Southern Branch 
 of the 
 
 University of California 
 
 Los Angeles 
 
 Form L-l
 
 This book is DUE on last date stamped below 
 
 * 4 
 
 t9 
 
 1958
 
 BOOKS 
 
 BY 
 
 MINNIE GOODNOW, R. N. 
 
 First-Year Nursing 
 12mo of 351 pages, illustrated. 
 Cloth, $1.75 net. Second Edition. 
 
 Outlines of Nursing History 
 12mo of 370 pages, with 88 illus- 
 trations. Cloth, $2.00 net. 
 
 War Nursing 
 
 12mo of 172 pages, illustrated. 
 Cloth, $1.50 net. 
 
 Practical Physics for Nurses 
 12mo of 203 pages, with 100 illus- 
 trations. Just Ready.
 
 PRACTICAL PHYSICS 
 FOR NURSES 
 
 By 
 
 MINNIE GOODNOW, R. N. 
 
 Author of " First-Year Nursing," " Outlines of Nursing History," 
 " War Nursing," "Ten Lessons in Chemistry for Nurses," and "The 
 Nursing of Children"; formerly Directress of Nurses, Milwaukee 
 County Hospital; formerly Superintendent of the Woman's Hospital, 
 Denver, and of the Bronsonl Hospital, Kalamazoo ; Specialist in 
 Hospital Equipment 
 
 WITH 100 ILLUSTRATIONS 
 
 PHILADELPHIA AND LONDON 
 
 W. B. SAUNDERS COMPANY 
 
 1919
 
 Copyright, 1919, by W. B. Saunders Company 
 
 PAINTED IN AMERICA 
 
 PRESS OF 
 
 W. B. SAUNDERS COMPANY 
 PHILADELPHIA
 
 G 
 
 FOREWORD 
 
 THE criticism is often made that nurses are not 
 
 intelligent about the handling of ordinary household 
 
 . and hospital appliances, and that they make no attempt 
 
 A 1 to understand the workings of plumbing, heating and 
 
 ventilating apparatus, surgical instruments and appa- 
 
 _, ratus, etc. 
 
 The fault lies not so much in the nurse herself, nor 
 
 in any lack of inclination to learn, as it does in the fact 
 N that she has not been taught the laws which govern 
 & some of the simplest activities of life. Very many 
 ** nurses are not high-school graduates, and of those who 
 
 are, not all have studied physics, nor know how to 
 
 apply their knowledge to nursing. 
 
 I Both Physics and Chemistry are of great impor- 
 I tance to a nurse, because they are, at bottom, sciences 
 of common life. The human anatomy is built in accord- 
 ance with the laws of physics, and its movements are 
 governed by them. It is necessary, therefore, if a 
 nurse is to do intelligent work, that she should know 
 some of the existing laws of physics, and how her 
 patients, her hospital environment, and all her work are 
 controlled by them. 
 
 This subject has been a much-neglected one in 
 hospital training-schools, chiefly because there was no 
 text-book concerning it which was suited to nurses. 
 
 13
 
 14 FOREWORD 
 
 The following lessons have been prepared in the endeavor 
 to give briefly some of the more important laws of 
 physics, especially those which apply to daily life and 
 to a nurse's work. No effort has been made to cover 
 the whole subject, but only to select from it some of the 
 principles which apply most obviously and directly to 
 hospital life and to nursing. There are many laws of 
 physics not even mentioned in the following pages. 
 
 The apparatus and supplies for the illustrative ex- 
 periments are of the simplest sort. Most hospitals will 
 already have them in stock. 
 
 The author wishes to acknowledge her indebtedness 
 to Mr. William H. Smiley, educator, and to Dr. Horace 
 Greeley Wetherill, surgeon, for careful and invaluable 
 criticism of the manuscript, and to Miss Kinsey for cor- 
 rection. 
 
 MINNIE GOODNOW, R. N.. 
 
 September, 1919.
 
 CONTENTS 
 
 PAGE 
 
 SUPPLIES 17 
 
 INTRODUCTION.. . 
 
 CHAPTER I 
 MATTER. ITS COMPOSITION. . . 
 
 CHAPTER II 
 MECHANICS 32 
 
 CHAPTER III 
 MECHANICS (Continued) 41 
 
 CHAPTER IV 
 HYDRAULICS 60 
 
 CHAPTER V 
 PNEUMATICS 73 
 
 CHAPTER VI 
 PNEUMATICS (Continued) 85 
 
 CHAPTER VII 
 HEAT 98 
 
 CHAPTER VIII 
 HEAT (Continued) 115 
 
 CHAPTER IX 
 SOUND 130 
 
 CHAPTER X 
 LIGHT. . . . 141
 
 16 CONTENTS 
 
 CHAPTER XI PAGE 
 
 ELECTRICITY 163 
 
 CHAPTER XII 
 THE X-RAY. RADIUM 180 
 
 CHAPTER XIII 
 QUESTIONS FOR REVIEW OF PRINCIPLES AND ORIGINAL THINKING 190 
 
 INDEX . 197
 
 PRACTICAL PHYSICS FOR iNURSES 
 
 SUPPLIES 
 
 THE following will be sufficient to enable one to make 
 the experiments suggested in this book: 
 
 Two quart flasks. 
 
 Several large corks, one which shall fit flask, being perforated 
 
 for two tubes. 
 Glass tubing, pieces 6 to 18 inches long, two sizes; one piece 
 
 bent into a U-shape. 
 
 Rubber tubing, a few short pieces to fit glass tubing. 
 One dozen test-tubes, with holder. 
 A few microscope slides. 
 
 Two bath thermometers, or other unmounted thermometers. 
 One thermometer with scale to 250 F. 
 A glass prism. 
 A square bottle. 
 Two lamp chimneys. 
 Small quantities of sulphuric acid, copper sulphate, alum, 
 
 sugar, touch-paper. 
 
 APPARATUS 
 
 If possible, bring into class or arrange to have class see 
 the following: 
 
 Axis-traction forceps. 
 
 Bulb syringe. 
 
 Electric cautery. 
 
 Electric battery or cell, wet form. 
 
 Electric toaster. 
 
 Glass dressing syringe. 
 
 Glass irrigator, with uterine point. 
 
 2 I 7
 
 18 PRACTICAL PHYSICS FOR NURSES 
 
 Head-mirror. 
 
 Hypodermic syringe. 
 
 Laryngoscope. 
 
 Microscope. 
 
 Obstetric chart, showing progress through pelvis. 
 
 Rectal dilators. 
 
 Reading glass. 
 
 Stomach-tube. 
 
 Sphygmomanometer. 
 
 Urine centrifuge. 
 
 Urinometer. 
 
 Uterine dilator. 
 
 x-Ray apparatus.
 
 INTRODUCTION 
 
 Physics is the science of every-day life, and relates 
 to most of our ordinary activities. The wind and 
 weather, our houses and their contents, all work and 
 play, all personal and commercial activities involve the 
 laws of physics. 
 
 We find ourselves annoyed or defeated because things 
 "won't work" as we wish them to. Usually the reason 
 is that we are attempting to make them act in opposi- 
 tion to the laws of nature; we do this because we do not 
 know what those laws are, nor to what extent they 
 govern the world. A very elementary knowledge of 
 these common laws will not only help us to do our daily 
 tasks with greater ease, but will make them vastly 
 more interesting and meaningful. 
 
 A knowledge of physics is essential not only to the 
 skilful use of hospital and nursing appliances and equip- 
 ment, but to an understanding of the structure and func- 
 tions of the human body. Dr. John C. Draper says: 
 "There is not a tissue, organ, nor function of the body 
 the proper comprehension of which does not involve a 
 knowledge of the laws of physics. There is hardly a 
 principle of physics which does not apply to the human 
 body." 
 
 The bony structure, the attachment of muscles, the 
 
 19
 
 20 PRACTICAL PHYSICS FOR NURSES 
 
 working of the heart, blood-vessels and respiratory 
 organs, the acts of seeing and hearing, etc., all depend 
 upon the laws of physics; while apparatus and ap- 
 pliances for the treatment of disease can hardly be used 
 intelligently or effectively without a comprehension of 
 these same laws. 
 
 Physics, in its logical limits, is an abstruse and diffi- 
 cult subject. The fundamental principles are, however, 
 extremely simple and can be understood even by un- 
 trained minds. The mere committing to memory of 
 some of its laws will serve to elucidate, throughout 
 one's life, many appliances and occurrences. 
 
 It is recommended that all the experiments given, 
 however simple or familiar, be actually made in class, 
 so that the full force of their meaning and application 
 may come at the psychologic moment.
 
 CHAPTER I 
 MATTER. ITS COMPOSITION 
 
 MAN has always been eager to know of what things 
 were made, and why inanimate objects act as they do. 
 Physics and Chemistry are the two sciences which 
 have been developed in this search for knoweldge. 
 Chemistry is, in reality, a branch of Physics. 
 
 Physics is the science of matter, its properties, changes, 
 and motions. 
 
 Matter is anything which we can see, feel, or handle; 
 anything which occupies space. 
 
 Simple and Complex Substances.- Some substances, 
 or portions of matter, are simple; some are complex. 
 
 Wood, for example, is a complex substance. If, in 
 attempting to find out of what it is made, we divide 
 it into minute pieces, we spoil or destroy it and cannot 
 make it into wood again. If we heat it, we also de- 
 stroy it. 
 
 Iron, on the other hand, is a simple substance. If 
 we divide it into ever so fine particles, we can still iden- 
 tify it as iron; if we heat it ever so hot, as soon as it 
 cools it is plainly iron ; we have not spoiled nor destroyed 
 it by what we have done to it. 
 
 The Ultimate Composition of Matter. With even the
 
 22 PRACTICAL PHYSICS FOR NURSES 
 
 simplest substance, after we have divided it into the 
 smallest particles possible, we have not found out its 
 real composition. We imagine that if we were able to 
 divide it still further we might get at this knowledge. 
 We find that scientists have been able, in what seem 
 rather roundabout ways, but which are none the less 
 exact, to accomplish this. 
 
 Scientists have agreed that all matter is made up of 
 tiny particles, called molecules, 1 which in a simple sub- 
 stance like iron are all alike. 
 
 It is agreed that molecules are composed of still smaller 
 particles, called atoms, which may or may not be alike, 
 but which together form a definite substance, either 
 simple or complex. There may be few or many atoms 
 in a molecule, the number varying from two to fifty or 
 more. 
 
 The assumption that matter is composed of mole- 
 cules, which are themselves composed of atoms, is called 
 the Atomic Theory, While merely a theory which it 
 is not possible to prove, it so well accounts for every- 
 thing which man has observed that it is generally ac- 
 cepted as fact. 
 
 A particle is the smallest subdivision of matter that 
 can be obtained by mechanical means. 
 
 A molecule is the smallest portion of matter which 
 can exist alone. 
 
 1 It is estimated that there are 2,000,000,000,000,000,000,000,000 
 molecules in a drop.
 
 MATTER. ITS COMPOSITION 23 
 
 An atom is the smallest portion of matter which can 
 exist in combination. 
 
 Much modern research has been directed toward 
 discovering the make-up of atoms; the electron theory 
 has been formulated, and is by some scientists regarded 
 as proved. This theory holds that each atom is com- 
 posed of many infinitely small particles, which are 
 called corpuscles. All of these corpuscles are electric- 
 ally charged, part of them being positive and part 
 negative; such being the case, they mutually attract 
 one another and hold together to form the atom. Heat 
 or other forces may loosen the attraction, so that some 
 of the negatively electrified corpuscles may fall off, in 
 which case they promptly attach themselves to some 
 other atom. In certain substances which we call 
 "radio-active" (See Chapter XII) corpuscles are more 
 or less constantly and forcibly being expelled from the 
 atom. 
 
 Physics concerns itself with molecules. Chemistry 
 concerns itself with atoms, and deals with the minute 
 structures and. change of matter. 
 
 Chemical and Physical Changes. If we heat water 
 to the boiling-point, it changes into steam. If we sub- 
 ject it to sufficient cold, it changes into ice. These are 
 changes inform only. They are called physical changes. 
 
 If we heat sugar, it melts, bubbles, boils, turns brown, 
 gives off smoke, and finally becomes a charred, black 
 mass, which is plainly no longer sugar.
 
 24 PRACTICAL PHYSICS FOR NURSES 
 
 Experiment. Take a small tin plate or dish, grasp it with for- 
 ceps, place on it a small amount of white sugar, and hold it over a 
 gas, alcohol, or other flame. Note the various changes which take 
 place as the heating progresses, and the resulting black mass, which 
 is almost pure carbon. This is a change in composition. It is 
 called a chemical change. 
 
 A physical change is a change in inform of a substance. 
 A chemical change is a change in the composition of a 
 substance. 
 
 PROPERTIES OF MATTER 
 
 The molecules of any substance, no matter how com- 
 pact it seems to be, do not touch each other. In hard, 
 firm substances they are close together; in soft or loose 
 substances, further apart; but they are always slightly 
 separated, the distance between being very little, yet 
 enough to admit of motion. (See Heat.} 
 
 The force which holds molecules in place or together 
 is called cohesion. 
 
 The force which holds atoms together is called chemical 
 affinity. 
 
 Cohesion holds molecules of the same sort together, 
 as iron to iron. It is cohesion which makes an iron bar 
 or a piece of wood firm and strong. 
 
 Adhesion is the force which holds molecules of unlike 
 substances together; for example, grease or dirt adheres 
 to a utensil. 
 
 Experiment. Press two plates of glass (microscope slides or 
 window glass) together. You will find it somewhat difficult to 
 separate them; it is most easily done by sliding, which separates 
 them particle by particle. Wet the surface with water or oil and 
 again press together; they will separate with still greater difficulty. 
 The water or oil has greater adhesion than the glass.
 
 MATTER. ITS COMPOSITION 25 
 
 Reduce the force of cohesion and you increase the 
 force of adhesion. Water or oil has less cohesion than 
 glass i. e., is less firmly held together and therefore 
 adheres more closely to the solid object. Grind rock 
 salt to powder and it dissolves more readily; the cohesion 
 in the large lump being broken up, adhesion between 
 the salt and water, unlike substances, takes place more 
 easily. 
 
 Some of the properties, or inherent qualities, of matter 
 are as follows: 
 
 GENERAL PROPERTIES 
 
 Extension is self-evident. Divisibility is also self- 
 evident. 
 
 Mobility. It is readily apparent that all substances 
 are movable if sufficient force is applied. 
 
 Impenetrability. One thing cannot occupy the same 
 space as another at the same time. In instances where 
 it seems to occur, as when a sponge is placed in water, 
 it is merely that the molecules of one substance are 
 between those of the other; the water, in this case, fits 
 around the sponge, but is not occupying the same 
 space. 
 
 Experiment. Fit a funnel tightly into the mouth of a bottle, 
 so that no air can pass around the stem of the funnel. Pour water 
 into the funnel; only a little of it runs into the bottle, though the 
 latter is apparently empty. Why? Because the bottle is already 
 full of air. Loosen the funnel so that the air in the bottle can es- 
 cape, and the water readily runs in. Difficulty in filling a hot- 
 water bag arises when so large a stream of water is used that it 
 blocks the exit of the air; a smaller stream overcomes the difficulty.
 
 26 PRACTICAL PHYSICS FOR NURSES 
 
 Inertia is a quality which all matter possesses to a 
 marked degree. It is the property which makes matter, 
 when let alone, continue to do what it is doing. If it is 
 moving, it tends to keep on. If it is at rest, it tends to 
 remain so. When we attempt to move an object, we 
 feel the resistance of its inertia; when we attempt to 
 stop a moving object, we also feel the resistance of in- 
 ertia. A railroad train, for example, is difficult to either 
 start or stop because of its inertia. A ball thrown from 
 the hands stops only because of the pull of gravity and 
 the resistance of the air; it tends to go on. 
 
 Experiment. Place a card on the end of the finger, and a coin 
 on the card. Strike the card lightly out of its place. The coin will 
 remain, because of its inertia. 
 
 Porosity. If we accept the molecular theory, all 
 matter is porous. We usually apply the term, however, 
 only to substances in which the quality is marked. 
 
 Experiment. Take a quantity of loose absorbent cotton, and 
 put it piece by piece into a small tumblerful of alcohol; nearly a 
 quart can be put into the alcohol before the tumbler overflows. 
 This is due to the porosity of both alcohol and cotton. Examine 
 the stone filter from a water-sterilizing apparatus; one would say 
 that it is not porous at all, yet water goes through it if under pres- 
 sure. 
 
 Porosity involves compressibility. All substances are 
 compressible, but in varying degrees; it is merely a 
 question of applying sufficient force to drive the mole- 
 cules closer together. Air and all gases are readily 
 compressible. Some solids are. Liquids are hardly 
 compressible at all.
 
 MATTER. ITS COMPOSITION 27 
 
 Elasticity is a quality which substances possess in 
 varying degrees. Some return to their original shape 
 and size when compressed, some do to an extent, some 
 not at all. Some substances are rapidly elastic, some 
 slowly. 
 
 SPECIFIC QUALITIES 
 
 There are numerous special qualities, those possessed 
 only by certain substances. 
 
 Hardness occurs in varying degrees. Lead and wood 
 seem hard, but may be easily cut. The diamond is 
 the hardest known substance. 
 
 Opacity, the quality which prevents light from passing 
 through a substance, and transparency, the quality 
 which permits its passage, are important qualities which 
 vary greatly in different sorts of matter. 
 
 Tenacity, that is, the ability to keep its particles to- 
 gether, varies greatly in different substances. Its op- 
 posite is brittleness. Important manifestations of te- 
 nacity are: malleability, the quality which permits a sub- 
 stance to be hammered into thin sheets, and ductility, 
 the quality which permits it to be drawn out into fine 
 threads. For example, gold may be beaten into sheets 
 4000000 inch in thickness, or so thin that 1 ounce will 
 cover 100 square feet. Platinum is extremely ductile, 
 but the finest thread we know is that of the spider's 
 web; this is used in some scientific apparatus (the mi- 
 croscope, surveying instruments) because no artificial 
 thread is so fine.
 
 28 PRACTICAL PHYSICS FOR NURSES 
 
 Tendency to crystallize is a property of nearly all 
 solid substances. Under favorable circumstances most 
 substances tend to arrange themselves in the form of 
 crystals. 
 
 Experiment. Make a tumblerful of a saturated solution of 
 alum, hot. Hang in it a circle of wire or stiff string and leave it 
 overnight or longer; the circle will be covered with crystals. 
 
 When water crystallizes, in freezing, the crystals require more 
 room than the liquid and insist upon expanding; this is the reason 
 that water-pipes burst when they freeze. 
 
 FORMS OF MATTER 
 
 Original Forms of Matter. Matter exists normally 
 in three forms: solid, liquid, and gas. 
 
 These forms are due to the weakness or strength of 
 the force of cohesion between their molecules. Solids 
 have their molecules close together and are held firmly; 
 in liquids the molecules are farther apart and are held 
 loosely; in gases they are still farther apart and tend to 
 recede from each other. 
 
 We think of these three forms as characteristic of 
 certain substances themselves, whereas, in reality, they 
 depend entirely upon temperature. 
 
 Change of Form. Water is the best example of a 
 substance which can be converted into the form of a 
 solid, liquid, or gas. The same changes are possible in 
 all substances, but with many the change is difficult to 
 accomplish, and in some cases we have not yet learned 
 how to do it without damage. For example, iron can 
 be liquefied by applying a very high temperature; it may
 
 MATTER. ITS COMPOSITION 29 
 
 also be vaporized, but it takes an incredible degree of 
 heat to accomplish it. Sugar is an example of a solid 
 substance which, if carefully heated, may be changed to 
 a liquid. Air, which we think of as a gas, can be made 
 liquid by an extreme degree of cold; and it has even 
 been changed into a solid mass by still greater cold. 
 
 Diffusion. Solids may be diffused i. e., the molecules 
 driven farther apart (1) by melting; (2) by solution; 
 (3) by dialysis. 
 
 Fig. I. Dialyzer (Bliss and Olive). 
 
 In dialysis, the given mixture is placed in a small 
 jar having a parchment paper bottom; this is set into 
 a jar of pure water. Any crystalloid substance will 
 soak out through the parchment into the water, where 
 its presence may be discovered by chemical tests. This 
 method is used for examining stomach contents in cases 
 of suspected poisoning. It is not applicable to colloid 
 substances.
 
 30 PRACTICAL PHYSICS FOR NURSES 
 
 BRANCHES OF PHYSICS 
 
 Mechanics is the branch of physics which deals with 
 solid bodies and the laws that govern them. 
 
 Hydraulics is the branch which deals with liquids and 
 the laws that govern them. 
 
 Pneumatics is the branch which deals with gases and 
 the laws that govern them. 
 
 All three of these branches of science apply to daily 
 life, to the human body, and to nursing. 
 
 SUMMARY 
 
 Physics is the science of every-day life. It treats of 
 matter, its properties, changes, and motions. A knowl- 
 edge of it is necessary in order to deal satisfactorily with 
 household or hospital appliances, and for a correct 
 understanding of the human body and its functions. 
 
 Substances are simple or complex, i. e., composed of 
 one or several elements. 
 
 The Atomic Theory has been accepted because it 
 accounts for all natural phenomena. It assumes that 
 all matter is composed of molecules (the smallest por- 
 tions of matter that can exist alone), which are them- 
 selves composed of atoms (the smallest portions of mat- 
 ter that can exist in combination). Physics concerns 
 itself with molecules. Chemistry, a branch of physics, 
 concerns itself with atoms. 
 
 A physical change is the change in the form of a sub- 
 stance.
 
 MATTER. ITS COMPOSITION 31 
 
 A chemical change is the change in the composition 
 of a substance. 
 
 Neither atoms nor molecules are in actual contact 
 with each other. Atoms are held together by chemical 
 affinity; molecules of the same sort by cohesion; mole- 
 cules of different sorts by adhesion. 
 
 The general properties or characteristics of matter 
 are extension, divisibility, mobility, inertia, porosity, 
 compressibility, etc. 
 
 Some of the specific properties of matter are hardness, 
 opacity, transparency, tenacity, brittleness, tendency 
 to crystallize, etc. 
 
 Matter exists in three forms solid, liquid, and gas. 
 These forms are due to the strength or weakness of co- 
 hesion between their molecules. This depends upon 
 their temperature, which is a relative matter. As a 
 rule, low temperatures cause matter to solidify, high 
 temperatures cause it to liquefy, still higher cause it to 
 become gaseous. 
 
 Mechanics is the science of solids. Hydraulics is 
 the science of liquids. Pneumatics, the science of gases.
 
 CHAPTER II 
 MECHANICS 
 
 LAWS RELATING TO SOLIDS 
 
 Gravity is the force which the earth exerts on all 
 sorts of matter. The earth pulls everything solids, 
 liquids, or gases toward its center. This pull is exerted 
 in a straight line, directly to the center of the earth. 
 It is called the "line of direction." The exact direction 
 of this pull is shown by the plumb line used by builders, 
 artists, etc. A building which is "out of plumb" is 
 likely to fall sooner or later, since the foundation may 
 be unable to hold the top against the pull of the earth. 
 
 It is this pull of the earth which causes objects to 
 fall when not supported, makes the rain and snow de- 
 scend, water to run down hill, etc. 
 
 Weight. Another manifestation of the pull of the 
 earth is what we call weight. Since the earth pulls 
 equally on every molecule, it give us a convenient method 
 of finding out the quantity of matter in a mass. Weight 
 may be denned as the measure of the force of gravity 
 upon an object. 
 
 We must distinguish clearly between amount of matter, 
 which refers to the number of molecules in it; and 
 volume, which refers to the space it occupies. There 
 is the same amount of matter in a pound of lead and a
 
 MECHANICS 33 
 
 pound of feathers, but there is a very great difference 
 in the volume of the two. Weight indicates the amount 
 of matter, but has no relation to volume. 
 
 The specific gravity, or specific weight, of any sub- 
 stance is its weight as compared with an equal volume 
 of some substance taken as a standard. In the case of 
 solids and liquids water is used as the standard (dis- 
 tilled water at a temperature of 4 C.); with gases, hy- 
 drogen gas at C. For- example, water is called 
 1.000. Gold is 19.5 (meaning that it is 19| times as 
 heavy as an equal volume of water); copper is 8.788; 
 coal, 1.270; urine, about 1.020; olive oil, .970; alcohol, 
 .797; ether, .734; wood, .580; cork, .240, and so on. 
 
 Fig. 2. Center of gravity. 
 
 The Center of Gravity of an object is the point on 
 which it will just balance itself, no matter in what 
 position it is placed. It is, to state it differently, the 
 weight center of the object.
 
 34 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 Equilibrium is poise or balance between two or more 
 forces. It causes a body to remain stable when there 
 are forces tending to move it. 
 
 The stability of an object depends upon the relation 
 of its center of gravity to its base. A large base or a 
 low-down center of gravity gives a greater stability. 
 
 There are three sorts of equilibrium : (a) Stable when 
 a body has a broad or heavy base and a low center of 
 
 Fig. 3. Stable and unstable equilibrium. 
 
 gravity. Examples, a cone or pyramid, a chair with 
 four spreading legs, a quadruped. (6) Unstable, when 
 a slight force will push an object over, that is, when 
 its center of gravity is high up or falls toward one side 
 of the base. Examples, a book standing on edge, a 
 biped; extreme examples, a person standing on one leg, 
 a tight-rope walker, (c) Neutral, when a slight force 
 would not act upon it, nor change its center of gravity. 
 Example, a three-legged stool, which stands well until 
 a heavy weight is put upon one side of it, bringing the 
 center of gravity outside of the base. 
 Standing and Walking. Learning to stand or walk is
 
 MECHANICS 35 
 
 difficult because in the human body the center of gravity 
 is high up from the ground (in the abdomen), and the 
 base (the space enclosed by the feet) is small in pro- 
 portion. Standing is the process of maintaining one- 
 self in equilibrium on a small base. Walking is a proc- 
 ess of alternately falling forward and saving oneself, 
 the center of gravity being thrown first over one foot, 
 then over the other. When one carries a load on his 
 back he bends forward so as to have the center of gravity 
 well inside his base; in carrying a weight in the hand he 
 bends to one side for the same reason. 
 
