in crowded cities f It is gradually diffused through the air, absorbed by vegetation and by water, and wafted by the winds to different localities. 1408 Does not this constant diffusion of carbonic acid affect the purity of the whole air 1 No ; because it is wafted by the wind from place to place, and absorbed in its passage by the vegetable world. 1409 What is choke damp ? Carbonic acid gas accumulated at the bottom of wells and pits, which renders them noxious, and often fatal to life. It is called choke damp, because it chokes (or suf- focates) every animal that attempts to inhale it. It suffocates without getting into the lungs, by closing the glottis spas' modicatty. 1410 Why is not this carbonic acid taken up by the air and diffused, as it is in tities f Because (being heavier than common air) it cannot readily rise from the well or pit ; and no wind can get to it to blow it away. By the chemical law of diffusion, a portion of the carbonic acid which accumulates at the bottom of wells and pits, is removed ; but in many cases this abstraction is more than counterbalanced by an increased supply. 1411 How much carbon in the form of carbonic acid passes through the lungs of a healthy person every twenty-four hours f The quantity would be very accurately represented by a mass of charcoal of the weight of fifteen ounces. The volume of carbon in the atmosphere, although it forms but one per cent, of the carbonic acid existing in it, exceeds in amount all the carbon 212 SCIENCE OF COMMON THINGS. Sources of carbonic acid. The air always in motion. that is stored in the earth in the form of coal, or spread over its surface in the form of animals or vegetables. 141S What are the chief sources of carbonic acid ? Combustion, respiration of men and animals, the decomposition of organic substances, and the exhalations of volcanoes. Carbonic acid also exists in large quan- tities in the atmosphere, in most waters, and combined with minerals in a solid state, as in marble, which con- sists of lime united to carbonic acid. 1413 From which of these sources is carbonic acid most likely to accu- mulate to a noxious extent f From the fermentation arid putrefaction of decaying vegetable and animal matters. 1414 How can this accumulation of carbonic acid be prevented? By throwing quicklime into places where such fer- mentation ana putrefaction are going on. 1415 How will quicklime prevent the accumulation of carbonic acid? Quicklime will absorb the carbonic acid, and produce a combination called " carbonate of lime." 1416 Does not heavy rain, as well as quicklime, prevent the accumula- tion of carbonic acidf Yes ; an abundant supply of water will prevent the accumulation of carbonic acid, by dissolving it. 1417 Is the external air always in motion? Some portion of the atmosphere is always in motion. Currents of warm air ascending, and currents of cold air descending. 1418 7s the air of our rooms always in motion f Yes ; there are always two currents of air in the room we occupy ; one of hot air flowing out of the room, and another of cold air flowing into the room. 1419 How do you know that there are these two currents of air in wery occupied room f If I hold a lighted candle near the crevice at the top of the door, the flame will be blown outwards (towards me hall) ; but if I hold the candle at the bottom of the door, the flame will be blown inwards (into the room). SCIENCE OF COMMON THINGS. 213 Causo of air currents at windows and doors. What is a vacuum ? This is not the case if a fire be in the room. When a fire is lighted, an inward current is drawn through all the crevices. 1430 Why would the flame 'be blown outvjards (towards the hall) if a candle be held at the top of the door ? Because the air of the room being heated, and con- sequently ratified, ascends, and (floating about the upper part of the room) some of it escapes through the crevice at the top of the door, producing a current of air outwards (into the hall). 1431 Why would the flame be blown inwards (into the room) if the candle be held at the bottom of the door ? Because a partial vacuum is made at the bottom of the room, as soon as the warm air of the room has ascended to the ceiling or made its escape from the room ; and the cold air from the hall ruslies under the door to supply the void. 1433 What is meant by a partial vacuum being made at the bottom of the room ? It here signifies a place from which the air has been taken / and a " partial vacuum" means a place from which a part of the air has been taken away. Thus, when the air near the floor ascends to the ceiling, a partial vacuum is made near the floor. 1433 And how is the vacuum filled up again f It is filled up by colder air, which rushes (under the door, and through the window crevices) into the room. 1434 Give me an illustration. If I dip a pail into a pond and fill it with water, a hole (or vacuum) is made in the pond as big as the pail ; but the moment I draw the pail out, the hole is Jilled up by the water around. 1435 Show how this illustration applies. The heated air which ascends from the bottom of a room is as much taken away as the water in the pail, and (as the void was instantly supplied by other water in the pond) so the void of air is supplied by the air around. 1436 Why is a room (even without a fire) generally warmer than ifa epsn air? 10 214 SCIENCE OF COMMON THINGS. "Why smoke ascends the chimney. What is the draught of a chimney ? Because the air in a room is not subject to much change, and soon partakes of the same temperature as our bodies, when it no longer feels cold. 1437* Why do we generally feel colder out-of-doors than in-doorsf Because the air (which surrounds us) is always changing / and as fast as one portion of air has become warmer by contact with our body, another colder por- tion surrounds us, to absorb more heat. 1458 Why is there always a draught through the window crevices ? Because the external air (being colder than the air of the room we occupy) rushes through the window crevices, to supply the deficiency caused by the escape of warm air up the chimney, etc. 1459 Why, when we kindle a fire in a stove or grate, does the smoke ascend the chimney ? When a fire is lighted to warm a room, the smoke and other gaseous products of combustion, being lighter than the air of the room, ascend, and soon fill the chim- ney with a column of air lighter, bulk for bulk, than a column of atmospheric air. 143O /s the column of light air in the chimney pressed up by a column of equal size on the exterior of the chimney f It is. 1431 What, then, is the draught of a chimney f It is the rate or speed with which the column of cold air outside the chimney pushes up the column of warm air inside the chimney, and this draught will be strong and effective just in the same proportion as the column of air in the chimney is kept warm. Fig. 47 represents a section of a grate and chimney. C D represents the light and warm column of air with- in the chimney, and A B the cold and heavy column of air outside the chim- A! 47 SCIENCE OF COMMON THINGS. 215 Use of chimneys. Utility of long chimneys. ney. The column A B being cold and heavy presses down, the column C t) being light and warm rushes up, and the greater the difference between the weight of these two columns, the greater will be the draught. 14353 IIow do chimneys quicken the ascent of hot air ? By keeping a long column of it together. A column of two feet high rises, or is pressed up, with twice as much force as a column of one foot, and so in propor- tion for all other lengths just as two or more corks, strung together and immersed in water, tend upwards with proportionally more force than a single cork. In a chimney where one foot in height of the column of hot air is one or.r.ce lighter than the same bulk of external cold air, if the chimney be one undred feet high, the air or smoke in it is propelled upwards with a fore, of one hundred ounces. 143. To what is the draught of a chimney in all cases proportioned to f With sufficient fire, to the length of the chimney. 1434 Why are the chimneys of large manufactories generally very high ? A long chimney causes a current of air to pass through a fire very rapidly, and at the same time very uniformly. On these accounts, for the fires of steam-engines, etc., long chim- neys are preferred. 1435 When the temperature of the air in a room and of the air outside are the same, will there be any draught up the chimney ? There will be no draught. 143 6 When there is no fire in stove or grate, and the air of a room is warmer than the air outside, will there be a circulation up and down the chimney? In such cases there will generally bo two currents, up and down the chim- ney, especially if the doors and win- dows of the room be tight. The warm air of the room will ascend through the chimney, and the cold air descend by the side of it, two currents readily cir- culating through one tube. The direc- tion of the arrows, in Fig. 48, will show Fig. 48. 216 SCIENCE OF COMMON THINGS. How to construct a chimney. Use of a cowl upon a chimney. the lines of the current, descending the chimney and circulating round the apartment. 143 7* Why does an apartment often smell disagreeably of soot in sum- mer-time ? Because the air in the chimney (being colder than the air in the apartment) descends into the room, and leaves a disagreeable smell of soot behind. 1438 How ought chimneys to be constructed? A chimney should be constructed in such a way that the flue or passage will gradually contract from the bottom to the top, being widest at the bottom, and the smallest at the top. 1439 Why is it expedient to construct a chimney in iliis manner f At the base of the chimney, the hot column of air fills the entire passage ; but as the hot air ascends it gradually cools and contracts, occupying less space. If, therefore, the chimney were of the same size all the way up, the tendency would be, that the cold external air would rush down to fill up the space left by the con- traction of the hot column of air. This action would still farther cool the hot air of the chimney and diminish the draught. 14:40 Why will a long chimney smoke, unless the fire be pretty fierce f Because the heat of the fire will not be sufncient to rarefy all the air in the chimney. 1441 Why will the chimney smoke, unless the fire be fierce enough to heat all the air in the chimney-flue f Because the cold air (condensed in the upper part of the flue) will sink from its own weight ; and sweep the ascending smoke back into the room. 144S What is the use of a cowl upon a chimney-pot f It acts as a screen, to prevent the wind from blowing into the chimney. 1443 What harm would the wind do if it were to blow into a chim- ney? 1. It would prevent the smoke from getting out ; and 2. The cold air (introduced into the chimney by the SCIENCE OF COMMON THINGS. 217 Use of a blower upon a grate. Hottest arid coolest portions of a room. wind) would fall down the fiue, and drive the smoke with it into the room. 1444 Why do some chimneys smoJce ? Because fresh air is not admitted into a room as fast as it is consigned by the fire ; in consequence of which a current of air rushes down the chimney to supply the deficiency, driving the smoke along with it. 1445 Why do Mowers, when placed before a grate, tend to kindle the fire? A blower is a sheet of iron that stops up the space above the grate bars, and prevents any air from enter- ing the chimney except that which passes through the fuel and produces combustion. This soon causes the column of air in the chimney to become heated, and a draught of considerable force is speedily produced through the fire. The increase of draught increases the intensity of the lire. 1446 Which is the hottest part of a room ? The upper part, near the ceiling. The warm air being the lightest seeks the highest position. 1447 Which is the coolest part of a room f The lowest part, near the floor. Cold air being dense and heavy seeks the lowest position. 144S By which means is a room better ventilated, by opening the uppef or the lower sash ? A room is better ventilated by opening the upper sash because the hot vitiated air (which always as- cends towards the ceiling) can escape more easily. 1449 What temperature is most proper for keeping an apartment in a healthy and pleasant condition during the cold season f From 65 to 70 F., with a free ventilation. 1450 How are houses and other buildings heated with hot air f The fire is kindled in a furnace which is erected in the cellar. This fire heats the air in contact with it in the air-chainber, as it is called, and as heated air always ascends, it is forced up into the different apart- ments of the building. 218 SCIENCE OF COMMON THINGS. What is smoke ? Open fireplaces 111 adapted for heating rooms. 1451 Which would prove the warmest upon a bed a blanket, or an oiled silk, or India-rubber air-tight covering f The air-tight covering. 1453 Why do we not use oiled silk or India-rubber bed coverings in the winter ? Because they prevent ventilation, and, by shutting in the insensible perspiration, soon produce dampness. 1453 What is smoke? Small particles of carbon separated by combustion from the fuel, but not consumed. 1454 Is there a circulation of the air through the bed coverings at night? Yes ; from every part of the bed-clothes immediately over the person there is a constant outward oozing of warm air, and an oozing inwards of cold air in lower situations around. 1455 In what two ways is heat communicated to apartments by fires kept in them ? By radiation and immediate contact. The first portion passes through the air in diverging lines with great velocity. The second penetrates slowly through the substance of the densest bodies. To enjoy the full effect of radiated heat, we mus,t be in the presence or sight of the radiating object. To receive conducted heat, we must be in contact, either directly or through some intervening me- dium, with the body that imparts it. 1456 Does a person who sits by afire in the open air receive any heat by conduction? Very little; for the air which surrounds the fire having nothing to confine it, ascends by its diminished specific gravity as fast as it is warmed, and its place is immediately supplied by strata of cold air from beneath. 1457 Will a person sitting beside a fire in the open air be exposed, ipon the side of his body removed from the fire, to additional cold? He will, because cold currents rush in from every nde towards the fire. 1458 Why are open fireplaces ill adapted for the economical heating ")f apartments ? In an open fireplace the air flows from the room to the fire, becomes heated, and passes off directly into the chimney, without having an opportunity of parting SCIENCE OF COMMON THINGS. 219 Advantages of stoves over fireplaces. Disadvantages of stoves. with its heat for any useful purpose. In addition to this, a quantity of the air of the room, which has been warmed by radiation, is uselessly carried away by the draught. 1459 What are Vie advantages of a stove over an open fireplace ? 1. Being detached from the walls of the room, the greater part of the heat produced by combustion is saved. The radiated heat being thrown into the walls of the stove, they become hot, and in turn radiate heat on all sides to the room. The conducted heat is also received by successive portions of the air of the room, which pass in contact with the stove ; 2. The air being made to pass through the fuel, a small supply is sufficient to keep up the combustion, so that little need be taken out of the room ; and 3. The smoke, in passing off by a pipe, parts with the greater part of its heat before it leaves the room. 1460 What are the disadvantages of stoves ? Houses containing them are generally ill ventilated. The air coming in contact with the hot metal surfaces is rendered impure, which impurity is increased by the burning of the dust and other substances which settle upon the stove. The air is, in most cases, kept so dry as to render it oppressive. 1461 Upon what principle are the common hot-air furnaces for warm- A stove, having large radiating surfaces, is inclosed in a chamber (generally of masonry). This chamber is generally built with double walls, that it may be a better non-conductor of heat. A current of air from without is brought by a pipe or box, and delivered un- der the stove. A part of this air is admitted to supply the combustion ; the rest passes upwards in the cavity between the hot stove and the walls of the brick cham- ber, and, after becoming thoroughly heated, is con- ducted through passages in which its lightness causes it to ascend, and be delivered in any apartment of the house. 220 SCIENCE OF COMMON THINGS. Construction of furnaces. Combustion. 1463 In the construction and arrangement of a furnace for warming, what two points are of special importance, so far as regards the economy of fuel? 1. The perfect combustion of the fuel ; and 2. The best possible transmission of all the heat formed, into the air that is to pass into the rooms of the house. 1463 How is the first of these requisites obtained? By having a good draught and a fire-box which is broad and shallow, so that the coal shall form a thin stratum ; by which arrangement the carbonic acid gas will be freely formed, and pass off without a previous production of an imperfectly burnt product. 1464 How is the second of these requisites attained ? By providing a great quantity of surface in the form of pipes, drums, or cylinders, through which the smoke and hot gases must pass on their way to the chimney, and to which their heat will be imparted, to be in turn delivered to the cold and pure air of the rooms of the house. CIIAPTEE II. t COMBUSTION. 1465 What is combustion ? Every species of combustion with which we are familiarly acquainted is the rapid chemical union of the oxygen of the air with a combustible body, attended with the evolution of light and heat. 1466 flow may combustion, as we ordinarily see it, be regarded ? It may be regarded as simply & process of oxidation. 1467* What do we mean by the term oxidation f SCIENCE OF COMMON THINGS. 221 Matter not destroyed by combustion. Heat, how originated by combustion. The combination of some substance with oxygen, - or the act of combining with oxygen. 1468 Js there not always an increase in weight during the combustion of inflammable materials, rather than a loss f The products of combustion always exceed the weight of the original substance burned, by an amount equal to the weight of the oxygen gas absorbed during the combustion. 1469 What becomes of the oxidized products of combustion f They for the most part combine with oxygen to form gases and vapors. We apply to these products the general term smoke. 147*0 What is an essential requisite to every process of combustion f That there should be a free supply of air, and that the products of combustion, or the smoke, should be conducted off. 147*1 Why, when we burn a candle or a piece of wood in the air, does there always seem to be a loss of matter f Because the results of combustion in these cases are either gases or vapors, the existence of which, not being apparent to common observation, requires to be made known by experiment. Until nearly the close of the last century it was generally believed and taught, that when a body was burned, something went out of it, that it lost weight. Lavoisier, a celebrated French chemist, overthrew this doc- trine by burning a substance in connexion with an arrangement whereby all the results or products of the combustion were saved. These on being weighed showed a gain rather than a loss, the amount being equal to the quantity of oxygen which had been absorbed from the air during the process of combustion, by the burning substance itself. 147*3 How is heat evolved by combustion ? By chemical action. As latent heat is liberated, when water is poured upon lime, by chemical action, so latent heat is liberated in combustion by chemical action also. 147*3 What chemical action takes place in combustion f The elements of the fuel combine with the oxygen of the air. 147*4 What is the temperature required to induce the combination of oxygen with any substance called ? 