The elements of natural philosophy. For the use of schools and academies

Front matter

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MEMORIAL COLLECTION

Preface

that a more general introduction of the study has been prevented. The author has introduced into “ The Elements of Natural Philosophy,” a feature which he trusts will to a great extent remove this objection. Throughout the text will be found descriptions of simple experiments that can be made with apparatus so easily contrived, as not only to render it possible for the teacher to illustrate the subject inexpensively, but also to permit the experiments to he made by the students themselves, thus enabling them to acquire that intimate knowledge of the subject that can come only by self-conducted experiments.

While the book is thus suited to the use of such schools as are \inable to provide costly cabinets of ajsparatus, the standard pieces found in well selected cabinets are carefully described and figured, thus adapting the book to the use of schools well provided with apparatus.

A carefully prepared syllabus, and series of questions for review, will be found following each chapter.

An examination of the book will show that no expense has been spared to bring it up to the highest standard as regards illustrations, typography, paper, and printing.

The author desires to acknowledge his indebtedness to his friend Prof. Elihu Thomson for critical examination of the proof-sheets.

E. J. H.

Central High School, Philadelphia, May, 1879.

Matter and Force.

Chapter I. Matter

1. Matter is anything which occupies space, and prevents other things from occupying the same space.

If the thing merely occupies space, but does not prevent other things from occupying the same space, then it is not matter.

Both iron and gold are kinds of matter, since they occupy space, and prevent other pieces of matter from being placed where they are. The shadow of an object, however, does not prevent other things from being placed in it, and is not, therefore, a kind of matter.

Both air aud water are kinds of matter. When we move other bodies through them, these bodies do not occupy the same place the air or the water does, but merely push the air or the water out of the way, and then occupy the place they have thus cleared for themselves. If a vessel be filled to the brim with water, a stone dropped into it will cause as much water to run out of the vessel as will just fill the space the stone occupies. The same vessel, however, can be placed

NATURAL PHILOSOPHY.

where it will be filled with sunlight, without any of the water running out.

2. The Senses. — We acquire knowledge bj means of our senses, and by them become aware of the existence of matter, which we can see, feel, taste, or smell.

Our senses form the avenues or channels through which impressions are received from things outside ; thus, light entering the eye enables us to see the peculiarities of color and form of the object from which it came. By means of the touch, we learn to distinguish the nature of the surface and the texture ; by the taste or smell, we are enabled to select the pleasant and wholesome from the noxious ; and, finally, by our hearing, we are enabled to understand the thoughts of others when expressed in language.

3. Substances. Elements. — The different kind.s of matter are called substances. Iron, wood, water, milk, air, and steam are substances.

Substances are either elementary or compound. Elementary substances.! or elements, are those which have never been resolved into more than one kind of matter.

Compound stibstances are those which are formed by the union of tw'o or more elemexttary substances.

Gold is an elementary substance. We cannot, by any known means, break it up or separate it into anjffhing but gold. Brass is a compound substance, since we can separate it into copper and zinc ; or, by melting copper and zinc together in the right proportions, Ave can produce brass.

All the compound substances in the Avorld are formed by various combinations of about seA'entA' elementary substances.

Any definite piece of matter is called a body. Bodies may be either large or small ; thus, both the

MA TTER.

eartli and a grain of sand are bodies, since they both are pieces of matter.

4. Changes of Matter. — All kinds of matter have different peculiarities or properties, by means of which we are enabled to recognize them. Thus, gold can be readily distinguished from marble, since its color and weight are different ; and then, too, it can be drawn out into wire, or beaten into thin sheets, while marble cannot. They differ also in other respects.

Matter is constantly undergoing change. This change is of two distinct kinds, viz. :

1st. Physical change, or that which may occur without the loss of those peculiarities or properties by which we recognize the substance ; and,

2d. Chemical change, or that which cannot occur without the loss of such peculiarities or properties.

As an example of a physical change, we may take a piece of steel, such as a common pen, and after examining it carefully, so as to note its peculiarities, ruh it once or twice against a magnet. The pen will now have acquired a property it did not possess before ; it will attract iron filings to it ; but if we again examine the pen carefully, we cannot see that it has lost any of the properties it previously possessed.

If, however, we expose the pen for some time to damp air, it will become covered with a thick, brown rust, which is formed by oxygen, a substance in the air, combining with the iron of the pen. Now the rust so formed in no way resembles either of the things out of which it was formed, since one of them was the pen itself, and the other an invisible gas. This change, then, is a chemical change, since both bodies have lost the properties or peculiarities by which they are generally recognized.