 Both standing and walking are accomplished by the 
 combined action of many muscles, corresponding sets 
 on each side pulling against each other to stiffen the 
 framework and maintain it erect, while other muscles 
 are moving a portion or the whole. The processes are 
 exceedingly complex, and it is not surprising that it 
 takes some months to acquire them. 
 
 In using a cane or crutches one enlarges his base, 
 thereby making his equilibrium more stable. 
 
 ENERGY. WORK 
 
 Whenever anything happens, or is done, there is some 
 driving force behind it. This driving force is what we 
 call energy. There are various sorts of energy, heat 
 being the commonest; others are light energy, sound 
 energy, muscular energy, electric energy, chemical 
 energy, etc. All these bring about changes in matter.
 
 36 PRACTICAL PHYSICS FOR NURSES 
 
 One form of energy may be changed into another, as 
 chemical action may produce heat, motion may produce 
 heat, electricity may produce light, etc. All sorts of 
 methods and appliances have been devised to ac- 
 complish such changes. 
 
 Energy is Indestructible. It may change from one 
 form to another, but none of it is lost. When it dis- 
 appears at one spot, it reappears at another. This is 
 called the law of conservation of energy. Examples: 
 coal (stored-up energy derived primarily from the sun) 
 is burned, producing heat, which in its turn produces 
 steam, which in its turn produces motion, which may be 
 utilized in various ways; energy used in winding a clock 
 reappears in the movements of the clock; electricity may 
 be converted into sound by means of the mechanism of 
 a bell. Many examples will occur to anyone. 
 
 Work. Whenever any of the forms of energy mani- 
 fest themselves, work is done. 
 
 Whenever work is done, it means that an opposition 
 of some sort, a resistance, is overcome, and some change 
 in condition results. This change may be motion or 
 any other form of action. 
 
 WORK AND MOTION 
 
 Whenever force produces motion, work is done. 
 This amount of work is measured by the distance through 
 which a body is moved multiplied by the force which 
 moves it.
 
 MECHANICS 37 
 
 The fundamental laws of motion are those formulated 
 by Sir Isaac Newton. They are as follows: 
 
 1. A moving body always follows a straight line, unless 
 it is acted upon by another force which changes its direc- 
 tion. A stone dropped from a height moves in a straight 
 
 a b 
 
 Fig. 4. a, Cream separator; b, detail of mechanism. 
 
 line because it is acted upon by but one force, that of 
 gravity. A ball thrown from the hand moves in a 
 curve because it is being acted upon by two forces, the 
 muscular energy which started it and the pull of the 
 earth; the resultant of the two forces determines its path. 1 
 1 In neither case do we take into account the resistance of the air.
 
 38 PRACTICAL PHYSICS FOR NURSES 
 
 Centrifugal Force. Swing a weight around by a thread; 
 one is conscious that it is trying to fly off in a straight 
 line, but is held by the thread; therefore it moves in a 
 circle; if the thread breaks, it flies in a straight line un- 
 til pulled toward the earth by gravity. This tendency 
 of a moving body to flee from a fixed center is called 
 centrifugal force (from centrum, center, and fugere, to 
 flee, Latin). The cream separator comes under this 
 law. The milk is whirled rapidly and tends to fly into 
 space, but is held back by the container. Cream and 
 skimmed milk being of different densities, they separate 
 in the whirling, the milk going to the outer part of the 
 container, the cream remaining nearer the center. The 
 urine centrifuge works upon the same principle, the 
 lighter fluid being whirled to the outside, the heavier 
 sediment remaining at the center. 
 
 2. Every change in motion is in proportion to the force 
 or forces applied, and lakes places- in the straight line in 
 which that force (or forces) act. 
 
 3. To every action there is always an equal and op- 
 posite reaction. This principle of rebound is important 
 and should be borne constantly in mind. Surprisingly 
 enough, it has a counterpart in the realm of psychology; 
 one notes how depression invariably follows excitement. 
 
 MACHINES 
 
 Machines are devices by which work may be done more 
 conveniently or advantageously than without them. 
 Man's hands are unsuited to many processes, so he calls
 
 MECHANICS 39 
 
 things, or combinations of things, to his aid. A pencil 
 is a machine, strictly speaking, because it enables us to 
 do easily what would otherwise be very troublesome. 
 
 Machines convert a small force acting through a long 
 distance into a great force acting through a small distance, 
 or vice versa. In the first case we obtain greater power; 
 in the second, we obtain greater exactness. 
 
 Machines enable us to do things which without them 
 would be too large for us, too rapid for us, or too exact 
 for us, to accomplish. 
 
 The body is sometimes referred to as "the human 
 machine." This is in a sense correct, since many 
 parts of it are constructed like other machines, and 
 portions literally are machines. 
 
 The Driving Force. A machine does not, by itself, 
 literally do the work demanded of it. There must 
 always be a driving force, and it is this which in reality 
 does the work. The machine is that through which the 
 driving force acts. 
 
 Our most interesting and useful machines are those in 
 which the power, or driving force, is some other than our 
 own. Some machines are driven by horse power or 
 the energy of other animals; some run by the forces of 
 nature, as wind or water; steam engines use the energy 
 stored up in coal; motor cars utilize that stored in gaso- 
 line; electric appliances make use of the power obtained 
 from electricity, which may in its turn be derived from 
 some other source of energy. 
 
 Types and Classes of Machines. Machines are of
 
 40 PRACTICAL PHYSICS FOR NURSES 
 
 two general types and are divided into six classes. 
 The lever, the -wheel and axle, and the pulley are of one 
 type; the inclined plane, the wedge, and the screw are of 
 the other type. 
 
 SUMMARY 
 
 Gravity is the force by which the earth pulls everything 
 toward its center. Its action produces weight, which 
 enables us to know the amount of matter in any given 
 mass or object. 
 
 Specific gravity is the weight of any given substance 
 compared with water as a standard. 
 
 Equilibrium, the balance between two or more forces, 
 may be stable, unstable, or neutral. Man, in walking 
 upright, is in a state of unstable equilibrium, as his 
 base is small and his center of gravity high up. 
 
 The driving force behind any action is called energy. 
 There are various forms of energy, light, heat, chemical, 
 muscular, electric, etc. One form of energy may be 
 changed into another, but none is ever lost or destroyed. 
 
 Manifestations of energy are called work. This is 
 an overcoming of resistance or some change in condition. 
 
 Newton's three laws of motion cover the fundamentals. 
 
 Machines are devices by means of which we may ac- 
 complish things otherwise too large, too rapid, or too 
 exact for us to do unaided. 
 
 Behind the machine there must always be a driving 
 force, such as that supplied by the strength of animals, 
 by water-power, wind, electricity, gasoline, coal, etc. 
 
 There are six classes of machines.
 
 CHAPTER III 
 
 . 
 
 MECHANICS (Continued) 
 
 THE lever is the most common and most useful ma- 
 chine; in fact, nearly all machines are, in a sense, va- 
 rieties of lever or combinations of levers. 
 
 A lever is a rigid bar, straight or curved, resting on a 
 fixed point or edge, called the fulcrum. It is used to 
 move weight or overcome resistance. The hand-spike 
 is a common form of the simple lever. 
 
 There are three things concerned in the action of a 
 lever: 1. The weight to be lifted or moved. 2. The 
 power which shall move it. 3. The fulcrum, or point 
 upon which the movement is to take place. 
 
 There are three classes of levers: In the first class the 
 fulcrum is between the weight and the power. In the 
 second class the weight is between the fulcrum and the 
 power. In the third class the power is between the 
 fulcrum and the weight. 
 
 In all cases it is possible to calculate, by mathematical 
 means, the exact power that will be required to move a 
 given weight through a given distance. 
 
 In levers of the first class, the fulcrum being between 
 the power and the weight, the weight moves in an op- 
 posite direction to that in which the power is applied. Com- 
 
 41
 
 42 PRACTICAL PHYSICS FOR NURSES 
 
 mon examples are the tack lifter, the can opener, the 
 pump handle, the grocer's scales, etc. 
 
 II 
 
 III 
 
 -A. 
 
 Fig- 5- The three classes of lever. 
 
 Scissors, pliers, artery clamps, etc., are double levers 
 of the first class, the weight being between the blades,
 
 MECHANICS 
 
 43 
 
 the power the force applied by the hand, the fulcrum 
 the joint. The bivalve speculum is a double lever, the 
 weight being the walls of the cavity into which it is in- 
 
 Fig. 6. Levers of the first class: A, Uterine dilator; B, can opener; 
 C, claw hammer; D, chisel. (Butler, "Household Physics.")
 
 44 PRACTICAL PHYSICS FOR NURSES 
 
 serted. The long uterine dilator with two handles is 
 also a double lever. (The small, graduated dilators are 
 wedges, not levers.) 
 
 If the power arm of the lever is long and the weight 
 arm short, the work is more easily done than if the re- 
 verse is the case; the distance an object can be moved 
 in this case is lessened, but force and time are gained. 
 
 Fig. 7. Levers of the first class, with long and short power 
 arms: a, Paper-cutting shears; b, metal-cutting shears. (Butler, 
 "Household Physics.") 
 
 In the large uterine dilator great force is gained because 
 of the excessive length of the handles. It is for this 
 reason that metal-cutting shears have long handles, 
 while scissors for cutting paper have very short handles; 
 the first requires great power; the second, little power 
 but a long sweep. 
 
 In the human anatomy there are many portions which 
 can be used as levers of the first class. In grasping an 
 object with the hand, the object is the weight, the 
 ringer joints are the fulcrum, the flexor muscles the 
 power. In putting the head back the joint at the top 
 of the spine is the fulcrum, the head is the weight, and 
 the muscles at the back of the neck are the power
 
 MECHANICS 
 
 45 
 
 (see Fig. 11). In pushing an object with the foot, the 
 object is the weight, the ankle- or knee-joint is the ful- 
 crum, the leg muscles the power. 
 
 AF 
 
 Fig. 8. Levers of the second class: a, Nut-cracker; b, wheelbarrow. 
 (Butler, "Household Physics.") 
 
 In levers of the second class the weight being be- 
 tween the power and the fulcrum, the weight moves in 
 
 Fig- 9- Levers: a, Jaw of human being; b, foot when we rise on the 
 toes. (Butler, "Household Physics.") 
 
 the same direction as that in which the power is applied. 
 The wheelbarrow is a common example. The nut
 
 4 6 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 cracker and the lemon squeezer are double levers of 
 the second class. 
 
 Fig. 10. Levers of the third class: a, Sugar tongs; b, fork; c, 
 forearm; d, spoon, knife, potato masher, pliers, wrench, and fire 
 tongs. (Butler, "Household Physics.")
 
 MECHANICS 47 
 
 In lifting the weight of the body to the tip-toes, the 
 toes form the fulcrum, the calf muscle the power. 
 
 In this class of lever also, if the weight is near the ful- 
 crum, and the power arm is long, the work is more easily 
 accomplished. 
 
 In levers of the third class the fulcrum is at one end, 
 the weight at the other, the power between them. Com- 
 mon examples are the fork and spoon, as used in eating. 
 Sugar tongs and thumb forceps are double levers of the 
 third class. 
 
 It will readily be seen that this form of lever is not of 
 advantage in lifting weights, since the power must always 
 be greater than the weight to be lifted. It is used 
 chiefly when we wish to produce a rapid motion through 
 a considerable distance, or to facilitate small, exact 
 movements. 
 
 The flexing of the forearm constitutes a lever of the 
 third class. The weight is the hand and anything it 
 may contain, the fulcrum is the elbow-joint, the power 
 is the biceps muscle, applied at its point of attachment 
 below the elbow. It is clear that this is not designed 
 for the lifting of great weights, but for quick, dextrous 
 movements. 
 
 The bending of the head forward is done by a leverage 
 of the third class; the sternomastoid muscle is the 
 power, the sternoclavicular attachment the fulcrum, 
 the head the weight. 
 
 Another example is the use of the lower jaw in masti-
 
 4 8 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 cation. The weight or resistance is the food between 
 the teeth, the fulcrum is the articulation near the ear, 
 the power is the masseter muscle. 
 
 Complicated Movements. Most of the movements 
 of the body are complicated, two or more fulcrums and 
 a number of muscles being brought into play. (This is 
 also true of a great many machines.) We commonly 
 
 Fie. ii. Muscles of neck as levers (Dorland's Dictionary). 
 
 lift a heavy object by using the muscles of the shoulders 
 and back, somewhat assisted by those of the arm, the 
 elbow and shoulder-joints being the fulcrums, and the 
 action being a combination of W e rs of the first and third 
 classes. 
 
 An example of a powerful double lever is observed 
 when the body is raised from a squatting position. 
 The knee-joints are the fulcrums, the power is the leg
 
 MECHANICS 
 
 49 
 
 muscles. In machinery such an arrangement is called 
 the toggle-joint or Stanhope lever. 
 
 OTHER MACHINES 
 
 The crank-and-axle (or wheel-and-axle) is a variety 
 of lever, a sort of continuous lever. Common examples 
 are the coffee-mill, the clothes-wringer, the bread-mixer, 
 
 Fig. 12. The crank and axle: a, Treadle of sewing machine; b, 
 bread mixer. (Butler, "Household Physics.") 
 
 the Dover .egg-beater, the ice-cream freezer, etc. The 
 weight is the material to be acted upon or moved, the 
 fulcrum the axle or bearing upon which the movement 
 takes place, the power the muscle of the operator, acting 
 through the wheel or crank. 
 The driving mechanism of a sewing machine is a
 
 5 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 combination of the wheel-and-axle and a lever (the 
 treadle). 
 
 The pulley consists of a grooved wheel called a sheave, 
 set into a frame, the block; the weight to be lifted is at- 
 tached to one end of a rope which runs over the sheave, 
 
 a b 
 
 Fig. 13. The pulley: a, Simple; b, compound. 
 
 the power being applied at the other end of the rope. 
 Adding more sheaves multiplies the power, so that very 
 little force may be needed to move a considerable weight. 
 The extension apparatus used in fractures of the 
 thigh is a simple pulley, the weight being the body of 
 the patient, the power being the weights attached at
 
 MECHANICS 51 
 
 the foot of the bed. The action is not movement, 
 but merely pull. The superior oblique muscle of the 
 eye is a pulley, also the omohyoid muscle. 
 
 The inclined plane needs little explanation, it being 
 obvious that a weight can be pushed or pulled up an 
 incline with much less effort than it can be lifted verti- 
 cally to the same height. 
 
 P 
 
 Fig. 14. The inclined plane. 
 
 A series of rules have been formulated by which one 
 may calculate the exact force necessary to move a given 
 weight up an incline of a given angle. 
 
 The screw is a curved inclined plane. It is com- 
 monly used to increase the pressure of one object upon 
 another, usually with the purpose of holding one or both 
 in place. It is also used to produce a small, very exact 
 adjustment. The adjusting mechanism of the micro- 
 scope is an example of how a screw changes a long move- 
 ment into a short, exact one. 
 
 The screw-driver is a lever which assists the placing 
 of the screw. In forms of screw like the letter press, 
 the beef-juice press, the meat grinder, the bread slicer,
 
 52 PRACTICAL PHYSICS FOR NURSES 
 
 etc., the handle is a lever; in the two latter the handle 
 is a modified lever, the crank and axle. 
 
 The wedge is a double inclined plane which is forced 
 in between two surfaces or portions of matter in order 
 to separate them or in order to hold them against re- 
 sistance. The power used is applied in the form of 
 blows rather than as a continuous push. The wedge 
 is a very powerful machine. 
 
 Fig. 15. The wedge. 
 
 Knives are wedges with delicate edges. Rectal di- 
 lators and the small uterine dilators are round wedges. 
 
 The mechanics of obstetrics is most interesting, 
 though somewhat complicated. The child is the weight, 
 and the tissues of the cervix, the vagina, and perineum 
 the resistance to be overcome. The muscles of the ab- 
 dominal wall and of the uterus are the power. If the
 
 MECHANICS 
 
 53 
 
 woman is on her feet, gravity assists the process. If she 
 is in bed, additional force may be obtained by the pull 
 of her arm and leg muscles against some firm objects. 
 
 The child's head, in combination with the sac of 
 amniotic fluid which acts as a cushion to prevent in- 
 jury to the tissues, acts as a wedge to force the tis- 
 
 
 Fig. 16. Child's head acting as wedge (DeLee). 
 
 sues apart. Note how the power is applied inter- 
 mittently during the pains. The great force employed is 
 appreciated by anyone who has actually delivered a child. 
 The birth canal is not straight, but much curved, 
 being about one-third of a circle. It is, in effect, a 
 series of inclined planes, which in succession change 
 the direction of the child's progress.
 
 54 
 
 JPRACTICAL PHYSICS FOR NURSES 
 
 If the natural forces are not sufficient to produce the 
 necessary progress, the obstetric forceps, a double lever 
 
 Fig. 17. Diagram showing the advancement of the head through 
 the pelvis (Leishman). 
 
 Fig. 18. Forceps: a, Obstetric; b, axis-traction. 
 
 of the first class, is used to assist the process. With 
 them the obstetrician holds the progress that has been
 
 MECHANICS 55 
 
 made, or aids it by pulling in the direction that the 
 other forces are pushing, and in which the child's head 
 is moving. Since the passage is not straight, the for- 
 ceps must be curved, and the pull must be made in the 
 direction that the child's head is traveling. "Axis- 
 traction" forceps enable the operator to get his pull in 
 the proper direction while the head is still far up and 
 the curve is very great. Watch the direction taken by 
 the handles of the forceps during a delivery and note how 
 great a curve they describe during the descent of the 
 child. At first they point somewhat downward, and 
 at the end of the delivery almost upward. 
 
 FRICTION 
 
 When the surface of one body is made to move over 
 that of another, a resistance to the movement is felt. 
 This resistance is friction. If perfectly smooth surfaces 
 could be obtained, there would be little or no friction; 
 but this is impossible. There is always more or less 
 roughness, and therefore some resistance. Roughness 
 increases friction, smoothness reduces it. 
 
 Without the action of friction we should find it ex- 
 ceedingly difficult to hold anything in place; everything 
 would tend to slip from our hands or slide away at a 
 touch. Without friction we should be unable to walk 
 or drive, as we should constantly slip. It is an impor- 
 tant factor in life. 
 
 There are two sorts of friction, rolling and sliding.
 
 56 PRACTICAL PHYSICS FOR NURSES 
 
 The former gives the least resistance. In machines with 
 which we wish to do work easily we make use of smooth, 
 rolling surfaces, since they move with greater ease. 
 
 Fig. 19. Friction. Sliding and rolling. 
 
 The so-called ball-bearings, where there are a number of 
 parts which roll over one another, produce a very 
 easy-running joint. 
 
 CoronoicL 
 
 -Ulna* 
 
 Fig. 20. Construction of joint (after Toldt). 
 
 On the other hand, a brake set to a wheel changes 
 rolling into sliding friction, and so checks the motion. 
 
 Lubricants reduce friction; it is for this reason that 
 we oil or grease machinery.
 
 MECHANICS 57 
 
 Great friction produces heat (see page 98) which may 
 interfere markedly with the action of a machine. 
 
 The human body presents very perfect examples of 
 reduction of friction. The joints are nearly all rolling 
 joints, rather than sliding, thus offering the least re- 
 sistance to movement, and constitute a great economy 
 of force or power. The cartilages that cover the working 
 portions of the joints are practically perfect in their 
 smoothness, and the synovial fluid is a fine and perfect 
 lubricant, continually renewed. It is when joints are 
 roughened or dried by disease that they work with 
 difficulty. 
 
 SUMMARY 
 
 The lever is one of the most used of mechanical devices. 
 There are three essentials to its -action the weight, 
 the power, and the fulcrum or point on which the 
 motion takes place. 
 
 There are three classes of levers; they vary according 
 to the relative positions of weight, power, and fulcrum. 
 Examples of each sort, may be found among appliances 
 in every-day use, and in muscular actions taking place 
 in the human body. 
 
 Many of the body movements are complicated, being 
 produced by the combined action of many muscles, and 
 involving two or more joints as fulcrums. 
 
 The wheel-and-axle is a continuous lever. It is used 
 in many domestic appliances.
 
 $8 PRACTICAL PHYSICS FOR NURSES 
 
 The pulley consists of a sheave set into a block; 
 over this runs a cord attached to both weight and power. 
 A pulley with several sheaves facilitates the moving of 
 a weight. 
 
 The inclined plane is another machine which de- 
 creases labor in the lifting of weights. 
 
 The screw is a curved inclined plane with a rather 
 complex mechanism. It has many applications in 
 domestic and hospital life. 
 
 A wedge is a double inclined plane driven by inter- 
 mittent blows; it is used when great force is needed to 
 separate or hold objects. 
 
 Most of our so-called machines are complex combina- 
 tions of two or more of the simple machines. 
 
 An obstetric delivery is essentially a mechanical proc- 
 ess. The child's head acts as a wedge to overcome the 
 resistance of the cervical, vaginal, and perineal tissues. 
 The force employed is that of the abdominal and uterine 
 muscles; it may when necessary be aided by the pull of 
 obstetric forceps. The birth canal being curved prac- 
 tically a series of inclined planes the shape of the 
 forceps and the direction of the pull must correspond 
 with it. 
 
 Friction is the resistance between two surfaces, one 
 of which moves over the other. It is inevitable, since 
 a perfectly smooth surface is impossible to obtain. It 
 is of advantage in holding or placing objects, but is a 
 disadvantage when we wish to move them. Sliding
 
 MECHANICS 59 
 
 friction may be changed to rolling friction, and therefore 
 reduced, by the use of lubricants. 
 
 The human body presents many excellent examples of 
 the advantages of the reduction of friction.
 
 CHAPTER IV 
 
 HYDRAULICS 
 
 LAWS RELATING TO LIQUIDS 
 
 Properties of Liquids. Liquids tend to keep their 
 molecules together, but not strongly. The force of 
 their cohesion is not enough to overcome the action of 
 gravity; therefore they "run" to the earth unless pre- 
 vented by other forces. 
 
 Different liquids possess different degrees of cohesion. 
 We note this in the varying size of drops of different 
 liquids. Castor oil, for example, coheres rather strongly, 
 and its drops are correspondingly large. Alcohol has 
 less cohesive force, and its drops are smaller. Chloro- 
 form drops are very small. 
 
 (Sixty drops of water make a dram by measure. Carbolic 
 acid takes 118 drops to make a dram; tincture of aconite, 150; 
 ether, 180; chloroform, 240.) 
 
 Liquids are very much less compressible than solids; in 
 fact, most of them are not compressible to any appreciable 
 extent. This is an important characteristic in their 
 use in practical life. 
 
 Water is the most common and the most important 
 liquid. It is therefore used as a standard for measuring 
 the qualities of other fluids. 1 
 
 1 Specific gravity, or the weight of a substance compared with 
 the same amount of water, as before noted, refers to both liquids 
 and solids. 
 60
 
 HYDRAULICS 61 
 
 Liquids vary greatly in their weight. Note the dif- 
 ference in weight of equal-sized bottles of oil and of 
 sulphuric acid. A cubic foot of cold water weighs 62.42 
 pounds. In hot water the molecules are farther apart, 
 therefore it requires a little more space and weighs a 
 little less. 
 
 Fig. 21. Water pressure on bottom of container. 
 
 Pressure in Liquids. If 1 cubic foot of water is placed 
 on top of another, the weight is 124.84 pounds; that is, 
 the pressure upon the bottom of the container is that 
 amount. So, if water is 5 feet deep, the bottom of the 
 container must bear a weight of more than 300 pounds 
 to the square foot. From this one can see that the
 
 62 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 pressure in deep water is very great. It is for this 
 reason the great pressure that sea divers cannot 
 
 
 
 Fig. 22. Irrigator hung high. The whole column of water makes 
 pressure (DeLee). 
 
 go to any great depth; and they must always wear 
 suits of material heavy enough and stiff enough to re-
 
 HYDRAULICS 63 
 
 sist the weight of the water and keep it from crushing 
 them. 
 
 The irrigators which we use in hospital work also 
 illustrate the pressure of fluids. If an irrigator is hung 
 high, there is more water in the tube, i. e., it is deeper, 
 
 Fig. 23. Irrigator hung low. There is very little pressure, because 
 the depth of water in irrigator and tube is not great (DeLee). 
 
 and the pressure exerted upon its lower part, upon the 
 small surface which is the caliber of the tube, is that of 
 the whole column of water in both irrigator and tubing. 
 If hung low, there is very little pressure, and the water 
 when released finds its escape easily and gently. It
 
 64 PRACTICAL PHYSICS FOR NURSES 
 
 is, we observe, the depth and not the amount of water 
 which regulates the pressure upon the bottom. 
 
 Pascal's law formulates another important fact. 
 The pressure in a liquid is tlie same in all directions.. 
 Solids press only downward; liquids press sideways 
 and upward as well. 
 
 Experiments. (a) Fill a hot-water bag quite full of water, 
 getting out all the air; lay on the hand; press the top or side of the 
 bag and note that the resistance is as great in one place as in another. 
 (b) Let water run from an irrigator to the tubing of which is at- 
 tached a uterine tip, one having several holes; note that the water 
 runs with equal force from all of the holes, not more forcibly from 
 the bottom hole, as one would expect. 
 