10* 222 SCIENCE OF COMMON THINGS. The burning point rust flame fire. The burning point. 14*75 Is this point different for different substances f It is ,' thus phosphorus will combine slowly at 77 F., but does not enter into rapid combustion until the tem- perature is raised to 104 F. Charcoal burns slowly below a red heat. 14*70 Is the quantity of heat given out, when a body combines slowly with oxygen, the same as when it combines rapidly with it, the relative quantities of the combining bodies remaining the same in both cases ? The total quantity of heat given out is the same, whether the combustion takes place slowly or quickly ; but in the case of slow combustion, the heat is much less intense, and often becomes insensible, because during the long time occupied in combination the greater part is carried away by conduction. 147"7 Is the quantity of light given out the same, whether the combus- tion be rapid or slow ? No : the quantity of light given out during the com- bination of oxygen with a given quantity of a com- bustible body varies greatly, according to the rapidity of the combustion. 1478 What is rust f The oxidation of iron in moist air. 14*79 When iron rusts in the air is heat given outf Certainly ; but the process of rusting takes place so slowly that the amount of heat given out at any one time is imperceptible to our senses. 148 O What is flame f Burning gas or vapor. 1481 What is fire? Heat and light produced by the combustion of in- flammable substances. 1483 What does the brightness or illuminating power of flame depend fnf It depends on the degree of heat in part, but mainly on the presence or absence of solid particles in the flame, which may act as radiating points. 1483 Are there solid particles in every illuminating flume t SCIENCE OF COMMON THINGS. 223 W hen will a lamp smoke ? Benefit of glass chimney on lamp. There are / and if we present a cold surface to the flame, they become deposited on it in the form of soot. 1484 When we Say a lamp smokes, what do we mean * That the solid parts of the flame are passing off in an unconsumed state, 1485 When the flame burns properly, why does the smoke cease to be emitted f Because the solid particles of carbon constituting the smoke are burned up, or are completely united with oxygen, forming an invisible gas carbonic acid. 1480 From what source is the carbon, constituting the illuminating par- ticles in tiie one case and the soot in the other, derived? It was originally a part of the burning or combustible body, 148 7 When will a flame smoke f When the supply of oxygen received from the air ig insufficient to consume all the carbon which the heat separates from the combustible body in the form of soot. 1488 What benefit arises from surrounding aflame with a glass cylin- der of chimney open at the bottom and top ? When a flame burns without a chimney, the hot air radiates in all directions ; but when it is surrounded by a chimney, the hot air is confined within the walls of the cylinder: consequently, the hot air will issue rapidly from the top of the chimney, and cold air will- enter equally fast at the bottom to replace it. In this Way a constant current of fresh air is kept up through the centre of the flame, causing a more perfect com- bustion, and a brighter and stronger flame. 148Q Why in solar and astral lamps do we use a hollow or circular wick? In order that a current of air may rusn up through the interior surface of the flame as well as aiong the exterior. 1490 What is fuel? Any substance which serves as aliment or food for '(ire. In ordinary language we mean by fuel the pecu- liar substance of plants, or the products resulting from 224 SCIENCE OF COMMON THINGS. "What is fuel carbon charcoal soot ? their decomposition, designated under the various names of wood, peat, and coal. 1401 What are the constituents of wood? Carbon, hydrogen, and oxygen, combined together, make up the chief part of its bulk ; all wood also con- tains water. 1403 What is hydrogen? It is an inflammable gas, one of the elements of which water is composed. The gas used in our streets is in great part hydrogen. Hydrogen, when pure, has neither taste nor odor. 1403 What are the peculiar characteristics of hydrogen gast 1. It is the lightest of all known substances ; 2. It will burn immediately on being ignited ; and 3. A lighted candle (immersed in this gas) will be instantly extinguished. 1404 What is carbon f A solid elementary substance, generally of a dark or black color, well known under the forms of charcoal, lampblack, coke, etc. 1405 What is charcoal? "Wood which has been exposed to heat until it has been deprived of all its gases and volatile parts. 1406 Can all animal and vegetable substances, by partial burning, be converted into coal f They can. 1407* In the charring of animal and vegetable substances, do we gene- rate charcoal, or did it exist there before % The carbon or coal existed there previously, though in chemical combination with other bodies, which are principally driven off by heat, as is apparent from the fact that a charred body weighs much less than the original substance ; animal and vegetable substances consist, therefore, in part of coal. 1408 Wliatissoot? Coal in a state of minute division, which is deposited from the flame of bituminous or pit-coal, wood, oil, SCIENCE OF COMMON THINGS. 225 How charcoal is prepared. "What is mineral coal. resin, etc., when, during the combustion of these sub- stances, there is an insufficient supply of air. 1499 How is charcoal prepared f By charring wood in mounds or pits, covered with turf or soil in such a way as to exclude in a great degree the admission of air, and thus prevent complete com- bustion. 1500 What is mineral or hard coal? Coal is the product of a vast accumulation of vege- table matter, deposited during a remote geological period in beds or layers in the earth, and which, by the action of pressure, heat, and other causes, has become consolidated and hardened into its present form. 15 Ol How does the coal occur in the earth ? In strata or layers, varying from a few inches to several feet in thickness, inclosed between other strata of limestone, clay, or iron ore. 15OS In what manner is it supposed that this great accumulation of vegetable, material took place 1 The vegetable matter of which coal is composed is supposed, by some, to have grown in immense swamps or marshes. By others, the vegetable matter is sup- posed to have been swept down ~by rivers, and deposited at their mouths or estuaries in immense beds. 1503 Are such accumulations of vegetable matter, through the agency of rivers, going on at the present day ? At the present time the Red River of Texas is abso- lutely choked up with a raft composed of trunks of trees and other vegetable matter, many miles in extent, and of unknown thickness. Other rivers of the South- western United States bring down vegetable materials annually, sufficient for the production of vast beds of coal. 1504 How do we know that coal is all vegetable matter ? Because in every coal mine we find the leaves, trunks, and fruits of trees in immense numbers, many of them in a most perfect state of preservation ; so much eo, that the botany of the coal period can be 226 SCIENCE OF COMMON THINGS. Difference between anthracite and bituminous coal. studied with nearly as great ease and facility as the botany of any given section of the present surface of the earth. 1505 What occasions the difference between bituminous and anthracite coal? Bituminous coal contains a large amount of bitumen and other pitchy volatile substances which readily ignite and burn with smoke and flame. In anthracite coal these substances have been driven out ; it is there- fore a purer variety of carbon, and burns without smoke or flame. 1506 Are the deposits of coal of very great extent f They are ; mineral coal exists in all the great divi- sions of the earth. The largest deposits of coal, how- ever, occur, in the United States, in Pennsylvania and the Yalley of the Mississippi. 1507 Why will not stones do for fuel as well as coal f Because they contain no hydrogen, and little or no carbon. 1508 Of what are oil, tallow, and wax composed t Principally of carbon and hydrogen gas. The solid part is carbon, the volatile part is hydrogen gas. 1509 At what period of the year does wood contain the greatest amount of water ? In the spring and summer, when the sap flows freely and the influence of vegetation is the greatest. 1510 Why is wood generally cut in the winter season f Because at that season there is but little sap in the tissues, and the w r ood is drier than at any other period. 1511 Why is it difficult to inflame coal or hard wood with the blaze of a match f Coal and hard wood on account of their density are good conductors, and carry off the heat of the kindling substance, so as to extinguish it, before they themselves become raised to the temperature necessary for their combustion. 1513 Why is it easy to ignite light fuel with a smatt blaze f Light fuel being a slow conductor of heat kindles SCIENCE OF COMMON THINGS. 227 Amount of water in green and dry wood. Weight of wood. easily, and, from the admixture of atmospheric air in its pores and crevices, burns out rapidly, producing a com- paratively temporary, though often strong heat. 1513 In recently cut wood, what proportion of its weight is water ? From one-fifth to one-half. 1514 After wood has been dried in the air for ten or twelve months, how much water does it usually contain ? From twenty to twenty-Jive per cent. 1515 Why do we call some woods hard, and others soft f This distinction is grounded upon the facility with which they are worked, and upon their power of pro- ducing heat. Hard woods, as the oak, beech, w T afnut, elm, and alder, contain in the same bulk more solid fibre, and their vessels are narrower and more closely packed than those of the softer kinds, such as pine, larch, chestnut, etc. 1516 How many pounds avoirdupois are there in a cord of dry, hard wood? From forty-four hundred pounds in a cord of dry hickory, to twenty-six hundred in a cord of dry, soft maple. 151*7 What is the most valuable wood for fuel? , The varieties of hickory ; after that, in order, the oak, the apple-tree, the white-ash, the dog-wood, and the leech. 1518 What woods give out the least heat in burning f The white-pine, white-birch, and poplar. 1519 Why is it unprofitable to burn green wood or wet coal f It is a well-known law of heat that the evaporation of liquids, or their conversion into steam, consumes or renders latent a great amount of caloric. When green wood or wet coal are added to the fire, they abstract from it by degrees a sufficient amount of heat to con- vert their, own" sap or moisture into steam before they are capable of being burnt. As long as any consider- able part of this fluid remains unevaporated, the com- bustion goes on slowly, the fire is dull, and the heat feeble. 228 SCIENCE OF COMMON THINGS. Unprofitable to burn green wood. Chemical changes produced by combustion. 1530 Js there any truth in the remark often made " that it is economy to burn green wood because it is more durable, and therefore in the end more cheap ?" No j it is true that the consumption of green wood is less rapid than dry, but to produce a given amount of heat, a far greater amount of fuel must be con- sumed. 1531 J n ordinary fuel, what three elements enter into the process of combustion f Hydrogen gas, carbon., and oxygen gas; the two former in the fuel, and the latter principally in the air which surrounds the fuel. 1533 What chemical changes in air and fuel are produced by com- bustion ? 1. Some of the oxygen of the air, combining with the hydrogen of the fuel, forms vapor of water ; and 2. Some of the oxygen of the air, combining with the carbon of the fuel, forms carbonic acid gas. 1523 Why is there more smoke when fresh fuel is added than when the fuel is red hot ? Because more carbon and volatile matters are sepa- rated from the fuel than can be reduced by combustion / and the surplus flies off in smoke. 1534 Why is there so little smoke with a red-hot fir ef Because the entire surface of the coals is in a state of combustion ; and, as very little of the escaping carbon remains unconsumed, there is but little smoke. 1535 When a coal fire is lighted, why are paper and wood laid at the bottom, against the grate f That the flame may ascend through the fuel to heat it. If the fire were kindled from the top, the flame would not come in contact with the fuel placed below. 1536 Why do we cover up afire with ashes or cinders to preserve it f The covering of ashes or cinders protects the fire from the action of the air, and when fuel is deprived of air it ceases to burn. 1537 Why does afire burn so fiercely in windy weather ? Because the air is rapidly changed, and affords plentiful nourishment to the fire. SCIENCE OF COMMON THINGS. 229 "Why water extinguishes a fire. Cause of the heat of a dunghill. 15SS Why does a pair of bellows aid in kindling afire ? Because it drives the air more rapidly to theft-re, and the plentiful supply of oxygen soon makes the tire burn intensely. 15S9 Why does water extinguish a fire 1 1. Because the water forms a coating over the fuel, which keeps it from the air ; and 2. The conversion of water into steam draws off the heat of the burning fuel. 1530 Why does a Uast of air from a pair of bellows often extinguish a red-hot coal of anthracite ? Because the cold air absorbs the heat of the coal so quickly that it extinguishes it. 1531 Why can you not light a candle or lamp with a match so long as the sulphur on the end of it is burning f The chemical reason for this well known fact is, that the sulphurous acid, formed by combustion of sulphur in the air, surrounds the wick, and abstracts the oxygen from the air, by passing to a higher state of oxidation ; and this heavy vapor hangs about the wick and excludes the air. 153S Cannot wood be made to blaze without actual contact with fire? Yes ; if a piece of wood be held near the fire for a little time, it will blaze, even though it does not touch the fire. 1533 Why will wood blaze, even if it does not touch the fire ? Because the heat of the fire drives out the inflam- mable gas of the wood, which gas is ignited by contact with the red-hot coals. 1534 What causes the heat of fire 1 The carbon of fuel (when heated) combines with the oxygen of the air, and produces carbonic acid gas. Again, the hydrogen of the fuel combining with other portions of oxygen, condenses into water ; by which chemical actions heat is evolved. 1535 Whence does the heal of a dunghill arise f As the strawy etc., of the dunghill decays, it under- 230 SCIENCE OF COMMON THINGS. Benefit of stirring a dull fire. How to extinguish a chimney on fire. goes fermentation, which produces carbonic acid gas / and heat is evolved through a species of combustion. 153G On what does the intensity of fire depend ? The intensity of fire is always in proportion to the quantity of oxygen with which it is supplied. 1537 Why does stirring a dull fire serve to quicken it ? Because it breaks up the compacted cinders and coals, making a passage for the air into the very heart of the fire. 1538 Why is the fiame of a candle extinguished when bloion by the breath, and not made more intense, like a fire f Because the flame of a candle is confined to a very small wick, from which it is severed by the breath, and (being unsupported) must go out. 1539 When a chimney with an open fireplace gets on fire, and burns so as to endanger the house, how may it at once be extinguished? By throwing a quantity of brimstone or sulphur into the fire, and closing up the fireplace with a fireboard or screen. The sulphurous acid soon fills the chimney, and taking up all the oxygen from the contained air, ex- tinguishes the fire. Even the fire, after it has extended into the woodwork of the house, may be extinguished by this simple method. 1540 Fire in a chimney may be also extinguished by closing the top of thefiue with a damper : how does this extinguish the fire f It cuts off the draught, and the carbonic acid gene- rated by the combustion soon puts an end to the fire. 1541 What is meant by spontaneous combustion ? Combustion produced without contact with fire or flame. 1543 Give me an example of spontaneous combustion. Oiled cotton and rags imbued with any drying oil, when packed in mass in a barrel, take fire, after a time, at ordinary temperatures. Mixed lampblack and lin- seed-oil cake take fire at ordinary temperatures, if the lampblack is in excess, or a portion of it is dry. 1543 What is generally the cause of spontaneous combustion ? The absorption of oxygen. Porous bodies, that are SCIENCE OF COMMON THINGS. 231 Why all flames are not equally luminous. Cause of the color of a fire. at the same time bad conductors of heat, by the absorption of oxygen may become red hot, and finally burst into a flame. 1544 Is pine charcoal capable of taking fire at an extremely low tem- perature ? Porous bodies, like pine charcoal, when perfectly dry, absorb oxygen rapidly from the air, and take fire at a temperature below 212 Fahrenheit, or the boil- ing-point of water. This has been proved by actual experiment, a piece of light pine char- coal taking fire on a surface of sheet iron, heated below the boiling-point of water. 1545 Why are not all flames equally luminous t In all flames, the light is mainly emitted from mi- nute particles of matter, intensely heated, and floating in the burning gas or vapor ; and hence a flame con- taining few such particles, will emit but a feeble light, even though its temperature is very great. 1546 Upon what fact does the production of artificial light depend ? Upon the fact that at certain high temperatures all matter becomes luminous. 3-547 In order that we may profitably use a combustible body for illu- minating purposes, what is required of the products of the combustion f That they should be volatile, and freely escape from the immediate vicinity of the illuminating centre. 1548 The product of all the ordinary forms of combustion is a gas carbonic acid : what would have been the result if the product of every com- bustion had been a permanent solid ? The world would have been buried beneath its own ashes. 1549 Why is the flame of an ordinary fire ydloto f Because the heat is not sufficient to render the car- bon white hot. Increase the intensity of combustion, arid the color of the burning bodies or the flames rises from red to yellow, and from yellow to white. 1550 A candle burns when lighted : explain how this is 1 The heat of the lighted wick decomposes the tallow into its elementary constituents, hydrogen and carbon. The hydrogen is nrst consumed as a gas by itself with 232 SCIENCE OF COMMON THINGS. Phenomena of combustion in the flame of a candle. an almost imperceptible light, but with a powerful evolution of heat; this causes the carbon, simultane- ously eliminated, to become incandescent and conse- quently luminous. 1551 As more carbon is successively -eliminated, what becomes of it ? The moment the incandescent floating carbon comes to the edge of the flame, it finds the oxygen of the air, unites with it, and becomes converted into the invisible gas, carbonic acid, while its place is occupied immedi- ately by another portion of solid carbon. 1553 What if there is not sufficient oxygen to consume the carbon 1 It then passes off as soot, and we say the candle smokes. 1553 Where is the tallow or wax of a candle decomposed f In the wick. The melted tallow or wax rises up the wick by capillary attraction, and is rapidly decom- posed by the heat of the flame. 