5. Physics or Natural Philosophy, and Chemistry.

— Natural Philosophy or Physics is that study tvbicb considers the causes and effects of the physical changes to which matter is subject.

Chemistry is that study which considers the causes

NATURAL PHILOSOPHY.

and effects of tlie chemical changes to which matter is subject.

6. Phenomena. — Anything which happens in the ordinary course of nature is called a phenomenon. As the word is commonly used, it means something unusual or strange ; as used in science, it means anything which, happens naturally. The fall of a leaf, the shining of the sun, the fall of a rain-drop, or the growth of a plant, are all natural phenomena.

7. Cause and Effect. — Nothing happens of itself. All natural phenomena are produced by certain causes ; for example, unsupported bodies fall to the earth : here all we see is the effect, namely, the motion. The cause of the motion is the attraction which the earth has for the body.

An effect may itself be the cause of some succeeding effect ; thus, the body, in falling to the earth, may give some of its motion to another body which it strikes, and this effect may in turn be the cause of some other effect, and so on indefinitely.

The causes which produce natural phenomena can all be traced to certain forces, one of the most important of which is heat.

8. Natural Law. — If we observe any natural phenomenon, we will notice that the relation between cause and effect is constant and invariable. The same cause, acting in the same way, alwavs produces the same effect. Thus, unsupported bodies always fall to the earth ; a steel pen rubbed against a magnet alwa3"s becomes magnetic, and acquires the property of attracting iroiT filings ; the same pen, unless specialh^ protected, alwaj's becomes covered with rust when exposed for some time to damp air.

MA TTER.

When, by observation, we have discovered the cause of any natural phenomenon, and have ascertained the order in which cause and effect follow each other, this order, expressed in language, forms what is called a natural law.

Natural Philosophy has for its object the study of natural laws. This definition, it will be seen, embraces the study of all natural phenomena; but natural philosophy is generally restricted to the study of the laws concerning the physical changes that take place.

9. Method of Study. Experiment, — There is only one way by which we can discover natural laws, and that is by observation. If we wish to know what effect will follow a certain cause, we must make the trial, and observe what happens. If, after repeated trials, we obtain the same effects, we may conclude that Ave have discovered the law.

10. Force and Energy. — All changes in nature are caused by the action of certain forces. The term energy is employed to designate the amount of work Avhich can be accomplished by the action of any force.

By the muscular force of the arm, a pound weight may be raised a certain distance, say one foot;' if the same force continue to act, the Aveight may be raised two feet. Here, in each case, the cause of the motion is the same, viz., the muscular force of the arm ; but the energy, or the amount of Avork done, is tAvice as great in the latter case as in the former.

11. Indestructibility of Matter and Energy. — It

is believed that there exists in the universe a certain definite quantity of matter and of energj'’. Neither of these can by any known means be increased or diminished. Matter and energy may, during changes, disappear, but only to reappear in other forms. Thus, 2

NATURAL PHILOSOPHY.

when a piece of paper or wood is burned, it disappears, and the heat set free is apparently lost ; but the paper or wood has, by the process of burning, been changed into invisible gases, and the heat set free has acted on the matter around it, and produced changes therein. Matter may change from one form to another, and energy may be converted into some other form of energy, but neither can be destroyed.

Syllabus.

Matter is anything which occupies space and prevents other things from occupying the same space.

No two pieces of matter can be in the same place at the same time, for all matter fills the space it occupies, and prevents other matter from occupying the same space.

Air and water are kinds of matter, since they occupy space and exclude other bodies from the space they occupy. We know of the existence of matter by means of our senses ; we can see, feel, smell, or taste it.

Different kinds of matter are called substances; substances are either elementary or compound. Elementary substances are called elements.

Matter is constantly undergoing change. A physical change is one which may happen without the substance losing those peculiarities or properties which generally enable us to recognize it. A chemical change is one which obliterates or removes such properties.

Physics or Natural Philosophy studies the causes and efiects of physical changes ; chemistry studies the causes and effects of chemical changes.

A phenomenon is a natural event, or anything which occurs in the usual course of nature.

Nothing happens without a cause. The causes which produce natural phenomena may be traced to certain forces, one of the most important of which is heat.

A natural law is that which expresses the order in which cause and effect follow each other. Natural laws are discovered by means of observation.

QUESTIONS FOR REVIEW.

By the term energy, we mean the amount of work which can he accomplished by the action of any force, flatter and energy are both indestructible. During changes, matter and energy may both disappear, but only to reappear in some other forms.

Questions for Review.

How can you tell whether the things you see are composed of matter or not ? Prove that both air and water are forms of matter. Is a shadow a form of matter ? Why ?