 The discomfort of a patient from a full bladder is due 
 to this law, because the urine is pressing in all directions. 
 
 A water-bed is useful because it makes pressure upon 
 the surface of the patient's body equally in all places, 
 
 Fig. 24. Water-bed. 
 
 unlike the ordinary bed, which presses harder against 
 the more prominent portions. 
 
 It is this law which causes the force of the heart-beat 
 to be distributed evenly throughout the body, so that 
 blood-pressure is the same in all arteries, large or small, 
 far away from or near to the heart. 
 
 It is this law which makes the sac of amniotic fluid so
 
 HYDRAULICS 65 
 
 efficient yet so gentle a dilator in obstetric cases. It 
 presses in every direction at once, yet without possi- 
 bility of injury to the tissues. 
 
 Water Seeks its Own Level. Because water presses 
 in all directions it runs through any available openings, 
 and stops only when there is a resistance ahead of it 
 equal to the force or weight behind it. 
 
 Our city water systems are based upon this law. The 
 source of supply is a lake or river higher than the city, 
 or, failing this, the water is pumped up to a reservoir 
 
 Fig. 25. Diagram of artesian well. 
 
 or standpipe situated upon high ground. (The supply 
 in this case may be a low river, a spring, a well, etc.) 
 All water which is permitted to flow from this reservoir 
 or source of supply attempts to rise as high as its origin. 
 The great height of the large body of water gives us 
 the desired pressure. Water coming from a hose used 
 to sprinkle a lawn would rise to the top of the water in 
 the reservoir from which it flows if it were not for other
 
 66 PRACTICAL PHYSICS FOR NURSES 
 
 forces, the friction against the inside of the hose, the re- 
 sistance of the air, and the action of gravity. 
 
 Artesian wells are produced by water trying to find 
 its level. The source of the water is in the hills that 
 are above the well; the water, soaking through the 
 earth and running along an impervious layer of rock or 
 clay, finds an opening and pushes up through it, or, 
 more correctly, is pushed up through it by the body of 
 water behind it. In some cases artesian wells spout 
 high above the ground. 
 
 Buoyancy. Push a block of wood under water and 
 release it; it rises to the surface and floats with its bulk 
 almost out of the water. This is due to the buoyancy 
 (not of the wood, but) of the water, i. e., its tendency 
 to raise all bodies to its surface. This is due to the facts 
 already discussed, that pressure increases with depth 
 and that it acts in all directions. This results in the 
 pressure upward on the bottom of a submerged object 
 being greater than the pressure downward upon its top. 
 If the additional weight of the body itself is not more than 
 this difference of pressure against top and bottom, the 
 object floats. 
 
 Heavy substances, which displace less than their own 
 weight of water, sink. Light substances, which dis- 
 place more than their weight, float. The law of Archim- 
 edes a floating body sinks until it displaces its own 
 weight of liquid is a summary of the above facts and 
 other similar ones.
 
 HYDRAULICS 67 
 
 Swimming. The human body, partly because of 
 the air in its tissues and in the lungs, is but slightly 
 heavier than water, so that it floats just below the sur- 
 face. With slight effort a portion of the head mouth, 
 nose, and eyes can be kept above the water, making 
 it possible for a person to swim. The balance is so 
 nearly equal that it takes only a small quantity of water 
 getting into the lungs and replacing the air to cause one 
 to sink, i. e., drown. 1 
 
 Experiment. A fine needle, especially if dipped in oil, can be 
 made to float on water if it is laid gently and evenly upon the 
 surface. Its weight is not sufficient to overcome the force of the 
 cohesion of the molecules of water. 
 
 Loss of Weight in Water. On account of this quality 
 of buoyancy, all objects weigh less in water than they 
 do in air. The water pushes up or sustains a con- 
 siderable portion of their weight. Experiments are 
 easily made which prove this. 
 
 Hydrometers. The hydrometer is a device used for 
 ascertaining the specific gravity of liquids. It is based 
 upon the law of Archimedes. It consists of a tube 
 weighted at one end with the requisite amount of mer- 
 cury, and marked with a scale. The point marked is 
 the point to which it sinks in water. Placed in a liquid 
 
 1 Bodies of drowned persons sometimes float after being in 
 water a considerable length of time. This is because chemical 
 changes have taken place, producing in the tissues gases that are 
 lighter than water.
 
 68 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 heavier than water, it tends to float; in a liquid lighter 
 
 than water, it sinks deeply. The scale is arranged so 
 that it designates the specific 
 gravity. 
 
 The urinometer and the 
 cream tester are hydrometers. 
 The urinometer is of impor- 
 tance because: (1) If urine is 
 of low specific gravity, i. e., 
 nearly that of water, it indi- 
 cates that not enough solid 
 matter is being eliminated 
 from the body. (2) If it is 
 of high specific gravity, there 
 is too much solid matter, 
 i. e., not enough fluid is being 
 taken, or some abnormal con- 
 dition is causing the elimina- 
 tion of materials that should 
 remain in the body. 
 
 The specific gravity of nor- 
 mal milk is 1029. If the cream 
 tester shows it lower than this, 
 there is a suspicion that water 
 
 may have been added. Excess of cream may change the 
 
 test somewhat. 
 
 Fig. 26. Hydrometers.
 
 HYDRAULICS 69 
 
 CAPILLARITY 
 
 Capillarity, or capillary attraction, is the quality that 
 causes liquids to adhere to solids in opposition to the force 
 of gravity. Its action is most marked in fine tubes and 
 in porous substances. 
 
 Experiments. Hang a wick of gauze over the edge of a tumbler 
 half full of water; water will soon be dripping from the outer end 
 of the wick. Hang up a cloth so that its lower edge or corner 
 dips into water; the whole cloth will gradually become wet. Dip 
 the corner of a lump of sugar into coffee or cocoa; the whole lump 
 very quickly becomes colored with the fluid. Place a white carna- 
 tion or other white flower for a few hours in a bottle of red ink; 
 the ink stains it, especially along the veins. 
 
 It is capillarity which causes the sap to rise in plants, 
 since they have no circulatory system. It is this force 
 which helps the small blood-vessels of the intestines, the 
 lacteals, and the lymphatics, to absorb liquid nourish- 
 ment from the intestinal contents. It is this which 
 makes possible the capillary circulation and the flow 
 of blood in the very small veins; the force of the heart- 
 beat pushes the blood only part way through the smallest 
 vessels, but capillarity assists and continues the process, 
 especially when it is necessary for the blood to ascend, 
 in opposition to gravity. 
 
 It is capillarity upon which we depend largely in our 
 drainage of wounds. Gravity, of course, assists the 
 process, but a gauze wick will drain even though the 
 fluid to be removed must go upward. Drainage stops 
 when the gauze becomes blocked with solid particles.
 
 70 PRACTICAL PHYSICS FOR NURSES 
 
 Waterproofed cloth is that which has been treated 
 with something which prevents capillary action. 
 
 DIFFUSION 
 
 Diffusion is the force that makes fluids tend to mix 
 when they are brought into contact. 
 
 Experiments. Put some solution of blue vitriol in the bottom 
 of a test-tube; tip the tube and with a medicine-dropper put carefully 
 on top of it a layer of water; left undisturbed, they gradually mix, 
 till the whole is blue. Put milk at the bottom of a test-tube and 
 water on top; watch them mix. 
 
 Osmosis. A similar process takes place through thin 
 animal or vegetable membranes. It is called osmosis. 
 It applies only to solutions of crystalline substances, 
 however. 
 
 Experiment. Procure a pig's bladder or other thin animal 
 membrane; put some colored fluid into it a solution of potassium 
 permanganate is good and hang it in or touching some water. 
 The colored fluid will penetrate the membrane, and color the water, 
 the latter exchanging places with it. 
 
 It is the combination of this force with capillarity 
 which makes possible the absorption of stomach and 
 intestinal contents. Osmosis occurs rapidly through the 
 stomach wall. Note that the drinking of hot water 
 causes diuresis within fifteen or twenty minutes, long 
 before the fluid could have reached the intestines; it is 
 absorbed directly from the stomach. Medicines given 
 in hot water are quickly absorbed and an effect produced 
 in a short time. Osmosis effects this by carrying the 
 medication through the stomach wall into the circulation.
 
 HYDRAULICS 71 
 
 When a saline cathartic is given, the saline matter 
 absorbs much water from the tissues of the intestines, 
 pulling it through the membrane of the intestinal wall; 
 the excess of fluid so obtained produces a watery or very 
 soft bowel movement. 
 
 Edema. We find that osmosis takes place toward 
 the more concentrated solution, and that saline substances 
 increase it. When, therefore, in certain diseased con- 
 ditions the kidneys fail to eliminate a sufficient quantity 
 of saline material from the body and it accumulates in 
 the tissues, it produces an osmosis of the body fluids 
 and we have the condition which we call edema. 
 
 SUMMARY 
 
 Cohesion is not strong in liquids, therefore they are 
 easily affected by gravity. Liquids are very slightly 
 compressible. 
 
 It is the depth of water rather than the amount pres- 
 ent which determines the pressure upon the bottom of 
 the container. This law is illustrated by the ordinary 
 hospital irrigator. 
 
 The pressure in a liquid is the same in all directions. 
 This is illustrated by the fact that quality of pulse is 
 the same in all parts of the body. 
 
 Water seeks its own level. City water systems, 
 artesian wells, irrigators, etc., illustrate this law. 
 
 A floating body sinks until it displaces its own weight
 
 72 . PRACTICAL PHYSICS FOR NURSES 
 
 of the liquid. This law governs the use of the urinom- 
 eter, etc., and explains ability to swim. 
 
 Capillarity is the property that causes liquids to rise 
 in small tubes and other restricted places in opposition 
 to the action of gravity. It is this force which aids the 
 capillary circulation, absorption from the alimentary 
 canal, the drainage of wounds, etc. 
 
 Waterproofing is the prevention of capillarity. 
 
 Diffusion is the property which causes liquids to mix 
 when they are brought into contact. When it takes 
 place through a membrane it is termed "osmosis." 
 
 Osmosis is especially active in saline solutions; it 
 takes place toward the more concentrated solution. 
 This explains the occurrence of edema when there is 
 faulty elimination.
 
 CHAPTER V 
 PNEUMATICS 
 
 LAWS RELATING TO GASES 
 
 Properties of Gases. In gases the molecules are con- 
 siderably separated and have no cohesion; in fact, they 
 are always trying to get farther apart and fail only be- 
 cause outside forces prevent them. 
 
 Experiment. Produce dense smoke by burning sugar or setting 
 fire to "touch-paper" (unsized paper soaked in a strong solution of 
 saltpeter and dried). The smoke quickly becomes diffused through 
 the room, even though there are no apparent currents of air. 
 
 The law of diffusion of gases corresponds to that of 
 liquids. Gases which are in contact tend to mix. If it 
 were not for this law we should, in a closed room, be- 
 come quickly surrounded by a lake of impure air which 
 we should be compelled to rebreathe.; this is prevented 
 by the rapid diffusion of gases, and by the fact that air 
 is so readily disturbed, so that the opening of a door or 
 the moving of an object in the room keeps the air "stirred 
 up." 
 
 Elasticity of Gases. Gases, because of the tendency 
 of their molecules to get away from each other, are very 
 elastic. Note the great elasticity of the air confined in 
 an air-cushion, an automobile or bicycle tire. Observe 
 
 7?
 
 74 PRACTICAL PHYSICS FOR NURSES 
 
 the rapidity and force with which it escapes when even" 
 a small opening is made. 
 
 Compressibility of Gases. All gases are compressible, 
 most of them to a very marked degree. It is well known 
 that a large quantity of oxygen, compressed air, carbon 
 dioxid, etc., may be forced into a tank. 
 
 Illuminating gas is collected in very large iron tanks, 
 the weight of which is sufficient to hold it in place. The 
 tank is set in a deep cistern of water, through which the 
 gas passes with great difficulty, and the tank rises or 
 falls in it according to the amount of gas it con- 
 tains. Pipes are laid from this tank; the weight of 
 the tank and the elasticity of the gas itself force it 
 through the pipes in every direction and with an even 
 pressure. 
 
 Air is the Most Important Gas. It is composed of a 
 mixture (not a combination) of two gases, nitrogen 
 (four-fifths) and oxygen (one-fifth). 1 If it were not for 
 the constant action of the law of diffusion of gases the 
 air would be an irregular mixture, somewhat like marble 
 cake, with spots and streaks of the two gases, causing 
 endless inconvenience and danger. 
 
 The air surrounds the earth, but is not very deep over 
 its surface, about 50 miles. There is probably some 
 air as far up as 200 miles, but at a distance of 7 or 8 
 miles above the surface it is very rare, i. e., its molecules 
 
 1 There is also a small amount of carbon dioxid, watery vapor, 
 and of various impurities in minute quantities.
 
 PNEUMATICS 75 
 
 are far apart. Man has never been more than about 5 
 miles (25,000 feet) above sea-level. 
 
 Air has Weight. Air is matter and all matter is at- 
 tracted by the earth. In the case of air, the force with 
 which the molecules try to get away from each other is 
 slightly less than the attraction of gravity. The weight 
 of air is 1.28 ounces per cubic foot. 
 
 Some gases are lighter than air, some heavier. A 
 balloon rises in the air because it is filled with some gas 
 lighter than air, usually hydrogen. 
 
 Air Pressure. Air is like water in that the pressure 
 increases with its depth. It is denser at the bottom, 
 i. e., near the earth's surface, or, rather, at sea-level. 
 
 Fig. 27. Diagram illustrating increase of pressure with depth. 
 
 Illustration. Place several pillows in a pile; note that the 
 lower one is much flattened, each successive one less so. This 
 illustrates how the weight of the upper air compresses the lower 
 portions and drives the molecules closer together. 
 
 The air pressure at any point equals the weight of 
 the column of air which is above it, the height of this 
 column being the distance that the atmosphere extends.
 
 76 PRACTICAL PHYSICS FOR NURSES 
 
 It can be readily seen that this pressure is greater at 
 sea-level than at an altitude. 
 
 Experiments. Tie a piece of thin rubber (the wrist of an old 
 rubber glove is suitable) over the mouth of a small funnel. Connect 
 the funnel with a piece of rubber tubing. With your mouth with- 
 draw some of the air in the funnel and clamp the tube. The rub- 
 ber stretched over the funnel will bulge inward because of the external 
 air pressure. 
 
 Remove the rubber, leave the tubing. Place the funnel against 
 the cheek, if it is small enough to fit snugly; withdraw air by means 
 of the tubing. The cheek will be pulled into the funnel, or, in 
 reality, pushed in by the air in the tissues and the cavity of the 
 mouth pressing outward. The blood in the small vessels is also 
 forced in shown by the redness which appears because the 
 blood-pressure from within remains the same while the air pressure 
 from without is relieved. This is the principle of dry cupping, 
 which is used to bring blood to the surface of a small area. The 
 breast-pump works upon the same principle. 
 
 Fig. 28. Breast-pump and cupping-glass. 
 
 The air pressure at sea-level is 14.7 pounds to the square 
 inch. Our bodies, therefore, are constantly sustaining 
 a weight of about 15 tons of air. We do not feel it (1) 
 because the solid portions of the body are very resist- 
 ant, (2) because the body fluids are not compressible,
 
 PNEUMATICS 77 
 
 (3) but chiefly because the gases in the body are of the 
 same density as the air and so equalize the pressure. 
 
 The feeling of pressure experienced by those who climb 
 high mountains is due to the fact that the air in their 
 tissues does not escape nor become thin as rapidly as 
 that outside. The ear drum has been known to burst 
 at a high altitude on account of the difference in air 
 pressure on its two sides, especially if the eustachian 
 tube be partly blocked- 
 
 Effects of Air Pressure. Scientists of the old times 
 formulated a law, "Nature abhors a vacuum." Later 
 scientists explained this law by the discovery of the laws 
 of air pressure. A vacuum is the term used to describe 
 an enclosed space where there is little or no air. A perfect 
 vacuum has never been obtained. 
 
 When we begin to expel the air from any space, more 
 air tries to get in. If a possible opening is blocked by 
 liquid or solid material, the external air will, if possible, 
 push the liquid or solid in ahead of itself in its struggle 
 to enter. In using a medicine-dropper we press the 
 air out of the rubber bulb and dip the glass point into 
 a liquid; since the air outside, pressing on all the liquid 
 in the container, is kept away from the entrance to the 
 tube by it, it forces the fluid into the tube. 
 
 Experiments. Push an empty tumbler mouth downward into 
 water. Note that the water rises only a very little way into the 
 glass, being kept out by the air which is there. Note the shape 
 of the surface of the water inside the glass. Push a large cork into 
 the water and release it under the tumbler. What occurs, and why?
 
 78 PRACTICAL PHYSICS FOR NURSES 
 
 Fill a glass tube with water, close the upper end with the finger, 
 and dip the lower end in water. The water remains in the tube 
 because of the pressure of the air upon the surface of the water in 
 
 Fig. 29. Tumbler inverted in water, showing how the air prevents 
 the water from entering. (Note shape of water surface.) 
 
 the vessel. When the finger is removed from the top of the tube, 
 the air pressure comes directly upon the water in the tube and 
 causes it to fall. 
 
 Fig. 30. Upward pressure of the air (Butler, "Household Physics"). 
 
 Fill a small tumbler brimful of water; press a smooth piece of 
 paper on top; holding the paper tightly, turn the tumbler upside 
 down; remove the hand which holds the paper in place. The paper
 
 PNEUMATICS 
 
 79 
 
 remains. The water also remains in the tumbler. Both are held 
 in place by the air pressure from below upward, the glass prevent- 
 ing the air pressure from above from acting upon the water. (Grav- 
 ity is also partly overcome by the adhesion between the wet paper 
 and the edge of the tumbler.) 
 
 Vacuum Fountain (Fountain in Vacua). Have a 
 quart flask fitted with a tight cork, through which is a 
 
 Fig. 31. Fountain in vacua. 
 
 small glass tube reaching halfway to the bottom. Ex- 
 haust as much air as possible from the flask by suction 
 upon the tube, put the ringer tightly over the end of the 
 tube, dip the end in water, and release the finger. The
 
 8o 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 water will rush into the flask with force enough to pro- 
 duce a fountain. 
 
 Hero's Fountain. Put some water into the flask, 
 well above the end of the tube. Blow through the tube 
 until the air inside is compressed as much as possible. 
 
 Fig. 32. Hero's fountain. 
 
 Place the finger over the end of the tube to keep the com- 
 pressed air from escaping. Release it suddenly, and 
 the confined air will force water out through the tube 
 like a fountain. 
 
 Applications of the Laws of Air Pressure. Hypoder- 
 mic or dressing syringes to work well must have pistons
 
 PNEUMATICS 8 1 
 
 that are air-tight. When the end of the syringe is 
 
 dipped in fluid and the piston drawn back in an attempt 
 
 to create a vacuum, the pressure of the outside air 
 
 forces the fluid up into the syringe and 
 
 so fills it. Any air remaining in the 
 
 syringe will force the fluid out ahead 
 
 of it, so long as the syringe is held with 
 
 its needle pointing down. If we wish to 
 
 get the air all out of the syringe, we 
 
 must hold it with the needle pointing 
 
 directly up, so that the lighter air may 
 
 make its exit through the needle before 
 
 the heavier fluid. (In injecting under 
 
 the skin, we force the liquid, by means 
 
 of the piston and our fingers, into the 
 
 resisting tissues.) 
 
 The atomizer is dependent upon the 
 principles of air pressure. A stream of 
 
 air from the bulb is forced over the top Fig> 33- Hypo- 
 dermic syringe 
 of the upright tube which dips into the (Morrow). 
 
 reservoir of liquid; this reduces the ex- 
 ternal air pressure upon the contents of this tube. The 
 pressure upon the surface of the body of fluid in the 
 reservoir pushes the fluid up this tube in consequence. 
 The jet of air from the bulb at the same time blows the 
 liquid away in the form of a fine spray. 
 
 The siphon is a tube bent into a U shape, open at both 
 ends, one arm being longer than the other. Fill the entire
 
 2 PRACTICAL PHYSICS FOR NURSES 
 
 tube with water, and holding a finger over the end to 
 prevent its escape, dip the short arm into a container 
 of water, dropping the longer arm outside. Release the 
 
 Fig. 34. Diagram of atomizer. 
 
 finger and the water will run out through the siphon so 
 long as the short arm dips into the water in the container. 
 The explanation is as follows: The pressure upon the 
 fluid in either arm is the atmosphere minus the weight 
 
 Fig- 35- The siphon. 
 
 of the water in that arm. This makes the pressure 
 greater in the short arm and less in the long arm; the 
 fluid moves in the direction of least resistance.
 
 PNEUMATICS 83 
 
 The stomach-tube is a siphon. The short arm is in- 
 side the stomach, the long arm outside. Water poured 
 into the container (the stomach) will run out again 
 when the long arm is lowered, providing the tube re- 
 mains filled with water while the change in the position 
 of the long arm is being made. If all the fluid in the 
 tube is allowed to run into the stomach before reversing, 
 there will be no siphon action. 1 The bulb which is 
 placed on some of the stomach-tubes is a variety of 
 pump (see Chapter VI) which can be used instead of the 
 siphon. 
 
 SUMMARY 
 
 In gases the molecules have no cohesion, but tend to 
 flee from each other. 
 
 Gases are very elastic and very compressible. 
 
 Whenever gases are brought into contact, they dif- 
 fuse as liquids do, but more rapidly. Upon this fact 
 depends our ability to ventilate rooms and buildings. 
 
 Air is the most important gas. It is a mixture of 
 four-fifths nitrogen, one-fifth oxygen, a little carbon 
 dioxid, watery vapor, and other materials. It covers 
 the earth's surface 7 or 8 miles deep, being more dense 
 at sea-level because of the weight of the upper layers. 
 Air pressure increases with depth. 
 
 The air pressure at sea-level is 14.7 pounds to the 
 square inch. We do not feel it because the solid por- 
 
 1 It is wise to have this actually illustrated in class, using a 
 pitcher or other container in place of the stomach.
 
 84 PRACTICAL PHYSICS FOR NURSES 
 
 tions of our bodies are very resistant, because the body 
 fluids are not compressible, and because the body con- 
 tains considerable air and so equalizes the pressure 
 outward and inward. 
 
 The breast-pump, the hypodermic, the dressing syr- 
 inge, cupping-glasses, the stomach-tube, etc., are based 
 upon the laws of air pressure. Explain the working 
 of each of them.
 
 CHAPTER VI 
 PNEUMATICS (Continued) 
 
 LAWS RELATING TO GASES 
 
 Pumps are machines for lifting and transferring fluids 
 from one place to another. Their action depends upon 
 air pressure. They are of two sorts lifting and force- 
 pumps. 
 
 The lifting pump has a tube which dips into water 
 or other fluid, at its lower end, where there is placed a 
 valve that opens only inward. High above this, at- 
 tached to the pump handle, there is a "sucker," a 
 tight-fitting piston pierced by a valve that opens only 
 upward. When the sucker is raised by means of the 
 handle (a lever), air pressure is taken off the surface of 
 the small body of water in the tube; the air pressure 
 upon the surface of the water in the well forces it up 
 the tube. (See Laws and Experiments in Chapter V.) 
 When by the action of the pump handle the sucker is 
 lowered, the weight of the water in the tube closes the 
 valve at its lower end and prevents the contents from 
 running back into the well. By repeating the process, 
 more and more water accumulates in the tube until it 
 is high enough to run out of the spout near the top. 
 
 The force-pump has a one-way valve at the lower 
 
 85
 
 86 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 end of the tube the same as in the lifting pump, but its 
 piston is solid. The second valve is at the side of the 
 tube, and opens only outward, emptying into a tube 
 which forms the spout. When the piston is raised, the 
 
 Fig. 36. Lifting pump (Butler, "Household Physics"). 
 
 main tube partly fills with water, exactly as in the lift- 
 ing pump; when it is lowered, the weight of the water 
 closes the valve at the bottom. The movement being
 
 PNEUMATICS 87 
 
 repeated, continued pressure forces the side valve open 
 and the water up the side tube and out at the spout. 
 
 A Davidson (or bulb) syringe is a variety of force- 
 pump, at least so far as the action of the valves is con- 
 cerned. Pressing the bulb while the end of the tube 
 dips into water tends to create a vacuum, and when the 
 pressure is released, water runs up into the tube and 
 
 Fig- 37- Force-pump (Butler, "Household Physics"). 
 
 bulb. A second pressure forces the water in the tube 
 against the valve at its lower end and closes it, at the 
 same time pushing it against the outward-opening 
 valve of the rectal or delivery tube and forcing the wa- 
 ter out through it. 
 
 The bulb of a stomach-tube works exactly as does that 
 of a Davidson syringe.
 
 88 PRACTICAL PHYSICS FOR NURSES 
 
 The heart is a force-pump. The hollow organ re- 
 sembles the bulb of a syringe, except that the force 
 which contracts it is furnished by the heart muscle 
 itself, situated in the wall. There is no piston, but the 
 expansion and relaxation makes the cavity alternately 
 larger and smaller. When the auricles contract, the one- 
 way valves (the bicuspid and tricuspid) are forced open 
 and the blood runs into the ventricles. When the 
 
 Fig. 38. Dilation and contraction of ventricles of the heart. 
 
 ventricles contract, these valves are forced shut by the 
 weight of the blood against them, and the semilunar 
 valves are pushed open; the blood is thus forced out into 
 the vessels, from the right ventricle to the lungs for 
 purification, and from the left ventricle into the aorta, 
 and so through the body. The impulse of the heart- 
 beat as it forces the blood out through the arteries is 
 transmitted to the very ends of the vessels and starts 
 the blood on its way through the capillaries. 
 In the return venous circulation the flow is largely
 
 PNEUMATICS 8<J 
 
 due to the pressure of fluid back of it and to muscular 
 action. In the large veins of the lower limbs, however, 
 this pressure is not enough to overcome the action of 
 gravity. One-way valves are, therefore, introduced, 
 which hold the blood in place until additional force 
 from behind pushes them open and makes the blood rise. 
 The action is much like that of the lifting pump. 
 