1554 Of what three parts does the flame of every lamp or candle consist ? The flame of every lamp or candle consists of three cones. The innermost cone (a, Fig. 49) consists of gaseous matter produced by the decomposition of the tallow ; this is at a tem- perature below redness. Around it is the lu- minous cone (b\ consisting of burning hydro- gen, in which the particles of carbon float at a white heat ; and on the very outside (c), a thin, hardly-perceptible veil in which carbon is burning. The veil is of a blue color, most plainly seen at the bottom of the flame. 1555 Which is the hottest part of thejlame f The pale Hue flame ; this marks the point where the combination of the oxygen, supplied from without, with the combustible matter evolved from the interior takes place. 155G Why does thejlame of a candle point upwards ? Because it heats the surrounding air, which SCIENCE OF COMMON THINGS. 233 Use of a hole in the top of a lamp. Use of ground glass lamp shades. hot) rapidly ascends, driving the flame upwards at the same time. 1557* Why does the hand, held above a candle, suffer more from heat than when it is placed below the flame, or on one side of it t Because the hot gases and air (in their ascent) come in contact with the hand placed above the flame ; but when the hand is placed below the flame, or on one side, it only feels heat from radiation. 1553 Why is not the wick of a candle consumed f The wick, although it is blackened by the heat, is prevented from consuming, merely because it is sur- rounded by inflammable vapor, so that the oxygen of the atmosphere has no access to it. 1559 Why do att closed lamps require a small hole in the top f To admit the air otherwise the pressure of the atmosphere will prevent the oil from ascending the wick ; if the hole be obstructed, the oil will sometimes overflow from the expansion of the confined air. 1560 Why do we use ground-glass globes for lamp shades ? To relieve the eye from the glare of light. Ground- glass shades have the effect to disperse the rays by the numerous reflections and refractions w T hich they occa- sion ; until at length the light issues from all parts of their surface, and it appears as though the glass itself were the luminous body. CHAPTER III. RESPIRATION AND NUTRITION. 15 SI What is respiration? The act of inhaling air into the lungs, and again expelling it. 234: SCIENCE OF COMMON THINGS. Combustion a form of respiration. Construction of the lungs. 1562 What is the object of drawing air into the lungs and again expel- ling it ? To oxidize the carbon and hydrogen of the blood. 1563 We receive into the lungs oxygen through the medium of the atmo- sphere, mingled with nitrogen : what do we expel from the lungs f The nitrogen returns unaltered ; the oxygen unites with the carbon of the blood to form a gas carbonic acid, and with hydrogen to form the vapor of water. 1564 Are not these the same products of every ordinary form of com- bustion f They are ; therefore respiration or breathing is but a form of combustion. 1565 It is estimated that a man receives into his system about eight hundred pounds of oxygen from the atmosphere in a year, but his weight at the end of the year has increased but little, or not at all : what becomes of all this oxygen ? No part of it remains in the 'body, but is given out again, combined with carbon and hydrogen. 1566 How much carbon passes out of the system of an adult man by the agency of respiration daily ? About fifteen ounces. 1567 How is this great abstraction of material from the body made up T By the food which we eat. 1568 What are the lungs ? Lungs are made up of bloodvessels imbedded in a fleshy substance which we denominate cellular tissue, and expanded over the walls of a series of chambers or cavities. They are so situated in the thorax (or chest) that the air must enter into them whenever the cavities of the thorax are enlarged. The process of breathing is performed thus : When we INHALE, the thorax (or chest) is expanded ; in consequence of which a vacuum is formed round the lungs, and the heavy external air instantly enters (through the mouth and throat) to supply this vacuum. When we EXHALE, the thorax contracts again; in consequence of which it can no longer contain the same quantity of air as it did before, and some of it is necessarily expelled. When this expulsion of air takes place, the lungs and muscular fibres of the windpipe and gullet contract in order to assist the process. 1569 To what may the mechanism of the lungs in respiration be con* pared ? To the action of a bellows. SCIENCE OF COMMON THINGS. 235 Necessity of cleanliness. Color of the blood. 157*0 Do we respire or absorb and expel oxygen in any oilier way than, through the lungs ? We breathe also in a degree through the pores of the skin, absorbing oxygen and expelling carbonic acid. 157*1 Do extensive burns on the surface of tht body frequently produce diseases of the lungs f They do. 157*3 Why should extensive burns on the surface of the, body tend to produce diseases of the lungs ? While in a condition of health, the skin tranquilly aids the lungs in the expulsion of carbonic acid from the body ; but the portion of the skin which has been scorched by an extensive burn, no longer being able to perform that function, the lungs are obliged to assume an extra duty, and suffer as a consequence of their exertion. 157*3 //j by neglect of washing, we suffer the sJcin to become covered with impurities, do we not disturb the healthy action of the system f We do ; there is no better-established law of health, than that the surface of the whole body should be kept clean and free from all impurities. 157*4 If the carbon taken from the system through the agency of the lungs be not t estored, what is the consequence ? Starvation ensues. 157*5 How does the oxygen we inhale mingle with the blood? The oxygen of the air is absorbed in the lungs by the blood, and imparts to it a bright red color. 157*6 How does oxygen convert the color of blood into a bright red f The coloring matter of the blood is formed by very minute globules floating in it. The oxygen uniting with these globules changes their color, to a bright red. The blood contains iron, and this metal is supposed to play an important part in the coloration of the blood. 157*7* What color is the blood before it is oxidized in the lungs ? A dark purple ; the oxygen turns it to a bright red* 157* S Do plants respire as well as animals t They do; and their leaves may be regarded as per- forming for them similar offices as the lungs of animals. They are the breathing organs of plants. SCIENCE OF COMMON THINGS. How water plants purify the water. Cause of animal beat. 1579 Js there any difference between the respiration of plants and animals f The process of respiration in plants is exactly the reverse of that in animals. Animals absorb oxygen, and give out carlo nic acid ; plants, on the contrary, absorb carbonic acid, and return oxygen. 15SO It is estimated that the population of London adds to the atmo- sphere daily. 4, 500,000 pounds of carbonic acid: how is this immense quan- tity of deleterious gas removed from the atmosphere f Principally through the agency of plants, which absorb it. 1581 Do water-plants purify and free water from carbonic acid in the same manner that land-plants purify the atmosphere ? The respiration of fishes produces carbonic acid, and anless this is removed from the water, animal life will cease to exist in it. Water-plants absorb the carbonic acid from the water, and restore the oxygen. 1583 During bright weather, the leaves of water-plants, it will be no- ticed, are covered with little bubbks : what are these bubbles 1 Oxygen gas, liberated by the organs of the plant. 1583 It is good policy, in fountains and reservoirs of water, to free them wholly from the presence of vegetable and animal organisms ? It is not : they are both dependent on one another, and the joint action of the two serves to keep the water pure and wholesome. 1584 What is the cause of animal heat? The oxygen of the atmosphere, received into the blood in the lungs, and circulated throughout every part of the animal body, acting upon the elements of the food, is the chief source of animal heat. 1585 Why does oxygen received into the blood produce heat ? Through the medium of the capillary vessels oxygen absorbed from the atmosphere unites with carbon and hydrogen. This union is a species of combustion, and produces heat in the same manner as when oxygen unites with fuel in an ordinary fire. 1586 What are the capillary vessels f Minute bloodvessels or tubes as small as hairs run- SCIENCE OF COMMON THINGS. 237 Why no heat In the hair. Two kinds of blood, venous and arterial. ning all over the body ; they are called capillary from the Latin word capillaris, " like a hair." 1537* Do these capillary vessels run all over the human body f Yes. Whenever Hood flows from a wound, some vein or vessel must be divided ; and as you can bring blood from any part of the body by a very slight wound, these little vessels must run through every part of the human frame. 1588 How do hydrogen gas and carbon get into these very small vessels ? The food we eat is converted into blood, and blood contains both hydrogen and carbon. 1580 Does this combustion, and the consequent production of animal heat, take place in every part of the body ? In the animal body, heat is produced only in those parts to which arterial Hood, and with it the oxygen absorbed in respiration, is conveyed. 1590 Why is there no heat developed in hair, wool, andfeaffiers f Because they receive no arterial Hood, and therefore in them no heat is developed. 1591 What two kinds of blood are tliere in the animal body ? Arterial Hood and venous Hood. 159 S What is the difference between the two? The arterial blood going from the lungs conveys the oxygen which it has absorbed in the lungs to the capil- lary vessels. In these the combustion takes place, and the color of the blood changes from a bright to a dark red color. 1593 What becomes of the blood after it has given up its oxygen to the hydrogen and carbon in the capillary vessels f It enters the veins, carrying with it the products of combustion. The venous blood passes to the lungs, throws off the products of combustion, absorbs more oxygen, becomes converted into arterial blood, with a renewal of color, and is again returned into the system. 1594 What becomes of the carbonic acid gas formed in the human blood ? 11 238 SCIENCE OF COMMON (THINGS. Why a dead body is cold. "Why we perspire. The lungs throw off almost all of it into the air, by the act of respiration. 1595 Does the heat of the human body arise from the same cause as the heat of fire ? Yes, precisely. The carbon of the blood combines with the oxygen of the air inhaled, and produces car- bonic acid gas, which action developes heat. ; 1590 If animal heat is produced by combustion, why does not the human body burn up like a coal or candle ? It actually does so. Every muscle, nerve, and organ of the body actually wastes away like a burning candle and (being reduced to air and ashes) is rejected from the system as useless. 1597 If every bone, muscle, nerve, and organ is thus consumed by com- bustion, why is not the body entirely consumed? It would be so, unless the parts destroyed were per- petually renewed ; but as a lamp will not go out so long as it is supplied with fresh oil, neither will the body be consumed so long as it is supplied with sufficient food. 1598 What is the principal difference between the combustion of a fire or lamp, and that of the human body ? In the human body, the combustion is effected at a much lower temperature, and is carried on more slowly, than it is in a lamp or fire. 1599 Why is a dead body cold? Because air is no longer conveyed to the lungs after respiration has ceased ; and therefore animal heat is no longer generated by combustion. 1600 Why do we perspire when very hot ? The pores of the body are like the safety-valves of a steam-engine ; when the heat of the body is very great, some of the combustible matter of the blood is thrown off in perspiration, and the heat of the body is thereby reduced. 1601 Why does exercise make us warm ? Because we inhale air more rapidly when we exer- cise, and cause the blood to pass more rapidly through the lungs in contact with it. SCIENCE OF COMMON THINGS. 2S9 Starvation and its effects. Food the fuel of the body. 16OS Why does inhaling air rapidly make the body feel warm? Because more oxygen is introduced into the body ; in consequence of which the combustion of the blood is more rapid, the blood itself more heated, and every part of the body is made warmer. 16O3 When a man is starved what part of the body goes first f First the fat, because it is the most combustible ; then, the muscles ; last of all, the brain ; and then the man dies, like a candle which is burnt out. 1QO4 Why does a man shrink when starved f Because the capillary fires feed upon the human body when they are not supplied with food-fuel. A starved man shrinks just as a fire does when it is not supplied with fuel. 1BO5 What is fuel of the body f Food is the fuel of the ~body. The carbon of the food, mixed with the oxygen of the air, evolves heat in the same way that a fire or candle does. 16O0 Why does hard work produce hunger f Because it produces quicker respiration ; by^ which means a larger amount of oxygen is introduced into the lungs, and the capillary combustion increased. Hun- ger is the notice (given by our body) to remind us that our food-fuel must be replenished. 16O7" Why do persons feel lazy and averse to exercise when they are half-starved or ill fed f Because desire for muscular action ceases when the body is not supplied with nutritious food. ISO 8 Why do we like strong meat and greasy food when the weather is very cold ? Because strong meat and grease contain large pro- portions of carbon and hydrogen, which (when burned in the blood) produce a larger amount of heat than any other kind of food. 1SO0 Why are the Esquimaux so passionately fond of train oil and whale blubber f Because oil and blubber contain large quantities of carbon and hydrogen, which are exceedingly combus- 240 SCIENCE OF COMMON THINGS. Activity disagreeable in warm weather. tible ; and as these people live in climates of intense cold, the heat of their bodies is increased by the greasy nature of their food. 1610 Why do we feel lazy and averse to activity in very hot weather 1 Because muscular activity inweases the heat of our body by quickening respiration, and lessens our desire for active exertion. 1611 How much more carbon do we throw off from the system by respi- ration in winter than in summer f Full one-eighth more. SCIENCE OF COMMON THINGS. 241 What is light ? Light possesses no weight. PAET VII. LIGHT, AND HOW WE SEE. CIIAPTEE I. NATURE AND LAWS OF LIGHT. ISIS Through what agency alone are we enabled to enjoy the sense of sight f Through the agency of light. 1613 What is light? Light is now believed to be caused by the agitation, vibration, or undulation of an elastic fluid which is sup- posed to occupy and pervade all space. "We call this supposed fluid ether, and its undulations or vibrations, reaching the eye, affect the optic nerve, and produce the sensation which we call light. 1614 What analogy is there between the eye and the ear f The vibrations or undulations of the ether pass along the space intervening between the visible object and the eye in the same manner that the undulations of the air, produced by a sounding body, pass through the air between this body and the ear. 1615 If we collect a large quantity of light in one point by means of a glass, and throw it upon the most sensitive balance, does it indicate any per- ceptible weight f It does not, in the slightest degree. 1616 What are the chief sources of light? The sun, the stars, ftre or combustion, electricity, and phosphorescence. 1617 With what velocity does light move through space 1 24:2 SCIENCE OF COMMON THINGS. Velocity of light Why some surfaces are brilliant and others dull. With a velocity of one hundred and ninety-two thou- sand miles in a second of time. 1618 Does all light travel equally fast? Yes ; the light of the sun, the light of a candle, or the light from houses, trees, and fields. 1619 How long a time does it require for light to pass from the sun to the earth f Eight minutes and thirteen seconds. 102 O How much time is required for a ray of light to traverse the space intervening between the nearest fixed stars and the earth f More than three years ; and from the farthest nebulae hundreds of years will be required. 1621 What, therefore, would be the consequence if one oj the remote fixed stars were to-day " blotted from the heavens?" Several generations of the earth would pass away before the obliteration could be known to man. 1622 In wJiat manner do the moon and the planets give light f They shine only by means of the surfs light, which is reflected from their surfaces. 1623 Where does the light of houses, trees, and fields come from? The light of the sun (or of some artificial light) is re- flected from their surfaces. 1624 Why are some surfaces brilliant (like glass and steel) and others dull, like lead ? Those surfaces which reflect the most light are the most brilliant / and those which absorb light are dull. 1625 How does the velocity of light compare with the speed of a loco- motive ? Light passes from the sun to the earth in about eight minutes ; a locomotive engine, travelling at the rate of a mile in a minute, would require upwards of one hundred and eighty years to accomplish the same journey. 1626 How does the light of the full moon compare with that of the sun? It is estimated to be three hundred thousand times weaker than sunlight. 1627 The velocity of light is demonstrated by observations on the satellites of Jupiter. Witt you explain how this can be proved? SCIENCE OF COMMON THINGS. 24:3 Velocity of light determined from observations on Jupiter's satellites. The earth revolves around the sun in an orbit of which the sun is the centre. We are able to calculate the exact time when an observer standing in the centre of the earth's orbit, that is, in the sun, would see an eclipse of Jupiter's satellite ; but as the earth moves round the sun in its orbit, it is brought at one time ninety-five million of miles nearer Jupiter than the sun is, and at another time it is carried ninety-five millions of miles further off. Now, when the earth is nearest to Jupiter, the eclipse takes place eight minutes in advance of the calculated time, and when it is ninety- five millions of miles farther off, the eclipse occurs eight minutes later than the calculated time. This delay is occasioned by the fact, that in the one case the light coming from the satellite to the earth has to traverse a much greater distance than in the other ; and if the light requires eight minutes, or 480 seconds, to move over 95,000,000 of miles, it will require one second to move over 197,000 miles, or, with more exact data, 192.000 miles in one second. Fig. 50. The explanation above given will be made clear by reference to the following diagram, Fig. 50. S represents the sun, a b the orbit of the earth, and T T' the position of the earth at different and opposite points of its orbit. J represents Jupiter, and E, its satellite, about to be eclipsed by passing within the shadow of the planet. Now the time of the com- mencement or termination of an eclipse of the satellite, as stated from calculation in tables, is the instant at which the satellite would appear to enter or emerge from the shadow, if it could be seen by an observer from the sun, S. If the transmission of light were instantaneous, it is obvious that the light coming from Jupiter's satellite, E, would be seen at the same moment at the points T^ Sand T'. But repeated observation shows 244 SCIENCE OF COMMON THINGS. How a multitude of persons see the same object. Shadows. that the eclipse takes place eight minutes earlier than the calculated period when the earth is in the nearest point of its orbit, as at T, and eight minutes later when she is in the opposite part of her orbit, as at 7", the difference in the distance of these two points from Jubiter being 190,000,000, of miles. 