How do we become acquainted with different kinds of matter? What are substances? Name some different substances. What are elementary substances ? What are compound substances ? Give some examples of each. What is a body ?

What do you understand by the properties of a body ? To what two different kinds of change is matter subject? What is the difference between these changes ? Give an example of each of these kinds of change. What is Physics or Natural Philosophy ? What is chemistry ?

What is the difference between the scientific and the common use of the word pheuomeuon? Name some different natural phenomena. What do you understand by the cause of a natural phenomenon ? What is an effect ? What relation always exists between cause and effect? Name any important cause which produces many natural phenomena.

Define natural law. Give an example of any natural law. What has the study of natural philosophy to do with natural law ? In what way only can any law of nature be discovered ?

Define energy. Can the amount of either matter or energy which now exists in the universe be increased or diminished? What is indestructibility ?

Chapter II. General, Properties Of Matter

12. Names of General Properties. — Bj the properties of a body we understand those peculiarities or qualities which, enable ns to recognize it. Properties are either general or specific. General properties are those which are common to all matter. Specific or particular properties are those which are possessed only by certain kinds of matter.

The most important of the general properties of matter are magnitude or extension, impenetr ability, divisibility, porosity, compressibility , expjansibility, mobility, and inertia.

13. Magnitude or Extension. — All matter occupies space or fills room, that is, it has size. This property is generally knoAvn by the name of magnitude or extension. Matter extends or fills space in three difterent directions, namely, in length, in breadth, in thickness ; or, in other words, all matter possesses volume.

14. Units of Measurements. — In this country, the dimensions of a, body are measured in inches, feet, yards, or miles. In France and Europe, generallj', dimensions are measured in metres or in decimals or multiples of a metre.

The following tables give the values of these units, viz. ;

English Measure.

Measures of Length. Measures of Surface. Measures of Volume.

12 in. make one ft. 144 sq. in. =1 sq. ft. 1728 cub. in.= 1 cub. ft.

3 ft. “ “ yd. 9 sq. ft. = 1 sq. yd. 27 cub. ft. = 1 cub. yd.

make one mile.

French Measure.

Measures of Length.

1 metre equals

39.37

Eng. in., or 3.280 ft.

1 decametre, or 10 metres “

393.7

1 hectometre, or 100 metres “

1 kilometre, or 1000 “ “

39370.

1 decimetre, or y’j- “ “

3.937

1 centimetre, or “ “

.3937

1 millimetre, or '* "

.03937

“ “ or in. nearly.

Measures of Area or Surface.

1 square metre equals . . . 1550.06 sq. in., or 10.764 sq. ft.

1 square decimetre equals . 15.5006 “ “

1 square centimetre “ . .155006 “ “

1 square millimetre “ . .00155006 “ “

Measures of Volume.

1 cubic metre equals . . . 61027.1 cub. in., or 35.3166 cub.ft.

1 cubic centimetre equals .0610271 “ “

The measures of surface are obtained by squaring the measures of length. Thus, 12 ins. X 12 = 144 square inches, or one square foot ; 3 ft. X3 = 9 square feet, or one square yard; 39.37 ins. X 39.37 = 1550.06 square inches, or one square metre.

The measures of volume are obtained by cubing the measures of length; thus, 12 ins. X 12 X 12 = 1728 cubic inches, or one cubic foot.

The following table will be found convenient in changing English into French units :

1 inch 1 foot 1 yard 1 mile

25.40 millimetres. .3048 metre.

1.609 kilometres.

The value of one square inch can be obtained by squaring 25.40 millimetres = 645.16 sq. millimetres. The value of one cubic inch can be obtained by cubing 25.40 =16387.06 cubic millimetres.

NATURAL PEILOSOPHY.

Figure 1 represents the actual lengths of the French decimetre, and Figure 2 of four English inches. Since a decimetre equals 3.937 ^ inches, it is but a trifle shorter than four English inches. From to i? is one decimetre; from A to a is one centimetre, of which there are ten in one decimetre, or in the whole length of A B. From .A to 6 is one millimetre, of which there are ten in every centimetre.

From C to D is four English inches; from C S _ to a is one inch ; from C to i is one-tenth of an

inch. There are about twenty-five millimetres in one inch.

15. Impenetrability is that property wliicli prevents any ttvo particles of matter from occupying the same space at the same time.

As we have already seen, magnitude or extension and impenetrability are necessary to the existence of matter. They are^ therefore, sometimes called the essential properties of matter.