 The sphygmograph, or sphygmomanometer, is a machine which re- 
 cords the force of the heart-beat. A button is fastened over some 
 artery that comes conveniently near the surface, and a series of levers 
 transmit the impulse against it to a fine needle which traces the 
 record of its rise and fall upon a specially prepared paper. Any 
 irregularities or lack of force are noted by this tracing. 
 
 Fig- 39- Valves in vein. 
 
 Steam Apparatus. Steam is a gas. It occupies about 
 1700 times as much space as the water from which it 
 is made. When confined within a boiler or other con- 
 tainer and kept hot (*'. e., in a gaseous state) it struggles 
 to escape. This attempt to escape is used to produce 
 motion, work of various sorts. (In many steam appli- 
 ances the heat is an important factor. See Chapter 
 VII.) In the steam engine the steam, in its effort to 
 escape, drives before it with considerable force the 
 piston, a solid body. The piston is attached to a wheel 
 by one or more levers, and the wheel moves with the 
 movement of the piston. The motion thus gained is
 
 QO PRACTICAL PHYSICS FOR NURSES 
 
 transferred by one mechanism or another to whatever 
 machinery it is desired to drive. 
 
 Respiration. The act of breathing involves the laws of 
 pneumatics. When the chest wall is pulled outward by 
 the action of the chest muscles, and the diaphragm is 
 lowered, the external air rushes in to fill what would 
 otherwise be a vacuum. When the chest muscles relax 
 and let the chest wall fall inward and the diaphragm 
 
 Fig. 40. Diagram of air-cell of lung. 
 
 rise, making the space smaller, the air in the chest is 
 forced out. This alternate intake and expulsion of 
 air we call inspiration and expiration. About 30 cubic 
 inches of air enter and are expelled with each respiration. 
 The muscular action takes air into the lungs as far 
 as the smaller bronchi. Then the law of diffusion of 
 gases comes into action, and an interchange takes place 
 between the incoming oxygen and the carbon dioxid in
 
 PNEUMATICS 91 
 
 the blood-stream in the lungs. This carbon dioxid, 
 one of the important waste materials of the body, is 
 a gas carried by the venous blood into all the capillaries 
 of the lungs. The very thin membrane between the 
 capillaries and the air cells of the lungs permits it to 
 escape, by osmosis, into the air cells, and at the same 
 time allows the oxygen which has come in to pass, by 
 the same force, into the blood-stream. (Note that air 
 is a mixture, not a compound; its oxygen is, therefore, 
 free and ready to exchange places with the carbon 
 dioxid.) The membrane lining the air-cells is just 
 strong enough to prevent the fluid blood from passing. 
 If it is weakened by disease, we have hemorrhage from 
 the lungs. 
 
 VENTILATION 
 
 Principles of Ventilation. If we open a window on a 
 warm, perfectly still day, we presently feel the outside 
 air coming in. This is due to the law of diffusion of 
 gases. A certain amount of such exchange of outdoor 
 and indoor air also takes place constantly through the 
 cracks in our dwellings and even through the walls 
 themselves, which are more or less porous. The phe- 
 nomenon is more evident when a larger opening, like a 
 window or door, is provided. 
 
 Diffusion of gases takes place more rapidly when there 
 is wind to drive the molecules forward. It is also in- 
 creased by marked difference in temperature. 
 
 Heat pushes the molecules of air farther apart, so
 
 92 PRACTICAL PHYSICS FOR NURSES 
 
 that warm air always struggles more vigorously to get 
 away than does cold air. Upon opening the window in 
 very cold weather, you can feel the warm air going out 
 for some time before the cold air appears to come in. 
 
 Warm air, because its molecules are farther apart, 
 is lighter than cold air. In a closed room warm air rises, 
 partly because of its lighter weight and partly because 
 of the pressure of the cooler air which remains at the 
 bottom. Hang two thermometers in a closed room, 
 one near the floor and one near the ceiling. There will 
 be a number of degrees variation in their readings, es- 
 pecially in a room which is artifically heated. 
 
 Fig. 41. How the draft in a chimney is produced. 
 
 The Draft in a Chimney. Warm air, produced by a 
 fire, rises because the cold air, which is heavier, pushes 
 it up from the bottom. We say that a chimney draws,
 
 PNEUMATICS 93 
 
 but the word is incorrect, since the draft is due to the 
 push of the cold air from the room below, not to any 
 pull of warm air from above. The effect is the same, but 
 our mode of expression creates confusion in our minds. 
 
 Experiment. Prepare an air-tight box with two holes in the 
 lid; over each hole set a lamp-chimney and make the joint air- 
 tight. Lower a bit of lighted candle into one of the chimneys; 
 the air thus heated rises, and fresh, cool air passes down through 
 the other chimney to take its place. Show the draft thus produced 
 by burning touch paper or something which smokes freely over the 
 cool chimney. This method of introducing fresh air into a room 
 is called gravity ventilation. 
 
 The above simple principles are the basis of our heat- 
 ing and ventilating systems, no matter how compli- 
 cated they may seem. 
 
 To heat a room economically, the warmth should come 
 from near the floor, because warm air always rises. 
 
 To "ventilate a room we must have somewhere openings 
 of sufficient size to permit diffusion of gases to take place 
 as rapidly as is required by the number of occupants; 
 1000 cubic feet of air space for each person (a space 10 
 feet square by 10 feet high) is estimated to be the mini- 
 mum requirement in a closed room. Ventilation must be 
 rapid and thorough to keep this air properly oxygenated. 
 If the openings provided for the entrance of warmed air 
 and the escape of impure air are not properly located, 
 diffusion will not be satisfactorily accomplished. Figure 
 42 shows the possibilities in such cases. 
 
 In the so-called "natural" ventilation i. e., by open-
 
 94 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 ing the windows one should open them at both top 
 and bottom, so as to provide for proper circulation of air. 
 
 1 
 
 
 
 INLET 
 
 ' ^ ^ --^ 
 
 
 1 
 
 ----- '- L -/---- 
 
 
 OVTL6T 
 
 ^~~" v^^^^^X^X^ 
 
 
 Fig. 42. Air circulation in forced ventilation systems. 
 
 Ventilating Systems. "Natural" ventilation is un-
 
 PNEUMATICS 95 
 
 satisfactory in very hot or very cold weather; in very 
 warm weather the diffusion of air takes place too slowly; 
 in cold weather, too rapidly. 
 
 Artificial ventilation is a combination of heating with 
 ventilation. Some systems embody the theory that 
 fresh warmed air goes to the ceiling, while foul air drops 
 to the floor; but authorities do not agree in this matter. 
 
 Fig. 43. Natural ventilation (Butler, "Household Physics"). 
 
 The correct and efficient method is to arrange the loca- 
 tion of inlets and outlets so that the air in every room 
 must be thoroughly stirred by the draft from the heating 
 system; just what these locations are is still under dis- 
 cussion. 
 
 There are two sorts of heating-ventilating systems in 
 use. One is the vacuum, in which the air is drawn out 
 of the rooms by suction. The other is the plenum, in
 
 96 PRACTICAL PHYSICS FOR NURSES 
 
 which air is forced into the room, usually by means of a 
 fan driven by a motor. Neither system works well in 
 combination with open windows. 
 
 An objection to all forced ventilating systems is that 
 they stir up dust and bacteria. This is overcome in 
 some cases by using a "washed air" system, in which 
 dust and bacteria are removed from the air before it 
 enters the room. This is only partially successful, 
 because it does not take care of the dust and bacteria 
 which originate in the room. 
 
 SUMMARY 
 
 Pumps are machines for transferring fluids from one 
 place, or one level, to another. 
 
 Lifting and force-pumps are similar in their action. 
 Each has a piston working in a tube which dips into the 
 water or other fluid. Each has a one-way valve at the 
 lower end of the tube, which permits the fluid to enter, 
 but not to return. The lifting pump has a valve in 
 the piston; the force-pump, one at the side of the tube. 
 In each form of machine the repeated action of the pump- 
 handle transferred to the piston lifts a portion of the 
 liquid into the tube, until a sufficient quantity accumu- 
 lates to run or be forced out of the spout. 
 
 The bulb syringe and the bulb of the stomach-tube 
 are force-pumps. 
 
 The action of the human heart is like that of a force- 
 pump, the power being the muscle in its wall.
 
 PNEUMATICS 97 
 
 In the steam engine the piston is driven by the force 
 of steam trying to escape its bounds. The motion thus 
 produced is transferred by an appropriate mechanism 
 to any desired machine. 
 
 Respiration is carried on in accordance with the laws 
 of pneumatics. The actual exchange of oxygen and 
 carbon dioxid is due to osmosis. 
 
 The ventilation of rooms and buildings involves the 
 law of diffusion of gases, and the law that heated gases 
 rise and cold ones fall. 
 
 Natural ventilation is satisfactory only in moderate 
 weather. Artificial heating and ventilating systems 
 work better in very cold weather; they are of two prin- 
 cipal sorts, one in which the air is drawn out of the rooms 
 by suction, the other in which it is forced in by a fan. 
 All artificial ventilation stirs up dust and, therefore, 
 bacteria. 
 
 Authorities disagree in regard to both theories and 
 methods of ventilation.
 
 CHAPTER VII 
 
 HEAT 
 
 Heat is motion. We have learned that the molecules 
 of all substances, however dense, are separated from 
 each other, no one touching another. We have now to 
 learn that these molecules are always in motion. (The 
 motion is probably vibratory.) This molecular motion 
 is heat. 
 
 Intensity of Heat. A substance whose molecules are 
 moving very slowly is cold. One in which they are 
 moving more rapidly is warm. One in which they 
 move with great rapidity is hot. When we heat an ob- 
 ject, we stimulate its molecules to more rapid motion. 
 When we cool it, we quiet their movements. 
 
 Heat may be transferred from one body to another 
 just as motion or other sorts of energy may, by obedience 
 to the laws that govern the transfer. 
 
 Sources of Heat. Directly or indirectly nearly all of 
 our heat comes from the sun. Coal is indirectly the 
 energy of the sun stored up ages ago; petroleum likewise. 
 
 Heat may be produced by (1) friction; (2) percussion; 
 (3) chemical action, and (4) electric action. 
 
 Experiment. Rub a smooth metal button rapidly back and 
 forth on a rough woolen cloth. The button becomes quite warm, 
 an example of heat produced by friction. 
 98
 
 HEAT 99 
 
 Friction is arrested motion, i. e., motion converted into 
 heat, merely a different manifestation of the same force. 
 
 Because of this, we must often take means to get 
 rid of friction when it is producing heat which we 
 do not want (see page 56). For example, unless the 
 bearings of wheels are kept oiled the two portions of 
 metal separated by means of the oil the friction caused 
 by their rapid movement makes them become hot and 
 may even cause fire. A "hot box" on a railway car is 
 the result of friction. 
 
 Experiment. Strike a coin or other bit of metal hard and 
 rapidly with a hammer. Both hammer and coin become warm, 
 the heat being produced by percussion. Here again we have heat 
 as the result of arrested motion. 
 
 Add sulphuric acid to a small quantity of cold water. Test 
 with a thermometer. The liquid and the container become hot, 
 an example of heat produced by chemical action. 
 
 The incandescent electric light, the electric flat-iron, 
 and the electric cooker are examples of heat produced 
 by electric action. (See Chapter XI.) 
 
 Bodily heat is produced by muscular action, by the 
 chemical changes which take place in the process of nutri- 
 tion, by the circulation, etc. Bodily heat is lost by con- 
 duction, radiation, and evaporation (see pages 107, 115, 
 and 125). The heat loss and production are regulated 
 by certain centers in the brain. Normal temperature is 
 the result of a perfect balance between the heat-produc- 
 ing and the heat-losing processes. Fever is the result 
 of either overproduction or poor elimination of heat,
 
 100 PRACTICAL PHYSICS FOR NURSES 
 
 usually the latter. Subnormal temperature is usually 
 due to lack of heat production, very occasionally to ex- 
 cessive loss of heat. 
 
 Burning is a chemical process, in which the oxygen of 
 the air combines actively with the material of the fuel, 
 changing it into an entirely different substance. The 
 products are smoke, gases, and ashes, with the inci- 
 dental products of heat and light. 
 
 Fig. 44. Drafts in a kitchen stove (Butler, "Household Physics"). 
 
 If we wish a fire to burn well we must provide for 
 the admission to it of plenty of oxygen; we do this by 
 openings in our stoves and heaters which we call drafts 
 or dampers. Closing a stove draft shuts off the supply 
 of oxygen, therefore checks the process of combustion. 
 
 In a kitchen stove there are usually four drafts or 
 dampers which regulate the activity of the fire and
 
 HEAT 101 
 
 determine the direction in which the heat is to be thrown. 
 When the under damper at the fire-box is open there 
 is a draft of air through the fire, making it burn better. 
 If this is closed and the upper one is opened the draft 
 passes over the fire and it burns more slowly. The 
 damper in the smoke pipe is an additional check upon 
 the draft, slowing the fire still more. The oven damper 
 directs the hot gases around the oven instead of over it. 
 
 Temperature is the degree of heat in an object or sub- 
 stance. It is not the amount of heat, or large bodies 
 would always be hotter than small ones. 
 
 We use the term "warm" for things which are of a 
 temperature about that of the human body (98| F.). 
 We say things are hot or cold when they are considerably 
 above or below that temperature. Our statements in 
 this respect are only relative, since we call tea cold when 
 it has a temperature of 105 F., while a bath at 105 F. 
 is considered hot. 
 
 Our own sensations are not sufficiently accurate to 
 enable us to judge heat by them, as they are dependent 
 upon so many factors. A blindfolded person cannot 
 be sure whether a substance is very cold or very hot, 
 since the sensation is almost exactly the same in each 
 case. 
 
 Experiment. Have three containers, one of hot water, one of 
 cold, and one of lukewarm. Put the fingers of one hand into 
 the cold water while those of the other hand are in the hot. After 
 a moment put both hands into the lukewarm water. It will feel 
 cool to the hand from the hot water and warm to the hand from the 
 cool water.
 
 102 PRACTICAL PHYSICS FOR NURSES 
 
 Effect of Heat. Heat produces the following effects: 
 
 1. Rise in temperature. 
 
 2. Increase in volume (the molecules being driven 
 farther apart, the substance requires more room.) 
 
 3. Increase of pressure upon the container. This is 
 due to the increased volume. 
 
 4. Change in physical state, as melting, vaporization, 
 etc. 
 
 5. Change in character, as in burning or other chem- 
 ical process. 
 
 Expansion and Contraction. Since heat is motion, 
 and increased motion tends to drive the molecules of a 
 substance farther apart, it is easy to understand that 
 heat increases the volume of a substance, i. e., expands 
 it. Absence or lessening of heat causes the opposite 
 effect, contraction. We have, therefore, the law, Heat 
 expands and cold contracts. 1 
 
 Experiment. Use the flask with a bent tube through the cork. 
 Place the end of this tube in water. Heat the empty flask. Bubbles 
 of air will be seen pushing their way through the water because the 
 heat expands the air in the flask. Without removing the end of 
 the tube from the water, cool the flask by pouring cold water over 
 it. Water will be forced up into the tube on account of the les- 
 sened air pressure in the flask. 
 
 Uneven expansion or contraction may encounter re- 
 sistance at some point and a crack or breakage result, 
 if the material is brittle. This is observed in glassware, 
 
 1 We are familiar with the fact that gloves and shoes fit more 
 snugly when the hands and feet are very warm. This is almost 
 entirely due to the above law.
 
 HEAT 103 
 
 which is almost sure to crack if either heat or cold is 
 suddenly applied to one portion; this portion expands 
 or contracts, as the case may be, while the rest of the 
 utensil remains unaffected. It is this uneven expansion 
 or contraction which causes the breakage. 
 
 Water is the one great exception to the rule of con- 
 traction upon cooling. It acts like ordinary materials 
 and contracts while cooling until a temperature of 4 C. 
 is reached, when it begins to expand. Ice occupies 
 more space than did the water from which it was made. 
 To this fact is due the bursting of water-pipes when 
 frozen. 
 
 Measurement of Heat. In order to accurately 
 measure heat the thermometer has been devised. Its 
 bulb contains some fluid which is especially sensitive 
 to heat and readily expands when warmed. The tube 
 provides an outlet for the expanding fluid. The scale 
 records the amount of expansion or contraction. 
 
 Mercury is used in thermometers because it is sensi- 
 tive to heat, easy to see, etc. Colored alcohol is also 
 used, especially in thermometers for use in very cold 
 regions where mercury would freeze. (Mercury freezes 
 at 40 F. below zero.) 
 
 If a thermometer bulb is placed in contact with any- 
 thing hotter than is provided for by the length of its 
 tube, the force of the expansion of the mercury will 
 burst the tube. (We all know the unfortunate pro- 
 bationer who washes a thermometer in hot water.)
 
 104 PRACTICAL PHYSICS FOR NURSES 
 
 If a thermometer bulb is placed in contact with any- 
 thing colder than the tube provides for, the mercury goes 
 into the bulb and we cannot register it. 
 
 The clinical thermometer is provided with a contrac- 
 tion in the tube at a point below the scale. This inter- 
 feres with the free return of the mercury when cooling 
 takes place, and so keeps in place what has run up the 
 tube until it is shaken down, i. e., urged back into the 
 bulb or toward it. 
 
 A thermometer must be very accurately made, 
 scaled, and tested to be of value. 
 
 There are two sorts of thermometers in use, those 
 having the Fahrenheit and those the Centigrade scale. 1 
 In the Fahrenheit scale, 32 is the freezing-point of 
 water and 212 its boiling-point. In the Centigrade 
 scale (Centigrade means "one hundred steps") zero is 
 the freezing-point of water and 100 its boiling-point. 
 
 A calorie is the standard of measurement for chemical 
 heat. It is the amount of heat required to raise the 
 temperature of 1 pound of water 4 degrees Centigrade. 
 
 Boiling. Liquids are said to boil when their tem- 
 perature is raised to the point where they begin to change 
 into vapor. When water is heated to 100 C. bubbles 
 of steam are formed, which, being lighter than the 
 water, push their way to the surface and discharge into 
 the air. This gives the appearance which we call 
 boiling. 
 
 1 The Reaumur scale is not much used.
 
 HEAT 105 
 
 The temperature of water to which heat is being ap- 
 plied rises gradually until full boiling-point is reached, 
 when it remains stationary, After a liquid is once 
 boiling, it cannot be made any hotter, though heat is still 
 going into it. (See Latent Heat, page 127.) Test with a 
 thermometer, and see if there is a difference in tempera- 
 ture between water that is boiling gently and that boil- 
 ing vigorously. 
 
 Variation in Boiling-point. All liquids do not boil at 
 the same temperature. Alcohol boils at 78 C., and 
 ether at 37 C. Mercury (a liquid metal) requires a 
 temperature of 357 C. to make it boil. 
 
 Raising the Boiling-point of Water. When a liquid 
 has a solid substance dissolved in it the boiling-point be- 
 comes higher. A familiar example is found in the fact 
 that vegetables cook more rapidly in salted water, 
 because its boiling-point is higher and more heat is 
 being used. 
 
 Experiment. Put water into two containers of the same size. 
 Dissolve 2 or 3 teaspoonfuls of salt in one of them. Heat both 
 until they boil. Test the temperature of each with a thermometer 
 that has a scale above 212 F. The salted water will be found 
 several degrees hotter than the unsalted. 
 
 Air Pressure and Boiling. The boiling-point of a 
 liquid is changed when the air pressure upon it is changed. 
 The boiling-point of water is 212 F. at sea-level. As 
 one goes to a higher altitude it becomes less, the difference 
 being 1 degree Fahrenheit for every 500 feet of alti-
 
 106 PRACTICAL PHYSICS FOR NURSES 
 
 tude. In Denver, 1 mile above sea-level, water boils 
 ar 202 F.; on the top of Pike's Peak (14,000 feet) it 
 boils at 184 F.; at the latter place it is impossible to 
 cook eggs hard, because there is not enough heat in 
 boiling water to coagulate the albumen. Even at 1 
 mile above sea-level it takes appreciably longer to cook 
 vegetables, etc., because boiling water is not as hot as 
 at sea-level. 
 
 Experiment. Put some water into a flask and heat it to the 
 boiling-point. Remove from the fire and at once cork tightly. 
 Turn the flask upside down and pour cold water over it. The cold 
 condenses the steam which is in the flask and thus removes its pres- 
 sure from the surface of the water. The water begins to boil again 
 from the release of pressure. When it again stops boiling, test 
 the temperature. It will be found considerably less than 212 F. 
 
 This phenomenon is utilized in a practical way in the 
 vacuum kettle. Condensed milk, for example, is made 
 by evaporating the moisture from milk at a temperature 
 below 212 F., i. e., boiling it in a kettle from which a 
 portion of the air has been pumped, so that the pressure 
 on the surface of the liquid is much less and the boiling- 
 point considerably lowered. 
 
 Steam Pressure Apparatus. Conversely, if we in- 
 crease the pressure upon the surface of a liquid, we raise 
 its boiling-point. "Pressure cookers" and sterilizing 
 apparatus take advantage of the fact that steam under 
 pressure is hotter than that which is in contact with 
 the air. Cookers of this sort are made steam tight and 
 strong enough to resist several pounds' pressure. They
 
 HEAT 107 
 
 cook their contents at a temperature higher than 212 F., 
 therefore more rapidly and thoroughly. (They also 
 keep in the flavors which would otherwise escape with 
 the steam. 1 ) 
 
 In a dressing sterilizer 15 or more pounds of pressure 
 are used to raise the steam to a temperature of 240 F. 
 or more. We call this "superheated" steam, and find 
 that it remains dry, that is, uncondensed. This makes 
 the sterilizing process more sure because of the higher 
 temperature to which possible germs are subjected. 
 The pressure also serves to force the steam in among 
 the dressings, so that it may reach every portion of the 
 materials to be sterilized. The dryness of the steam is 
 an additional advantage. Such sterilizers must, of 
 course, be fitted with safety-valves, so that the pressure 
 may not run so high as to endanger the apparatus. 
 
 (Water sterilizers ordinarily are devices for boiling 
 water under normal air pressure, and afterward either 
 keeping it hot or cooling it. They may be arranged to 
 sterilize under pressure at a higher temperature. Uten- 
 sil and instrument sterilizers are merely pans in which 
 the boiling is accomplished by gas, steam, or electric 
 heat.) 
 
 Evaporation is the process of changing a liquid into a 
 gas. When a liquid, especially if warm, is left exposed 
 to the air the molecules on its surface are constantly 
 
 1 The action of heat in cooking food is largely due to the chem- 
 ical changes which it produces.
 
 Io8 PRACTICAL PHYSICS FOR NURSES 
 
 leaving and going into the air. With time, all the 
 liquid goes into the air in this way and disappears. It 
 has become vapor evaporated. The process is, as we 
 know, hastened by heat, and by a draft of air or wind, 
 which enable the molecules to detach themselves more 
 easily; the current also carries them away, making room 
 for more to rise. Evaporation also takes place more 
 rapidly from a large surface, since there are a greater 
 number of molecules exposed to the air and ready to 
 take flight. 
 
 Applications of these principles are familiar. We 
 heat a liquid when we wish it to evaporate quickly. 
 We hang wet clothing in a breeze to dry it: We spread 
 out damp materials when we wish them to dry. We 
 use a large open pan when we wish its contents to evapo- 
 rate or dry out, and a smaller one with a tight cover when 
 we wish to keep materials moist. 
 
 Evaporation Cools. Experiments. Pour a little alcohol or 
 ether upon the hand. It feels cool, i. e., it cools the hand as it 
 evaporates. Hang two thermometers side by side. Cover the 
 bulb of one with a bit of gauze, the end of which dips into water. 
 Fan them vigorously. The wet-bulb thermometer shows a con- 
 siderably lower temperature than the other. 1 
 
 The evaporation of perspiration from the surface of 
 the body cools it. Fanning cools a person who is per- 
 spiring by hastening evaporation. Since there is a 
 constant "insensible" perspiration going on even in 
 cool weather (the amount is 20 to 30 ounces in twenty- 
 
 1 The Mexican olio, a porous water-jar, hung in a draft, keeps 
 water cool in hot weather by evaporation.
 
 HEAT 109 
 
 four hours), its evaporation produces a considerable 
 cooling of the body. Profuse perspiration causes a 
 very marked cooling. On a damp day the evaporation 
 of perspiration takes place slowly, and we do not get the 
 cooling action to any extent; we therefore "feel the heat." 
 
 The fan bath which is given to reduce temperature 
 constitutes a method of causing moisture to evaporate 
 rapidly from the surface of the body, thus extracting 
 heat from the patient. For a similar reason a tepid 
 bath often reduces temperature as well as a cold one. 
 
 A cold compress should always be thin, so that evapo- 
 ration may prolong and add to the cooling process, and 
 obviate frequent changing. (Conversely, a hot com- 
 press should always be thick and covered well, in order 
 to prevent both evaporation and radiation of heat.) 
 
 Condensation is the opposite of evaporation, and is 
 produced in an opposite way. If a warm vapor is cooled, 
 it condenses, i. e., becomes a liquid again. This is the 
 cause of rain; the heat of the sun vaporizes water from 
 the sea, lakes, etc., and it is stored, still warm, in the 
 form of clouds. When these clouds are struck by a 
 cold wind or come into a cooler layer of air, the vapor 
 of which they are composed condenses into drops and 
 we have rain. 
 