1638 Why can a thousand persons see the same object at Hie same time? Because it throws off from its surface an infinite number of rays in all directions ; and one person sees one portion of these rays, and another person another. 16J39 Why can we not see the stars in the day-time f Because the light of the sun is so powerful that it eclipses the feeble light of the stars ; in consequence of whicli they are invisible by day. 1Q3O In what manner is light propagated f In right lines from every luminous point, every such line being called a ray of light. 1631 Wliat do we mean by a pencil of light? A collection of radiating lines or rays, as seen in Fig. 51. 163S What is darkness? The absence of light. 1633 What is a shadow? A shadow is the name given to the comparative darkness of places or objects, which are prevented by intervening things from receiving the direct rays of some luminous body shining on the objects around. 1634 Why cannot we see through a crooked tube as well as through a straight one ? Because light moves only in straight lines. 1635 What is the philosophy of taking aim with a gun or arrow ? In taking aim with a gun or arrow, we proceed upon the supposition that light moves in straight lines, and try to make the projectile go to the desired object as nearly as possible by the path along which the lig/it comes from the object to the eye. 1636 Why does a carpenter look along the edge of a plank to see if it is straight ? SCIENCE OF COMMON THINGS. 245 Mirrors. Reflection of light. Incidence and reflection. If the edge be straight and uniform, the light from all points of the edge will come to the eye regularly and uniformly ; if irregularities, however, exist, they will cause the light to be irregular, and the eye at once notices the confusion and the point which occa- sions it. 37* What is a mirror f Any substance reflecting light. The term is gene- rally applied to glass covered on the back with quiet silver. 1038 When liglit falls upon a body, in what three ways may it dispose of itself? It may be reflected, refracted, or absorbed. 1039 What do we mean when we speak of light being reflected? When a ray of light strikes against a surface, and is caused to turn back or rebound in a direction different from whence it proceeded, it is said to be reflected. 1040 Why do we see ourselves in a mirror f Because the rays of light from our face strike against the glass, and (instead or being transmitted) are reflect- ed, or sent back again to our eye. 1041 Why are flie rays of light reflected by a mirror ? Because they cannot pass through the impenetrable metal with which the back of the glass is covered ; so they rebound back, just as a marble would do if it were thrown against a wall. 1043 When a marble is rotted towards a waU, what is the path through which it runs called ? The line of incidence. 1043 When a marbk, rebounds back again, what is the path it then describes called? The line of reflection. (See Fig. 52.) If A B be the line of incidence, then B E is the line of reflection; and vice versa. 1044 When the light of our face goes to the glass, what is the path rough which it goes catted ? 11* 246 SCIENCE OF COMMON THINGS. Lines of incidence and reflection. Why images appear inverted in water. The line of incidence. 1645 When the light of our face is reflected back again from the mir- ror, what is this returning path called f The line of reflection. 1646 What is the angle of incidence f The angle between the line of incidence and the per- pendicular. 1647 What is the angle of reflection ? The angle between the line of reflection and the per- pendicular. (See Fig. 52.) Let F B C (Fig. 53) be any surface ; D B a perpendicular to it. If a marble were thrown from E to B, and bounded back to A, then E B D would be the angle of incidence, and DBA the angle of reflection. 1648 Why does the image of any object in water always appear in- verted f Because the angles of incidence being always equal to the angles of reflection, the light of the object, reflect- ed to our eyes from the surface of the water, comes to us with the same direction as it would have done, had it proceeded directly from an inverted object in the water. In Fig. 53, the light proceeding from the ar- row-head, A, strikes the water at F, and is re- flected to G and that from the barb, B, strikes the water at E, and is reflected toG. A spec- tator standing at G will see the reflected lines, E G and F G, as if they proceeded di- rectly from C and D. Now we always judge of the position of an object according to the direction in which the rays of light repre- senting it come to the eye, and for this reason the image of the arrow, A B, reflect- ed from the surface of water, appears to be located at C D. It is also plain that A (the more elevated object) will strike the water, and be projected from it more perpendicularly than the point B ; and therefore the image will seem inverted. 164O If we lay a looking-glass upon the floor, with its face uppermost, and place a candle beside it, why will the image of the candle seen in the mirror by a person standing opposite to the candle, seem as much below the surface of the glass as the candle itself stands above the glass ? Because the incident ray coming from the top of the candle, strikes the surface of the glass, and is reflected Fig. 53. SCIENCE OF COMMON THINGS. 247 Why the image in a mirror seems behind the glass. in the same direction that a ray of light would have taken, had it really come from a candle situated as much below the surface of the glass, as the first candle was above the surface. This fact will be clearly shown by referring to Fig. 54. F,g. 54. 165O Why, when we look into a plane mirror (the common looking- glass) does our image appear to be at the same distance behind the surface of the glass, as we are before the surface f Because the lines and angles of incidence being always equal to the lines and angles of reflection, the rays which proceed from each point of our body before the mirror will, after reflection, proceed as if they came from a point holding a corresponding posi- tion behind the mirror ; and therefore produce the same effect upon the eye of an observer as if they actually had come from that point. For this reason our reflec- tion in a mirror seems to ap- proach us as we walk towards it, and to retire from us as we retire. The whole subject of the re- flection of images being gene- rally of difficult comprehen- sion by most persons, Fig. 55 is introduced as a means of further explanation. Let A be a part of an object placed before a looking- glass M N. Let A B and A C be two rays diverging from it, and refl 3cted from B and C to an eye at 0, After reflexion ' Fi g 55, 248 SCIENCE OF COMMON THINGS. Peculiarities of reflected light. they will proceed as if they had issued from a point a as far behind the surface of the looking-glass, as A is before it that is to say, the dis- tance A N will be equal to the distance a N. In seeing an object with the eye, we fix upon its position according to the direction in which the rays of light coming from it proceed, and do not take into account the fact that the rays have been reflected from their original course. 1651 Is the same quantity of light reflected at all angles, or inclina- tions ? It is not : when the angle or inclination with which a ray of light strikes upon a reflecting surface is great, the amount of light reflected to the eye will be con- siderable ; when the angle, or inclination is small, the amount of light reflected will be diminished 1653 Why does a spectator, standing upon the bank of a river, see the images of the opposite bank, and objects upon it reflected in the water, but not the images of any near object ? Because the rays of light coming from distant objects strike the surface of the water very obliquely, and the light reflected is sufficient to make a sensible impres- sion upon the eye, while the light proceeding from near objects strikes the water with little obliquity, and the light reflected is not sufficient to make a sensible impression upon the eye. Tliis fact may be clearly seen by reference to Fig. 56. Fig- 56. Let S be the position of the spectator ; O and B the position of distant objects. The rays O R and B R which proceed from them, strike the surface of the water very obliquely, and the light which is reflected in the direction R S is sufficient to make a sensible impression upon the eye. But in regard to objects such as A placed near the spectator, they are not seen reflected, because the rays A R' which proceed from them strike the water with but little obliquity ; and consequently, the part of their SCIENCE OF COMMON THINGS. 240 Why windows blaze at sunset. light which is reflected in the direction R' S, towards the spectator, is not sufficient to produce a sensible impression upon the eye. 1653 Why do windows seem to blaze at sunrise and sunset f Because glass is a good reflector of light, and the rays of the sun (striking against the window-glass) are reflected, or thrown back. 1054 On a lake of water the moon seems to make a path of light towards the eye of the spectator, while ail the rest of the lake seems dark : why is this ? The reason of this appearance is that eveiy little wave, in an extent perhaps of miles, has some part of its rounded surface with the direction or obliquity which, according to the required relation of the angles of incidence and reflection, fits it to reflect the light to the eye, and hence every wave in that extent sends its momentary gleam, which is succeeded by others. 1S55 In a sheet of water at noon, the sun appears to shine upon only one spot, and all the rest of the water seems dark : why is this f Because the rays fall at various degrees of obliquity on the water, and are reflected at similar angles / but as only those which meet the eye of the spectator are visible, all the water will appear dark ex- cept that one spot. Here, of the rays S A, S B, and S C, only the ray S C meets the eye of the specta- tor D. The spot C, therefore, will appear luminous to the spectator D, but no other spot of the water ABC. 1050 Why can we not see into the street or road when candle* are lighted f 1. Because glass is a reflector, and throws the candle- light lack into the room again ; and 2. The pupil of the eye (having become contracted by the light of the room) is too small to collect rays Fig. 67 250 SCIENCE OF COMMON THINGS. When are shadows large, and when small ? enough from the dark street to enable us to see into ^t. 1657 Why do we often see the fire reflected in our windows in winter- time f Because glass is a good reflector, and the rays of the fire (striking against the window-glass) are reflected back into the room again. 1058 If the shadow of an object be thrown on a wall, the closer the object is held to the candle, the larger ,.---|I will be its shadow : why is thisf ,,/"'' Because the rays of light diverge (from the flame of a candle) in straight lines, like lines drawn from the centre of a circle. Here the arrow A, held close to the candle, will cast the shadow B F on a wall ; while ~^\, V the same arrow, held at C, "x would cast only the little sha- *.* dowDE - 1659 How do we judge of the position, distance, and size of an object f We judge of the position and distance and size of an object by the relative direction of lines drawn from the object to the eye, and by the angle which the intersec- tion of these lines makes with the eye. This angle is called the angle of vision. """ > "~ti Fig, 50. The student will bear in mind that an angle is simply the inclination of two lines without any regard to their length. Thus, in Fig. 59, the inclination of the lines, caused by rays of light proceeding from A and B, SCIENCE OF COMMON THINGS. 251 How we estimaUthe size and position of distant objects. and from C and 7>, and meeting at the eye, forms an angle at the point of intersection, which is the eye. This angle is the angle of vision. As the inclination of the ines proceeding from A and B, and from C and Z>, is the same, the angles will be equal, and the man and the bird will ap- pear of the same size. 1660 Why does a man on the top of a mountain or church-spire seem ti be no larger than a crow t Because the angle made in our eye by the perpen- dicular height of the man at that distance is no larger than that made by a crow close by. Let A B (Fig. 59) be a man on a distant mountain or spire, and C I) A crow close by, the man will appear only as high as the line C D, which is the height of the crow. For the same reason the trees and houses far down a street or avenue appear smaller than those near by. 1661 Why does the moon appear to us so much larger than the stars, though, in fact, it is a great deal smaller ? Because the moon is very much nearer to us than any of the stars. Fig. 60. Let A B represent a fixed star, and C D the moon. The angle of vision, A G B, which the fixed star, A B, makes with the eye is evidently less than the angle of vision, G G D, which the moon makes with the eye. But we judge of the size of a body by the size of the angle, and therefore the moon, which is nearest and makes the greatest angle of vision, ap- pears the largest. A B, though much the larger body, will appear no bigger than E F; whereas the moon (CD) will appear as large as the line, D, to the spectator, G. The moon is 240,000 miles from the earth, not quite a quarter of a million of miles. The nearest fixed stars are 20,000,000,000,000 (that is, twenty billions). 1663 Why does the moon (which is a sphere) appear to be a fiat sur- face f Because it is so far off that we cannot distinguish any difference between the length of the rays issuing from 'the edge and those which issue from the centre. 253 SCIENCE OF COMMON THINGS. Why objects in the shade seem dark, t Telescopes. The rays A D and C D appear to be no longer than the ray B 1) ; but if all the rays seem of the same length, the part B will not seem to be nearer to us than A and C ' ; and therefore ABO will look like a flat or straight line. The rays A D and C D are 240,000 miles long. The ray B D is 238,910 miles long. 1603 An object in the shade is not so bright and apparent as an object in the sun : why is it not f Because objects in the shade are seen by reflected light reflected ; that is, the light is twice reflected ; and, as the rays of light are always absorbed in some measure by every substance on which they fall, and also scattered by irregular reflections, therefore in the two reflections much light is lost, and the object is seen with less distinctness. Part of the rays are absorbed, and part are scattered in all directions by irregular reflections ; so that rarely more than half are reflected, even from the most polished metals. 1664 Why is it light when the sky is covered with thick clouds ? Partially because the sun's light is transmitted through the clouds, and partially on account of the multiplied reflections of light in the atmosphere. 1665 What is the use of telescopes f They gather together the rays of light, and a greater number are thus brought to the eye. 1666 How can these rays be gathered together ? Rays of light diverge that is, spread out in all direc- tions from a luminous object. The number of these diverging rays which will enter the eye is limited by the size of the pupil. But before they reach the eye, they may be received upon a glass lens of a convex form, which will have the effect of collecting them into a space less in magnitude than the pupil of the eye. If the eye be placed where the rays are thus collected, all the light will enter the pupil. The light which produces vision, as will be more fully explained here- after, enters the eye through a circular opening called the pupil, which is the black circular spot surrounded by a colored ring, appearing in the SCIENCE OF COMMON THINGS. 253 How telescopes assist the sight. Fig. 62. FiK.es. centre of the front of the eye. Noy, as the rays of light proceeding from an object diverge, or spread out, the number which will enter the eye will be limited by the size of the pupil. At a great distance from an object, as will be seen in Fig. 62, few rays will enter the eye ; but if, as in Fig. 63, we place before the eye a piece of glass, called a lens, so constructed as to collect all the diverging rays together, the light will be concentrated at one point, and in sufficient quantity to enable us to see distinctly. 1607 Why do telescopes enable us to see objects invisible to the naked eyef Because they gather together more luminous rays from obscure objects than the eye can, and form a bright image of them m the tube of the telescope, where by means of lenses they are magnified. 1608 When a ship (out at sea) is approaching the shore, why do we see the small masts before we see the bulky hull ? Because the earth is round; and the curve of the sea hides the hull from our eyes after the tall moists have become visible. Fig 64. Here only that part of the ship above the line A C can be seen by the gpectator, A ; the rest of the ship is hidden by the swell of the curve D E. The diminution of the size of a ship seen at sea, owing to the convexity of the earth and the distance of the observer, is also illustrated in Fig. 65k, 1669 What is meant by the rejraction of light? Light traverses a given transparent substance, such as 254: SCIENCE OF COMMON THINGS. Refraction of light. A stick partially in water seems broken. Fig. 66- Fig 65. air, water, or glass, in a straight line, provided no reflection occurs and there is no change of density in the composition of the medium ; but when light passes from one medium into another, or from one part of the same medium into another part of a different density, it is lent from a straight line, or refracted. In Fig. 66, suppose n m to represent the sur- face of water, and S a ray of light striking upon its surface. When this ray S O enters the water, it will no longer pursue a straight course, but will be refracted, or bent towards the perpendicular line, A B, as in the case of S H. The denser the water, or other fluid, may be, the more the ray S O H will be refracted, or turned towards A B. 167O Does air possess the property of refracting light f Yes ; the more dense the air, the greater is its refrac- tive power. 167 f 1 Why does the part of a stick immersed in the water appear lent or broken ? The water and the air being of different densities, the rays of light proceeding from the part of the stick contained in the water are refracted, or caused to deviate from a straight line as they pass from the water into i the air ; consequently that portion of the [stick immersed in the water will appear to be lifted up, or to be lent in such a manner as to form an angle with the part | out of the water. The bent appearance of the stick in water is repre- || sented in Fig. 67. For the same reason, a spoon in a glass of water, or an oar partially immersed in water, always appears beut. SCIENCE OF COMMON THINGS. 255 Rivera deeper than they appear to be. Compound nature of white light. 167*8 Why does a river always appear more shallow than it really is 1 Because the light proceeding from the bottom of the river is refracted as it emerges out of the water, and causes the bottom to appear elevated. 167*3 How much deeper is a river than it seems to be? About one-third. If, therefore, a river seems only four feet deep, it is really six feet deep. Many persons get out of their depth in bathing in consequence of this deception. The following simple experi- ment illustrates the effect of re- fraction: Place a silver coin, i m, at the bottom of a basin, Fig. 68. The rays, i *, proceeding to the eye from the silver surface, render the coin visible. The point a, the eye, is then moved farther back, so that the edge of the basin obstructs the direct rays, and of course the coin is no longer seen. If an attendant carefully pours water into the basin, so that the object is not moved, it will presently, as the water rises in the basin, become again visible. This arises from the refraction of the rays by the water, the image, indeed, appearing at n instead of at m. 167*4 Is a ray of white light simple or compound? Every ray of white light is compounded of other rays of colored light. 