Experiment. — If an empty glass goblet be held, mouth downwards, in a vessel of water, it will be found that the water will not rise and fill the goblet, since it is already full of air. This proves that air and water cannot be in the same space at the same time. If, however, a vessel open at both ends, as, for example, a glass lamp ^ chimney, be dipped into water, it will be found

that the water will rise as high inside the chimney as it is on the outside, for, as the water rises in the chimney, it pushes the air out at the top.

Caution. — Unless the goblet be held with its mouth quite level with the water, some of the air will escape, and mar the experiment.

Although, in many cases, two different bodies seem to occupy the same place, yet, in reality, this is not the case. Like the body moving through air or water, they merely move parts of the other body out of the space they occupy. Thus, a nail driven into a board can only enter it by crowding some of the particles of the board more clc.«ely

GENERAL PROPERTIES OF 31 ALTER. 19 together. If, too, in the experiment just described, the goblet be pushed far down into the water, the water will rise some little distance inside it, because the pressure has packed the particles of air more closely together.

16. Divisibility is tliat property of matter wlrich enables us to cut it up or divide it into a number of smaller pieces. So far as simple experiment shows, there would appear to be no practical limit to the divisibility of matter. AYe can continue to divide it until the particles are too small to be directly seen, and even then, by using a microscope, we can carry the division still further.

The following examples will show the wonderful extent to which it is possible to carry the division of matter. Gold can be beaten into leaves so thin that it would take about three hundred thousand of such leaves, placed one upon the other, to make a pile one inch thick, and yet each of these leaves can be cut into very small pieces.

A grain of musk will continue for yeans to give off its odorous particles to the air around it, without decreasing very perceptibly in weight.

A very small quantity of certain coloring matters will give a decided tint to a large quantity of water. Now, since the water so colored may be divided into a very great number of parts, in each of which the color is distinctly visible, the quantity of coloring matter in each must be exceedingly minute.

The microscope has revealed to us the existence of animalcules so small that millions can easily swim about in the space of a cubic inch without touching one another.

17. Atoms and Molecules. — Notwithstanding the above, and other wonderful instances of the extreme divisibility of matter, we have reasons for believing that matter is not infinitely or indefinitely divisible, but that if we could continue to divide a piece of matter far enough, we would reach a limit beyond which it would be impossible further to divide it. These final particles of matter are called atoms. The word atom means that which cannot be cut.

NATURAL PHILOSOPHY.

Since we know hj actual trial that we can divnde matter into very small particles, the atoms must be exceedingly small; but of their real nature, no definite knowledge has as yet been obtained. The atoms seldom, if ever, exist separately, but combine with one another, and form groups of two or more atoms, called molecules. The force which causes the atoms to combine is the chemical force. Molecules, though larger than atoms, are still exceedingly small — smaller, indeed, than the smallest particles into which we have been able to divide bodies.

The molecule of a compound substance is the smallest possible quantity of that substance that can exist. Water is a compound substance, composed of two atoms of hyi'lrogeu combined with one atom of oxygen. Any compound containing less than two atoms of hydrogen combined with one atom of ox}'- gen, would not be water. The molecule of water, or the smallest quantity of water that can exist, will therefore contain two atoms of h_\xlrogen and one of oxygen. The molecule of an elementary body consists of a group of atoms of that body.

The very small particles of matter obtnined artificially, by continued division or by grinding, are neither atoms nor molecules. The word particle is sometimes used in the sense of atom or molecule ; such use is only correct when we mean the smallest possible particle.

18. Porosity. — Neither the atoms nor the molecules touch one another; though they are nearer together in solids than in liquids or gases, yet it is believed they are not in actual contact, even in the most solid substances known. The spaces tvliich separate them are called pores. The size of the pores varies greatly. In some kinds of matter, the pores can readily be seen, as, for example, in most woods, or in sponges.

In otliers we cannot see tlie pores, even Avitli tlie aid of a microscope. A¥e can, however, in many cases, show that they exist, by forcing liquids through them. Thus, if water be placed in a strong vessel of gold, and a powerful pressure be exerted on the water, it can be forced to pass through the vessel without rupturing it. The water must therefore have passed through the pores.

19. Compressibility. — All matter, when subjected to sufficient pressure, can be made to occupy a smaller space ; or, in other words, all matter possesses the property of compressihility . Substances vary in their degree of compressibility. Of the three conditions in which matter is found, gases are the most compressible, and solids the least. The compressibility of most solids and liquids is very small, considerable force being required to produce a perceptible change in their volume. The compressibility of- gases is very much greater than that of solids or liquids.

All matter, when cooled, decreases in bulk. This decrease is called contraction., and is to be distinguished from compression.

As a rule, gases contract more than liquids, and liquids more than solids, on the loss of equal quantities of heat.

20. Expansibility. — • As matter contracts or decreases in bulk by a loss of heat, so also it expands or increases in bulk by an increase of heat. Gases expand more than liquids, and liquids more than solids, by the same change of temperature.

To the above general statement there exist exceptions, a few substances expanding on a loss, and cortracting on an increase, of heat.

NATURAL PHILOSOPHY.

If, as is believed, the size of neither the atoms nor the molecules is changed during expansion or contraction, then the increase or decrease in the bulk so produced can only be due to the increase in the size of the pores or spaces between the atoms and molecules. As, therefore, all matter expands or contracts when subjected to changes of temperature, all matter must contain pores.

Experiment. — If an empty glass bottle be held, mouth downwards, in a plate of w'ater, so that the mouth is just under the water, and the hand be made to cover as much of the outside of the bottle as possible, the heat of the hand will cause the air inside the bottle to expand, so that the bottle will no longer be able to hold it all, and it will be seen to bubble out from the mouth of the bottle.

Caution. — The bottle should be comparatively large, so as to hold a fair amount of air, and made of glass as thin as possible.

Pig, 3.-Expansion of Air.

quickly communicated to the air within.

If the bottle be dipped too far down in the water, it will take a longer time for the bubbles of air to escape, on account of the pressure of the water on the outside.

21. Mobility is tliat property of matter -vs-iiicli enables it to be moved or to change its place.

Since the earth is ahvays rotating on its axis and revolving around the sun, it is clear that nothing on the earth is ever actually at rest. We generally say, however, that a body is at rest when it is not changing its position as regards neighboring bodies.

Besides the more apparent motions that occur around us. like the flowing of a river, the flight of a bird, or the fall of a stone, there are other motions too minute to be seen. The molecules are never at rest, but are in rapid motions towards and from each other. These motions cause various phenomena of heat and light.

22. Inertia. — A body never begins to move, stops moving, or changes the direction in Avhich it has been moving, unless force of some kind acts upon it. In

GENERAL PROPERTIES OF MATTER.

other words, matter can do nothing of itself towards changing its condition, either of rest or motion.

If we attempt to move a comparatively large body from a state of rest, as, for example, a wheel revolving freely on an axis, we will find it necessary to exert onr strength for some time before we can get the wheel to move rapidly ; that is, we find that a body at rest apparently offers a resistance to changing its state of rest. On the other hand, when the wheel has been set in motion, we will also find it necessary to exert our strength, but this time in the opposite direction, before we can bring the body to rest again ; that is, we find that a body in motion apparently offers a resistance to chano'ino- its state or condition of motion.

O O

By the inertia of matter we understand its tendency to continue in whatever condition it may be, whether of rest or of motion, until some force acts upon it. Therefore it follows, from the property of inertia,

1st. That a body at rest tvill continue at rest forever., unless some force acts upon it ; and,

2d. That a body in motion will continue moving in a straight line forever, unless some force acts upon it.

It is very easy to believe that a body once at rest will continue at rest forever, until acted on by some force, since such is our common experience. But it is difficult, at first, to believe that the same thing is true of a body in motion. If, for example, we throw a stone straight up in the air, we know that it will not continue moving upwards forever. In reality, it moves more and more slowly every moment, and at last entirely stops, and begins to fall to the earth. But in this case the body does not stop its own motion. It is stopped because the earth is constantly pulling it down towards it, and because the air is

NATURAL PHILOSOPHY.

resisting its motion. Could we go out into tlie empty space, beyond the influence of any other force, and throw the stone in any direction, it w’ould continue moving in a straight line in that direction forever, since, as it is inert, it has no more force or power to stop its motion than it has to begin to move.

fl’he earth moves through the apparently empty space around the sun, and, since there is nothing to stop its motion, must continue moving forever.

23. Examples of Inertia. — When a train of cars begins to move, it takes some time before it reaches its full speed, on account of the inertia of the train. When, hoAvever, the train has attained this speed, considerable force must be exerted to stop it.

Before a moving body can be brought to rest, it must lose an amount of energy equal to that wdiich caused its motion. Cannon-balls owe their great destructive power to the fact that they have been set in motion by the explosion of gunpowder, and hence will overcome considerable resistance before stopping.

If w'e jump from a rapidly moving coach, w'e are very apt to fall over, because, on reaching the ground, the motion of our feet is stopped while the rest of our body continues to move forward. A running jump will carry us much farther than a standing jump, because, if we first run rapidly in the direction in which we wish to jump, the motion thus given to the body wdll help to carry it in that direction.