 (Snow is frozen crystallized water vapor. Dew is caused 
 by the moisture in the air condensing upon a surface which is 
 colder than the air. The earth, grass, plants, etc., radiate their 
 heat readily, therefore soon become cooler than the air. Frost is 
 frozen crystallized dew.)
 
 no PRACTICAL PHYSICS FOR NURSES 
 
 Distillation is the process whereby a liquid is vaporized 
 by heat and the vapor collected and cooled, making 
 it into a liquid again. It is commonly done by boiling 
 the liquid in a closed vessel, letting the vapor escape 
 through a long tube which runs through cold water; 
 the large surface presented to the cooling process makes 
 the vapor condense rapidly; it drips from the end of 
 the tube into a container. 
 
 Fig. 45. Water still : A and B, Inlet and outlet for water to cool 
 it; C, boiler for water; D, inlet for heating gas; E, condenser; G, 
 collecting pipe for steam ; I, outlet for distilled water. 
 
 The so-called "dry" or destructive distillation consists 
 of heating solid substances in tightly closed vessels, 
 i. e., in the absence of air. It is a chemical process,
 
 HEAT III 
 
 the substance being broken up and other substances 
 formed. 
 
 Distillation is used to free a liquid from some sub- 
 stance dissolved in it, since the liquid alone vaporizes, 
 the solid matter needing a much greater degree of heat 
 to drive its molecules apart. 
 
 When a mixture of liquids or a solution of solid matter 
 in one or more liquids is heated, the most "volatile (that is, 
 the one which boils at the lowest temperature) is naturally 
 the first to be vaporized. For example, if a mixture of 
 ether and water be heated, the ether will be evaporated 
 and disappear long before the water begins to boil. 
 In this way liquids that have different boiling-points 
 may be separated and purified by distillation. 1 
 
 Distilled water is absolutely pure, since it has by the process 
 undergone been freed from any matter dissolved in it. Water 
 from a well, a river, or a lake may be pure in the sense that it has 
 no harmful matter in it, but since it usually has in solution some 
 mineral or other matter, it is not pure in the chemical or scientific 
 sense. Stills are sometimes attached to water sterilizers so that 
 the water may be distilled, and so freed from all mineral as well as 
 vegetable or animal impurities. 
 
 SUMMARY 
 
 Heat is molecular motion, probably a species of vibra- 
 tion. When the molecules are moving very rapidly, 
 the substance is said to be hot; when less rapidly, 
 warm; when still less rapidly, cool or cold. 
 
 1 An interesting example of this occurs in the manufacture of 
 petroleum products. Benzine, being very volatile, is the first to 
 be collected in the process of distillation, then gasoline, then kero- 
 sene, and so on.
 
 112 PRACTICAL PHYSICS FOR NURSES 
 
 The chief source of heat is the sun. Heat is also pro- 
 duced by friction, by percussion, by chemical and by 
 electric action. Bodily heat is the result of the chem- 
 ical processes occurring in nutrition, of muscular action, 
 the circulation, etc. It is lost by radiation and evapo- 
 ration. 
 
 Normal temperature is the condition of balance be- 
 tween production and loss of heat. High temperature 
 is the result of overproduction or insufficient elimination 
 or radiation of heat. Subnormal temperature is usually 
 due to underproduction of heat. 
 
 Burning is a chemical process in which matter changes 
 not merely its form, but its actual composition and 
 hence its identity. 
 
 Temperature is degree of heat. The terms "warm" 
 and "cold" are relative, and our sensations are not 
 sufficiently accurate to judge of them. 
 
 Heat produces five general effects: rise in tempera- 
 ture, increase in volume, increase of pressure, in the 
 container, change in state, or change in character. 
 
 Heat expands substances. Cold contracts them. 
 Water is the marked exception to this rule, in that it 
 expands upon freezing. 
 
 Uneven expansion or contraction causes breakage in 
 brittle substances. 
 
 The thermometer is a device for the accurate measure- 
 ment of the degree of heat. The clinical thermometer 
 is made with a contraction in the tube which prevents
 
 HEAT 113 
 
 the mercury from returning to the bulb unless shaken 
 back. 
 
 In the Centigrade scale zero is freezing-point, 100 
 boiling-point. 
 
 A calorie is the amount of heat required to raise 1 
 pound of water 4 degrees Centigrade in temperature. 
 
 In boiling, portions of water are successively vaporized, 
 the light steam rising in bubbles, which break at the 
 surface. The temperature at which liquids boil varies 
 greatly. Water is taken as the standard. 
 
 Dissolving a substance in water raises the boiling- 
 point of the water. Increase in the air pressure upon 
 the surface of water raises its boiling-point. Decrease 
 in the pressure lowers its boiling-point. 
 
 Dressing sterilizers employ superheated (dry) steam 
 under a pressure of 15 or more pounds; this forces its 
 way into the materials and the higher temperature ob- 
 tained makes the bactericidal action more certain. 
 Water sterilizers boil the water to render it germ free, 
 then cool or reheat it as desired. Utensil and instru- 
 ment sterilizers are merely vessels arranged conveniently 
 for boiling. 
 
 By evaporation liquids are changed into gases and 
 diffused into the air. 
 
 Evaporation cools. In bathing or other procedures 
 to reduce temperature as much evaporation as possible 
 should be obtained. The evaporation of the perspira- 
 tion cools the body under normal circumstances.
 
 114 PRACTICAL PHYSICS FOR NURSES 
 
 Condensation is the opposite of evaporation. 
 
 Distillation is the process of vaporizing a liquid, 
 collecting the vapor and recondensing it. Distillation 
 is used to free liquids from impurities or to separate 
 liquids that have different boiling-points. Only the 
 liquid vaporizes, any solid substance in solution being 
 left behind. Distilled water is chemically pure. 
 
 Dry distillation is a chemical process.
 
 CHAPTER VIII 
 HEAT (Continued) 
 
 TRANSMISSION OF HEAT 
 
 SINCE heat is motion, we can easily understand how 
 it may be transmitted from one thing to another. There 
 are three methods by which this occurs: conduction, 
 convection, and radiation. Conduction refers to solids; 
 convection, to liquids and gases. 
 
 Conduction. When one portion of a solid body is 
 heated, its molecules transmit their motion to those 
 next them, and the heat travels throughout the whole 
 body. In other words, the heat is conducted from 
 one portion to another. 
 
 Substances differ greatly in their power of conducting 
 heat. Upon this fact many of the conveniences of life 
 depend, temperature being a very large factor in our 
 comfort. 
 
 Metals are, as a rule, good conductors of heat. Cloth 
 and most porous materials are poor conductors. 
 
 Experiments. Put the end of a short iron wire into a flame; 
 note how soon the end held by the fingers becomes hot. Put the 
 end of a sliver of wood or a straw into a flame; it burns close to the 
 fingers before any heat is observed in the straw itself. 
 
 "5
 
 Il6 PRACTICAL PHYSICS FOR NURSES 
 
 Flat-iron handles, tea-pot handles, etc., are made of 
 wood because it is a poor conductor of heat. 1 A kitchen 
 "holder" is merely a substance that is a poor conductor 
 of heat. 
 
 Wool is a poorer conductor of heat than cotton, cot- 
 ton poorer than linen. Linen clothing and bedding 
 tend to cool the body by conducting heat away from it. 
 Wool keeps the bodily heat to a great extent where it 
 is. Cotton conducts it away but slowly. Asbestos, 
 which is a very poor conductor of heat, is used for cover- 
 ing steam-pipes when we wish to keep their heat from 
 escaping. 
 
 Wool is used for fomentation cloths because it is a 
 poor conductor of heat and so retains it for a long time. 
 Cotton fomentation cloths give up their heat quickly 
 and so are not satisfactory. 
 
 Water is a poor conductor of heat. 
 
 Experiment. Hold a test-tube nearly filled with water by its 
 bottom and heat the top of the water in a flame; the top will boil 
 while the bottom is barely warmed. 
 
 Large bodies of water tend to keep the temperature 
 of the ah* in their vicinity even. Towns built near a 
 large body of water are not as likely to be hot in summer 
 as corresponding inland towns, while in winter they are 
 often warmer. Farmers on the shores of the great lakes 
 
 1 The so-called "cold handle," though made of metal, is ar- 
 ranged so that heat must travel a long way; the handle becomes 
 "air-cooled" in the process.
 
 HEAT 117 
 
 find that the lake keeps away frost by preventing sudden 
 drops in temperature. (Other factors, of course, modify 
 this general rule.) 
 
 Air and all gases are poor conductors of heat because 
 their molecules are so far apart that they do not readily 
 convey their motion to their neighbors. Much practical 
 use is made of this fact. 
 
 It is well known that loose clothing keeps the body 
 warmer than tight clothing, not only because the cir- 
 culation is less impeded, but because it encloses a 
 considerable quantity of air which does not conduct 
 the bodily heat away. Several layers of light clothing 
 are warmer than few heavier ones because of the layers 
 of air between them. 
 
 If a house be built with a double wall, having an air 
 space between the two parts, it will be warmer in winter 
 and cooler in summer than one built with a. solid wall 
 twice as thick. Double windows keep heat in because 
 of the air enclosed between them. 
 
 Refrigerators are devices for keeping out heat as well 
 as for retaining cold. (Cold is merely absence of heat.) 
 Their walls are made of materials which are poor con- 
 ductors of heat, as wood, paper, cork, sawdust, air. It 
 is the number and thickness as well as the particular 
 material of these layers that makes a refrigerator a 
 good one. In choosing a refrigerator, one with thick 
 walls is pretty certain to be better than one with thin 
 walls. In ice-houses the walls usually have large
 
 118 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 "dead air" spaces, since air which cannot be disturbed 
 prevents the passage of heat very effectively. 
 
 
 
 
 
 iP 
 
 vj 
 
 ^J 
 
 1 
 
 1 
 
 MINERAL 
 WOOL 
 
 1 
 
 1 
 
 1 
 
 I 
 
 ct 
 
 1 
 
 
 r ~'^ s 
 
 
 r*- 
 
 1 
 
 
 Sheathing. 
 
 Fig. 46. Section of a refrigerator wall (Butler, "Household 
 Physics"). 
 
 (There should be circulation of air in the interior of a refrigera- 
 tor. The ice is always placed at the top; it cools the air there, which 
 drops because of its weight and because it is pushed aside by the 
 lighter, warmer air below. This warmer air, in turn, becomes 
 cool and drops; thus a circulation is maintained, keeping the food 
 cold. Any food having a pronounced odor should be kept in a 
 separate tight compartment, or any food like butter or milk which 
 readily absorbs odors.) 
 
 One can keep ice for a considerable length of time by 
 wrapping it in a woolen cloth and hanging it in the air. 
 In the refrigerator, however, the object is not to keep the 
 ice, but to cool the food. Ice in a refrigerator should, 
 therefore, be left uncovered.
 
 HEAT 
 
 119 
 
 Capacity for Heat. If a substance is a poor conductor 
 of heat, it follows that it holds or retains heat for a 
 longer time than does a substance which is a good con- 
 ductor of heat. Hot-water bottles are of advantage 
 because the water retains its heat so well. Bricks or 
 stones hold heat well. Stove-lids or other metal articles 
 impart their heat quickly to objects that are in contact 
 with them, and so become cool themselves. The best 
 
 Fig. 47. Circulation of air in a refrigerator (Butler, "Household 
 Physics"). 
 
 heater is a stone jug of water, because both water and 
 stone are poor conductors of heat, i. e., retain heat well. 
 The fireless cooker is a device that makes use of sub- 
 stances which are poor conductors of heat, such as as- 
 bestos, felt, dead air, hay, etc., to prevent heat from es- 
 caping from the contents of a vessel which has been 
 heated to boiling-point. The apparatus keeps the food 
 at a temperature somewhat less than boiling-point, 
 but sufficiently high to continue the cooking process.
 
 120 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 If, in addition, heated soapstone disks are laid over the 
 food containers, still more heat is retained and further 
 cooking made possible. 
 
 The vacuum bottle has a space in its wall from which 
 some of the air has been withdrawn, leaving a partial 
 vacuum; this leaves so few molecules of air in the con- 
 fined space that (in addition to the fact that they .are 
 
 nner Bottfe 
 Outer Bottle 
 Outer Casing 
 
 Fig. 48. Section ol vacuum bottle (Butler, "Household Physics"). 
 
 confined) they do not transmit their motion to one 
 another nor to their surroundings except with the 
 greatest difficulty. By this means heat within the 
 bottle is kept in; or if it is desired to keep the contents 
 cold, the outside heat is prevented from getting in. 
 
 Convection is the movement of liquids or gases by 
 means of which heat is distributed through them. Air
 
 HEAT 
 
 or water heated at the bottom starts rapid currents of 
 convection, because the heated portion is lighter and so 
 rises, stirring the whole mass. We have seen that 
 water may be heated to boiling at the top without 
 marked effect upon that below; boiling would be almost 
 impossible if we applied heat only at the top. 
 
 Experiments. Water: Put a small quantity of sawdust into 
 water; apply heat to the bottom ol the container and watch the 
 convection currents. Air: Repeat the experiment given on page 
 92. This illustrates the convection of gases. 
 
 Fig. 49. Convection currents in water (Butler, "Household 
 Physics"). 
 
 Plumbing and Heating. The principle of convection 
 in liquids and gases underlies most of our arrangements 
 for plumbing and heating.
 
 122 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 Hot water, being lighter, always rises. When we use 
 the kitchen range for supplying hot water the arrange- 
 ment is as follows: The cold water enters the "water- 
 back" of the range (a flat thin tank set next to the fire 
 so as to expose a large surface to be heated) from the 
 bottom of the tank in the kitchen. 1 As it becomes 
 
 Fig. 50. Heating water with kitchen range (Butler, "Household 
 Physics"). 
 
 heated, it rises through the pipe which discharges near 
 the middle of the tank. From here it continues to rise, 
 the hottest water always being at the top of the tank. 
 
 1 This tank is incorrectly called a boiler.
 
 HEAT 123 
 
 It circulates by means of a pipe branching to all the 
 
 Fig. 51. Hot-water heating system (Butler, "Household Physics"), 
 fixtures in the house, where it is drawn off at the faucets.
 
 124 PRACTICAL PHYSICS FOR NURSES 
 
 The supply is kept renewed by the entrance of cold 
 water into the tank. 
 
 When hot water is supplied from a tank connected 
 with the heating system and heated by it, the principle 
 of convection is the same. 
 
 A hot-water heating system is arranged so that water 
 heated in a boiler in the basement rises through pipes 
 and circulates in radiators placed in the various rooms. 
 As it cools in the radiators it falls, and so returns to the 
 heater. Since hot water expands so greatly, such a 
 system must be provided \\ith an expansion tank at 
 its highest point (usually in the attic) into which the 
 excess of hot water runs. If the pipes were not provided 
 with this outlet they would burst when the water was 
 heated. 
 
 Steam heating systems take advantage of the law of 
 expansion of gases. Steam set free from a boiler in the 
 basement rises and struggles to escape. It forces its 
 way through the pipes provided for it into the radiators. 
 There it gives up its heat, cools, and in consequence 
 condenses, falling to the bottom and dripping through 
 the "return" pipe back to the basement. It re-enters 
 the boiler as cold water, coming in at the bottom, and 
 again ascending as it is heated and changed into 
 steam. 
 
 (It can be readily seen that the heat from steam is much more 
 intense than that from hot water; to this is due the almost universal 
 overheating of buildings where the former is used.)
 
 HEAT 
 
 125 
 
 Radiation of Heat. A heated body starts in the air 
 about it molecular movements which radiate or move 
 in all directions; by this means it loses its heat, trans- 
 mitting it to the air and thence to surrounding objects. 
 The heat of a fire literally strikes your face or body when 
 you are near it. 
 
 Fig. 52. Steam heating system (Butler, "Household Physics"). 
 
 Hold your hand between your face and a fire, and the 
 heat is shut off from your face. Why? Because you 
 have intercepted the waves of molecular motion which 
 were coming from the fire. 
 
 Radiation takes place slowly from smooth surfaces, 
 more rapidly from rough ones. Is it for this reason
 
 126 PRACTICAL PHYSICS FOR NURSES 
 
 that objects which we wish to have retain their heat 
 are made smooth (as the tea-kettle, hot-water bottle, 
 etc.), while those which we wish to give up their heat 
 rapidly are rough (as stoves, steam radiators, etc.). 
 
 Steam or hot-water radiators are exactly what their 
 name implies. They are hot bodies which start heat 
 movements in the air about them. The larger their 
 surface, the more heat they radiate or give off; this is 
 the reason for making them in the usual form, with many 
 pipes, thus presenting a large surface which is in con- 
 tact with the air. If they were flat boxes they would 
 need to be very much larger in order to present the same 
 amount of radiating surface. Hospital engineers object 
 to having the radiators in an operating room covered 
 with sheets, because it makes them in effect a flat box and 
 reduces the actual radiating surface so greatly that it 
 becomes impossible to heat the room. 
 
 Radiators are commonly placed at the bottom of the 
 room and in its coldest part, i. e., next the windows, so 
 that they may start convection currents of -warm air 
 in the portion where it is most needed and the room be 
 heated more evenly. 
 
 The human body is of a higher temperature than the 
 air which usually surrounds it. It therefore radiates 
 its heat. If heat were not constantly being produced 
 in the body 1 we should become cold from the mere fact 
 of radiation. Other conditions being equal, small 
 1 Much of the bodily heat is produced by chemical action.
 
 HEAT 127 
 
 persons presenting a larger surface in proportion for 
 radiation tend to lose their heat more rapidly than do 
 large persons; for this reason it is necessary to protect 
 babies from sudden cooling. 
 
 Clothing, especially that made of materials which are 
 poor conductors of heat (as wool), prevents radiation of 
 bodily heat, and so keeps the body warm. On the other 
 hand, thin clothing, or that made of materials which are 
 good conductors of heat (as linen), allows the bodily 
 heat to radiate and so be lost. Thin clothing also per- 
 mits rapid evaporation of perspiration, which assists 
 the cooling process. 
 
 Sunstroke occurs as follows: The high temperature of 
 the surrounding air practically abolishes both radiation 
 and conduction of heat. If, in addition, there be high 
 humidity, so that evaporation from the skin is also 
 stopped, while heat production in the body continues, 
 excessive elevation of bodily temperature takes place, 
 and sunstroke is the result. 
 
 LATENT HEAT 
 
 When heat goes into a substance, yet does not change 
 its temperature, it is called latent (hidden) heat. 
 
 Experiments. (a) Put cracked ice into a small vessel, set a 
 thermometer in it (keeping the bulb of the thermometer off the 
 bottom), and apply heat. The thermometer registers the same 
 temperature, just above freezing-point, until all the ice is melted. 
 (b) Boil water for ten minutes, testing with the thermometer. 
 The water is changed to steam, yet gets no hotter than 212 F. In 
 each case we are sure that heat is entering the vessel and contents, 
 yet we find no record of it.
 
 128 PRACTICAL PHYSICS FOR NURSES 
 
 Latent heat is that which disappears when a substance 
 changes its form. 
 
 The explanation is as follows: The molecules in either 
 solids or liquids, being held together by cohesion, take 
 considerable force, or energy, to separate them. The 
 heat energy which we put into them in the process of 
 heating is used in overcoming this cohesion and enabling 
 them to change their form. 
 
 Artificial Cold. It should be, and is, possible to re- 
 cover this lost energy. It is done by reversing the 
 process of liquefaction or evaporation. Water under 
 normal conditions freezes very slowly because it takes 
 time to get rid of the latent heat or energy which it 
 acquired upon liquefying. If we wish to make ice 
 artificially and rapidly, we hasten the process by rapidly 
 vaporizing some volatile liquid, such as ammonia or 
 compressed carbon dioxid; it extracts heat for this 
 change from water which is placed adjoining it; the 
 water, therefore, freezes. 
 
 In freezing ice-cream, the salt hastens the melting of 
 the ice, causing it to extract heat from any nearby object, 
 which in this case happens to be the cream. 
 
 SUMMARY 
 
 Solids conduct or radiate heat. Liquids or gases con- 
 vey it by currents. Conduction, convection, and radia- 
 tion are all modes of transference of molecular motion. 
 
 Metals are, as a rule, good conductors of heat. Wood,
 
 HEAT 129 
 
 wool, etc., are poor conductors. Water is not a good 
 conductor of heat, nor is air. We choose our clothing, 
 and utensils, build our homes, etc., with reference to 
 these qualities in materials. The hot-water bottle, fo- 
 mentation flannels, double windows, the fireless cooker, 
 the vacuum bottle, refrigerators, etc., are examples 
 of the practical application of the principles of heat 
 conduction and radiation. 
 
 Objects which conduct heat poorly hold it well, and 
 vice versa. 
 
 Convection of heat by currents of water or air is the 
 underlying principle of our heating, ventilating, and 
 hot-water supply systems. 
 
 Objects give off heat by radiation from their surface. 
 Rough surfaces radiate better than smooth ones. 
 
 The human body loses heat by radiation. Clothing 
 tends to prevent this loss. 
 
 Sunstroke is due to lack of heat radiation and evapora- 
 tion of the perspiration, coupled with excessive heat 
 production. 
 
 During boiling and melting no change in temperature 
 takes place, even though heat is constantly entering the 
 substance under observation. This heat which is 
 apparently lost and produces no effect is called latent 
 heat. It may be recovered by reversing the processes.
 
 CHAPTER IX 
 SOUND 
 
 What Sound Is. Drop a pebble into a pool of still 
 water. It starts small waves or movements which travel 
 in all directions and which strike the shore or rim with 
 a definite force. 
 
 We live in what is practically a lake of air. Any dis- 
 turbance in the air creates waves which travel con- 
 siderable distances, until their force expends itself. 
 The sort of air disturbance with which we are most 
 familiar is sound. There has always been much dis- 
 cussion as to whether sound was the air wave itself or 
 the effect produced by it upon the ear and brain; the 
 latter is now regarded as correct. 
 
 Production of Sound. Sound is produced by the 
 vibration of bodies. Such bodies may be strings, mem- 
 branes, thin plates, etc. The vibration may be pro- 
 duced by a current of air, a blow, etc. In some in- 
 stances the vibrations may be felt or seen. Place your 
 hand lightly against a large bell that has just been rung; 
 note that the sound ceases when your hand checks the 
 vibration. 
 
 Sound waves travel outward in every direction, not 
 only on a plane, as those in water do, but up and down 
 130
 
 SOUND 131 
 
 also, along all possible radii of a sphere whose center 
 is the spot where the vibrations are produced. Each 
 wave-like vibration compresses the air ahead of it, press- 
 
 Fig- 53- Sound wave movement (Butler, "Household Physics"). 
 
 ing the molecules closer together; these rebound, coming 
 wider apart; the rebound produces pressure, the pres- 
 sure a rebound, and so on; thus the vibratory move- 
 ment consists of an alternate condensation and rare- 
 faction of the sound medium. The molecules of air 
 do not travel in carrying a sound, but merely vibrate 
 to and fro. 
 
 Fig. 54. Diagram of sound waves. 
 
 Upon the amplitude of such vibrations depends the 
 intensity and pitch of the sound.
 
 132 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 The Human Voice is produced by the vibrations of the 
 vocal cords. The vocal cords of the human throat 
 resemble strings or bands. They are pulled together 
 or separated, tightened or loosened, by muscular action 
 
 ABC 
 
 Fig- 55- Top view of larynx: A, small or highest register; B, upper 
 thin or middle register; C, lower thin or middle register. 
 
 (voluntary). Air from the lungs is forced across them, 
 between them, making them vibrate. Low tones are 
 produced by relaxation of the muscles which control 
 them; high tones, by tightening. 
 
 Fig- 56- How voice is modified (Butler, "Household Physics"). 
 
 The voice is modified by the movements of the cords 
 themselves, the tongue, lips, and cavity of the mouth, 
 as well as by the size and shape of the nasal cavity, and 
 changes in the shape of the throat. The whole process 
 is very complicated and takes much practice to get per- 
 fect results. To a certain extent quality of voice de-
 
 SOUND 133 
 
 pends upon inborn characteristics, but it is largely the 
 result of training. Perfect control of breath, vocal 
 cords, and the muscles of throat and mouth is necessary 
 for excellence in speaking or singing. 
 
 Organs of Hearing. Our ears are the organs which 
 collect a portion of the sound waves and transmit the 
 impression gained therefrom to the brain. The sound 
 waves, collected by the external ear, cause the tightly 
 
 Eustachlan 
 tube 
 
 Fig- 57- Transmission of sound by mechanism of ear (Butler, 
 "Household Physics"). 
 
 stretched ear drum to vibrate. This vibration is taken 
 up by the chain of tiny bones in the middle ear and trans- 
 mitted to the fluid and otoliths of the inner ear. These, 
 in turn, stimulate the tiny fibers of the endings of the 
 auditory nerve, which conducts the impulse to the brain 
 where its meaning is interpreted. The eustachian tube 
 equalizes the air pressure between the middle ear and 
 the outside world.
 
 134 PRACTICAL PHYSICS FOR NURSES 
 
 Ability to distinguish between sounds and to know 
 their meaning is the result of a long process of educa- 
 tion and practice. 
 
 Diseased conditions, temporary or permanent, in- 
 flammatory processes which cause swelling, pus, etc., 
 interfere greatly with the transmission of sound by the 
 ear mechanism, or even stop it altogether. The ear 
 drum may be tightened or relaxed by disease, the 
 chain of ossicles stiffened, the eustachian tube blocked 
 so that there is not a proper adjustment of air pressure, 
 or the inner ear or auditory nerve may be effected; any 
 of these cause partial or complete deafness. 
 