1675 Into how many parts may a ray of light be divided f Into three parts : blue, yellow, and red. These three colors, by combination, make seven : 1, red ; 2, orange (or red and yellow) ; 3, yettow ; 4, green (or yellow and blue) ; 5, blue ; 6, in- digo (a shade of blue) ; and, 7, viokt (or blue and red). 1676 How is it known that a ray of light consists of several different colors f Because if a ray of light be cast upon a triangular piece of glass (called a prism), it will be distinctly divided into seven colors : 1, red ; 2, orange ; 3, yel- low ; 4, green ; 5, blue ; 6, indigo ; and, 7, violet. 1677 Why does a prism divide a ray of light into various colors f Because all these colors are refracted, or bent out of their course differently. Red is refracted least, and blue the most ; therefore, the blue ray will be bent to 256 SCIENCE OF COMMON THINGS. Effects of a prism In separating the rays of light. the top of the prism, and the red will remain at the bottom. Violet Indigo. Blue? Green. Yellow. Orange. Ked. Fig. by. This separation of a ray of solar light into different colors, by refraction, is represented in Fig. 69. A ray of light, A, is admitted through an aperture in a window-shutter into a darkened chamber, and caused to fall on a prism, P. The ray thus entering would, if allowed to pass unob- structedly, have moved in a straight line to the point K, on the floor of the room ; but the prism being so placed that the ray may enter and quit it at equal angles, it will be refracted in such a manner as to form on the opposite side of the room an oblong image called the solar spectrum, divided horizontally into seven colored spaces or bands of unequal extent, succeeding each other in the order represented: red, orange, yellow, green, blue, indigo, viokt. 1678 Are the colored rays, once separated and refracted from the prism, capable of being analyzed by refraction again ? They are not, and are hence designated as primary colors. 1679 If the seven different colors as separated by the prism be again collected together, what will they form ? White light. 1G8O To what is the great brilliancy of the diamond and other precious stones due ? To their power of refracting light ; they are also artificially cut in such a manner as to form a series of prisms,, which separate the rays of light falling on mem into their component colored rays. 1GS1 What is a rainbow f The rainbow is a semicircular l>and or arc, composed SCIENCE OF COMMON THINGS. 257 Production and explanation of the rainbow of the different colors, generally exhibited upon the clouds during the occurrence of rain in sunshine. If we take a glass globe filled with water, and suspend it at a certain height in the solar rays above the eye, a spectator standing with his back to the sun will see the refraction and reflection of red light ; if, then, the globe be lowered slowly, the observer retaining his position, the red light will be replaced by orange, and this in its turn by yellow, and so on, the globe at different heights presenting to the eye the seven primitive colors iri succession. If now, in the place of the globe occupying different posi- tions, we substitute drops of water, we have a ready explanation of the phenomena of the rainbow. Fig 70. Let -A, B, and C be three drops of rain ; S A, S B, and S C, three rays of the sun. A is divided into three colors ; the blue and yellow are bent above the eye, D, and the red enters it. The ray, S B, is divided into three colors ; the blue is bent above the eye, and the red falls below the eye, D, but the yellow enters it. The ray, S C, is also divided into the three colors. The blue (which is bent most) enters the eye ; and the other two fall below it. Thus the eye sees the blue of (7, and of all drops in the position of C; the yellow of B, and of all drops in the position of B ; and the red of A, and of all drops in the position of A ; and thus it sees a rainbow. 1683 What is the occasion of the rainbow f The rainbow is produced by the refraction ana re- flection of the solar rays in the drops oi falling rain. 1683 What are the conditions necessary in order that we may see a rainbow f The rainbow can be seen only when it rains, and in that point of the heavens which is opposite to the sun. It is necessary also that the sun should not have too 258 SCIENCE OF COMMON THINGS. No two persons see the same rainbow. Formation of two rainbows at the same time great an altitude above the horizon. Hence, within a certain interval each day, no visible rainbows can be formed, on account of the sun's high altitude above the horizon. 1684 How do we know that the rainbow results from the decomposition of the solar rays by drops of water 1 Because in the case of cascades and water-falls, the \spray and the drops of moisture dispersed over the igrass and the spiders -webs produce the same phenomena. 1635 Does every person see the same colors from the same drops? No ; no two persons see the same rainbow. To another spectator, the rays from S B (Fig. 70) might be red instead of yellow ; the ray from S C, yellow ; and the blue might be reflected from some drop below C. To a third person, the red may issue from a drop above A, and then A would reflect the yellow, and B the blue, and so on. 1686 Why are there often two rainbows at one and the same time f The first, or primary bow, is formed by two refrac- tions of the solar ray, and one reflection, tne rays of the sun entering the drops at the top, and being reflected to the eye from the bottom. Thus in Fig. 71, the ray S A of the primary rainbow strikes the drop at A, is refracted or bent to B, the back part of the inner surface of the drop ; it is then refracted to C, the lower part of the drop, when it is refracted again, and so bent as to come directly to the eye of the spectator. The secondary, or outer bow, is pro- duced, on the contrary, by two refrac- tions and two reflections, the ray of light entering the drops from the bot- tom, and being reflected to the eye from the top. Thus in Fig. 72, the ray S B of the secondary bow strikes the bottom of the drop at B, is refracted to A, is then reflected to C, is again reflected to D, when it is again refracted or bent, till it reaches the eye of the spectator. 1687 Why are the colors of the second bow all reversed 1 jn e . re. Because in one bow we sea SCIENCE OF COMMON THINGS. 259 Colors in a soap-bubble. Origin of morning and evening twilight. the rays which enter at the top of the rain-drops, refracted from the bottom : But in the other bow we see the rays which enter at the bottom of the rain-drops (after two reflections) refracted from the top. The position and formation of the primary and secondary rainbows are represented in Fig. 73. Thus in the formation of the primary bow, the ray of light S strikes the drop n at a, is refracted to n &, thence to g, and leaving the drop at this point, proceeds to the eyes of the spectator at 0. In the formation of the secondary bow, the ray S' strikes the drop p at the bottom at the point i, is refracted to rf, thence to/, and again to e, pro- ceeding from the top of the drop, also to the eye of the spectator at 0. The reason why the primary bow exhibits the stronger colors is, be- cause the colors are seen after one reflection and two refractions ; but the colors of the secondary (or upper) rainbow undergo two reflections and two refractions. Fig. 73. 1688 Why does a soap bubble exhibit such a variety of colors f Because the thickness of the film through which the rays pass is constantly varying. 1680 Why is a soap bubble so constantly changing its thickness t Because the water runs down from the top to the bottom of the bubble, till the crown becomes so thin as to burst. 3 60O Wliat is the cause of morning and evening twilight f When the sun is below the horizon, the rays which strike upon the atmosphere or clouds are bent down 260 SCIENCE OF COMMON THINGS. Lenses and their varieties. What is a focus of light? towards the earth, and produce a little light called twi- light. 1691 What is a lens f A piece of glass or other transparent substance, bounded on both sides by polished spherical surfaces, or on the one side by a spherical, and on the other by a plane surface. Rays of light passing through it are made to change their direction, and to magnify or diminish the appearance of objects at a certain distance. 1603 Sow many varieties of lenses are generally recognised f Two : convex and concave. Fij?. 74. Among convex lenses are the double convex A (Fig. 74) to which the appellation lens was originally applied from its resemblance to a lentil- seed (kns in Latin) being bounded by two convex spherical surfaces whose centres are on opposite sides of the lens ; the plano-convex B, having one side bounded by a plane surface, and the other by a convex surface ; and the meniscus or concavo-convex C, bounded on one side by a concave, and on the other by a convex surface. There are also three principal varieties of concave glasses; as the double concave D, bounded by two concave surfaces, forming portions of spheres whose centres are on opposite sides of the lens; the plano- concave E, bounded on one side by a plane, and on the other by a concave surface ; and convexo-concave F, bounded by a convex surface on one side, and by a concave one on the other. 1693 What is a focus of light f "When rays of light continually approach each other, as in moving to a point, they are said to converge, and the point at which the converging rays meet is called tliejocus. 1694 What sort of a lens is a common burn- ing-glass ? A double convex lens. Fig. 75 represents the action of a double con- vex lens in causing the rays of light to converge and meet at a focus. Fi gi 75. 1695 What are transparent bodies f SCIENCE OF COMMON THINGS. 261 Opaque and transparent bodies. Absorption of light. Those which do not irvterrupt the , passage of light, or which admit of other bodies being seen through them. 1606 When is a body said io be opaque ? When it entirely prevents the passage of light. 1607 Is there any body perfectly transparent f No ; some light is evidently lost in passing even through space, and still more in traversing our atmo- sphere. 160S Row much of Vie sun's light is supposed to be intercepted by the atmosphere ? It has been calculated that the atmosphere, when the rajs of the sun ^>ass perpendicularly through it, inter- cepts from one-fifth to one-fourth of their light; but when the sun is near the horizon, and the mass of air through which the solar rays pass is consequently vastly increased in thickness, only one two hundred and twelfth part of their light can reach the surface of the earth. 1S00 Why is charcoal black f Because it absorbs all the light which falls upon it, and reflects none. 1*700 What becomes of the light which is absorbed? This question cannot be satisfactorily answered. In all probability it is permanently retained within the substance of the absorbing body. 1*7O1 To what depth is light supposed to penetrate tJie ocean f It is calculated that sea water loses all its transpa- rency at the depth of seven hundred and thirty feet ; but a dim twilight must prevail much deeper in the ocean. 12 262 SCIENCE OF COMMON THINGS. Structure of the eye. How the eye is moved. CHAPTER II. STRUCTURE OF THE EYE AND THE PHENOMENA OF VISION. 1*703 What is the structure of the human eye ? In man the organ of vision consists of two hollow spheres, each about an inch in diameter, filled with certain transparent liquids, and deposited in cavities of suitable magnitude and form in the upper part of the front of the head on each side the nose. 7O3 How is it that we are enabled to move the eye in various directions t By means of muscles attached to different points of its surface. These are shown in Fig. 76. where the external bones of the temple are supposed to be removed in order to render visible the muscular arrangements. The muscle, 1, raises the eye-lid, and is constantly in action while we are awake. During sleep, the muscle being in repose and relaxed, the eye-lid falls and protects the eye from the action of light. The muscle, 4, turns the eye upwards ; 5, downwards ; 6, outwards ; and a corresponding one on the inside, not seen in the figure, turns it inwards. No. 2 and 10 turn the eye round its axis. No. 11 is tue great optic SCIENCE OF COMMON THINGS. 263 Eetina. Iris. Pupil. Cornea nerve, which conveys the sensation to the brain. If this nerve were cut, notwithstanding the eye might be in other respects perfect, the sense of sight would be destroyed. 1704 Of what parts does the eye consist f The eye is of globular form, and is composed of three coats or membranes, called the sclerotic, the choroid, and the retina; and three humors, denominated the aqueous ', the crystalline, and the vitreous. 1705 What is meant by the " retina of the eye ?" The network which lines the back of the eye is called the retina ; it is composed of an expansion of the optic nerve. 1706 What is that portion of the eye called ivhich in some persons is blue, in others gray or hazel ? It is called the iris. 17*O 7* In the centre of the iris is a circular "black opening : what is this called 1 It is called the pupil. But this spot is not a black substance, but an aperture, which appears black only because the chamber within it is dark. It is properly speaking the window of the eye, through which light is admitted, which strikes on the retina. 17*O8 Does light admitted through the pupil to the retina produce vision ? Yes, provided the light enter in sufficient quantity. How by the arrangement of the several parts of the eye are we enabled to see? The rays of light falling upon the cornea, enter the interior of the eye through the pupil, and by the joint action of the cornea and crystalline lens are brought to a focus at the back part of the eve, upon the retina. Here an image is formed, and the impression it makes is conveyed along the optic nerve to the brain. 17*1O What is meant "by Hie " cornea of the eye ?" All the outside of the visible part of the eyeball. Fig. 77 represents the interior construction of the eye. It is composed, in the first place, of the cornea, a, a transparent membrane in front of the globe of the eye. Next is the sclerotic coat, t, which joins on the cornea, and upon which the external form of the eye depends. The cornea is united to, or fixed in, the sclerotic coat, like the glass into the case of a watch : d, c represents the iris, with an opening in it, forming the pupil SCIENCE OF COMMON THINGS. Explanation of near-sightedness. Next in order is the aqueous humor, &, e, in the middle of which is the iris, d, c. Behind the pupil we have the crystalline. lens, /, and then the vitreous humor, A, filling all the interior of the ball of the eye. m indi- cates the retina, which is an expansion of the optic nerve, n. k is the choroid coat, a membrane interposed between the retina and the sclerotic coat ; it terminates in form in a series of folds or filaments, #, called the ciliary ligament or processes. 1711 Why are some persons near-sighted ? Because the curvature of the cornea and the crystal- line lens is too great, and the rays of light which form the image are brought to a focus before they reach the retina or the back part of the eye. The object, there- fore, is not distinctly seen. Fig. 79 represents the manner in which the image is formed upon the retina in the perfect eye. The curvature of the cornea, s s, and of the crystalline lens, c c, is just sufficient to cause the rays of light proceeding from the im- age, e e, to converge to the right focus, m, upon the retina. Fig. 78 represents the man- ner in which the image is formed in the eye of a near-sighted per- son. The curvature of the cor- nea, s 5, and of the crystalline lens, c c, is so great that the im- age is formed at m m in advance of the retina. SCIENCE OF COMMON THINGS. Explanation of far-sightedness. What sort of glasses do near-sighted persons wear ? If the cornea and crystalline lens be too convex (or projecting), the person must wear double concave glasses to counteract it. 17*13 What is meant by " double concave glasses ?" Glasses hollowed-in on both sides. 1 714 Why are old people far-sighted ? < Because the humors of their eves are dried up by age; in consequence of which the cornea sinks in, or becomes flattened. 17*15 Why does the flattening of the cornea prevent persons seeing objects which are near ? Because the cornea is too flat, and the image of ob- jects is not completely formed when their rays reach the retina / in consequence of which the image is imper- fect and confused. Fig. 80 represents the man- ner in which the image is formed in the eye, when the cornea or crystalline lens is flattened. The perfect image would be produced at m m, behind the retina, and, of course, beyond the point ne- FJ ^ cessary to secure perfect vision. 17*16 What sort of spectacle-glasses are suitable for old people f Double-convex glasses, or those which curve outwards on both sides. These shorten the focus of the eye, and produce an image upon the right point, the retina. 1717* Why do near-sighted persons bring objects close to the eye in order to see them ? Because the distance between the front and back of the eye is so great, that the image of distant objects is formed m front of the retina; but when objects are brought near to the eye, their image is thrown farther made to fall on the retina. 1718 Why do old people hold objects far off in order to see them better t Because the distance between the front and back of their eyes is not great enough / when, however, objects 266 SCIENCE OF COMMON THINGS. Use of the e} r ebrows and eyelashes. are held farther off, it compensates for this defect, and a perfect image is formed on the retina. Birds of prey are enabled to adjust their eyes so as to see objects at a great distance, and again those which are very near. The first is accom- plished by means of a muscle in the eye, which enables them to flatten the cornea by drawing back the crystalline lens ; and to enable them to perceive distinctly very near objects, their eyes are furnished with a flexible bony rim. by which the cornea is thrown forward at will, and the eye thus rendered near-sighted. 1*710 Why do persons who are short-sighted in youth, gradually have this failing corrected as they grow old ? They are short-sighted because the cornea of the eye is too globular ; but as age advances, the fluids are not secreted as before, the eye becomes flattened, and natural sight is again restored. 1730 What is the use of the eyebrows ? The eyebrows defend the eyes from too strong a light, and serve to turn away substances which might other- wise fall into the eye. 1731 What is the use of the eyelashes? The eyelashes guard the eye from danger, and pro- tect it from dust or insects floating or flying in the atmo- sphere. 17*33 Why is the eye pained by a sudden light f Because the nerve of the eye is burdened with rays before the pupil has had time to contract. 1733 What is the pupil of the eye ? The circular black opening in front of the eye. 1734 Why does it give us pain if a bright light is brought suddenly towards us at night-time ? Because the pupil of the eye dilates very much in the dark in order to admit more rays. When therefore a light is brought suddenly before us, the enlarged pupils overload the optic nerves with rays, which causes pain. 1735 Why can we bear the light Rafter a few moments f Because the pupils contract again almost instantly, and adjust themselves to the quantity of light which falls upon them. 1736 Why can we see nothing when we leave a well-lighted room, and go into the darker road or street ? SCIENCE OF COMMON THINGS. 