 Fig. 58. Megaphone, showing reflection of sound (Butler, "House- 
 hold Physics"). 
 
 Artificial Aids to Hearing. Ear trumpets or conver- 
 sation tubes are merely instruments which collect a 
 quantity of the waves of sound, intensify them (usually 
 by reflection) and convey them to the ear, thus producing 
 a greater vibration of the ear drum than would the few 
 waves which come in ordinary circumstances. 1 The 
 
 1 Other devices for the deaf are in the form of telephones. 
 (See Chapter XI.)
 
 SOUND 135 
 
 megaphone is similar; it not only collects, but greatly 
 reflects and intensifies the waves of sound. 
 
 Speed of Sound. Sound waves move through the 
 air at a rate of 1125 feet per second. The rate varies 
 slightly with the temperature of the air, with its humid- 
 ity, density, etc. 
 
 Sound travels much more slowly than does light. 
 Witness the well-known facts that you see a gun fired 
 long before you hear its report, or that you see a work- 
 man at a distance strike a blow long before you hear it, 
 or that lightning and thunder which are practically 
 simultaneous sometimes appear to be far apart. 
 
 Conduction of Sound. Sound waves are transmitted 
 more readily by other substances than by air. They 
 move through water four times as fast as through air, 
 through wood ten times as fast, through steel fifteen 
 times as fast. 
 
 Water, the earth, wood, metal, etc., are, therefore, 
 better conductors of sound than is air. 
 
 Experiments. Place the ear at one end of a long table or board 
 and listen for the tick of a watch at the other end; it can be heard 
 at a considerably greater distance than it can through the air. 
 Scratch with the finger or a pin on a table to which the ear is ap- 
 plied; the sound is much louder than when it comes through the 
 air. Listen to approaching footsteps or wheels by placing your 
 ear to the ground; they will be heard long before it is possible to 
 detect them through the air. 
 
 The stethoscope takes advantage of this. It collects, 
 by means of a wide tube and a vibrating membrane,
 
 136 PRACTICAL PHYSICS FOR NURSES 
 
 the waves of sound made by the action of heart or lungs, 
 conducting them to the ears by means of tubes and 
 ear-pieces. The phonendoscope magnifies or increases 
 the intensity of the sounds it transmits, and is there- 
 fore sometimes preferred in making delicate distinctions. 
 
 Intensity of Sound. Sounds differ greatly in in- 
 tensity because of the great variation in the force of the 
 vibration that produces them. Intensity is influenced 
 by the medium of transmission, the nearness of the 
 hearer, the action of reflectors, concentrators, etc. 
 
 Pitch. Sounds differ in pitch, being high, low, or 
 medium. Difference in pitch is due to a difference in 
 the number of vibrations per second produced by the 
 object which makes the sound. High pitch is due to 
 rapid vibration; low pitch, to slower vibration. Also, 
 small cords or objects give tones of high pitch; large 
 ones, tones of low pitch. Also, tightly stretched strings 
 give higher tones than loose ones. (These facts may be 
 verified by examining the strings of a piano while they 
 are being struck.) The human ear is able to distinguish 
 sounds having from 16 to 32,500 vibrations per second. 1 
 
 This is the reason that women and children have 
 high-pitched voices, because their vocal cords are small 
 and light, and readily drawn tight. 
 
 1 We are told that there are sounds of such extremely high pitch 
 that the human ear cannot respond to them. Animals and insects 
 undoubtedly hear sounds outside of the range of our ears, because 
 of the different or more delicate construction of their auditory ap- 
 paratus,
 
 SOUND 137 
 
 Hoarseness is due to a swelling of the vocal cords or a 
 gathering of mucus between or upon them. 
 
 Reflection of Sound. Sound waves are reflected 
 from any surface which they strike (see Fig. 58) , but not 
 noticeably from small or rough surfaces, nor those com- 
 posed of soft or porous materials. If the surface is 
 broad, flat, and smooth, the reflection is more perfect. 
 This reflection, or echo, coming from a large surface 
 situated at an exact distance is often very clear. In an 
 ordinary room there is this same reflection of sound, 
 from walls and ceiling, but it comes so quickly after the 
 sound itself that we hear them as one. In large rooms 
 it may be very annoying. Fireproof hospital buildings 
 are often troublesome because of their resonance; being 
 built of hard, smooth materials (metals, hard plaster, 
 etc.) they reflect sound and often even magnify it. 
 
 Interference with Sound. To prevent sound waves 
 from traveling we block their way by interposing a 
 different medium. A closed door reflects sounds rather 
 than transmits it, and only a few waves go through 
 the cracks around it. 
 
 One hears more easily indoors because the walls 
 keep the sound waves in, besides collecting and reflect-, 
 ing them, so retaining or increasing their intensity. 
 Out of doors, they go off in all directions. 
 
 Sound waves lose their force in passing a corner, so 
 that their greatest strength is evident when the recipient 
 is directly in front of the object or person producing the
 
 138 PRACTICAL PHYSICS FOR NURSES 
 
 sound. For this reason a nurse should stand or sit as 
 nearly as possible in front of a patient to whom she is 
 speaking, so that he may hear her without effort. 
 
 Music and Noise. We distinguish between noise and 
 music as it chances to be pleasing or displeasing to us 
 personally. It is agreed, however, that musical sounds 
 are those in which the vibrations are uniform and 
 regular, while noise is a succession of confused and 
 irregular vibrations. 
 
 Fig- 59- Sound waves of music and of noise. 
 
 Heart and Lung Sounds. The sounds made by the 
 normal heart in its contraction and relaxation resemble 
 "Lubb, dup." If, for any reason, the valves do not 
 close properly, blood gurgles back through them, pro- 
 ducing a characteristic sound. If the valve edges are 
 rough, or the valve stiffened by disease, the sound is 
 modified. By long practice and experience physicians 
 learn to recognize each slight change in sound and to 
 know its exact meaning. 
 
 The "normal sound made by the air passing in and out 
 of the lungs is like that of a steady, gentle breeze. 
 Bronchial secretion in excess may cause a rattling sound ;
 
 SOUND 139 
 
 tough mucus, the sound called "rales," a sort of whist- 
 ling; fluid in the air cells, a gurgling or crackling sound; 
 pleurisy may give a rubbing sound, the "friction mur- 
 mur." Absence of sound where it should be found 
 indicates consolidation of lung tissue. 
 
 SUMMARY 
 
 Sound is vibration which stimulates the auditory 
 nerve. This vibration, due to whatever cause, produces 
 waves which travel outward in every direction. Upon 
 their size and shape depend the quality of the sound 
 produced. 
 
 The human voice is produced by the vibration of the 
 vocal cords. It is modified by the muscles of the larynx, 
 throat, and mouth, and by the size and shape of the 
 mouth and nasal cavities. Abnormal or diseased con- 
 ditions also alter its quality. 
 
 The external ear collects sound waves, which cause 
 the ear drum to vibrate. The vibration is transmitted 
 by the mechanism of the middle and inner ear to the 
 auditory nerve, thence to the brain, which, after train- 
 ing, acts as interpreter. 
 
 Devices for the aid of the deaf collect, reflect, and 
 increase the force of sounds. 
 
 Sound waves travel about 1125 feet per second through 
 the air, and much more rapidly through water or solid 
 materials. 
 
 Sound waves are reflected, especially from hard,
 
 140 PRACTICAL PHYSICS FOR NURSES 
 
 smooth surfaces. A perfect reflection is called an echo. 
 Indoors reflection of sound assists us in hearing, because 
 it increases the force of sounds; but it may, in a large 
 room, tend to confuse sounds. 
 
 Sound waves may be stopped by interposing some 
 different material. Sound cannot travel around a 
 corner without considerable loss. 
 
 Intensity of sound is due to the character of the 
 force that produces it. 
 
 Pitch is due to the number of vibrations per second, 
 the size of the vibrating object, etc. 
 
 Music is regular vibration; noise, irregular. 
 
 Heart and lung sounds are indicative of the condition 
 of these organs, but it takes experience to interpret 
 them correctly. Changes in or stiffening of the valves 
 of the heart produce certain definite abnormal sounds. 
 The presence of secretion or tissue changes in the lungs 
 produce sounds that are of diagnostic value.
 
 CHAPTER X 
 LIGHT 
 
 What Light Is. Until about one hundred years ago 
 it was thought that light was a material substance 
 which came from the object seen. Now it has been 
 discovered that light is similar to heat and sound, in 
 that it is made up of waves. 
 
 Light waves are about 30000 inch in length, and they 
 move much more rapidly than do the waves of heat or 
 of sound. Light waves may be changed into heat 
 waves. 1 
 
 Transmission of Light. Light waves are transmitted 
 not through air nor through liquids, but through what 
 for want of a better term we call the ether. We do 
 not know what the ether is, but we know that every- 
 where, pervading all liquids and solids, filling every 
 space in the world, and all the spaces between the worlds 
 and stars and suns, there is something which transmits 
 light waves. 
 
 Light waves travel at the rate of about 185,000 miles 
 per second. It can be judged from this that air is too 
 coarse a material to transmit them. 
 
 1 Glass transmits light readily, heat with some difficulty. In 
 a cold frame, the light of the sun, passing easily through the glass, 
 is absorbed by the earth and the plants and turned into heat. 
 This heat is retained by the glass and so accumulates. 
 
 141
 
 142 PRACTICAL PHYSICS FOR NURSES 
 
 Sir Oliver Lodge, one of the world's greatest scientists, 
 considers that light waves may be electric waves. An 
 important point in support of his opinion is that light 
 and electricity travel at the same rate of speed. . 
 
 Direction of Light. Light waves always travel in 
 straight lines. They cannot turn a corner. We there- 
 fore call the direction of light waves rays, and think of 
 light as straight rays sent out in every direction from 
 the luminous or illuminated object. 
 
 Fig. 60. Direction of light waves. Light rays. 
 
 We see an object, however, in the direction in which 
 its light rays enter our eyes. For example, when we look 
 at an object reflected in a mirror we seem to see it behind 
 the mirror, though we know that it is in front. Figure 
 61 explains this. 
 
 Intensity of Light. We know that light becomes 
 dimmer as it travels away from its source. Figure 62 
 explains why. is a source of light. At the distance
 
 LIGHT 
 
 143 
 
 A a certain number of rays fall on a certain surface; 
 at the distance B, four times as large, only the same 
 
 object 
 
 Fig. 61. Reflection in mirror. 
 
 number of rays fall. At C, a surface much greater, 
 the illumination is very much less. 
 
 Fig. 62. Intensity of light according to distance. 
 
 How Materials Affect Light. Light cannot pass 
 through some sorts of material at all, but is absorbed by 
 them; such materials we call opaque. Material which
 
 144 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 transmits light easily is called transparent. Materials 
 which transmit a portion of the light which comes to 
 them, reflecting the rest, are translucent. Other mate- 
 rials reflect all the light which comes to them. 
 
 Fig. 63. Formation of a shadow: A, Source of light; B, object; 
 , umbra or shadow. 
 
 Shadows. When rays of light strike an opaque 
 body, a shadow is formed behind it. (The technical 
 name is umbra.) If the source of light is small in corn- 
 
 Fig. 64. Formation of penumbra: A, Source of light; B, object; 
 C, umbra; D, penumbra. 
 
 parison with the size of the object, the edge of the 
 shadow is sharp. If the source of light is large in com- 
 parison, the edge is blurred. There may be a distinct 
 band which is dimly lit, called the penumbra (Fig. 64).
 
 LIGHT 
 
 145 
 
 How We See. Light waves enter the eye, and pass 
 through the cornea, the pupil, the lens, and the vitreous 
 humor, being modified by each of them. They strike 
 the retina, which is the sensitive portion that receives 
 the image. The retina transfers the sensation to the 
 optic nerve, which sends it on to the brain for inter- 
 pretation. 
 
 OPT/C 
 
 -Vitreous humor 
 Fig. 65. Section of the eye (Butler, "Household Physics"). 
 
 What We See. We see only those objects from which 
 light comes to us. This light may be given out by the 
 object itself or reflected by it. 
 
 A body that gives out light is called luminous. The 
 sun, a fire, an electric light, a red-hot or white-hot piece 
 of metal, etc., are luminous. That is, they send out 
 waves of light. When these waves enter the eye, we 
 see the object. 
 
 Most objects are seen, however, by reflected light.
 
 146 PRACTICAL PHYSICS FOR NURSES 
 
 Light from a luminous object, usually the sun or an 
 artificial light, falls on the object and is reflected, just 
 as sound is, or as a rubber ball bounds back when thrown 
 against a wall. When we see an object by the light that 
 it reflects we say that it is illuminated. 
 
 Reflection of Light. All surfaces reflect light to some 
 extent, but in most cases it is hardly noticeable. Smooth 
 surfaces reflect light better than rough. Silvered glass, 
 forming a mirror, is one of the best. 
 
 Fig. 66. Reflection of light. 
 
 Figure 66 shows how reflection of light occurs. If the 
 light strikes the reflecting surface at an angle, it is thrown 
 off or reflected at an exactly corresponding angle. Only 
 when light strikes a reflecting surface at a right angle 
 does it come back in exactly the same direction from 
 which it came. This law of reflection enables us to
 
 LIGHT 
 
 147 
 
 illuminate objects in positions where we cannot throw a 
 direct light upon them. 
 
 v 
 
 
 
 
 \ 
 
 
 7 
 
 ^ 
 
 
 L 
 
 
 \ 
 
 L 
 
 / 
 
 Fig. 67. Seeing through a brick: B, Brick or other object; M, M, 
 M, M, mirrors; L, L, L, light ray. 
 
 Rays of light may be reflected two or more times, 
 and if the material of the reflecting surface is of the req- 
 uisite quality, it may not lose much in the transfer. 
 
 Fig. 68. Concave reflector. 
 
 Figure 67 shows how, by means of reflecting mirrors, 
 we may "see through a brick."
 
 148 PRACTICAL PHYSICS FOR NURSES 
 
 Reflectors placed behind lights are made smooth and 
 concave, so that they not only collect and reflect the 
 light, but intensify it. 
 
 REFRACTION 
 
 Whenever a ray of light passes obliquely from one 
 transparent substance to another, it is bent in its course. 
 This bending we call refraction. 
 
 Fig. 69. Refraction of light by water: R, Ray of light; R-A, line 
 of sight ; R-B, refracted ray. 
 
 Experiments. Thrust a stick into a dish of water at an angle, 
 and look at it from one side. It appears bent. Place a coin in a 
 dish in such a position that it is just hidden by the rim; have some 
 one pour water into the dish; the coin will be seen. In each in- 
 stance the surface of the water refracts or bends the rays of light 
 coming from the object. 
 
 When light enters a thick plate of glass, it is bent 
 (refracted) by the first surface which it encounters; 
 as it passes through and leaves the glass from the other 
 side, it is bent again, always in the same direction, 
 providing both surfaces of the glass are parallel.
 
 LIGHT 
 
 149 
 
 Experiments. Look at a pencil obliquely through a thick 
 piece of glass; it appears in a different position from what it is known 
 to occupy. Look at a candle flame through a square bottle filled 
 with water and held diagonally; the flame appears to be much 
 higher than it really is. 
 
 GLftSS 
 
 Fig. 70. Refraction of light by glass: R, Ray of light; R-A, line 
 ot sight; R -B, refracted ray. 
 
 Lenses are pieces of glass used for bending light rays. 
 Their surfaces are usually curved, so that light passing 
 
 Converging LOM Q, merging Ln 3 a -; "g f 
 
 'i! il I! 'i! Jj JJ'U II J! 
 
 Fig. 71. Types of lenses (Butler, "Household Physics"). 
 
 through them may be distributed or concentrated, as 
 the case may require. They may be concave or convex,
 
 150 PRACTICAL PHYSICS FOR NURSES 
 
 a combination of the two, or combined with a plane 
 surface. Figure 71 gives some of the common forms of 
 lenses. 
 
 Convex lenses refract rays of light so as to cause them 
 to come together. 
 
 Fig. 72. Refractions of light by convex lens. 
 
 Experiment. Hold a strong reading glass (a "burning glass" 
 so called, if it can be obtained) over a sheet of white paper. Find 
 the distance at which it gives the most concentrated light. The 
 glare is almost blinding, and the illuminated spot upon the paper 
 may scorch, smoke, or even take fire. The same effect can be had 
 with a piece of ice carefully molded. 
 
 ig- 73- Refractions of light by concave lens. 
 
 Concave lenses refract rays of light so as to cause 
 them to be distributed. 
 
 Focus. A convex lens whose curves are perfectly 
 even on all sides brings the rays of light together at a
 
 LIGHT 151 
 
 point. This point is called the focus (see Fig. 72). 
 If we are looking through the lens, it is at this point 
 that the image of the object which we are observing 
 appears distinct and clear cut. 
 
 Polarization. Light is said to be polarized when its 
 vibrations are made to take place in one direction, and 
 its rays become parallel. Polarization occurs by re- 
 flection from a mirror, or by refraction. Certain trans- 
 parent materials polarize light in a special way, turning 
 the rays always toward the right or toward the left, 
 as the case may be. Tourmaline is one of these. 
 
 Solutions of glucose (grape-sugar) polarize light, 
 turning the ray always to the right; the degree of rota- 
 tion is in proportion to the amount of glucose present 
 in the solution. Levulose (also called fructose) also 
 polarizes light, turning the ray to the left. These 
 phenomema are made use of in urinalysis to determine 
 the character and amount of sugar present. 
 
 THE EYE 
 
 The cornea of the eye is a convex lens which bends the 
 rays :f light that enter it, bringing them closer together. 
 The lens of the eye, situated a little behind the cornea, 
 is a double convex lens which bends them twice more, 
 bringing them still further together. It is by means 
 of this arrangement that our eyes are able to "take in" 
 so much at one time. 
 
 The normal eye is so constructed that its focus, the
 
 152 PRACTICAL PHYSICS FOR NURSES 
 
 point where the refracted rays meet evenly and exactly, 
 and the image of an object is distinct, is exactly on the 
 
 Fig. 74. Detail of eye (Butler, "Household Physics"). 
 
 Fig- 75- Accommodation of eye for distance: a, For distant ob- 
 jects; b, for near objects. (Butler, "Household Physics.") 
 
 retina. The muscles of accommodation, acting upon 
 the lens, flatten or thicken it, and change the focal 
 point as objects are near or far away.
 
 LIGHT 
 
 153 
 
 In eyes which are not normal the focal point falls too 
 far in front of or behind the retina, and the image formed 
 there is blurred. In the case of near-by objects we may 
 
 Fig. 76. Correction for far-sighted eye by glasses: a, Far-sighted 
 eye; b, correction. (Butler, "Household Physics.") 
 
 Fig 77- Correction for near-sighted eye by glasses: a, Near-sighted 
 eye; b, correction. (Butler, "Household Physics.")
 
 154 PRACTICAL PHYSICS FOR NURSES 
 
 remedy this somewhat by changing their distance from 
 the eye; as when we see a "far-sighted" person hold a 
 book at arm's length in order to read it easily, while a 
 "near-sighted" person holds it within a few inches of 
 the eye. 
 
 Defects in the structure of the eye may be congenital 
 or acquired. They are overcome by the use of glasses, 
 which are lenses of shapes varied to suit the needs of 
 the particular eye in question. They are so constructed 
 as to bring the focal point exactly on the retina. Correct 
 fitting of the frames or mountings is also important, so 
 that the focal point may remain in its proper position. 
 
 Fig. 78. Head-mirror (Morrow). 
 
 OPTICAL INSTRUMENTS 
 
 The head-mirror used by physicians has a concave 
 reflecting surface designed to concentrate light in order
 
 LIGHT 155 
 
 to throw in into a cavity, thereby illuminating it. The 
 hole at the center enables the operator to see the spot 
 upon which the light is thrown, while the dark back of 
 the mirror shades his eyes from the glare. 
 
 Fig- 79- Ophthalmoscopes. 
 
 The ophthalmoscope is similar to the head-mirror. 
 It sends into the interior of the eyeball, through the 
 pupil, light which is reflected from a lamp placed back 
 of and at one side of the patient's head. The rays re-
 
 156 PRACTICAL PHYSICS FOR NURSES 
 
 fleeted from the retina through the pupil come back to 
 the mirror, through the hole in which the operator may 
 observe, and so get a picture of the interior of the eye. 
 The laryngoscope uses a concave reflecting mirror or 
 an electric light to throw light into the throat, whence 
 it is reflected downward by a flat mirror placed at such an 
 
 Fig. 80. Laryngoscope and throat mirrors. 
 
 angle that it will throw the light into the larynx. This 
 mirror serves the double purpose of a reflector for the 
 light going into the larynx and for the image of the condi- 
 tion existing there which goes back to the observer's eye. 
 The camera is an artificial eye. It has a double convex 
 lens which acts exactly as does the lens of the human eye. 
 The accommodation, or change for objects at different
 
 LIGHT 157 
 
 distances, is made by changing the position of the lens 
 itself. Instead of the retina there is the sensitized 
 plate or film, which gives us a permanent record of the 
 object. 
 
 The microscope lens refracts the rays of light coming 
 from a very small object, so that the lens of the eye can 
 
 Fig. 81. Image in the compound microscope (Butler, "Household 
 Physics"). 
 
 make use of them. As the eye follows those rays out, 
 it sees the object larger than it really is. The compound 
 microscope has a double set of lenses, usually five or more
 
 158 PRACTICAL PHYSICS FOR NURSES 
 
 in all, thereby greatly increasing its refraction and con- 
 sequent magnifying power. 
 
 Fig. 82. Telescope (Butler, "Household Physics"). 
 
 The telescope is constructed upon principles similar 
 to those involved in the microscope. The larger tele- 
 scopes make use of reflection as well as refraction. 
 
 COLOR 
 
 A prism is a piece of glass or other transparent sub- 
 stance having two of its sides set at an angle to each 
 other. It may be used to refract light so as to break 
 it up into its component parts. 
 
 Experiment. Pass sunlight through a glass prism. We get 
 a band of rainbow-colored light. 
 
 By this means we discover that white light is com- 
 posed of seven "primary" colors violet, indigo, blue,
 
 LIGHT 159 
 
 green, yellow, orange, and red. Scientists have found 
 that the red rays are those that vibrate most slowly, 
 while the violet rays, at the other end of the spectrum, 
 vibrate the most rapidly. Correspondingly, the red 
 waves are longest, the violet waves shortest. 1 
 
 The Finsen light is a lamp which gives out ultra- 
 violet rays, that is, rays which vibrate more rapidly 
 
 Fig. 83. Prismatic spectrum. 
 
 than even the violet ones. These rays produce chemical 
 changes in the tissues which are exposed to them. 
 
 Color is the impression given to the eye by light of varied 
 rates of vibration. 
 
 A body is colored when it reflects only a portion of the 
 white light that comes to it -from the sun. An object 
 or substance is white when it reflects all the sunlight. 
 It appears black when it reflects almost no light, but, 
 on the contrary, absorbs it. 
 
 1 Red waves are about .0007 millimeter in length, violet waves 
 about .0004 millimeter.
 
 160 PRACTICAL PHYSICS FOR NURSES 
 
 Artificial lights have different wave lengths from 
 sunlight and are therefore colored. Their color mingles 
 with that reflected from objects or substances which 
 they illuminate, making these objects appear of a 
 different color from what they do in daylight. It is 
 for this reason that matching of colors is impossible 
 except in daylight. 
 
 SUMMARY 
 
 Light is made up of waves, as are heat and sound. 
 Light waves are very short (about aoooo inch) and 
 travel very rapidly (about 185,000 miles per second). 
 
 Light is transmitted by the ether, a material which 
 pervades the whole universe. 
 
 Light travels in all directions from its source. For 
 convenience we refer to rays of light, since the direction 
 is always perfectly straight. 
 
 Light waves may be absorbed by a substance or object, 
 transmitted by it, reflected, or refracted by it. 
 
 When light is stopped by an opaque body, a shadow 
 is produced on its farther side. This shadow has a 
 sharp edge if the light is small, blurred if it is large. 
 
 We see only objects from which light comes to us. 
 They may be luminous, i. e., giving out light, or they may 
 reflect light which comes to them from another source. 
 Most objects are seen by reflected light. 
 
 Light is reflected in the opposite direction from that 
 of its approach, and at exactly the same angle. If it
 
 LIGHT 161 
 
 comes from the right, it is reflected to the left, and vice 
 versa. 
 
 Light rays may be refracted or bent in passing from 
 one substance to another. This is done artificially by 
 means of lenses. Convex lenses concentrate light rays, 
 concave lenses distribute them. 
 
 A focus is the point at which converging rays of light 
 come together and produce a distinct, clear-cut image. 
 
 Light is polarized by making it vibrate in one direc- 
 tion only, in parallel rays. The direction and amount 
 of refraction caused by a substance or a solution which 
 polarizes light may be used as a test for determining its 
 presence. 
 
 Light enters the eye, is refracted by the cornea, passes 
 through the pupil, and is twice refracted and concen- 
 trated by the lens. Normally the focal point is exactly 
 on the retina, adjustment for near or far-away objects 
 being made by the ciliary muscle. The pupil regulates 
 the amount of light which enters the eye. The image 
 formed on the retina is transferred to the brain by the 
 optic nerve. 
 
 Eye defects may be overcome by means of glasses 
 whose lenses change the focal point or make other 
 needed adjustments. 
 
 The various optical instruments are combinations of 
 lenses, reflectors, or both. They may reduce or magnify 
 the apparent size of an object, illuminate cavities, and 
 reflect their contents, etc.
 