267 Vision in the light and in darkness. Cats how see in the dark. Because the pupil (which contracted in the bright room) does not dilate instantaneously ; and the con- tracted pupil is not able to collect rays enough from the darker road or street to enable us to see objects before us. IT'S? How does light cause the pupil of the eye to contract ? The pupil of the eye is a round hole in the midst of a movable muscular curtain or screen, called the iris. "When too much light falls on the nervous retina at the back of the eye, it irritates it ; and this irritation is conveyed to the muscular rings composing the curtain by small nervous fibres, causing them to contract. 17*38 Why do we see better when we get used to the dark f Because the pupil dilates again, and allows more rays to pass through its aperture.; in consequence of which we see more distinctly. 17*39 If we look at the sun for a few moments, why do all oilier things appear dark f Because the nerve of the eye, by looking at the sun, is so affected by the intensity of the light that it requires a few moments to recover its former sensibility. 17*30 Why can we see the proper colors of every object again after a few minutes f Because the eye again recovers its sensibility, and accommodates itself to the light around. 17*31 Why can tigers, cats, and owls see in the dark f Because they have the power of enlarging the pupil of their eyes so as to collect the scatterea rays of light ; in consequence of which they can see distinctly when it is not light enough for us to see anything at all. 17*33 Why is it that when we press slightly upon the ball of either eye, while viewing an object, we see double? \ Because the pressure of the finger prevents the ball of one eye from following the motion of the other, and the axis of vision in each eye being different, we see two images. 17*33 Do persons who squint see double 1 They do / but practice gives them p^ower of attending to the sensation of only one eye at a time. 268 SCIENCE OF COMMON THINGS. Cause of squinting. We see images and not objects themselves. 17*34 What is the cause of strabismus, or squinting ? The inability of one eye to follow the motions of the other ; this may arise from habit, imperfect power in one eye, or some defect in the muscular movements. 17*35 Why, when the eye is violently struck or pressed upon, do we seem to see light ? Because the pressure communicated to the optic nerve causes a violent and momentary sensation of light. 17*3G When we say we see an object, what do we in fact do f The mind is only taking cognizance of the picture or impression made on the retina. 17*37* If the mind, in seeing an object, sees in reality only a picture yainted on the back of the retina, how is it enabkd to judge of magnitudes, distances, etc., the picture being on a comparatively fiat surface f It is only by experience. " I see men as trees walk- ing," said the man born blind, when restored to sight. 17*33 Would a person whose eyes, although perfect, had been covered up from infancy to maturity, be able to see ? that is, comprehend any scene or prospect on which he first opened his eyes ? He would see the objects, but could no more under- stand them than a child understands the printed page on which it looks, although every word is clear and distinct. 17*39 Do we see the same lines and surfaces of an object alike wicheach eye? "We do not. We may convince ourselves that we do not, by placing two candles, fo? example, in such & position, that when they are looked at with the right eye, one is made to cover the other ; if now we close the right eye and look at them with the left, the most remote candle will be no longer screened by the front one, but will be seen about an inch to the left of it. 17*40 Why cannot we count the posts of a fence when wt are riding rapidly in a railroad car ? Every impression, according to the intensity of its effects, remains for a certain length of time on the retina, and a measurable period is necessary to produce the impression. The light from each post falls upon the eye in such rapid succession, that the different images become confused and blended, and we do not obtain a distinct vision of the particular parts. SCIENCE OF COMMON THINGS. 269 Why the sun and moon seem larger on the horizon than overhead. 17*41 Why do the sun and moon seem larger at their rising and setting than at any other time f The appearance is an illusion, in consequence of ter- restrial objects being placed in close comparison with them at one time, and not at the other. 1*74:3 Is this illusion an optical one, or a mental illusion t A mental one, since the organs of vision do not pre- sent to us a larger image of the moon or sun in the horizon than in the zenith. 17*43 What do we mean by the horizon ? The circle or line where the earth and sky appear to meet. 1744 What do we mean by the zenith f The point or part of the heavens immediately over- head. 17*45 Is the moon nearer or farther from us when upon the horizon f When the moon is on the horizon, it is about four thousand miles farther from us than when in the zenith ; its apparent diameter, therefore, instead of appearing larger, ought to appear about a sixtieth part less. 17*46 Why are we so often mistaken in respect to the actual distance of a conflagration at night ? Light radiating from a centre rapidly weakens as the distance from the centre increases, being, for instance, only one-fourth part as intense at double the distance. The eye learns to make these allowances, and by the clearness and intensity of the light proceeding from the object, judges with considerable accuracy of the com- parative distance. But a fire at night appears uncom- monly brilliant, and therefore seems near. 17*47* Why does the evening star rising over a hill-top appear as if situated directly over the top of the eminence ? Because we make brightness and clearness to depend on contiguity, as it ordinarily "does ; and as the star is bright, we unconsciously think it near us. 1748 What is the cause of colors t The action of light. 1749 How is thit proved ? 12* 270 SCIENCE OF COMMON THINGS. Color and its cause. Why are some bodies red and others white, black, &c. ? In the dark, bodies have no color, and in the light their colors may be altered by subjecting to certain mo- difications the light by which they are rendered visible. Thus a blue piece of cloth in a red light will appear red. 17*50 Why is it that we find it difficult to distinguish colors ~by candle- light? Because we have modified the light upon which the full effect of the color depends. 17*51 What then is the true definition of color ? The color of a substance is the effect of light on a surface adapted to reflect its particular color. 17*53 Why do some things reflect one color, and some another f Because the surface of things is so differently consti- tuted, both physically and chemically. 17*53 Why is a rose red ? Because the surface of a rose absorbs the Hue and yellow rays of light, and reflects only the red. 17*54 Why are some things black f Because they absorb all the rays of light, and reflect none. 1755 Is black a color f It is not / it is the absence of color. 17*56 Why are some things white f Because they absorb none of the rays of light, but reflect them all. 17*57* Why are clouds, snow, sugar, and salt white f Because they reflect 'back unchanged the white light which strikes upon them. 17*58 Why are not the crystals of frost and snow transparent like icef The crystals of frost and snow are not solid, but they contain air ; hence their brilliant whiteness : for the air preventing the ready transmission of light through the crystals, the rays are copiously reflected, from the mass of crystals. 17*59 Why is the darkness of night diminished by the presence, of snow f Because the snow reflects, instead of absorbing, like SCIENCE OF COMMON THINGS* 271 Origin of color in leaves of trees. Why is the sky blue ? the bare ground, the faint light that proceeds from the sky. 176O Why are the leaves of plants green f Because a peculiar chemical principle, called chloro- phyl, is formed within their cells, which has the property of absorbing the red rays, and of reflecting the blue and yellow, which mixture produces green. 17G1 Why are leaves a light green in spring f Because the chlorophyl is not fully formed. 17(33 Why do leaves turn brown in autumn f Because the chlorophyl undergoes decay, and is not replaced as it is in spring. 1763 Why do all things appear black in the dark f In the dark there is no color, because there is no light to be absorbed or reflected, and therefore none to be decomposed. Of course, in certain degrees of darkness, all objects are actually invi- sible. The question refers to that peculiar degree of darkness when the forms of objects may be seen, but not their hues. 1764 Why does the sky appear blue ? Because the atmosphere absorbs the red and yellow rays, and transmits the blue. 1765 Why does the sun most generally fade artificial colors f Generally the loss of color arises from the oxidation of the substances used in dyeing ; as tarnish and rust are an oxidation of metals. Sometimes, however, the ingredients of the dye are otherwise decomposed by the sun ; and the color (which is due to a combination of ingredients) undergoes a change as soon as the sun deranges or destroys that combination. 1766 What remarkable correspondence is there between the geographical position of a region, and the colors of its plants and animals f In the tropics, where the sun shines longest and brightest, the darkest green prevails over the leaves of plants, the flowers and fruits are colored brightly, and the plumage of the birds is of the richest description. 1767 What is the natural coloration exhibited -in temperate climates f In temperate climates everything is of a more sub- 272 SCIENCE OF COMMON THINGS. Colors in different regions of the earth. Contrasts of colors. dued variety the flowers are less bright ; the prevail- ing tint of the birds is brown ; and the dresses of the inhabitants are sombre. IT'S 8 How is this corfespondence further exemplified in the Arctic and Antarctic regions ? Here there is little color in natural objects ; the few flowers are white or yellow / and the animals are almost uniformly Hack or white. 17*69 In what part of the ocean do we find the brightest shells and sea- weeds ? Near the shore, in shallow water, where the influence of light is greatest. 17* 7*0 What fishes are distinguished for the brilliancy of their colors? Those that swim near the surface; whereas those which live at greater depths are gray, brown, and black. 17*7*1 What is the appearance of the sea-weeds and animals that live at great depths of the ocean ? They are nearly colorless. 17*7*3 Why is grass growing under a covering of a white or yellowish white color f Because it is secluded from the light, whose presence and action is necessary for the production of the material which imparts to it its green color. 17*7*3 Of the various rays composing solar light, which are the most visible to the human eye ? The yellow. 17*7*4 Which have the greatest heating effect f The faint red rays. 17*7*5 Why does a dress composed of cloths of different colors, look well much longer, although worn, than one of only a single color, the character of the cloth in both instances being identical ? It is owing to the effect of contrast between the colors. If a dress is composed of cloths of two colors, as red and green, orange and blue, yellow and violet, they will mutually heighten the effect of each, and make each portion appear to the best advantage. 17*7*0 Why will stains be less visible on a dress of different colors, than on one composed of only a single color ? Because there exists in general a greater contrast SCIENCE OF COMMON THINGS. Contrasts of colors In dress. Arrangement of bouquets. among the various parts of the first-named dress, than between the stain and the adjacent part, and this differ- ence renders the stain less apparent to the eye. 177 7 Why can a coat, waistcoat, and pants of the same color be worn with advantage together only when they are new f Because as soon as one of them loses its freshness from having been worn longer than the others, the difference will increase by contrast. 1778 Give an illustration. A pair of new black pants, worn with a vest of the same color, which is old and rusty, will make the tinge of the latter appear more conspicuous, and at the same time the black of the pants will appear more brilliant. White and other light-colored trowsers would produce a contrary effect. 1779 What is the general law upon which the harmony of colors depends ? Every color when placed beside another color is changed, appearing different from what it really is; and it moreover equally modifies the colur with whicn it is in proximity. 1780 What effect has rose-red upon a rosy complexion f It causes it to lose some of its freshness. 1781 For fair complexions, deficient in rose, which color is most favor* abkf A delicate green.,. 17SS What effect has black drapery upon the color of the skin 1 It makes it appear whiter. 1783 What rule should be observed in the grouping of flowers and the preparation of bouquets ? "We must separate pink flowers from those that are either scarlet or crimson ; orange, from orange yellow flowers ; yellow flowers from greenish-yellow flowers ; blue from violet-blue, red from orange, pink from violet ; blue flowers from violet flowers. 1784 What is the optical effect of dark colors and black upon the size of the figure f 2 74: SCIENCE OF COMMON THINGS. Most conspicuous colors. Colors of animals adapted to their necessities. It causes it to appear smaUer / therefore these colors are most suitable for stout persons. 1785 What effect do white and light-colored dresses have upon the size of the figure ? They cause it to appear larger. 178Q What effect do large patterns in dress make f They make the figure look shorter. 1787 What is the effect of narrow longitudinal stripes in dress t They add to the apparent height of the figure. 1788 What is the effect of fwrizontal stripes ? The effect of horizontal stripes is opposed to that of longitudinal, and under every condition they are un- graceful. 1789 What colors are most conspicuous in battle f It has been found by numerous observations that red is the most fatal color, and the least fatal is a light grey. 1790 What curious provision for the protection of animals does nature appear to make ? She appears to have adapted the color of the creature to its haunts in such a way as tends to preserve it from injury. Caterpillars and insects which feed on leaves are generally of the color of the leaves. As long as they remain still, it is almost impossible to distinguish the grasshopper from the herbage on which it rests. 1791 What curious change is noticed in the color of animals inhabiting the Arctic regions f During the snows of winter, foxes, hares, and some varieties of birds are white ; when the ground is free from snow in summer, they are of a 'brown color. SCIENCE OF COMMON THINGS. 275 What is electricity ? Means of exciting electricity. PART VIII. ELECTRICITY, GALVANISM, MAGNETISM, AND ELECTRO-MAGNETISM, CHAPTEE I. ELECTRICITY. 1793 What is electricity t Electricity is one of those imponderable agents that appear to be diffused through all nature, existing in all substances without affecting their volume or their tem- perature, or giving any indication of its presence when in a latent state. When, however, it is liberated from this repose, it is capable of producing the most sudden and destructive effects, or of exerting powerful influences by a quiet and long-continued action. 1*793 How may electricity be called into activity f By mechanical power, by chemical action, by heat, and by magnetic influence. 17*94 What is the most ordinary way of exciting electricity f By friction. 17*95 Do we know any reason why the means above enumerated should develope electricity from its latent condition? We are entirely ignorant upon this 'subject. 17*96 When you rub apiece of paper with India-rubber, why does it adhere to the table f Because tlie friction of the India-rubber against the surface of the paper developes electricity, to which this adhesiveness is mainly to be attributed. 17*97* Does electricity present any appearance by which it can be "known f No ; electricity, like heat, is in itself invisible, though often accompanied by both light and heat. 276 SCIENCE OF COMMON THINGS. Electrified and non-electrified bodies. 17*93 When a substance, by friction or by any other means, acquires the property of attracting other bodies, in what state is it said to be? It is said to be electrified^ or electrically excited / and its motion towards other bodies, or of other bodies to- wards it, is ascribed to a force called electric attraction. 17*09 Does an electrified body exercise any other influence than an, attractive onef It does ; for it will be found that light substances, after touching the electrified body, will recede from it just as actively as they approached it before contact. This is termed electric repulsion. Thus, if we take a dry glass rod, rub it well with silk, and present it to a light pith ball, or feather, suspended from a support by a silk thread, the ball or feather will be attracted towards the glass, as seen at G, Fig. 81. After it has adhered to it a mo- ment, it will fly off, or be repelled, as P' from G'. The same will happen if sealing-wax be rubbed with dry flannel, and a like ex- Fig. 81. periment made ; but with this remarkable difference, that when the glass repels the ball, the sealing-wax attracts it, and when the wax repels, the glass will attract. These phenomena are examples of electrical attraction and repulsion. 1800 What is a non-electrified body f One that holds its own natural quantity of electricity undisturbed. 1801 What happens when an electrified body touches one that is non- electrified f The electricity contained in the former is transferred in part to the latter. Thus, on touching the end of a suspended silk-thread with a piece of excited wax, the silk will be excited, as will be shown by its moving towards a book, piece of metal, or any other object placed near it. 18OS Do all bodies conduct or allow electricity to pass through them equally well? Although there is no substance that can entirely pre- vent the passage of electricity, nor any that does not oppose some resistance to its passage, yet it moves with a much greater facility through a certain class of sub- stances than through others. Those substances which SCIENCE OF COMMON THINGS. 277 Conductors and non-conductors of electricity. Electrical machines. facilitate its passage are called conductors ; those that retard or almost prevent it, are called non-conductors. 1803 What substances are good conductors of electricity ? The metals, charcoal, the earth, water, and most fluids, except oils, the human body, etc., are good conductors. 1804 What substances obstruct the passage of electricity, or are "non- conductors ?" Glass, resin, oil, silk, sulphur, dry air, etc., etc., are non-conductors. 1805 What is an electrical machine f An electrical machine is an arrangement by which quantities of electricity can bexollected and discharged. The electrical machine most usu- ally employed consists of a large circular plate of glass, see Fig. 82, mounted upon a metallic axis, and supported upon pillars fixed to a secure base, so that the plate can, by means of a handle, W, be turned with ease. Upon the supports of the glass, and fixed so as to press easily but uniformly on the plate, are four rubbers, marked r r r r in the figure ; and flaps of silk, s 5, oiled on one side, are attached to these, and secured to fixed sup- ports by several silk cords. "When the machine is put in motion, these flaps of silk are drawn tightly against the glass, and thus the friction is increased, and electricity excited. The points p p collect the electricity from the glass, and convey it to the conductor, c, which is sup- ported by the glass rod g. Fig. 83 represents another form of an electrical machine, constructed on similar principles. S being a glass cylinder turn- ing on an axis, Y the conductor, F the rubber, A A supports. 