 162 PRACTICAL PHYSICS FOR NURSES 
 
 Sunlight is white light. It may be broken up into its 
 seven primary colors. Some colors are formed by rapid 
 vibrations, some by slower vibrations. 
 
 An object appears colored when it reflects only part 
 of the light which comes to it from the sun. Black 
 objects absorb light instead of reflecting it; white ones 
 reflect all the light coming to .them. 
 
 Artificial lights are themselves colored, therefore they 
 change the apparent color of objects which they illumi- 
 nate.
 
 CHAPTER XI 
 
 ELECTRICITY 
 
 What We Know About It. Electricity is a force the 
 nature of which we do not know. We know how to pro- 
 duce it, how to control it, and we make constant use 
 of it; but no one has been able to define it nor find out 
 what it is. 
 
 Magnetism is a species of electricity. Magnetic 
 iron is a natural product, but magnets are also made 
 artificially. 
 
 Experiments. Show how a magnet attracts iron filings, tacks, 
 etc. Hold it outside a glass of water containing small tacks; it 
 will be found that its power is exerted through the glass and through 
 the water. 
 
 In a bar magnet, straight or curved, it is found that 
 the drawing force is exerted most strongly at the ends. 
 These are called the poles. 
 
 Fig. 84. Iron filings clinging to pole of magnet (Butler, "Household 
 Physics"). 
 
 The compass needle is a magnet freely suspended. 
 One end of such a magnet will always be found seeking 
 
 163
 
 164 PRACTICAL PHYSICS FOR NURSES 
 
 the magnetic pole of the earth, which is approximately 
 north. If two suspended magnets are brought near 
 each other, the north-seeking ends repel each other, 
 but a north- and a south-seeking end attract each other. 
 Thus we find that the poles of a magnet are of two sorts, 
 positive and negative. We also find that unlike poles 
 attract and like poles repel each other. 
 
 Fig. 85. Mariner's compass (Butler, "Household Physics"). 
 
 Electricity may be produced in three ways: (1) by 
 friction, (2) by chemical action, and (3) by means of a 
 dynamo. We recognize, therefore, three varieties of 
 electricity, yet it is likely that they are merely different 
 manifestations of the same force. 
 
 Frictional Electricity. Many different materials pro- 
 duce electricity when rubbed briskly under favorable 
 conditions. In dry, cold weather, the rubbing of the 
 feet on a carpet, the stroking of a cat's fur, the rubbing 
 of a piece of hard rubber with flannel, or a glass rod with 
 silk, etc., produce electricity. One can often see the
 
 ELECTRICITY 165 
 
 sparks caused by its discharge or escape. When fric- 
 tional electricity is produced by a machine it is done by 
 the rapid revolution of metal brushes against glass 
 plates; the electricity so produced is stored in Ley den 
 jars and is allowed to escape at the pleasure of the 
 operator. When the machine is in motion, a prickling 
 
 Fig. 86. Holtz's static machine. 
 
 sensation (due to the small sparks which come through 
 the air) is felt by a person standing in its vicinity, there 
 is a peculiar metallic odor due to the chemical effect, the 
 air is slightly heated, etc. This form of electricity is 
 called static (from the Greek statikos, brought to a stand- 
 still), because it may be stored.
 
 166 PRACTICAL PHYSICS FOR NURSES 
 
 Electricity by Chemical Means. In producing elec- 
 tricity by chemical action we use a combination of 
 materials which we call a cell. Two or more cells con- 
 nected are termed a battery. 1 
 
 The usual "wet" cell is composed of a piece of zinc 
 and another of carbon set into a solution of sal ammoniac, 
 and connected at their dry ends by a wire, usually of 
 copper. The chemical action of the solution upon the 
 
 Fig. 87. Wet cell (Butler, "Household Physics"). 
 
 elements (the zinc and carbon) starts a current, which 
 flows through the wire. The carbon is the negative 
 element, the zinc the positive; the current always flows 
 from the positive to the negative. 
 
 A "dry" cell is similar, except that the sal ammoniac 
 is merely damp instead of being wet, the moisture being 
 kept in by a tightly sealed container. . Dry cells do not 
 last as long as wet ones, and are more expensive in pro- 
 portion to their size, but require less attention. 
 
 1 These terms are often confused.
 
 ELECTRICITY 167 
 
 The wires connected with the elements of a cell com- 
 plete what is called the electrical circuit. When the 
 wire is continuous, the circuit is closed, and the current 
 flows. When the wire is broken, cut, or removed, the 
 circuit is open, and the current stops. 
 
 (It is possible, however, for electric current to leap 
 across a short break in the circuit, producing a spark.) 
 
 In the wiring for electric lights, the switch or button 
 makes the connection between the two open ends of 
 
 Fig. 88. Dry cell (Butler, "Household Physics"). 
 
 the circuit and allows the current to flow. The light 
 burns so long as the connection is maintained. When 
 the circuit is broken by turning the button or switch, 
 the light goes out because of the interruption of the 
 current. 
 
 Electricity by Dynamo. If a coil of wire be moved in 
 the immediate vicinity of a magnet, a current of elec- 
 tricity is set up in the wire. A machine which thus 
 converts motion into electric energy is called a dynamo.
 
 168 PRACTICAL PHYSICS FOR NURSES 
 
 Its essential parts are the rotating coil or armature, and 
 the large magnet, called the field magnet. 
 
 Motors. Conversely, machines have been made which 
 will convert electric energy into motion. Such machines 
 are called motors. 
 
 Fig. 89. Electric motor (Tousey). 
 
 Electric Heating. When a strong electric current is 
 passed through a wire which is too small to carry it properly, 
 the wire becomes heated. 1 Wires large enough to carry 
 the current do not become hot. 
 
 Electric heaters are made with fine wires, which are 
 also of a material which does not conduct electricity 
 well; these resist the passage of the current and so be- 
 come heated. The electric flat-iron, the electric toaster, 
 electric stove, electric heating pad, etc., have their 
 
 1 This may be the cause of some of the fires due to "defective 
 wiring."
 
 ELECTRICITY 169 
 
 "heating elements" made of fine wire surrounded by or 
 embedded in some substance which insulates it from the 
 
 a b 
 
 Fig. 90. Wiring in electric flatiron: a, Electric flatiron; b, wire 
 grid. (Butler, "Household Physics.") 
 
 surrounding objects, but permits the heat to be given 
 off in any desired direction. The electric cautery is 
 
 Fig. 91. Incandescent electric lamp (Butler, "Household Physics"). 
 
 constructed upon the same principles; its advantage is 
 that the degree of heat can be controlled, so that a high
 
 1 70 PRACTICAL PHYSICS FOR NURSES 
 
 or low temperature may be employed. (This is done by 
 means of special apparatus.) 
 
 If from any cause these appliances get too hot, they 
 "burn out," i. e., the wire is destroyed and must be re- 
 placed before they can be used. 
 
 Electric Lights. If a finer wire or a stronger current 
 is used than is employed in heating apparatus, the wire 
 may become white hot, so that it gives out light. This 
 is the principle underlying the incandescent electric 
 bulb, in which a strong current is passed through a very 
 fine filament. The thin glass which encloses it has had 
 the air pumped out of it and is sealed tightly, so that no 
 oxygen can get in to support combustion and cause the 
 filament to burn up. 
 
 The arc light is made with two sticks of carbon, a 
 substance which melts or burns up with difficulty. 
 These sticks are arranged so that the current has to 
 leap across a small space between them; in so doing, it 
 heats them white hot, producing a brilliant light. 
 
 The fuse in an electric lighting system is a bit of metal 
 which fuses or melts at a low temperature. If for any 
 reason the current becomes too strong, the fuse by 
 melting breaks the connection; in this way the lighting 
 system is protected against sudden increase of current 
 from trouble at the power-house, influence of electric 
 storms, etc. Telephones have similar arrangements at 
 the central station; when these fuses burn out (melt) 
 because of wires being struck by lightning, or from any
 
 ELECTRICITY 
 
 171 
 
 other cause, they can readily be renewed and the con- 
 nection re-established. 
 
 Electromagnet. If a bar of soft iron be wound with 
 wire and an electric current passed through the wire, the 
 
 Mains. Switch, 
 
 Fig. 92. i, Fuses and their action: a, Link fuse; b, screw in- 
 closed fuse and base; c, cartridge fuse and base; d, cartridge fuse 
 cut open, exposing fuse metal. 2, Lamps in house grouped in paral- 
 lel. (Butler, "Household Physics.") 
 
 iron becomes a magnet. It remains magnetized so 
 long as the current flows. This is called an electro- 
 magnet.
 
 172 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 An electromagnet is much stronger than any other 
 sort of magnet. Its power depends upon the strength 
 of the current flowing through the wire and upon the 
 number of turns of wire. Examine the coil in an elec 
 trie machine and you will find that there are a vast 
 number of turns of very fine wire. 
 
 The eye magnet, used to extract pieces of metal from 
 the eye or other portions of the body, is a strong electro- 
 
 Fig. 93. a, Straight bar electromagnet; b, horseshoe electromagnet. 
 (Butler, "Household Physics.") 
 
 magnet. If large enough, it will pull out a needle which 
 is embedded \ inch in the flesh. 
 
 The so-called "vibreur," or electromagnetic vibrator, 
 is used to locate metallic foreign bodies. They are first 
 located approximately by means of the #-ray; then, 
 if not too deeply embedded, they are found with great 
 accuracy by applying the vibrating magnet. The pa- 
 tient's sensations aid in the operation. 
 
 In the electric telegraph an electromagnet pulls down
 
 ELECTRICITY 
 
 173 
 
 an iron lever; this makes a mark upon or a puncture in a 
 moving paper ribbon, the result being a dot or a dash, 
 according to the length of time that the lever is held 
 down. The operator makes and breaks the circuit which 
 induces the power in the magnet, thus producing a series 
 of dots, dashes, and spaces; these constitute the Morse 
 alphabet. 
 
 Insulator 
 
 fed 
 
 Fig. 94. Telephone receiver and transmitter (Butler, "Household 
 Physics"). 
 
 In the telephone the voice striking against a thin 
 iron disk sets it vibrating. These vibrations make and 
 break the current induced in an electromagnet which is 
 in the receiver. The wire transmits the vibrations in 
 all their peculiar quality, and a similar instrument 
 at the other end reproduces them. 
 
 In the electric bell the push of the button makes the 
 connection between tw r o ends of wire which complete 
 the circuit. When the circuit is closed, current passes
 
 174 PRACTICAL PHYSICS FOR NURSES 
 
 through a small electromagnet which pulls the clapper 
 back, making it strike the bell. There is in the mechan- 
 ism an arrangement for a rapid making and breaking 
 of the circuit, producing the intermittent, buzzing ring. 
 When an electric bell does not work, one of several 
 things may be the difficulty. Nearly all of them may 
 be remedied by very simple measures. A new dry cell 
 
 Fig- 95- Electric bell (Butler, "Household Physics"). 
 
 may be needed for the battery; more water or fresh 
 solution, if it is a wet cell. The commonest trouble oc- 
 curs at the push-button, where the connection may fail 
 to be made because a wire has slipped or been worn 
 through. Frayed ends of wire cause the current to be 
 conducted to other things and so be useless. Accumula- 
 tion of dust on the electromagnet may prevent its work- 
 ing properly. Only very occasionally is there trouble 
 in the wire itself.
 
 ELECTRICITY 175 
 
 If a bell rings continuously, the difficulty is usually 
 in the push-button, or possibly in the wires. A simple 
 inspection of the interior of the button reveals the trouble 
 in most cases, and it is quickly remedied. The mere 
 stopping of the sound of the bell (by pushing something 
 between it and the clapper) is not advisable, since in 
 this case the battery or cell "runs down," i. e., is worn 
 out, very rapidly. 
 
 Rate of Speed. Electricity travels at the same rate 
 of speed that light does, 185,000 miles per second. 
 
 Electric Measures. A volt is the measure of electric 
 pressure or force. 
 
 An ohm is the measure of electric resistance. 
 
 An ampere is the measure of electric current. 
 
 When a force of 1 volt overcomes a resistance of 1 
 ohm, a current of 1 ampere results. 
 
 A watt is the measure of amount of electricity. 
 
 Conductors of Electricity. Some substance are good 
 conductors of electricity, other are not. Cotton, linen, 
 water, the human body, etc., are neutral, being neither 
 very good nor very poor. The most satisfactory con- 
 ductor of electricity and the one in most common use is 
 copper wire. Most metals are good conductors, though 
 they vary in degree. Acids are likewise good. 
 
 Poor conductors of electricity are called insulators. 
 They are used to interrupt or ward off electric current. 
 Such substances are hard rubber, glass, wood, etc. 
 
 Electric Treatments. Electricity is used in the treat-
 
 176 PRACTICAL PHYSICS FOR NURSES 
 
 ment of disease, usually in order to stimulate some por- 
 tion of the body to a proper performance of its function, 
 or to help the process of nutrition or metabolism. 
 
 Static electricity is produced in the so-called static 
 machine (see page 165) by friction. It is used to reg- 
 ulate functional processes, circulation, secretion, nu- 
 trition, etc. It is also of value in some inflammatory 
 conditions and paralyses. 
 
 Galvanic electricity is produced by a cell or battery, 
 and gives a vibration. It is used in the diagnosis and 
 treatment of nervous disorders and in some forms of 
 paralysis. 
 
 Fig. 96. Induction coil. 
 
 Faradic electricity is produced by an induction coil, 
 and is felt as vibration. It is used as a tonic, is em- 
 ployed in rheumatism, in eczema, and in nervous con- 
 ditions, etc. 
 
 High-frequency current is used to promote elimina- 
 tion, reduce blood-pressure, relieve pain, etc.
 
 ELECTRICITY 177 
 
 SUMMARY 
 
 Electricity is a force the nature of which we do not 
 know, though we use it commonly, can produce and 
 control it. 
 
 Magnetism, a species of electricity, occurs in nature 
 or may be produced artificially. The mariner's compass 
 has a magnetic needle one of whose ends or poles always 
 seeks the north. 
 
 Electricity may be produced by friction, by chemical 
 action, or by a dynamo. 
 
 Many different materials may be used to make fric- 
 tional electricity. In the static machine it is produced 
 by revolving metal brushes against plates of glass, and 
 is stored in Leyden jars. 
 
 Electricity is produced through chemical action by 
 means of certain combinations of materials called a cell. 
 The essential parts of a cell are its two elements (usually 
 metals), the solution, and the connecting wire. When 
 complete, it forms an electric circuit, through which 
 a current flows. This circuit may be closed or opened 
 (made or broken) at will by means of a switch or other 
 device. When electricity leaps across a break in a 
 circuit, it produces a spark. 
 
 The essential parts of a dynamo are the field magnet 
 and the armature (a rotating coil of wire). The magnet 
 induces an electric current in the wire. 
 
 Motors are machines which convert electric energy 
 into motion.
 
 178 PRACTICAL PHYSICS FOR NURSES 
 
 When an electric current is forced through a wire too 
 small to carry it, heat is produced. The various elec- 
 tric appliances in domestic and hospital use are con- 
 structed in accordance with this law. 
 
 Electric lighting comes under the same law. A still 
 smaller wire is used, or some substance, as carbon, 
 which fuses with great difficulty. The filaments of 
 incandescent lights are enclosed in vacuum globes so 
 as to cut off oxygen and so prevent their combustion. 
 
 A fuse is a piece of metal which melts at a low tem- 
 perature. It is used to protect electric light or tele- 
 phone systems from a sudden increase of current which 
 would cause them to burn out. 
 
 An electromagnet is a bar of soft iron wound with 
 wire through which an electric current is passed; the 
 iron becomes strongly magnetized. The electromagnet 
 is a vital part of the mechanism of the telegraph, tele- 
 phone, electric bell, etc. 
 
 When an electric bell does not work, it is usually due 
 to some simple trouble which can be revealed by in- 
 spection and easily remedied. 
 
 Electricity travels at the rate of 185,000 miles per 
 second. 
 
 The volt, the ohm, the ampere, and the watt are 
 electric measures. 
 
 Metals, acids, etc., are good conductors of electricity. 
 Wood, glass, rubber, etc., are poor conductors, and are 
 used to insulate against electricity. The human body
 
 ELECTRICITY 179 
 
 is neutral, neither good nor bad, as a conductor of elec- 
 tricity. 
 
 Static electricity (frictional), galvanic electricity 
 (chemical), faradic electricity (from an induction coil), 
 and the high-frequency current are used in medical 
 treatment.
 
 CHAPTER XII 
 
 THE x-RAY. RADIUM 
 
 THE ROENTGEN OR x-RAYS 
 
 History of the JC-Ray. It has long been known that an 
 electric spark would pass more readily, leap farther, 
 through rarefied air than through ordinary air. Late 
 in the nineteenth century Sir William Crookes worked 
 out a special vacuum tube, in which the air was so rare- 
 fied that there was but one-millionth as much as in a 
 
 Fig- 97- A Crookes tube, showing reflected "x-rays." 
 
 corresponding space in the atmosphere. He connected 
 this "high" vacuum tube between the terminals or poles 
 of a machine that produced the correct sort of electric 
 current. It was so arranged that the discharge or 
 spark took place between the two electrodes (metal con- 
 ductors which introduce and withdraw the current) in 
 the tube. 1 
 
 1 In the Crookes tube of high vacuum the electric force causes 
 the glass of the tube to become phosphorescent. 
 180
 
 THE z-RAY. RADIUM 181 
 
 It was found that in the Crookes tube connected with 
 an electric machine which was set in motion something 
 radiated in straight lines from the negative electrode or 
 terminal. This something was named the cathode ray. 
 Later Conrad Roentgen found that if the cathode rays 
 were reflected from the walls of the tube or from a 
 special reflector or obstacle placed in the tube, a new sort 
 of rays with special powers were produced. These he 
 named z-rays, x in algebra signifying an unknown 
 quantity. They are also called Roentgen rays. 
 
 Characteristics of the *-Ray. We know very little 
 of the nature of #-rays, but we make use of them in some 
 very definite ways. 
 
 They act upon a photographic plate exactly as daylight 
 does (the action is chemical), and produce a picture of 
 whatever is in front of the plate. 
 
 So far as we know, #-rays cannot be reflected nor re- 
 fracted, nor in other ways manipulated as light rays are. 
 They have very little effect upon the human eye. 
 
 At present we know of no means of bringing x-rays 
 to a focus; photographs taken by their means must 
 always be close to the object and, therefore, life size. 
 
 The most striking characteristic of the z-ray is that 
 it passes through substances which light will not pene- 
 trate, such as wood, clothing, cardboard, flesh, etc. 
 Most metals stop it, aluminum being the chief excep- 
 tion. Surgical dressings of gauze and cotton do not 
 interfere with the passage of the #-ray; but iodoform,
 
 182 
 
 PRACTICAL PHYSICS FOR NURSES 
 
 plaster casts, adhesive plaster, and wood splints are said 
 to cast shadows. If there is a metallic foreign body to 
 be located, these things do not interfere materially with 
 the process; but if the soft tissues are to be carefully 
 
 Fig. 98. x-Ray of intestine (Gant). 
 
 examined, it is wisest to remove any of the above dress- 
 ing materials. 
 Bismuth is quite opaque under the x-ray. Taken
 
 THE *-RAY. RADIUM 183 
 
 internally, bismuth coats the stomach and intestines, 
 making it possible to see very clearly their outlines under 
 the x-ray. Bismuth "meals" or enemata are, therefore, 
 used to aid in the diagnosis of conditions existing in the 
 alimentary canal. 
 
 The Fluoroscope. It was found that certain sub- 
 stances, fluorescent materials, such as calcium tungstate, 
 barium cyanid, etc., become luminous under the x-ray. 
 
 Fig. 99- Fluoroscope. 
 
 The fluoroscope was, therefore, constructed so that the 
 #-ray shadow picture falls on a screen of fluorescent 
 material, which illuminates it, causing it to be distinctly 
 seen. It is used in making x-ray examinations. 
 
 Uses of the x-Ray. The x-ray is used in medicine and 
 surgery to 
 
 (1) Locate foreign bodies. 
 
 (2) Locate fractures of the bones. 
 
 (3) Discover diseased conditions. These can be seen 
 when the tissue change involved is considerable.
 
 1 84 PRACTICAL PHYSICS FOR NURSES 
 
 (4) In stomach and intestinal work, to discover dis- 
 placements, strictures, ulcers, etc., and to note the 
 rapidity of functional processes. 
 
 (5) Produce permanent photographs of the findings. 
 
 (6) The #-ray has been used with some success in the 
 treatment of lupus, exophthalmic goiter, ulcers, etc. 
 
 x-Ray Burns. For some years after the x-ray came 
 into use it was found that too long or too frequent 
 
 Fig. IOO. ;c-Ray of fractured fibula (Scudder). 
 
 exposure to it produced burns 1 which were very difficult 
 to heal, and which were followed in some cases by 
 cancer or some malignant growth. 
 
 Protection against such burns is now had by the use 
 of sheets of lead as screens, by rubber gloves contain- 
 ing lead, by lead glass (glass into which lead is incor- 
 
 1 It is now also believed that the burns were sometimes due to 
 tubes in which the vacuum was poor,
 
 THE *-RAY. RADIUM 185 
 
 porated), etc. In consequence, these burns are now very 
 rare. 
 
 RADIUM 
 
 History and Characteristics. Radium is a very 
 mysterious substance, with some remarkable properties. 
 It was discovered and isolated in 1898 by Madame Curie 
 of France. 
 
 Radium is one of a group of substances (uranium, 
 helium, etc.) which give out energy at a very rapid rate. 
 They also emit rays, which affect a photographic plate, 
 produce phosphorescence, discharge electrified bodies, 
 and traverse bodies that are opaque to ordinary light. 
 Shenstone, in "The New Physics," sums it up as fol- 
 lows: "Radium gives off plentifully certain radiations 
 which exhibit wonderful powers of generating light 
 and heat, renders various minerals phosphorescent, and 
 causes the air to conduct electricity. It also emits an 
 emanation. 
 
 "It does these things for long periods, without any 
 perceptible diminution of its powers, and will, it is cal- 
 culated, continue to do them for thousands of years 
 before it is exhausted." 
 
 Theories in Regard to Radium. Nearly one hundred 
 years ago Faraday classified matter into four groups, 
 instead of the usual three. He called these groups solid, 
 liquid, gaseous, and radiant matter. He held that 
 while in solids the molecules were held firmly in place 
 by cohesion, in liquids less firmly, and while in gases
 
 1 86 PRACTICAL PHYSICS FOR NURSES 
 
 they were struggling gently to get away from each other, 
 in radiant matter they were fleeing from one another with 
 great force. 
 
 The present theory is that the atoms of a "radio- 
 active" substance are continually subject to a dis- 
 integration (breaking up) that takes place violently, 
 throwing off particles which constitute the "emanation," 
 i. e., radium gas. The wreck of the old atom gives rise 
 to a new atom, which may, in turn, go through a similar 
 disintegration. The process goes on till only stable 
 atoms are formed. 
 
 It is estimated that radium disintegrates one-half in 
 two thousand years. 
 
 Radium compounds, or "salts," also apparently 
 undergo a spontaneous and continuous disintegration, 
 or tearing apart. In this rapid and violent disintegration 
 energy is released to a remarkable degree. It amounts 
 to 100,000 times as much energy as is given off in any 
 known chemical change. There is doubtless a limit to 
 this radio-activity, but it has not yet been found. 
 
 Radium compounds are found to be always two de- 
 grees hotter than their surroundings, a fact suggestive 
 but unexplained. 
 
 Production of Light and Heat. Radium and all its 
 compounds evolve heat and light. Radium itself is lu- 
 minous. It burns the skin when exposed for any length 
 of time, or when exposed frequently for short periods. 
 Those who work with radium invariably have the
 
 THE x-RAY. RADIUM 187 
 
 papillae of the skin of their finger-ends burnt off, the 
 nails cracked and split, etc. Whether this is harmful 
 or not has not been determined. 
 
 Radium Rays. There are three distinct kinds of 
 rays given off by radium: the alpha (a), beta (/3), and 
 gamma (r) rays. The alpha rays can be stopped by a 
 sheet of paper; the beta rays penetrate thin aluminum; 
 the gamma rays affect a photographic plate as #-rays do, 
 and can be stopped only by thick plates of lead. The 
 beta and gamma rays penetrate the tissues of the 
 human body. 
 
 Uses of Radium. Treatment of disease with radium 
 is still in the experimental stage. It is being used with 
 apparent success in cancer (epithelioma, sarcoma, and 
 carcinoma), in exophthalmic goiter, in removing keloid, 
 and some sorts of scar, etc. It is used both internally 
 and externally. 
 
 Only a minute quantity is needed to produce a marked 
 effect. 
 
 Radium emanation (the gas) is also used in treatment. 
 It is given off from both radium and the compounds. 
 This gas remains radio-active for about four days, then 
 disintegrates and loses its power. The so-called radium 
 waters or solutions are, for this reason, usually inef- 
 fective. 
 
 The whole amount of radium in the world at the 
 present time is but a few ounces, but its remarkable 
 energy makes this in effect a very large quantity.
 
 1 88 PRACTICAL PHYSICS FOR NURSES 
 
 SUMMARY 
 
 The x-ray is produced by the discharge of an electric 
 current in a special sort of vacuum tube. 
 
 It penetrates many materials which are opaque to 
 light, such as flesh, clothing, surgical dressings, etc., 
 and to a lesser degree wood, plaster casts, and adhesive 
 plaster, etc. It cannot be refracted nor brought to a 
 focus. It does not impress the human eye, but acts 
 upon a photographic plate as light does. 
 
 The #-ray is used in locating foreign matter in the 
 human body, or fractures of bones, in discovering diseased 
 conditions, organic displacements, etc. Photographs of 
 the conditions found are taken by means of it. 
 