1806 What is the theory of electricity most generally adopted ? The theory proposed by Dr. ine tneory proposed by Ur. Franklin: this supposes the ex- istence of a single, imponderable Fig, 83. 278 SCIENCE OF COMMON THINGS. Positive and negative electricity. Velocity of electricity. fluid, equally distributed throughout nature : every substance being so constituted as to retain a certain quantity of this agent. Any disturbance of the natural state of a body produces evidences of electricity. ISOT* Does electricity seem to exist in two different states or conditions f It does ; and to designate these two conditions, the terms positive and negative have been employed. Thus a body which has an overplus of electricity is called posi- tive, and one that has less than its natui^l quantity is called negative. ISO 8 Do light, heat, and electricity appear to have some properties in common f They do / each may be made, under certain circum- stances, to produce or excite the other. All are so light, subtle, and diffusive, that it has been found impossible to recognise in them the ordinary characteristics of matter. Some suppose that light, heat, and electricity are all modifications of some common principle. 18O9 Why does the fur of a cat sparkle and crackle when rubbed with the hand in cold weatlier ? Because the friction between the hand and fur pro- duces an excitation of negative electricity in the hand and positive in the fur, and an interchange of the two causes a spark, with a slight noise. 1S1O Why does this experiment work best in very cold weather ? Because the air is then very dry, and does not convey away the electricity as fast as it is excited ; if the air, on the contrary, were moist, the electricity would be conducted off nearly as fast as it was excited by friction, and its effects would not therefore be so manifest. 1811 With what velocity is electricity transmitted through good conduc- tors f "With a velocity so great that the most rapid motion produced by art appears to be actual rest when com- pared to it. Some authorities have estimated that elec- tricity will pass through copper w r ire at the rate of two hundred and eighty-eight thousand miles in a second of time a velocity greater than that of light. The SCIENCE OF COMMON THINGS. 279 Principal agents in nature exciting electricity. results obtained, however, by the United States Coast Survey, with iron wire, show a velocity of from 15,000 to 20,000 miles per second. 1813 What agents are undoubtedly the most active in producing and exciting electricity in the operations of nature f The light and heat of the suds rays. 1813 It has become the habit with many to ascribe to electricity the agency of phenomena in the natural world, the cause of which may not be apparent: is there any reason for this? There certainly is not : electricity is diffused through all matter, and is ever active, and many of its pheno- mena cannot be satisfactorily explained ; but it is go- verned, like all other forces of nature, by certain fixed laws, and it is by no means a necessary agent in all the operations of nature. It argues great ignorance to refer without examination every mysteri- ous phenomenon to the influence of electricity. 1814 Do some animals have the power of exciting electricity within themselves f There are certain animals which are gifted with the extraordinary power of producing electncal phenomena by an effort of muscular or nervous energy. Among these the electrical eel and the torpedo are most re- markable. 1815 How powerful a charge of electricity can the electrical eel send forth when in full vigor f Sufficient to knock down a man or stun a horse. 1810 Is the electricity generated by these animals the same as that occa- sioned by tlie ordinary electrical machine ? It is the same, and produces the same effects. Do vital action and muscular movements in man and animals give rise to electricity f They do ; and it can be shown by direct experiment that a person cannot even contract the muscles of the arm without exciting an electrical action. 1818 Does change of form or state in bodies generally produce electrical excitation ? Change of form or state is one of the most powerful methods of exciting electricity. 280 SCIENCE OF COMMON THINGS. Lightning. Three forms of lightning. Water, in passing into steam by artificial heat, or in evaporating by the action of the sun or wind, generates large quantities of electricity. The crystallization of solids from liquids, all changes of temperature, the growth and decay of vegetables, are also instrumental in producing elec- trical phenomena. 1S1Q What is lightning f Lightning is accumulated electricity, generally dis- charged from the clouds to the earth, but sometimes from the earth to the clouds. 1S3O What causes the discharge of an electric cloud? When a cloud overcharged with electric fluid ap- proaches another which is undercharged, the fluid rushes from the former into the latter, till both contain the same quantity. 18J31 Is there any other cause of lightning besides the one just men- tioned ; Yes ; sometimes mountains, trees, and steeples will discharge the lightning from a cloud floating near, and sometimes the electricity passes from the earth, into the clouds. 1833 How high are the lightning clouds from the earth? Sometimes they are elevated four 01* five miles high, and sometimes actually touch the earth with one of their edges ; but they are rarely discharged in a thun- der storm when they are more than seven hundred yards above the surface of the earth. 1833 What is a thunder storm ? The disturbance caused" in the air when successive discharges of accumulated electricity take place. 1S34 Into how many kinds has lightning been divided ? Three. 1835 What are they ? The zig-zag lightning, sheet lightning, and hall light- ning. 1836 Why is lightning sometimes forked ? Because the lightning cloud is at a great distance ; and the resistance of the air is so great that the electri- cal current is diverted into a zig-zag course. SCIENCE OF COMMON THINGS. 281 Sheet and heat lightning. Duration of a flash of lightning. 1837 How does the resistance of the air make the lightning zig-zag ? As the lightning condenses the air in the immediate advance of its path, it flies from side to side, in order to pass where there is the least resistance. 18SS Why is the flash sometimes quite straight ? Because the lightning cloud is near the earth, and as the flash meets with very little resistance, it is not diverted ; in other words, the flash is straight. 183Q What is sheet lightning? Either the reflection of distant flashes not distinctly visible or beneath the horizon, or else several flashes intermingled. 1830 What other form does lightning occasionally assume ? Sometimes the flash is globular, which is the most dangerous form of lightning. 1831 Does a discharge produce a flash when it passes through good conductors f It does not, but passes quietly and invisibly. 1S3S What is heat lightning f Sometimes it is the reflection in the atmosphere of the lightnings of storms very remote, the storms them- selves being so far distant that their thunders cannot be heard. This phenomenon is also occasioned by the play of silent flashes of electricity between the earth and the clouds, the amount of electricity developed not being sufficient to produce any other effects than the mere flash of light. 1833 Why is lightning more common in summer and in autumn than in spring and winter f Because the heat of summer and autumn produces great evaporation, and the conversion of water into vapor always developes electricity. 1834 How long is the duration of a flash of lightning f Arago has demonstrated that it does not exceed the millionth part of a second. 1835 With ivhat velocity is lightning, or the electric fluid which gives rise to its appearance, supposed to move f 282 SCIENCE OF COMMON THINGS. Places dangerous in a thunder storm. How a tree influences lightning. Not less than two hundred and fifty thousand miles per second. 1836 Why does lightning sometimes kill men and leasts f Because, when the electric current passes through a man or beast, it produces so violent an action upon the nervous system, that it destroys life. 1337* When is a person struck dead by lightning 1 Only when his body forms a part of the lightning's path j that is, when the electric fluid (in its way to the earth) actually passes through his body. 1838 Wliat places are most dangerous during a thunder storm f It is very dangerous to be near a tree or lofty building. 1839 Why is it dangerous to be near a tree or lofty building during a thunder storm f Because a tall, pointed object (like a tree or spire) will frequently discharge a lightning cloud ; and if any one were standing near, the lightning might diverge from the tree and pass through the fluids of the human body. 1S4O How can a tree or spire discharge a lightning cloud f A lightning cloud, floating over a plain, may be too far off to be discharged by it ; but as a tree or spire would shorten this distance, it might no longer be too far off to be discharged. For example : If a lightning-cloud were seven hundred yards above the , earth, it might be too far off to be discharged ; but a tree or spire fifty yards high would make the cloud only six hundred and fifty yards off a conductor ; in consequence of which the cloud might be instantly dis- charged. 1841 What parts of a dwelling are most dangerous during a thunder- storm f The fireplace (especially if the fire be lighted). It is also imprudent to sit close by the walls. 1843 Why is it dangerous to sit before afire during a thunder storm f Because the heated air and soot are conductors of lightning, especially when connected with such excel- lent conductors as the stove, grate, or fire-irons. 1843 Why is it dangerous to lean against a wall during a thunder storm f SCIENCE OF COMMON THINGS. 283 Safest places in a thunder storm. Because the electric fluid will sometimes run down a watt, and (as the body of a person is a better conduc- tor than a wall) would leave the wall and run.' down the body. 184:4 Why is it dangerous to be in a crowd during a thunder storm f For two reasons : 1. Because a mass of people forms a better conductor than an individual', and 2. Because the vapor arising from a crowd increases its conducting power. 1845 Why is the danger increased by the vapor which rises from a crowd? Because vapor is a conductor, and the more conduc- tors there are, the greater the danger will be. 1846 If a person be abroad in a thunder storm, what place is the safest ? Any place about twenty or thirty feet from a tall tree, building, or stream of water. 1847* Why would it be safe to stand twenty or thirty feet from a tall tree during a thunder storm ? Because the lightning generally chooses tall trees as conductors, and we should not be sufficiently near the trees for the lightning to diverge from them to us. 1848 Why is the middle of a room more safe than any other part of it in a thunder storm ? Because the lightning (if it should strike the room at all) would come down the chimney or walls of the room; and therefore the farther distant from these, the better. 184Q Why is a mattress, bed, or hearth-rug a good security against injury from, lightning ? Because they are all non-conductors ; and as lightning always makes choice of the lest conductors, it would not choose for its path such things as these. 1850 What is the safest thing a person can do to avoid injury from lightning ? Lie upon a led in the middle of a room. A led filled with feathers is an excellent non-conductor. 1851 Is there not generally a greater apprehension of the danger from lightning than experience would justify ? The apprehension and solicitude respecting lightning 284: SCIENCE OF COMMON THINGS. Lightning conductors. Their proper principle of construction. are proportionate to the magnitude of the evils it pro- duces, rather than the frequency of its occurrence. The chances of an individual being killed by lightning are infinitely less than those which he encounters in his daily .walks, in his occupation, or even during his sleep from the destruction of the house in which he lodges by fire. 185S Why does the lightning in its course down a building generally dart from point to point, and not follow a direct path ? Because it always takes in its course the best conduc- tors ; and will fly both right and left in order to reach them. 1853 What is a lightning conductor f A metal rod fixed in the earth, running up the whole height of a building, and rising in a point above it. 185f, less pure than the country, why difficult at a very high 210 elevation, 72 Cleanliness, necessity of, 233 Bricks, burned, why red, 39 jClimate, meaning of the term, 104 why used for lining stoves and fur- Climates, peculiarities of, 104 naces, 151 temperature of, coloration pecu- Broth, cooled by convection, 159 liar to, 271 Bubbles, air, in ice, origin of, 178 ' Clock, common, what is a, 29 in a tea-cup, how attracted, 14 Clocks, why go faster in winter than ia on leaves of water plants, what the summer, 30 are they, 236 Clothing, contains no warmth in itself; eoap, why ascend, 56 | 152 INDEX*. 315 regetabl* De Clothing, how makes us warm, 147 use of, 148 Clouds and fog, difference between, 80 Clouds, cause of their various shapes appearances, 86 color of, 85 distance, above the earth, 84 size of, 84 sunset, why colored, 86 what are, 83 when high and low, 83 ffoai, anthracite, 225 bituminous, 225 deposits, extent of, 227 mineral, origin of, 225 produced from v matter, 225 Cohesive attraction, 11 illustrations of, 12 Cold, greatest artificial, 134 natural, 134 how occasioned by wet clothes, 197 what is, 130 Color, does not exist in the dark, 270 influence of, on the deposition of dew, 168 Colors, artificial, why fade in the sun, 271 dark, optical effects of, upon the size of the figure, 273 iSght, effect of, 274 disadvantages of a dress of uniform, most conspicuous in battle, 274 peculiar to arctic regions, 272 seven primary, 255 warmest for dresses, 175 Columns, why larger at the bottom than at the top, 42 Combustion, a process of oxidation, 220 chemical action of, 221 essential requisites of, 221 spontaneous, illustrations of. 230 what is, 220 Compass, does not always point north and south, 297 mariner's, 279 how constructed, 297 when discovered, 297 Compasses, ships', how affected by light- ning, 299 Compressibility, 6 Concord il -discord, what arc, 120 Contagion, susceptibility to, 810 what is, 811 Convection of h-eat, 153 Copper, poisonous effects of, 310 Cornea, effect of flattening, 265 of the eye, 263 Cornic 810 Coughing, what is, 122 Countries, least cloudy, 10S most cloudy, 107 some, why destitute of rain, 110 Cowl, use of, upon a chimney, 216 Cream-, why rises upon milk, 64 Crying, what Is, 123 Cultivation, how increases the "warmth of a country, 198 and Curtain, behind a pulpit, influence of on sound, 126 Cylinder, strength of -a, 36 Dead body, whycold,238 Decay ift substances, how occasioned and promoted, 806 Density, what is, 6 Diseases, when contagious, 811 Dew and rain, difference between, 163 Dew, cause of, 164 deposited most readily on cleat nights, 163 does not fall, 168 does not form on exposed parts (# the human body, reason of, 170 falls abundantly on cultivated soils, none on a windy night, 164 none on cloudy nights, 163 phenomenon of, 162 rarely observed in cities, 168 when converted into frost, 163 when most copious, 166 why more abundant 0*1 some sub- stances than others, 164 why rolls in drops on fcavcs, 169 Dewdrop, why round, 168 . Diamond, cause of its brilliancy, 256 Disinfecting agents, 307 Distillation, how effected, 196 what is, 195 Divisibility of matter, 5 Doors, why shrink in dry weather, 199 swell in damp weather, 199 Dovetailing, what is, 44 Draining lands, promotes warmth, 198 Draught of air, occasion of, 214 a chimney, 214 stove, 214 v/hcn there is none, 215 Dress, arrangement of colors in, 272, 273 Presses, white^" why adapted for summer, Drum, why sounds, 121 Drying and distilling, difference between^ 1$6 Ducks, why not made wet with water, 169 Ductility, 11 Dust, how expelled from a crtat or carpet by beating, 26 Dunghill, cause of the heat t>f, 229 Car, construction of, 115 drum of, 114 Sarthen vessels, why crack in cold we* thcr, 180 Earth, heat of, 136 315 IHDEX, Earth, how proved to be in motion, 22 poles of, 296 temperature of, influence on the distribution of animals, 142 why made colder after sunset, 162 Earthquakes, probable cause of, 136 Ebullition, what is, 155 Ech6, distance necessary to produce, 125 what is, 124 why sometimes double, 125 how produced, 124 where heard in greatest perfection, 124 Edge, straight, 243 Eel, electrical, 279 Elastic bodies, what are, 8 Electricity, 275 and lightning, identity of, 285 how proved, 285 1 Figure, 5 connection of light and heat, | Filtration, principles of, 7 Exercise \vhy makes us xvarm, 238 Expansion by heat, 176 Falling bodies, laws of, 25 Fan, a, does not cool the air, 174 Fanning the face, why cools, 173 utility of, 174 Far-sightedness, cause of, 265 how remedied, 265 Fat people, why throw back their shoul- ders, 17 Feathers, why called light, 6 Feather, how attracts the earth, 14 Ferment, what is a, 305 Fermentation, how induced by yeast, 305 278 conductors of, 276 galvanic, greatest quantity, how excited, 292 galvanic of two kinds, posi- tive and negative, 291 how called into action, 275 how excited by rubbing the fur of a cat, 278 invisible, 275 natural agents active in pro- ducing, "279 non-conductors of, 277" of muscular action, 279 positive and negative, 278 produces heat, 136 velocity of, 278 Electric cloud, discharge of, 2SO Electrical machines, how constructed, 277 repulsion, 276 Electrified and non-electrified bodies, 276 Electro-magnetism, what is, 299 when and how dis j covered, 299 metallurgy, 294 principles of, 294 Electrotype process, 294 Entablature, 47 Equinoxial storm, does it occur, 112 Esquimaux, why fond of oil and fat, 230 Ether, how removes grease, 307 what is, 307 Evaporation, daily amount from the sea, 110 effects of, 197 phenomena of, 195 Eye, human, structure of, 262 muscles of, 262 parts of, 263 retina of, 263 pained by sudden light, .266 pressure on, occasions the sensation of light, 26S Eyes, do not see alike with both, 263 Eyebrows, use of, 266 Eyelashes, use of, 266 Exertion, disagreeable in hot weather, why, 240 Fire, benefit of stirring a dull, 230 caused by friction, 139 heat of, cause of, 229 intensity depends on what, 230 reflection of, in our windows, 250 what is, 222 why feels hot as we approach it, 161 whv placed near the floor of a room, 160 in the niirht, why difficult to judge of the distance of, 269 places, open, advantages of, 219 not economical, 218 Flame, candle, hottest part of, 232 color of, 231 luminosity, depends on what, 222 of a lamp or candle, analysis of, 232 of a candle, why points upwards, 232 solid particles in, 222 what is, 222 when will it smoke, 223 Flames, why all not equally luminous, 231 Flues of stoves, why covered with black- lead, 162 Flannel, how preserves ice from melting, 143 Fluids, laws and phenomena of, 49 two classes of, 49 Flying, how differs from leaping, 28 Force^ what is, 22 Food, hot, cooled by blowing, 159 the fuel of the body, 238 Fogs, cause of, 84 when and where occur, 90 why does not become dew, S9 Franklin's, Dr., theory of electricity, 277 Friction, what is, 22 action of in exciting electricity, 275 Frieze, in architecture, 47 Frost, hoar, what is, 187 ^.^ rare under trees and shrul 1S5 how a thin covering protects plants from, 167 readers the earth friable, 184 INDEX. 317 Frost-work on windows, cause of, 185 Fruit, precautions to be used in packing, 306 Fuel, elements of, 228 perfect combustion of, bow attained, 220 Furnaces, hot air, how constructed, 219 Furs, why used for clothing, 147 Fumigation, 301 Galvanism, how discovered, 289 produced, 290 simple experiment illustrat- ing, 290 what is, 289 Galvanl, discovers galvanic electricity, 290 Galvanic battery, ordinary effects of, 293 Gas, what is a, 8 Gases, law of diffusion of, 207 not all invisible, 68 Glacier, what is a, 106 Glaciers, where occur, 106 Glass, burning, a double convex lens, 260 ground for shades, use of, 233 Glasses, burning, 131 Gold, melting point of, 135 Gothic architecture, origin of, 45 Grain-weight, origin and construction of, 20 Grapes, ripe, why sweet, 303 Grass, grown in the dark, of a light color, 272 Gravitation, what is, 13 Gravity, centre of, 15 illustrations of the laws and prin- ciples of, 15, 16 Oreasing carriage wheels, use of, 140 Greasy food, why relished in cold wea- ther, 239 Green colors suited to fair complexions, 2T3 Grindstones, In rapid motion why often burst, 23 Gun, essential properties of, 35 how we take aim with a, 244 Gunpowder, composition of, 34 power of. 34 when and how discovered, 35 II Habitations, probable form of the human, 41 Hail, what is, and how formed, 94 Hair, use of in mortar, 40. Halls, for speaking, how constructed, 126 Hardness, what is~ 10 Headache, how produced by bad air, 209 Hearth-rugs, why feel warm, 145 stone, why feel cold, 145 Heat and cold, sensations of, 131 animal, cause of, 236 best conductors of, 144 Heat, effects on the dissolving power ol liquids, 194 effects of, 131 effects of, on the bulk of some liquids, ITS expands all bodies, 176 illustrations of, 177 has no weight, 130 how communicated, 143 illustrations of, 4 how diffused, 130 how evolved by combustion, 221 how measured, 187 good absorbers of, not gooo* reflect- ors, 171 greatest artificial, how produced, 293 greatest artificial, how measured, 134 illustrations of radiation of, 161, 162 In ice, 130 latent, what is, 138 occasioned by chemical action, il- lustrations of, 137 of the sun, 132 produced by friction, 140 radiant, 160 rays of, 171 reflection of, 171 solar, extends below the earth's sur face how far, 136 sources of, 132 sun's differs from artificial, 133 velocity of transmission in different substances, illustrations of,- 144 vital, illustrations of, 141 what is, 129 Health injured by reduction of the tempe- rature of the body, 198 Height from which a body falls, how cal- culated, 29 Hiccough, what is, 123 Hides, how converted into leather by tan- ning, 305 Horizon, what is, 269 Horse-shoe magnets, 298 Horse-power, what is, 33 House, part most dangerous in a thunder storm, 282 House, haunted, origin of stories concern- ing, 128 Hurricane, what is a, 80, 81 Hurricanes, where prevail, 80 Huts, first form of human habitations, 41 Hydrochloric acid, 304 first Hydrogen gas, its properties, 224 the lightest of all bodies, 62 sulphuretted, 304 how formed, 304 what is, 224 Hydrostatics, definition of, 49 Ice, " anchor," what is, 179 318 INDEX. Ice, fractures in regular Hues and aagles, Light, chief sources of, 241 186 heat of, 180 what is, 179 why floats upon water, 62 why melted by the sun, 196 Icebergs, height of, 106 how formed, 106 Illusions, optical, 269 Images all appear inverted in water, 246 Impenetrability, 4 Incandescence, what is, 181 Incidence, line and angle of, 246 Induction in magnetism, 296 Inertia, illustrations of, 10 Inertia, what is, 9 Insects, how occasion sounds, 123, 124 Instrument, stringed, use of the body ot, 117 Ionic order of architecture, 45 Iris of the eye, 263. Iron, how made hot by striking, 139 meteoric, 96 where found, 96 why sinks in water, 62 why stronger than wood, 12 Kettle, why heat is not applied at the top of, 154 why sometimes boils over, 156 Kyanizing, what is, 311 Lakes, some never frozen, 183 Lamps, closed, use of a hole in the top, 233 gas generated by, 208 smokes, occasion of, 223 solar and astral, how constructed, 223 wicks, eottoa best adapted for, Land, configuration of, effect on tempe- rature, 107 Latent heat, what is, 189 Larynx, 122 Laundress, why boils starch, 802 how propagated, 244 intense, why causes pain to th eye, 266 most splendid artificial, how pro- duced, 293 moves in straight lines, 244 of the sun, how much intercepted by the atmosphere, 261 possesses no weight, 241 ray of, when reflected, 244, 245 refraction of, 2-54 the same quantity not reflected at all angles, illustrations of thi principle, 248 velocity of, how estimated; illus- trations of, 242, 243 what is, 241 white, composition of, 255 why, when it is cloudy, 252 zodiacal, 97 Lightning clouds, height above the earth, 280 conductors, best materials for, 284 different kinds of, 280 direction of a flash of, 281 does not follow a direct path, 284 heat, cause of, 281 how kills persons, 281 rod, what is a, 284 rods, how fastened to buildings, 285 how protect houses, 2S4 when productive of harnv, 284 why terminate in points, 284 sheet, 280 what is, 280 why most common in summer, 281 Lights, Northern, 287, 288 Lime, chloride of, 307 quick, 38 absorbs carhpnic acid, 212 slacked, 38 water poured on occasions heat, how, 137 Linen handkerchief, why preferred to A cotton one, 149 Linen, how dried by exposure to the air, 198 why touches saliva, 195 Laughing, what is, 123 Lead, a poison, 310 why called heavy, 6 Leather, how made, 805 Leaves, of plants, how radiate heat, 165 of plants, why green, 271 why brown in autumn, 271 Lens, double convex, 260 what is a, 260 Lenses, different varieties of, 260 Liht, absorption of, 261 trtmcialt vn what depends, 231 flat-iron with! why cooler thnn cotton, 149 Liquefaction, 192 Liquid, what is a, 8 Liquids, how to cool, 155 impart no additional heat after they boil, 157 Liquors, frothing, cause of, 74 Loadstone, what is a, 295 why so called, 295 Loudness, of sound, on what depend?., US Lunar caustic, 304 Lungs, description of, 234 INDEX. 319 vantages of, 31 Machine and a tool, difference between, Mortar, why becomes hard, 33 31 rhat Is a, 31 ,31 Machinery does not create power, Magnet, directive power of, 296 what occurs when one is broken, 293 Magnets, horse-shoe, 293 how constructed, 297 natural, where found, 295 weights, great, lifted by, ? Magnetism, communicated by contact, 295 connection with electricity, 295 Malleability, 11 Man alone capable of enduring all tempe- ratures, 143 method in which he can exert the greatest strength, 33 on a church spire, why scorns very small, 251 shrinks when starved, 233 Maps, coast survey, how produced, 294 Mastich, or mastic, 40 Matches, how ignited by friction, 141 Materials, strength of, 36 illustrations of, 36 Matter defined, 3 evidence of its existence, 3 limits to the division of, 5 particle of, 5 properties of, 4 the strongest form in which it can be arranged, 36, 37 Miasm, or miasmata, 311 Milk boils more readily than water, 155 Mirror, how we see ourselves in a, 245 why images appear behind a, 247 Moon, why seems a flat surface, 251 why seems larger than tho stare, Mortare, composition of, 38 Mortising, what is, 42 Motion, 22 Mountains, distant, why appear bluo, high, why covered with snow, 105 Mountain tops, why cold, 172 Muriatic acid, 304 Muscular energy, how exerted, 33 Music, scale of, 121 Musical instruments, how occasion sound, sounds, what are, 120 N Nails in old houses, why loose, 187 Near-sightedness, cause of, 264 how remedied, 265 Needle, magnetic, 296 Negro's skin never blisters from the sun, 174 Nitric acid, 304 Nitrogen, its properties and uses, 205 what is, 205 Objects, how we judge of the sizo and position of, 250 Ocean, colors of animals in, 272 depth to which light penetrates, Odors, 307 Oersted, Prof., his discovery, 299 Mirrors, 245 Oil and water, why not mix, 193 Mist and fog, distinction between, 89 Opaque bodies, 261 Meat, how preserved by smoking, 303 Orders in architecture, 45 when tough, 303 'Owls, why see in the dark, 267 Medicines, prescription by drops unsafe, Oxygen, now much required per hour, Mercury, freezes at what temperature, 191 of a barometer, why sinks in fine Oxidation, what is, 220 weather, 104 when freezes, 134 Metals, why melted by fire, 192 Meteorites, how supposed to originate, 96 what are, 94 Meteorology, what is, 74 Mist and fog, why vanish at sunrise, 164 Mist, on windows, cause of, 87 209 its properties and uses, 205 what is, 205 Paint, in tho vicinity of sowers, why dis- colored, 304 how preserves wood, 152 Paints, lead, when dangerous, 310 Mixture and solution, difference between, Paper, blotting, why absorbs ink, 66 193 Moon, lisht of, seems to make a path in 'the water, 249 influence of, on the weather, 111 light, how occasions putrefaction, Pendulums, compensating, 187 112 why appears largo on the borkon, 269 writing, why will not absorb ink, 66 Paste, adhesiveness due to irhat, 303 Pedestal, what is a, 46 length of, that beats seconds, 29 what fa a, 29 320 INDEX. Persons, why many. ROC the same object Rain, none if the air be dry, 104 at the same time, 244 Perpetual motion in nature, 23 instance of, 23 Perspiration, insensible, what is, S3 why caused by active exer- tion, 239 Pilasters, what are, 45 Pile, what is a, 42 Pipes, lead, how affected by water, 310 water, why liable to burst in freez- ing, 1S1 Pisa, leaning tower of, 17 Planets, how give light, 242 Plants, how purify the water, 236 respire as well as animals, 235 water, liberate oxygen, 236 Platina, the heaviest substance known, 62 Plastic bodies, what are, 9 Plinth of a column, 46 Pneumatics, what is, 49 Poison, what is a, 309 Poisoning, what to do in cases of, 309 Poles of a galvanic battery, 292 Pores of a body, 6 Portico, what is a, 45 Potatoes, frozen, why sweet, 303 Potato, starch constitutes the bulk of, 302 Posver, how we apply it, 31 horse, 33 of gunpowder, 34 sources of, 32 steam, 34 water, 33 Preserves, why turn sour, 306 Prism, how separates a ray of light, 255 Pump, chain, what is, 100 common, 98 forcing, construction of, 100 height to which water may be raised by, 99 why water rises in, 100 Pupil of the eye, 263 contracts by a sudden light, 266 Putrefaction, causes of, 307 Putty, what is, 40 Pyrometers, how constructed, 191 origin of, 91 water, why called soft, 56 where most abundant, 103 why cooler after, 199 why falls in drops, 91 yearly amount falling in different parts of the earth, IDS Rainbow, formation of, 257 when seen, 257 Rainbows at waterfalls, 253 double, when seen, 253 no two persons see the same, 253 Rain-gauge, what is a, 109 filed rays of light possess the greatest beak ! ing effect, 272 'Reflection, line and nnglc of, 246 of light, 24o Reflectors of heat, what arc good, 171 RefraagibiUty, 86 Refraction of light, 254 Remedies for poisons, 309, 310 Repulsion, what is, 11 Resonance, what is, 125 Respiration a form of combustion, 234 object of, 234 what is, 233 Retina of the eye, 263 Retort, what is a, 195 .Rifle, advantages of, over a musket, 35 River, always seems more shallow than it is,"255 bottom, rarely frozen, 181 part in which the water runs most rapidly, 50 Rocks and stones retain moisture, 107 cause of their rounded and weather- worn appearance, 179 why often split in cold weather, ISO Roman cement, 39 Room, air of. how affected by a current 209 coolest part of, 117 hottest part of, 217 Rose, why red, 270 SRust, what is, 222 Salt, how dissolves ice, 1S4 Qnadrrfpcd, never raises both feet on a, lakes, origin of, 5S side at once, 17 utility of, in the ocean, 58 Quadrupeds, why swim easier than man,|Sand, best suited for mortar, 39 63 Quick lime, what is, 33 Radiators, good, of heat, 161 Radiation, 160 of heat, on what depends, 161 Rain drops, form of, 169 why spheres, 160 Low measured, 109 Savages, how hear by placing the ear closo with ground, 117 Scarfing and interlocking, 43 Sea breeze, why cool, 79" effect of, on temperature, 107 rarely freezes, Ib3 water, why freezes less readily than fresh water, 135 why not full, 199 why salt, 47 vapor of, not salt, 199 Seasons, alternation of warm and cold, 112 INDEX. 321 Seeing, sense of, how exerted, 241 iBounds, when flat, 121 Senses, number of, 3 why seem louder in a church than what are th'jy, 3 in a plain, 128 Sewers, foul, why destructive to health, Soup, why keeps hot longer than water, Shade, why cool in the summer, 150 'Sparks of fire, what arc, 7 why objects seeui dark in, 252 Specific gravity defined, 62 Shadow, what is a, 244 iSpeetacles best suited for old people, 265 Shaft of a column, 46 Spoon, metal, how retards the boiling of a Sheets of a bed why feel cold, and the kettle, 150 blankets wann, 152 why tarnisbod by the yolk of eggs, Ship at sea, why the masts are seen before 304 the hull, 253 Spray of waves, cause of, 61 Ships, iron, why do not sink, 65 Springs, effect of drainage upon, 53 Sbces, hotter for being dusty, 172 Stones for building, bo\v" to estimate their Skull, the form of the, embodies the prin- durability, 43 ciples of the arch, 44 building, action of the weather Sight, difficult after leaving a lighted room on, 48 and going into the dark^"266 why lifted easier in water than on Size, 4 land, 65 Skating swiftly over thin ice, effect of, 27 Stove, advantages over an open fireplace, Skin, cleanliness essential to the healthy action of, 237 Sky, why appears blue, 271 Sleet, what is, 92 Smoke, what is, 218 why ascends, 13 Smoking, how preserves meat, 808 Sneezing, what is, 123 Snow, at the foot of a wall, why melts Stucco, what is, disadvantages of, 219 why crackles in cooling, 186 why crackles when a fire is kindled in it, 1S6 Stones, why not suitable for fuel, 226 Straw, use of, in the Egyptian bricks, 40 Stripes, effect of, in dresses, 279 rapidly, 161 flake, how formed, 93 heat of, how shown, 138 Sucker, the common, 72 Suction, height to which water may bo raised by, 98 how diminishes the darkness of 'Suffocation, how occurs, 123 night, 270 |Sugar and salt, how flavor water, 67 how protects the surface of the earth salt, &c., retard boiling, 157 in winter, 92, 93 melting absorbs heat, 138 various colors of, 94 what is, 92 why none in summer, 93 white, 93 Soap-bubble, origin of colors in, 259 Soap, utility of in washing, 57 SoiC a bad conductor of heat, 136 effects of on temperature, 107 Solid, what is a, S Solution, what is a, 193 when saturated, 193 Sonorous bodies, what are, 116 Soot, smell of, why sometimes noticed in a room, 216 of, 71 best conductors of, 120 how obstructed by fogs, rain, &c., 119 how produced, 114 louder by night than by day, 119 not heard alike by all persons, 120 velocity of, 118 bounds, musical, what are, 120 origin and transmission of, 114 rejection of, 124 transmission of by solids, 117 vibrations, to what compared, 117 vibrations in solids, how rendered visible, 118 Sulphur, product of when burned, 393 Sulphureous acid, 303 Sulphuric acid, 304 Summer, Indian, haziness of, 87 Sun, seen through a fog appears red, 87 the, a source of lu-at, 132 weight on the surface of, 19 why appears large on the horizon, 269 Sun's heat, why greater in some portions of the earth than in others, 133 Sunbeam, motes floating in, what arc, ICO Sunset, red, cause of, 86 Surf, what is, 61 Surfaces, some, why brilliant, 242 dull, 242 Swimmers, unskilful, why sink, 63 VJound, air necessary for the production Swimming why easier in salt than in fresh water. 63 philosophy of, 63 Springs in ponds prevent freezing, 163 mineral, cause of, 54 origin of, 51 why cool in summer, 150 why often fail in dry weather, 51 Sprinkling a hot room how cools it, 198 Squinting, occasion of, 268 occasions double vision, 267 Starch, how manufactured, 302 may be converted into sugar, 303 what is, 302 why necessary to boil before using, 802 34* 322 INDEX. Stars, shooting, 96 _ oacur periodicruly, 9T why not visible in the daytime, 244 Starvation, process of, 239 what is, 235 Steam, bulk of, compared with water, 201 how much lighter than water, 200 engine, what is a, 202 high pressure, 202 how used for cookery, 202 invisible, 107 its elasticity, 201 lighter than air, 68 mechanical force of, 203 illustrations of, 203 parts of a boiler where first formed, 200 power of, on what depends, 201 visible appearance how caused, 200 what is true, 200 Stems of grain -plants, why hollow tubes, 37 Stick immersed in water, why seems bro- ken, 254 Still, construction of, 191 Thunder, rolling of, cause of, 2S7 storm", places dangerous in, 282, 2S3 safest in, 233 what is a, 2SO varieties of, 2S7 what is, 2S6 why heard after the lightning is seen, 2S7 Tides, cause of, 59 when high and low, 59, 60 Toes, advantage of turning out the, io walking, 17 Tornadoes, 82 phenomena generally attend- ing, 82 Transparent bodies, what are, 260 Tree, centre of gravity in, 19 how discharges a lightning cloud, 2S2 Trees and flowers, how purify the air, 210 whv covered with straw in winter, 184 Tropics, rainy and dry seasons of, 109 Troy weight, origin of, 20 Trumpet, ear, construction of, 127 speaking, construction of, 127 Twilight, cause of~ 259 Telegraph, influence how transmitted by, to convey intelligence, 301 magnetic, Morse's, principle of, 300, 301 wire, why supported on glass, 301 ' Telegraphic current, what is meant by 301 Telescopss, construction and use of, 252, 253 why enable us to see objects, 253 Temperature, effect of the sea on the, 107 soil on, 107 mean daily, what is, 106 varies with altitude, 105 latitude, 105 variation, examples of, 105 why all places have same, 107 Temples, how cooled by ether, cologne, water, &c., 197 Tenon, what is a, 43 Terra-cotta, what is, 39 Thaw, mo-e chilly than a frost, 183 Thermometer, centigrade, 191 Fahrenheit's, 190 Eeaumer's, 191 indicates difference of heat only, 192 Thermometers and pyrometers, difference of, 188 construction of, 189 different, 190 how graduated, 189 Thunder, cause of, 286 Vacuum, illustration of, 213 what is a, 71 Valves, pump, 93, 99 Vapor from damp linen, what is it, 197 in a room, origin of, 88 of the air, how condensed into rain 91 Vaporization, meaning of, 194 Vegetables, why swell in boiling water, distant Vegetation, why luxurious on the margin of a river, 66 Ventilation, in what situations is it perfect, 205 what is, 204 Vibration, what is a, 116 Vibrations, sonorous, how illustrated, 116 Vinegar, what is, 305 not the Vitriol, oil of, 304 Voice, organs of, 122 tones of, how altered, 122 Volatile substances, 195 Volcanoes, probable cause of, 136 Wall, a, when stands securely, 17 Walls, partition, construction of, to int cept sound, 119 Warming and ventilation, 204 Water, a bad conductor of heat, 146 at what elevation above the earth remains frozen, 106 air in, boiled, why flat and insipid, 73 INDEX. 323 Water, composition of, 54 I Wheels, carriage, why sometimes take declivity sufficient to give fanning lire, 189 motion to, 50 fore, of carriages, why smaller of, why rolls upon hot iron, than the hind, 44 of carriages, utility of greasing, water, different kinds, 34 Whitewash, what is, 38 Wick of a candle, why not consumed, 233 Windpipe, what is the, 122 194 expands when freezing, 181 force of expansion in freezing, 179 hard, what is, 54 difficult to wash in, 56 bow extinguishes a fire, 229 hoAV heated, 153 hot, why hreaks glass, or earthen Windows, why blaze p.t sunset, 249 vessels, 185 in freezing, cracks earthen ves- sels, 180 images in, appear inverted, 246 power, 33, 34 pressure of. 53 how exerted, 53 of mineral matter con- tained in, 55 running, Avhy slow to freeze, 182 scalds at what temperature, 176 surface of, always level, 49 swells in boiling, 156 temperature ol'boiling, 135 what is the purest natural, 55 when affects lead pipes, 310 why a fluid, 54 why dissolves sugar and salt, 57 why freezes first at the surface, 182 why rises in a pump, 101 why sparkles, 56 why will not dissolve iron, 193 Waters, relative purity of, 55 Waterspout, what is a, 83 Waves, cause of, 60 spray of, 61 velocity of storm, 61 Well, ordinary, why water collects, 57 Wells, artesian, 52 why often covered with mist, 87 Wind, cause of, 75 Winds, force of, how measured, 78 high, difficult to walk against, 9 always blow, 76 effects of mountains, on the couira of, 76 land, generally dry, 76 north, why cold, 79 south, why Avarm, 79 regular, 77 on" the direction of, 78 trade, 77 velocity of, 77 Wine, why sours on exposure to air, 305 Wood, constituents of, 224 green, unprofitable to burn, 227 hard and soft, 227 how preserved from decay, 811 "; 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