 It has been used with some success in the treatment 
 of external troubles. 
 
 The fluoroscope is a screen of some material which 
 becomes luminous under the #-ray. It is used in mak- 
 ing examinations. 
 
 #-Ray burns, due to long or frequent exposures, were 
 formerly common and dangerous. They are now pre- 
 vented by screens of lead or lead glass. 
 
 Radium is a mysterious substance, similar to uranium 
 and helium, which is radio-active, i. e., generates heat 
 and light, causes phosphorescence, emits rays similar 
 to the #-ray, etc. It was discovered in 1898 by Madame 
 Curie. 
 
 It is thought that the atoms of radium are constantly 
 and violently disintegrating, thus releasing an enormous
 
 THE s-RAY. RADIUM 189 
 
 amount of energy. Its compounds and gas are similar 
 in action to the element itself. 
 
 Three sorts of rays are given off by radium, the alpha 
 rays being feeble, the beta and gamma more active. 
 The two latter penetrate the human body and cause 
 tissue changes therein. The gamma rays affect a pho- 
 tographic plate. 
 
 Radium and its compounds are being used with ap- 
 parent success in the treatment of cancer and some ex- 
 ternal conditions. 
 
 Radium emanation (the gas) remains active only a 
 comparatively short time. 
 
 There are but a few ounces of manufactured radium 
 in the world at the present time.
 
 CHAPTER XIII 
 
 QUESTIONS FOR REVIEW OF PRINCIPLES AND 
 ORIGINAL THINKING 
 
 1. ARE the following substances organic or inorganic? 
 Coal, wood, tile, marble, cork, a tumbler, absorbent 
 cotton, gauze, drainage-tubing, cement flooring, baking 
 powder, salt, corn flour, acetanilid, tincture of digitalis, 
 castor oil, antidiphtheric serum, bismuth subnitrate, 
 ichthyol, bichlorid of mercury. 
 
 2. Are the following physical or chemical processes? 
 Rising of cream, rising of bread, making salt solution, 
 toasting bread, melting butter, freezing ice-cream, 
 ringing an electric bell, purging by castor oil, sterilizing 
 instruments, disinfection of linen by carbolic solution, 
 production of the rainbow, making x-ray pictures. 
 
 3. Why does an automobile skid when turning a 
 corner? 
 
 4. Why is a passenger thrown backward or forward 
 when a car suddenly starts or stops? 
 
 5. Why is dancing easier than walking? 
 
 6. Why does stamping remove snow or mud from 
 one's shoes? 
 
 7. Why does beating remove dust from a rug? 
 
 8. Why do rubber heels make walking more com- 
 fortable? 
 
 190
 
 QUESTIONS FOR REVIEW 191 
 
 9. Why is the arch of the foot an advantage? 
 
 10. What is a crystalloid substance? A colloid 
 substance? 
 
 11. Why is it harder to carry a load upstairs than on 
 a level? 
 
 12. Why can a person crawl over thin ice when it 
 would give way were he walking? 
 
 13. Why is it dangerous to stand up in a small boat? 
 
 14. Why are ink bottles made with thick bottoms? 
 
 15. Upon what principle is the laundry extractor 
 made? 
 
 16. Why must sewing machines be frequently oiled? 
 
 17. Why do we put sand on icy sidewalks? 
 
 18. Why do knots stay tied? 
 
 19. How do chains prevent a motor car from skidding? 
 
 20. Why can a heavy piece of furniture be best 
 moved by pushing low down on it? 
 
 21. What sort of a machine is the coffee mill? The 
 claw of a hammer? Grass clippers? A retractor? 
 A nasal speculum? A needle? A curling iron? A door 
 knob? 
 
 22. Why does cream rise? 
 
 23. Explain the use of a life-preserver. 
 
 24. Why do we hang the container high in giving 
 hypodermoclysis? Why low in giving a Murphy drip? 
 
 25. Explain the action of a blotter, or of absorbent 
 cotton. 
 
 26. Why is a new towel inefficient for drying purposes?
 
 1 92 PRACTICAL PHYSICS FOR NURSES 
 
 27. Discuss the drainage of wounds from the stand- 
 point of physics. 
 
 28. Why does paint or varnish preserve wood? 
 
 29. Why do we wear rubbers? 
 
 30. What happens when one of the valves of the heart 
 fails to act? 
 
 31. What is a trap in plumbing? 
 
 32. What would you do if a kitchen "boiler" leaked? 
 A hot-water pipe? A cold-water pipe? 
 
 33. What happens when the chest wall is punctured, 
 an opening made through into the lung? 
 
 34. How does a pneumatic door-check work? 
 
 35. Explain how a medicine-dropper works? 
 
 36. Explain the draft in a chimney. 
 
 37. Why does a fireplace ventilate a room? 
 
 38. Why do we place the ice in the top of a refrigerator 
 rather than the bottom? 
 
 39. Why does a furnace sometimes fail to heat a 
 certain room? 
 
 40. Why do stoves sometimes smoke when a fire is 
 first started? 
 
 41. What is the best way to air a room? Why? 
 
 42. Why can a room be aired more quickly in winter 
 than in summer? 
 
 43. Why are heaters always placed in the basement? 
 
 44. Why may one sometimes be more comfortable on 
 a day when the thermometer stands at 90 degrees, than 
 on a day when it is 82 degrees?
 
 QUESTIONS FOR REVIEW 193 
 
 45. How can you loosen a glass stopper which sticks? 
 Why? 
 
 46. Why is water not used in a thermometer? 
 
 47. Why is the bulb of a clinical thermometer made 
 so long? Why is the bore made so small? 
 
 48. Why are the grates of stoves and furnaces fitted 
 loosely and not fastened? 
 
 49. Why do water pipes burst when they freeze? 
 
 50. Why is the amount of ice-cream produced by a. 
 freezer greater than the amount of liquid put in? 
 
 51. Why does a lamp chimney crack when a drop of 
 water falls on it? 
 
 52. Why are thin tumblers less likely to crack than 
 thick ones when placed in hot water? 
 
 53. Why is a cotton comfortable warmer than a wool 
 blanket? 
 
 54. Why is a vacuum bottle silvered? 
 
 55. Why does bread or cake rise when being baked? 
 
 56. Of what advantage is the fireless cooker? 
 
 57. Why are stone houses cooler than wooden ones in 
 summer? 
 
 58. Why are heating pipes or steam pipes sometimes 
 covered with asbestos or felt? 
 
 59. How does a tea-cosy keep the tea warm? 
 
 60. Why does a hot-water bag remain warm so long? 
 
 61. Why are soapstones used in a fireless cooker 
 rather than plates of iron? 
 
 62. Why do we cover an ice-cream freezer with a 
 
 13
 
 194 PRACTICAL PHYSICS FOR NURSES 
 
 blanket after the freezing has been accomplished? Why 
 do we not empty the melted ice from around the can? 
 
 63. Why is a wooden tub better than a metal one for 
 the outside of a freezer? 
 
 64. Why should we not wrap the ice that is put into 
 a refrigerator? 
 
 65. Why is ice better than ice water for cooling a 
 refrigerator? 
 
 66. Why must a laundry dry room have a fan in order 
 to do rapid work? 
 
 67. Which will dry more rapidly, gloves washed with 
 water or with gasoline? Why? 
 
 68. Why do we cover utensils in cooking? 
 
 69. How may potatoes be cooked in ten minutes? 
 
 70. Explain why we use a double boiler. 
 
 71. Why does water evaporate faster from a pan 
 than from a bottle? 
 
 72. Why is it a waste of gas to keep water boiling 
 violently in cooking? 
 
 73. Why does a tea-kettle have a large bottom? 
 
 74. Why does a person feel chilly in damp clothing? 
 
 75. Why does ethyl chlorid freeze the tissues? 
 
 76. Why do we "see our breath" when it is cold? 
 Why not when it is warm? 
 
 77. Why do one's glasses become covered with mist 
 on coming from the cold into a warm room? 
 
 78. Why do opinions differ as to whether a room is 
 warm or cold?
 
 QUESTIONS FOR REVIEW 195 
 
 79. What principles of physics are involved in the use 
 of the cold tub and the cold sponge in reducing temper- 
 ature? 
 
 80. Why is the thunder-clap not heard till some time 
 after its lightning flash is seen? 
 
 81. Why are sounds heard better across water? 
 
 82. Why does a person hear better by placing the 
 hand behind the ear? 
 
 83. Explain the use of the ear- trumpet. 
 
 84. Why is a grand piano used in preference to an 
 upright for concerts, etc.? 
 
 85. Explain the difference between men's and women's 
 voices. 
 
 86. What are some of the conditions that may pro- 
 duce deafness? 
 
 87. Why does the size of the pupil of the eye change? 
 
 88. Must a person be nearer the camera or farther away 
 for a full-length portrait than for the head only? 
 
 89. Explain the intense heat produced by a "burning 
 glass." 
 
 90. Why are ground-glass globes used on gas or 
 electric lights? 
 
 91. Why do the eyes become tired from close work or 
 reading more quickly than from looking at a distance? 
 
 92. Why do people have two pairs of glasses, or those 
 with double lenses? 
 
 93. Why should very near-sighted persons wear 
 glasses for reading?
 
 196 PRACTICAL PHYSICS FOR NURSES 
 
 94. Why is prismatic glass used in doors or windows 
 opening into dark corridors? 
 
 95. Why should colors be matched only in daylight? 
 
 96. How does an electric light switch work? 
 
 97. Why does not an electric bell ring unless the 
 button is pushed? 
 
 98. What precautions must one take in using an 
 electric heating pad? 
 
 99. Where would you look for trouble if a patient's 
 bell failed to ring? 
 
 100. If an electric light suddenly went out, to what 
 causes might it be due?
 
 INDEX 
 
 ACCOMMODATION in the human 
 
 eye, 152 
 Adhesion, 24 
 Affinity, chemical, 24 
 Air cells in lung, 90 
 
 composition of, 74 
 
 pressure, 75 et seq. 
 and boiling, 105 
 
 washing systems, 96 
 
 weight of, 75 
 Altitude and the boiling-point, 
 
 105, 106 
 Ampere, 175 
 Apparatus for experiments, 17, 
 
 18 
 
 Appliances, electric, 168 et seq. 
 Arc light, 170 
 Armature, 168 
 Artery clamp, 42 
 Artesian well, 65, 66 
 Artificial aids to hearing, 134 
 
 cold, 128 
 
 light, 160 
 Atomic theory, 22 
 Atoms, 22, 23 
 Attraction, capillary, 69 
 Axis-traction forceps, 54 
 
 BALL bearings, 56 
 
 Baths to reduce temperature, 109 
 
 Battery, electric, 166 
 
 Bell, electric, 173, 174 
 
 Bismuth in x-ray work, 183 
 
 Block of pulley, 50 
 
 Bodily heat, production of, 99 
 
 radiation of, 126 
 Boiling, 104 et seq. 
 Boiling-points, 105 
 Bottle, vacuum, 120 
 Bread mixer, 49 
 Breast pump, 76 
 Bulb syringe, 87 
 Buoyancy, 66 
 Burning, 100 
 Burns from x-ray, 184 
 
 CALORIE, 104 
 Camera, 156 
 Capillarity, 69 
 
 Cathartics, saline, action of, 71 
 Cathode rays, 181 
 Cell, electric, 166 
 Center of gravity, 33 
 Centigrade thermometer, 104 
 Centrifugal force, 38 
 Centrifuge, 38 
 
 Chemical action productive of 
 heat, 99 
 
 affinity, 24 
 
 changes, 23, 24 
 Chemistry denned, 21 
 Chimney draft, 92 
 Circuit, electric, 167 
 Circulation in hot-water systems, 
 122, 124 
 
 of blood, 88 
 
 197
 
 i 9 8 
 
 INDEX 
 
 City water systems, 65 
 
 Distillation, 110, 111 
 
 Clinical thermometer, 104 
 
 destructive, 110 
 
 Clothing, 127 
 
 Distilled water, 111 
 
 Cohesion, 24 
 
 Divers, deep sea, 62 
 
 in liquids, 60 
 
 Draft in a chimney, 92 
 
 Cold compress, 109 
 
 in a stove, 100, 101 
 
 frame, 141 
 
 Drainage of wounds, 69 
 
 Color, 158 et seq. 
 
 Dressing sterilizer, 107 
 
 waves, 159 
 
 Drops, size of, 60 
 
 Compass, mariner's, 164 
 
 Drowning, 67 
 
 Compressibility of gases, 74 
 
 Dry cells, electric, 166 
 
 of liquids, 60 
 
 Ductility, 27 
 
 Condensation of liquids, 109 
 
 Dynamo, 167 
 
 Conduction of electricity, 175 
 
 
 of heat, 115 et seq. 
 
 EAR, mechanism of, 133 
 
 of sound, 135 
 
 Edema, 71 
 
 Conservation of energy, 36 
 
 Elasticity, 27 
 
 Contraction due to cold, 102 
 
 of gases, 73 
 
 Convection of heat, 115, 120 et 
 
 Electric action productive of heat, 
 
 seq. 
 
 99 
 
 Cooker, fireless, 119 
 
 appliances, 168 et seq. 
 
 Cooking under pressure, 106 
 
 battery, 166 
 
 Cooling, artificial, 128 
 
 bell, 173, 174 
 
 by evaporation, 108, 109 
 
 cell, 166 
 
 Corpuscles, 41 
 
 circuit, 167 
 
 Cracking, cause of, 102 
 
 current, high-frequency, 176 
 
 Crank and axle, 49 
 
 flat-iron, 169 
 
 Cream separator, 37 
 
 fuse, 170 
 
 tester, 68 
 
 heating, 168 
 
 Crookes' tubes, 180 
 
 lamp, 169 
 
 Crystallization, 28 
 
 lighting, 170 
 
 Crystalloid substances, 29 
 
 motor, 168 
 
 Cupping glasses, 76 
 
 switch, 167 
 
 Current, electric, 166 
 
 telegraph, 172 et seq. 
 
 high-frequency, 176 
 
 treatments, 176 
 
 
 wiring, 167, 168 
 
 DEFECTIVE sight, 153, 154 
 
 Electricity, 163 et seq. 
 
 Dew, 109 
 
 and light, 142 
 
 Dialysis, 29 
 
 chemically produced, 166 
 
 Diffusion, 29, 70 
 
 conductors of, 175 
 
 of gases, 73, 91 
 
 faradic, 176 
 
 Dilator, uterine, 43, 44 
 
 frictional, 164
 
 INDEX 
 
 199 
 
 Electricity, galvanic, 176 
 
 how produced, 164 
 
 produced by dynamo, 167 
 
 rate of travel, 175 
 
 static, 165, 176 
 Electromagnet, 171, 172 
 Electron theory, 23 
 Emanation, radium, 186, 187 
 Energy, 35, 36 
 Equilibrium, stable and unstable, 
 
 34 
 
 Evaporation, 107 et seq. 
 Expansion by heat, 102 
 Extension apparatus, 50 
 Eye defects, 154 
 
 magnet, 172 
 
 the human, 151, 152 
 
 FAHRENHEIT thermometer, 104 
 
 Fan bath, 109 
 
 Faradic electricity, 176 
 
 Fever, 99 
 
 Field magnet, 168 
 
 Finsen light, 159 
 
 Fireless cooker, 119 
 
 Fireproof buildings, sound in, 137 
 
 Flat-iron, electric, 169 
 
 Fluoroscope, 183 
 
 Focus of light, 151 
 
 of the eye, 152 et seq. 
 Force, centrifugal, 38 
 
 driving, 39 
 
 pump, 86 
 
 the heart a, 88 
 Forceps, artery, 42 
 
 obstetric, 54 
 Forms of matter, 28 
 Fountain, Hero's, 80 
 
 vacuum, 79 
 Freezing of water, 103 
 Friction, 55 et seq., 98, 99 
 Frictional electricity, 164 
 
 Frost, 109 
 Fulcrum, 41, 45, 47 
 Fuse, electric, 170 
 
 GALVANIC electricity, 176 
 
 Gas, illuminating, 74 
 
 Gases as conductors of heat, 117 
 
 diffusion of, 73, 91 
 
 properties of, 73 
 
 structure of, 28 
 Gravity, 32 
 
 center of, 33 
 
 specific, 33, 60 
 
 HARDNESS, 27 
 Head mirror, 154 
 Hearing, aids to, 134 
 
 mechanism of, 133 
 Heart, action of, 88 
 
 sounds, 138 
 Heat, 98 
 
 bodily, 99, 126 
 
 effects of, 102 
 
 latent, 127 
 
 measurement of, 103 
 
 retention of, 119 
 
 sources of, 98 
 
 transmission of, 115 et seq. 
 Heating, electric, 168 
 
 systems, 121 et seq. 
 High-frequency electric current, 
 
 176 
 
 Hoarseness, 137 
 Hot-water heating, 124 
 Human voice, 132 
 Hydraulics, 60 
 
 denned, 30 
 Hydrometer, 67 
 Hypodermic syringe, 81 
 
 ICE-CREAM freezer, 49, 128 
 Illuminated objects, 146
 
 INDEX 
 
 Illuminating gas, 74 
 Impenetrability, 35 
 Importance of physics, 19 
 Incandescent electric lights, 170 
 Inclined plane, 51 
 Induction coil, 176 
 Inertia, 26 
 
 Instruments, optical, 154 et seq. 
 Insulators, electric, 175 
 Interference with sound, 137 
 Irrigators, 62, 63 
 
 JOINTS, construction of human, 
 56, 57 
 
 KITCHEN range, drafts in, 100, 
 
 101 
 for heating water, 122 
 
 LAMP, electric, 169 
 Laryngoscope, 156 
 Latent heat, 127, 128 
 Law, Newton's, 37 
 
 of Archimedes, 66 
 
 Pascal's, 64 
 Laws of air pressure, 80 et seq. 
 
 of motion, 37 
 Lead in x-ray work, 184 
 Lens of the eye, 151 . 
 Lenses, 149, 150 
 Lever, 41 et seq. 
 
 Stanhope, 29 
 
 Levers in the human body, 44, 47, 
 48 
 
 of the first class, 41-44 
 
 of the second class, 45, 46 
 
 of the third class, 47 
 Leyden jar, 165 
 Lifting pump, 85 
 Light, 141 et seq. 
 
 arc, 170 
 
 artificial, 160 
 
 Light, direction of, 142 
 
 electric, 170 
 
 incandescent, 169, 170 
 
 intensity of, 142, 143 
 
 rays of, 142 
 
 reflection of, 146, 157 
 
 refraction of, 148 
 
 transmission of, 141, 144 
 
 waves, 141 
 Liquids, compressibility of, 60 
 
 pressure in, 61 et seq. 
 
 properties of, 60 
 
 structure of, 28 
 
 weight of, 61 
 Lubricants, 56 
 Luminous objects, 145 
 Lung sounds, 138 
 Lungs, action of, 90 
 
 MACHINE, the human, 39 
 Machines, 38 et seq. 
 
 classes of, 41 
 Magnetism, 163 
 Magnets, 163 
 
 electro-, 171, 172 
 
 eye, 172 
 
 field, 168 
 Malleability, 27 
 Matching colors, 160, 
 Matter, composition of, 21 
 
 forms of, 28 
 
 properties of, 24 
 Measurement of heat, 103, 104 
 Measures, electric, 175 
 Mechanics, 32 et seq. 
 
 defined, 30 
 
 of obstetrics, 52 
 Medical uses of electricity, 176 
 of radium, 187 
 of the x-ray, 184 
 Microscope, 157 
 
 adjustment of, 51
 
 INDEX 
 
 201 
 
 Mirror, reflection in, 142, 143 
 Molecular motion, 98 
 Molecules, 22, 24 
 Motion, 25 
 
 laws of, 37, 38 
 Motors, electric, 168 
 Muscles as levers, 44, 47, 48 
 
 as pulleys, 51 
 Music, 136, 138 
 
 NOISE vs. music, 138 
 Normal temperature, 99 
 
 OBSTETRIC forceps, 54 
 
 Obstetrics, mechanics of, 52, 64 
 
 Ohm, 175 
 
 Opacity, 27 
 
 Ophthalmoscope, 155 
 
 Optical instruments, 153 et seq. 
 
 Osmosis, 70, 71 
 
 Oxygen in combustion. 100 
 
 PARTICLE, 22 
 Pascal's law, 64 
 Penumbra, 144 
 
 Perspiration, action of, 108, 109 
 Phonendoscope, 136 
 Photographs by jc-ray, 181 
 Physical changes, 23, 24 
 Physics denned, 21 
 
 importance of, 19 
 Pitch of sounds, 136 
 Plane, inclined, 51 
 Plenum system of ventilation, 95 
 Pliers, 42 
 
 Plumbing in kitchen, 21 
 Pneumatics, 30, 73 et seq. 
 Polarization of light, 151 
 Porosity, 26 
 Power in levers, 41 et seq. 
 
 in machinery, 39 
 Pressure in liquids, 64 
 
 Pressure in steam apparatus, 106 
 et seq. 
 
 of air, 75 et seq. 
 Primary colors, 158 
 Prism, 158 
 Properties of gases, 73 
 
 of liquids, 60 
 
 of matter, 24, 25, 27 
 Pulley, 50 
 Pumps, 85, 86 
 
 QUESTIONS for review, 190 
 
 RADIANT matter, 185 
 Radiation of heat, 125 et seq. 
 Radium, 185 
 
 compounds of, 186 
 
 emanation, 186, 187 
 
 history of, 185 
 
 uses of, 187 
 
 Rain, production of, 109 
 Rate of travel of electricity, 175 
 of light, 141 
 of sound, 135 
 Rays, radium, 187 
 
 x-, 180 
 Reaction, 38 
 Reflection of light, 146, 147 
 
 of sound, 137 
 Refraction of light, 148 
 Refrigerators, 117, 118 
 Respiration, 90, 91 
 Review questions, 190 
 Roentgen rays, 180 et seq. 
 Rolling friction, 56 
 
 SALINE cathartics, 71 
 Scissors, 42, 44 
 Screwdriver, 51 
 Separator for cream, 37 
 Sewing machine, 49 
 Shadows, formation of, 144
 
 202 
 
 INDEX 
 
 Sheave, 50 
 
 Sight, 145, 151 et seq. 
 
 Siphon, 81, 82 
 
 Sliding friction, 55 
 
 Snow, how produced, 109 
 
 Solids, structure, 28 
 
 Sound, 130 et seq. 
 
 conduction of, 135 
 
 interference with, 137 
 
 reflection of, 137 
 
 speed of, 135 
 
 Sounds of heart and lungs, 138 
 Specific gravity, 33, 60, 68 
 Speculum, bivalve, 43 
 Sphygmomanometer, 89 
 Stability, 34 
 Standing, 34, 35 
 Stanhope lever, 49 
 Static electricity, 165 
 Steam apparatus, 89 
 
 engine, 89 
 
 heating system, 124 
 
 pressure apparatus, 106 et seq. 
 Sterilizers, 107 
 Stethoscope, 135 
 Stomach-tube, 83 
 Subnormal temperature, 100 
 Substances, simple and complex, 
 
 21 
 
 Sunstroke, 127 
 Supplies for experiments, 17 
 Swimming, 67 
 Switch, electric, 167 
 Synovial fluid, 57 
 Syringe, bulb, 87 
 
 hypodermic, 81 
 Systems of heating, 121 et seq. 
 
 of ventilation, 94 
 
 TELEGRAPH, 172 et seq. 
 Telephone, 173 
 Telescope, 158 
 
 Temperature, bodily, 99, 100 
 
 defined, 101 
 
 its relation to form, 28 
 Tenacity, 27 
 
 Tendency to crystallize, 28 
 Testing milk, 68 
 
 Theories in regard to radium, 185 
 Theory, atomic, 22 
 
 electron, 23 
 
 Thermometers, 103, 104 
 Transmission of light, 144 
 Transparency, 27 
 Treatments, electric, 176 
 
 with radium, 187 
 
 URINALYSIS, polarized light in, 
 
 151 
 Urine centrifuge, 38 
 
 pressure in bladder, 64 
 Urinometer, 68 
 Uterine dilators, 44, 52 
 
 VACUUM, 77 
 
 bottle, 120 
 
 fountain, 79 
 
 kettle, 106 
 
 system of ventilation, 95 
 
 tube, 180 
 
 Valves in veins, 89 
 Venous circulation, 89 
 Ventilating systems, 94 
 Ventilation, 91 et seq. 
 Vibrations producing sound, 130, 
 
 136 
 
 Vibreur, electric, 172 
 Voice, human, 132, 136 
 Volt, 175 
 
 WALKING, 34, 35 
 Washed air ventilating system, 96 
 Water as a conductor of heat, 1 16 
 bed, 64
 
 INDEX 
 
 203 
 
 Water, distilled, 111 
 
 freezing of, 103 
 
 heating system, 122, 124 
 
 sterilizers, 107 
 
 systems, 65 
 Waterproofing, 70 
 Watt, 175 
 
 Wave movement of sounds, 131 
 Waves in colored light, 159 
 
 of light, 141 
 Wedge, 52 
 Weight, 33 
 
 of air, 75 
 
 Weight of liquids, 61 
 
 Weights moved with lever, 41 et 
 
 seq. 
 
 Well, artesian, 65 
 Wheel and axle, 49 
 Wiring, electric, 167, 168 
 Work, 35, 36 
 Wounds, drainage of, 69 
 
 JJC-RAY, 180 et seq. 
 burns from, 184 
 characteristics of, 181 
 uses of, 183
 
 bOO"94l"356 8 
 
 LIBRARY 
 
 ANGELES, CAUF,
 
 i iiliiil '!' ill 
 
 ill: