EASY EXPERIMENTS
IN
PHYSICAL SCIENCE,
FOR
ORAL INSTRUCTION IN COMMON SCHOOLS,
LE ROY C. COOLEY, PH. D,
PROFESSOR OF NATURAL SCIENCE IN THE NEW YORK STATE NORMAL SCHOOL.
NEW YORK:
SCRIBNER, ARMSTRONG & CO.,
1876.




Entered according to Act of Congress, in the year 1870,
BY LE ROY S. COOLEY.
In the Office of the Librarian of Congress at Washington.
JOHN F. TROW & SON, PRIMNTRS
a05-2I3 EAST IXTH ST., Naw YORni




PREFACE.
IT is coming to be very generally believed by educators
that one of the most important aims of primary instruction should be to discipline the child to habits of quick
and accurate observation, and to the power of making simple but correct inferences from the facts which his senses
reveal. Surely this result can be reached more easily by
means of those facts which nature communicates through
the senses than by subjects which have no natural dependence upon material forms; and hence the superior adaptation of the simple facts of physical science to the wants
of common-school instruction.
But the only way to strengthen mind is to make it
work. If the senses are to be developed and disciplined,
the child must be allowed, and, if need be, compelled, to
use his senses for himself. The teacher is to guide him,
but not to carry him. His mind is to be directed toward
material things, and taught to see their forms and characters as they themselves present them. The instructor is
to be his guide, but Nature is herself to be his teacher.
The intelligent teachers of common-schools are eagerly
asking how can this theory be wrought into practice.
Lack of time and lack of material seem to almost forbid




Iy                   PREFACE.
the attempt: lack of time, because custom and public
opinion demand so much knowledge of books in all the
branches which overcrowd the primary course; and lack
of material, because apparatus other than a blackboard
and a few maps is, in most common-schools, a thing unheard of. It is pleasant to anticipate a time when the
higher and theoretical parts of arithmetic and grammar
shall be reserved for the high-school course of study, and
their places in the common-school left to the more appropriate study of nature. It is pleasant to anticipate the time
when every common-school shall be provided with an appropriate set of apparatus, through which Nature may teach
her simple truths to children in her own playful and childlike manner. The time is doubtless coming when both
these anticipations will be realized, and all the quicker
will it come if teachers will only beyiln the work by using
the very little time and means already at their disposal.
Some have already begun: they find it possible to secure
time for a short exercise each day, or at least two or three
times a-week, in which they perform simple experiments
with such objects and utensils as they find at hand, much
to the delight and profit of their schools. Letters from
several of these announce their surprise at the interest
thus aroused, not only among pupils, but among parents
also. Whole neighborhoods are in some instances awakened, and it will not be difficult in such cases to obtain
money for the purchase of better means of illustration!
Now this little book is offered as an aid to the teachers




PREFACE.                     v
who are, or who desire to be, engaged in this work. It
is made up of experiments of the simplest kind, which,
with few exceptions, can be performed with such apparatus as can be collected anywhere almost without expense.
These experiments are arranged in groups, each group
teaching some elementary fact or principle of science.
They are selected from among those which the writer has
long been using in the earliest stages of his instructions
to his classes, and which are now being reproduced by
young teachers who have gone out into the public-schools
of the State, and from whom reports of abundant success
are received. There is, therefore, good reason to believe
that they are practical and instructive.
But there is another purpose which this little book is
designed to serve. The best teachers of natural science
are unanimously of the opinion that the very best results
can be secured only by allowing the student to make
experiments for himself. In the study of science in highschools and academies, good text-books are very desirable;
a full course of illustrative experiments by the teacher is
indispensable; but if, added to these, there can be a course
of simple experiments by the pupils themselves, the value
of both will be enhanced.
Now the experiments described in the following pages
are such as intelligent boys and girls can make with little
or no assistance. All that the teacher need to give them
is encouragement, and it is believed that he would find




Vi                   PREFACE.
his own work more productive if, in addition to the textbook and his lectures, this course of simple experiments
could be put into the hands of every pupil in his class.
Students can not too early begin to acquire the habit and
the power of verifying the statements in the science which
they study. This they can do in an elementary course of
study by experiments of the simplest character made with
apparatus the most inexpensive.




APPARATUS.
THE following list comprises the most important pieces
of apparatus needed for the performance of the experiments described in this book. The articles named in the
second column may be obtained very cheaply of apparatus
dealers: those in the first can be found at home in any
district. A great many other things will be used, but
they are too common to need even to be na:tled here.
Fruit-cans.         Glass tubing — lb. ass'd sizes.
Ale-glasses.        Rubber tubing-2 ft.
Bottles.            Alcohol lamp.
Corks.              Flask-glass, 1 pt.
Plates.             Test tubes- - doz. 6 inch.
File.               Convex lens.
Funnel.             Violin string.
Tuning-fork.        Glass tube-for frictional elec.
Shot.               Sealing-wax.
Besides this apparatus some chemicals are -necessary.
All these, except some which are too common to need
mentioning, are comprised in the following list. They
may also be obtained of the apparatus dealers at very
trifling expense.
Alcohol.               Sulphuric acid.
Cochineal.             Hydrochloric acid.
Litmus.                Nitric acid.
Sulphur.               Ammonia.
Copper clippings.








EiASY  EXPERIMENTS
IN
NATURAL PHILOSOPHY.
"Always bear in mind that the simplest experiments, or those most
easily imitated by the pupils, are the best."-Nature.








INTRODUCTION.
Divisibility. Ex. i.-Take a glass jar, holding half a
gallon,-a fruit-can answers the purpose well,-and fill it
with water. Next take a little powdered cochineal, as
much as will lie upon the end of a penknife-blade, which
will not be more than half a grain by weight, and dissolve
it in a thimbleful of water. Finally pour the coclineal
into the clear water in the jar. Notice the cloud-like
masses of colored water slowly making their way downward. After a little time stir the water briskly, and then
see that every part of it is distinctly colored.
Now it is said that there are as many as 30,000 drops
of water in a half-gallon, and that it must take as many
as 100 little particles of the cochineal to color a single
drop distinctly.
In this experiment, then, a single half-grain weight of
cochineal has been divided into not less than 3,000,000
pieces.
Ex. 2.-Place a goblet on the table and fill it about
one half full of water. Take a piece of loaf-sugar as large
as a walnut, and by blows break it into small pieces.
Put these pieces into tile water and stir them about vigorously. After a little time notice that the sugar has
entirely disappeared.
In this case the body has been divided into pieces so
small that, being colorless, they can not be seen at all.




12                INTRODUCTION.
Ex. 3.-Take a small piece of marble, and by pounding
it reduce it to the finest powder: the separate grains are
almost invisible, and yet each one of them is a piece of
the original block.
We learn from these experiments that some bodies can
be separated into many parts. And when we think of
others which we have not just now tried, we remember
that they too can be broken or cut into pieces. Now this
quality of matter, by virtue of which bodies may be separated into pieces, is called divisibility.
REMARKS.-Teachers will notice that the descriptions
of the foregoing experiments are minute and clear enough
to forbid any failure in the performance of them. But
these descriptions only show the work which teachers
must do: they do not give the language which they must
use. While making an experiment the teacher ought, by
skillful questions and appropriate remarks, to keep the
attention of the children upon it, so that every part of the
apparatus shall be observed and every action definitely
seen. Above all tilings ought care to be taken that the
final inference is seen to be the natural consequence of the
facts observed in the experiments. The tendency will
doubtless be for the teacher to do all the talking, while
the pupils rest contented with simply repeating what they
hear. This should be avoided.
The pupils should themselves be made to describe the
apparatus while they look at it; to announce the results
as they occur; and to interpret them as fully as possible
and with as little assistance as may be practicable.
No two intelligent teachers will ever work by exactly
the same method, but yet the principle just stated ought
to be the foundation of every plan and determine the




INTRODUCTION.                1 3
detail of every attempt to teach science, in its most elementary form, for which these experiments are designed.
The following conversation occurred between a teacler
and his class in regard to the experiments just described.
It will serve to illustrate the method of making the pupil
use his senses to acquire knowledge.
TEACHER.-I hlave here three substances about which
we want to learn something to-day. One of them-this
which you see (holding it up ill view of the class)-is
cochineal; another (showing it) is a lump of loaf-sugar;
and the third (showing it also) is a piece of marble. I
want to show you some things that can be done with
these, and I would like to have you to tell me exactly
what you see and learn.
1st Experiment.-Now notice (teacher takes a halfgallon jar and fills it with water): what have we here?
PUPILS. —-A jar of water.
TEACrHER.-I must tell you now that the jar holds one
half a gallon; and now think a moment, whether you
have not often seen water that looked very unlike this.
Tell me, then, what you see before you.
A FEW PUPILs.-A half-gallon of clear water in a jar.
TEACHER.-Yes; you all can see that the water is not
muddy nor colored; it is clear, and you know I told you
that the jar holds half a gallon.
Now here (dipping up a little cochineal upon his knifeblade) is the cochineal. It was not always as you see it
now. It was found in the shape of little balls about as
large as large shot, each covered with a grayish coating;
but now what do vou say of it?
PUPILs.-A reddish powder.
TEACHER.-The little balls have been broken into pieces




14                INTRODUCTION.
-indeed, crushed into this fine powder. But see what I
will do with it. Just the little on my knife-there is not
more than the weight of half a grain-remember this,
I will use in this way (putting a little water into a
goblet and the powder into it, and thoroughly stirring
them together). Now, John, come and look at this, and
tell your mates whether you can see the powder
JOHN.-There is a little at the bottom.
TEACHER.-Just a little; but where is all the rest?
JOHN.-It looks like red water.
TEACHER.-Yes; you do not see the powder in the
water, but the water looks red because the little particles
of powder are broken up into such very little pieces that
John could not see them, and these little pieces are scattered throughout every part of the water.
But now look again (pouring the "red water" into the
jar): who will tell me what is going on now?
SEVERAL PUPILS.-The coclineal is going to the bottom!
OTHERS.-It is mixing with the water!
TEACHER.-When we have watched these very pretty
cloud-like streams of colored water long enough, I will
stir the water thoroughly in the jar (doing so after a
pause). Now tell me if you see any change made in the
water.
PUPILS.-It is red now, all through!
TEACHER. —But you know there was a whole halgallon of water and only half a grain of cochineal!
Now let us see,-how many drops of water do you suppose there are in the jar? Of course you do not know,
and I will tell you that it is said that there are not less
than 30,000. It is thought, too, that it would need as
many, at least, as 100 little pieces of cochineal to color a




INTRODUCTION.                15
single drop, perfectly in every part of it. And yet the
half-grain has colored the half-gallon!
Now who will answer quickly,-If it take 100 pieces
of cochineal to color one drop of water, how many pieces
will it take to color 30,000 drops?
PUPILs. —One hundred times 30,000 are —(after hesitation a few answer correctly) 3,000,000.
TEACHER.-That is right.  Now look again at this
water: it is crimson-colored,-every drop of it. Into
how many pieces does this experiment show the halfgrain of cochineal to be divided?
MANY PUPILS.-Into 3,000,000 pieces!
TEACHER.-Surely it was a very little thing to be broken
up into such a multitude of pieces! But now for the
2d Experimenit.-Let us use this little lump of sugar.
What have we here? (Placing a goblet on the table and
half filling it with water).
PUPILS.-A goblet of water.
TEACHER.-Now watch the sugar (dropping it into the
water and stirring it about a little time). Well, what has
happened?
PUPILS.-It has fallen to pieces.
TEACHER.-I will continue stirring these pieces about in
the water (doing so until the sugar is dissolved); and now
can you see them? Come and look. (To those who came)
Well, where is the sugar?
PUPILS.-It is in the water.
TEACHER.-But can you see it?
PUPILS.-No.
TEACHER.-How then do you know that it is in the
water?
PUPILS.-We saw you put it in there.
TEACHER.-Very good: you saw it put there, and it has




16                INTRODUCTION.
not been taken out again. But you did see it in the water
at first: why can you not see it now?
PUPILS.-Because it is broken up and all scattered
through the water.
TEACHER.-That is it exactly! And now you can tell
me what this experiment shows us about sugar, can you
not?
PUPILS.-That sugar can be broken up into very little
pieces.
TEACHER.-Yes; or you might say,-it shows us that
sugar can be divided into pieces which are so small that
they can not be seen.
Now let us see about the marble.
3d Experiment. -George, now I place the marble upon
this brick which I have brought here oh purpose; won't
you come and strike it with this hammer? (He does so.)
There, what have you done to the marble?
GEORGE.-I have broken it.
TEACE1R.- - NOW  take one of the pieces and strike it.
(He does so.) There, what have you done to the piece?
GEORGE.-Crumbled it all to powder.
TEACHER.-But not to very fine powder; but now suppose you strike these little pieces, will they be broken
again? Try it, George. (He does so.) Well?
GEORGE.-The powder is fine now.
TEACHER.-Then you must have broken the little pieces
up into still smaller ones. We can hardly see them separately. And now, scholars, tell me: what all this shows
about marble.
PUPILS.-That marble may be divided into little pieces.
TEACHER.-Very good.    We have now tried three
things,-coclineal, sugar, and marble. We have found
that each may be divided into very little parts. They




INTRODUCTION.                 17
are alike in this respect, even though so very different in
most others. This quality of these bodies, which allows
them to be broken or separated into parts, is called
divisibility. Can you think of other substances which
can be divided? (Several things are quickly mentioned )
All these things have the same quality as you lhave seen
the cochineal, the sutar, and the marble, to possess. What
is that quality called?
PUPILS.-Divisibility.
TEACHKR. -What, then, does this word,-divisibility,mean? I will write its meaning on the blackboard for
you.
Divisibility is that quality of bodies which allows
them to be cut or broken into parts."
Perhaps no other teacher would do just exactly as this
one did, in conducting this exercise, but in some respects
his example is worthy of careful imitation.
1st. He evidently had a definite plan marked out
beforehand. No teacher should attempt a single experiment until he has tried it, studied it, and formed his plan
for using it.
2d. His object seemed to be to make tile pupils see
clearly what occurred, and to infer correctly from what
they saw. Let every teacher lay every plan and work out
every detail with direct reference to these two results.
3d. Hence he called upon /,is p''pils to tell him what
things were being used and what effects produced, instead
of describing them himself. So should every teacher do,
telling the pupils only those things which the apparatus
does not clearly show.
It will be found to be an excellent plan, especially after




18                INTRODUCTION.
pupils have had some experience in these exercises, to
first, put before them all the apparatus for an experiment
ready for use and ask some one pupil to describe it fully,
then to make the experiment deliberately and silently,
(f'terward calling upon a second pupil to tell you what
you did, and upon a third to tell you what changes or
effects he saw produced, and upon a fourth to tell you
what he thinks the experiment teaches. Repeat the experiment, if need be, to bring out any essential point
which the pupils did not at first discover.
It will also be well to encourage the pupils to make experiments for themselves. Call upon individuals to help
you at times. Especially if; during an exercise, one is seen
to be inattentive, nothing can be better than to ask him
to help you in the experiment being made. Let him do
some part of it which you know he can do well, and take
care that he do not fail. His success will do more than
any thing else can to secure his attention in the future.
The following experiments furnish abundant material
for such exercises as have just been indicated. If used at
all in common-schools, they can not fail to awaken lively
interest among the scholars, and will always leave their
minds in better condition to pursue their regular studies
to better advantage. If used skillfully by the methods
just pointed out, their own educational value will not be
surpassed by that of any other branch of study.




THE PROPERTIES OF MATTER.
Impenetrability. Experiment 4.-A glass jar may
be partly filled with water (Fig. 1). Let a block of wood
_-~     of convenient size and shape be then pushed
down into the water. Nlotice that as the
wood enters, the liquid rises in the jar, and
that it falls again when the wood is taken
out. We see that these two bodies, wood and
water, can not be put into the same place at
the same time.
Ex. 5.-Let an inverted goblet be held
Fig. 1.  with its mouth on the surface of the water
in the jar. Notice that the goblet is full of air. Next,
push the goblet down into the water. Notice, that the
goblet is still full of air, the water not rising into
it. We see, here, that water and air can not be
put into the same place at the same time.
Ex. 6.-Hold the inverted goblet in the water
as before, its mouth being an inch or more under
the surface.  Having a large cork, fixed upon
the end of a bent wire (Fig. 2) for a handle, push
it down under the edge of the goblet and then
up into the air within. Notice that as the cork Fig.2.
goes up into the air some air-bubbles escape through
the water. We seo that air and cork can not be put into
the same place at the same time.




20               PHYSICAL SCIENCE.
What is seen in these experiments is true of all bodies;
no two can be put into the same place at the same time.
This property of matter, by which no two bodies can
occupy the same space at once, is called impenetrability.
Indestructibility. Ex.'.-into a small tin cup put
a little fine sugar and carefully weigh them. (See Ex. 32,
Fig. 7.) Add water enough, afterward, to dissolve the
sugar. Notice that the sugar has all disappeared. Next
place the cup over a stove or a lamp-flame, and continue
the heat until the water is driven away and the cup and
its contents are thoroughly dry, taking care that nothing
is lost by boiling or flying over. Notice that the sugar is
to be seen in the cup again. Finally weigh the cup and
its sugar; the weight should be the same as before the
sugar was dissolved. We see that sugar may disappear
without being destroyed.
Whenever any substance disappears from any cause, its
form is changed, but the substance is never destroyed.
This property of matter, by virtue of which it can not be
destroyed, is called indestructibility.
Elasticity. Ex. 8.-Take a piece of steel wire and
hold one end firmly in one hand. With the other hand
take hold of the other end and pull it over to one side.
Notice that the wire yields to the force of the hand.
Next, let go the end which has been pulled away, and
notice that it springs back to its former place. We see
that this wire will yield to a force and spring back again
when the force is taken away.
Ex. 9. —Having a glass hall-an " agate" used by
boys in playing "marbles "-drop it upon a stone or other
hard surface. Notice that it bounds upward to consider



PROPERTIES OF MATTER.            21
able height. Now the ball bounds because it is, for the
moment, flattened a little just where it strikes the stone,
but at the next instant it springs back to its former shape,
and this,sprliningg back throws the ball upward. This
being so, we see that even glass will yield to a force and
afterward spring back.
This property of bodies, shown bv the wire and the
glass, by wlich tley spring back to their former position
or shape after having yielded to some force, is called
elasticity. All bodies are more or less elastic.
Ductility. Ex. 10.-Hold the middle of a small glass
tube in the flame of an alcohol lamp until about an inch
of its length is made red-hot. It will be necessary to roll
the tube over in the flame constantly to heat it on all sides
alike. When heated to redness, take it from the flame,
and at tue same time pull with both hands lengthwise of
the tube. Notice that the glass is drawn out into a long
and thread-like wire.
Many substances, like glass, may be drawn out into
wire. Metallic wires are very common. The property
of matter by which a body can be drawn into wire is
called ductility.
Ex. 11.-Taking hold of. the ends of the glass still
attached to the wire, use them as handles, and on moving
them about, notice how flexible fine threads of glass are.
Ex. 12.-Break one handle off, leaving tile fine wire
still attached to the other. Put the fine end down deep
into a vessel of water and the other end in the mouth.
Blow strongly, and notice the bubbles of air coming in a
steady stream up through the water, showing that the fine
thread is still a glass tube. It can not be drawn so fine as
not to be a tube.




22               PHYSICAL SCIENCE.
Combustibility. Ex. 13.-Take as much potassic
chlorate as may lie upon a penny and mix it with an
equal quantity of sugar. Put this mixture upon a piece
of card-board resting on the top of a goblet. Add next
two or three drops of strong sulphuric acid, and quickly
take the hand away from over the mixture. Notice
that a violent and surprising combustion immediately
follows.
Wood, coal, oil, and many other bodies burn freely.
This property of matter, by which it is able to burn, is
called comnbustibility.
Explosibility. Ex. 14.-Let as much potassic chlorate as may lie on the point of a penknife-blade be put
into a mortar with the same quantity of sulphur. Larger
quantities can not be safely handled. Next rub the mixture with the pestle. Notice a sharp report or perhaps
several reports in succession if the rubbing be continued.
Gunpowder will explode when touched with a burning
match, and some other substances have the same property.
This property of substances, by which they may be made
to explode, is called explosibility.




ATTRACTION.
Gravitation. Ex. 15. —Let a ball be dropped from
the hand. Its falling toward the earth is an example of
what is seen perhaps every day of our lives. All bodies
fall toward the earth.
But not only is this true; the astronomer finds also that
all the heavenly bodies are pulling each other toward
themselves. Indeed, all bodies tend to approach each
other. The attraction which pulls them toward each
other is called gravitation.
Cohesion. Ex. 16.-Take a half-sheet of letter-paper
and gum each end to a smooth bar of wood longer than
the width of the paper, so that each end will project beyond the edge. (Fig. 3.) Let the bars
be exactly parallel. Now with the pro-'
jecting bars as handles, two persons
may try to pull the paper apart. An
astonishingy force will be needed to do it
when the pull is steady and square.
Notice that the parts of the paper are
held together very firmly. We see that  pig. 3.
there is an attraction among its parts.
Ex. 17.-An apple being cut into two halves, let their
fresh surfaces be pressed together again, and notice how
hard it is to pull them apart again afterward. We see
that there is attraction between them.




24               PHYSICAL SCIENCE.
Ex. 18.-Let two oullets be flattened and then smoothed
on one side of each with a knife until they will fit each
other closely. Next press the two freshly-cut surfaces
firmly together, and afterward let them be pulled apart
again. Notice that it needs considerable force to pull
them apart.
In all these experiments we notice an attraction between
parts of one body or of two bodies of the same kind of
matter. Now the attraction which holds the parts of a
body or of different bodies of the same kind together is
called cohesion.
Adhesion. Ex. 19.-Having two test-tubes, or even
two small cups, put some oil into one and some mercury
into the other. Into the oil plunge a rod of wood and
into the mercury another. Now taking the wood from
the oil, we notice it covered with a film of that substance.
Next take the wood from the mercury, and notice not a
drop of the liquid upon it. We learn that there is an attraction between wood and oil, while none is shown between wood and mercury.
Ex. 20.-Have two cups of water: into one of them
plunge a rod of wood, into the other a piece of wax, or
even a candle. On taking them out, notice that water
clings to the wood, and wets it, but not to the wax or
candle. We learn that there is an attraction between
wood and water, but apparently none or very little between wax and water.
Ex. 21.-Draw a crayon along the surface of the blackboard, and notice its particles clinging thereto.
We learn from these experiments that there is, in some
cases, an attraction between different kinds of matter
which holds their particles together.  This attraction,




ATTRACTION.                 25
which holds particles of different kinds together, is called
adhesion. In some cases it is called capillary force.
Capillary Force. Ex. 22.-Let some water be
colored with ink, or, far better, with cochineal. Take a
small glass tube-its diameter not more than 0- of al
inch-and put one end of it into the colored liquid.
Notice the liquid springing up into the tube quickly
and remaining there much higher than it is outside.
Ex. 23.-Stand a piece of flat glass in the water, and
notice the liquid rising a little way up along its sides.
Now the attraction, shown in these experiments, by
which a liquid is lifted in small tubes or along the sides
of solid bodies, is called capillaryforce.
Ex. 24.-Wrap a common bottle in a strip of blottingpaper which is as wide as the bottle is high, and fasten its
edges with wax. Next fill the bottle with water made
black by ink. Finally, stand the bottle, thus prepared,
on a common dinler-plate, and pour water upon the plate
to come in contact with the lower edge of the paper on
the bottle. Notice that the water will be soon seen slowly
rising up the paper, and in a little time it will have
climbed to the top of the bottle.
Remember, also, that oil rises in a lamp-wick in the
same way; that water will wet a piece of cloth throughout in a little time, if only one corner touches the liquid;
that ink spreads on blotting-paper, and other similar and
familiar facts. In all these cases, as in the experiment,
capillary force is causing a liquid to penetrate porous
solids.
Ex. 25.-Having two strips of glass-three inches
long by an inch in width is a convenient size-put a narrow piece of card-board between their ends, and then
2




26                PHYSICAL SCIENCE.
cement them together with a little sealing-wax. The two
plates are then parallel and very near togetller-separated
only by the thickness of the card-board. Take the sealed
end in the hand and bring the other end of the plates
down into some colored water. Notice the fluid instantly
leaping up to some height, where it remains between the
plates.
Ex. 26.-Cement two other similar plates of glass so
that they shall not be parallel-one edge of the pair
being in contact, the other edges being separated perhaps
an eighth of an inch. Put the lower end of this pair of
plates into the colored water; it will spring up quickly
as before.  But notice that its surface is in the form
of a beautiful curve (Fig. 4), and farther, that the liquid
is lifted'highest where the plates are nearest
together.
Ex. 27.-Select two small glass tubes,
one of which shall have a diameter twice
as great as the other. Put one end of each
into the colored water and it will rise in
both. Notice that the fluid rises highest
in the smallest tube-just twice as high
if one tube is exactly one-half diameter
Fig. 4.  of the other. (See Cooley'8 Philosophy.)




WATER.
Mobility. Ex. 28.-Fill three goblets, one with small
marbles or large peas, another with fine shot, and a third
with water. Invert a dinner-plate as a cover over each.
By holding the plate tightly pressed upon the mouth of
the goblet with one hand, while the goblet itself is grasped
by the other, both may be turned over together without
spilling the contents of the glass. Do this with each in
turn, and the three goblets will be left standing, full,
but bottom upward, on the plates. Next carefully lift the
goblet containing the marbles, and notice how they spread
out upon the plate, and see that they do so because they
are such smooth balls, without force to hold them together.
Then lift the goblet containing shot, and notice that they
roll out upon the plate in the same way and for the same
reason.  Finally lift the goblet containing water, and
notice it, also, spread itself out upon the plate just as the
others did. We may give the same reason: water consists
of little, VERY little smooth balls, without force enough
among them to hold them together.
Because water consists of such very small and smooth
bodies, it is able to move about so freely as it does. They
roll over and around each other with the greatest ease.
This freedom of motion among its molecules is called
mobility. (See Cooley's Phil., p. 38.)
Pressure. Ex. 29.-Having a lamp-chimney, whose
lower end is smooth and even, cut a circle of tin large




28                PHYSICAL SCIENCE.
enough to cover it. Make a small hole in the center of
the disk and pass a string through it, letting a knot in the
lower end prevent the string from coming out.
Now run the string through the lamp-chimney,
and by means of it hold the tin up tightly
against the end of the glass until it is pushed
down to the middle of a jar of water. Then
let go the string (Fig. 5), and notice that the
tin-a heavy metal-does not sink. Notice
also that there is nothing but water to hold it
up. The experiment teaches that water exerts
an upward pressure.
Ex. 30.-Take a glass tube, bent in two
places at right-angles,* and hold the finger
tightly over one end, or close it with a cork. Let some
water, colored with ink or cochineal, be poured into the
other end; it will fill that arm of the tube and a part of
the horizontal portion. (Fig. 6.)
Now let the air slowly pass from
under the finger or the cork at
the closed end, and notice the
water moving downward in one
arm, sideways through the horizontal part, and upward in the
other arm of the tube. By this 
motion of the water we learn that it is exerting pressure
downward, sidewise, and upward, at the same time.
Ex. 31.-Place a small block of wood upon the surface
* A glass tube held in the flame of an alcohol lamp until it begins to
soften may be easily bent into any required shape. Roll it in the flame to
heat all sides alike, and when it begins to yield, press it gently into the
desired shape.




WATER.                    29
of water in a jar, and by means of a rod of wood or iron
try to push it down to the bottom. Notice its struggles
to stay at the top, and also that there is nothing but
water to push it up.
Ex. 32,-To the middle point of a bar of wood let a
cord be tied so that the bar
will balance when the string
is held in the hand. This
bar is a very good scale-beam.
From one end hang a stone  I
about the size of a hen's egg, 
and from the other end hang
a small cup, into which put 
just sand enough to make it
balance the stone. (Fig. 7.) 
Now let the stone be made          Fig. 7.
to hang down into a vessel of water. Notice that it is no
longer balanced by the cup of sand: it is lighter in the
water than out of it. See that it must be the water that
helps to hold it up.
From these two experiments we learn that water presses
upward against bodies immersed in it.
Ex. 33. —Fill a pitcher brimful of water.  Place a
dish under the lip to catch the water soon to run over,
and smear the under side of the edge of the lip with tallow to prevent water from running down the side of the
pitcher. Lay the block of wood (Ex. 31) carefully upon
the surface, and notice that water runs over the lip. Afterward notice that the upward pressure of water just sustains the wood, and hence must just equal the weight of
the block. Hang a cup from each end of the scale-beam;
make them just balance. Now dry the wood and put it
into one cup; take the water that was pushed over the




30               PHYSICAL SCIENCE.
lip of the pitcher by it and put it into the other cup.
Let all, this work be very carefully done. Then notice
that the wood and water just balance. We thus learn
that the water displaced by a body which floats, weighs
just as lmuch as the body itself.
Ex. 34.-Empty the water from the cnp and make the
two cups balance each other again. Then tie the stone
(Ex. 32) to one end of the'"scale-beam" by a string
long enough to let it hang down below the cup, and
put sand into the other cup to balance it. Next let the
stone hang into the pitcherfiZll of water and catch the
liquid displaced. Notice that the stone is lighter now
than before. How much lighlter? Another experiment
will tell.
Ex. 35.-Put the water that was displaced by the stone
into the cup above it, and not'ice that the balance is restored, and learn that the weight which this heavy body
loses in water is just equal to the weight of water it displaces.




AIR.
Compressibility. Ex. 36.-Take a glass tube several inches long and pass one end of it tightly through
a cork which has been selected to fit the neck of a
vial. Push the cork end of this tube into some colored
water and close the other end with the finger. Keeping
the end closed, lift the cork from the water, and press
it tightly into the neck of the vial, at the same time
taking the finger from the end of the tube. Notice now
that the colored water stands some distance up the tube
-the space below being filled with air.
(Fig. 8.)
Next slip the end of a piece of rubber 
tubing over the end of the glass tube.
Apply the lips to the end of this and gently
press the breath into it. Notice that the
water in the tube moves toward the vial.
But there is no escape for the air, and hence 
it must be crowded into smaller space than
it occupied before. We thus learn that air
is compressible.                          Fig. 8.
Expansibility. Ex. 37.-Now apply the lips to the
rubber tube again and draw the air out of it. Notice the
colored water moving away from the vial, and see that
the air now fills more space than before. We thus learn
that air is expansible.




32               PHYSICAL SCIENCE.
Elasticity. Ex. 38. —Using the same apparatus, let
the breath be alternately pressed gently into the tube and
then withdrawn, and notice the water alternately moving
back and forth in the tube. The air first yields to the
foree of the breath; it then springs back when the force
is withdrawn.  We see tllat it eis  te'.ic.
Pressure. Ex. 39.-Place one end of a straigllt glass
tube in colored water, and with the lips at the other end
withdraw the air. The colored water is seen rising in the
tube. It is pushed up, but znotiee that there is nothing to
push it up but the air that rests upon the surface of the
water in the vessel.
Ex. 40.-Push a glass jar (a fruit-can) down into a pail
of water until it is filled. Take hold of the bottom of the
jar and lift it until only thle edge of the mouth of it is
under the water in the pail. Notice that the jar is still
full of water. Sometlling holds the water up; there is
nothing to do it but air outside
If a shelf is fastened in one side of the pail just under
the surface of the water, as may be very' easily done, the full jar may be left mouth
ij downward on the shelf; the water will
not run out.
Ex. 41.-Fit a long-necked bottle with.   a cork through which two tubes pass.
Both tubes should reach some distance
into the bottle. One should reach some
inches outside, the other must be shorter.
To the shorter one the end of a rubber
tube must be attached. Fig. 9 slows the
full arrangement. Now let the lower end
Fig. 9.   of the longer tube be put into colored




AIR.                    33
water, the end of the rubber tube in the lips, and let
the air be drawn out of the bottle. Then notice a pretty
little fountain springing up instantly into the bottle.
There is nothing but air to push the water up.
These experiments teach us that air resting upon the
surface of water, or, indeed, of any body, exerts a downward pressure.
Ex. 42.-Take the straight glass tube used in Ex. 39
and push it nearly its whole length under water, and then
place the finger over one end to close it. Lift the tube
out of the water, open end downward, and notice that the
water does not run out of it. There is nothing but air to
keep it up in the tube.
Ex. 43.-Take a ncarrow-necked bottle, and ihaving
immersed it in a vessel of water until it is filled, almost
cover it with the finger, turn it mouth downward, and lift
it out of the water entirely. Yotice the water refusing to
run out, and that there is nothing but air to keep it in.
Ex. 44.-Take a wide(-mouthed bottle, or an ale-glass,
and proceed as follows: having filled it with water, slip
a piece of paper under its mouth and hold it against the
glass until the bottle is lifted out of the water.
The hand may then be taken away from the paper,
when the water will be seen remaining up in the 
bottle. (Fig. 10.)
In these experiments we see that the air is exert-  I 
ing upward pressure.                          r
Ex. 45.-Let the wide-mouthed bottle used in Fig. 10.
the last experiment be filled with water and covered
with the small piece of paper as before. Hold it in a
horizontal position, see that the water does not run out.
Turn it around to point in various directions horizon



34               PHYSICAL SCIENCE.
tally; the water is still kept in by the air.  Hold it
obliquely in various directions, and witness the same result. We thus see that air exerts pressure in all these
directions.
By considering all these experiments on pressure together, we are taught that airi exerts pressure in all
directions.
The Pump. Ex. 46.-Let a glass tube have one
open end in colored water. With the lips applied to
the other end, take the air out of the tube above the
water, and notice that the pressure of air pushes the
water up.
Ex. 47.-Next take a wire longer than the tube and
wind cotton upon one end until it is so large that it can
with some difficulty be drawn into the tube.
Pass the wire up throough the tube, and,
taking hold of the upper end, pull the cotton
into the other end, and then insert it in the
colored water. Next pull the cotton upward
in the tube, and see the water following it.
(Fig. 11.) Notice that the air is here taken
out of the tube above the water by lifting the
cotton.
We thus learn that water will be pushed up
in a pipe or tube whenever the air within is by
any means lifted out. Tilis is the principle of
Fig. 11. the common pump. (Cooley's Philosopihy, p. 31.)
The Siphon. Ex. 48.-Repeat Ex. 42, and notice
again that the pressure of air sustains the column of water
in the tube. (Fig. 12.) Study it further. See that the
weight of the water is pressing downwarld that the




AIR.                     35
air is pressing upward, and that the upward pressure is
strongest.
Ex. 49.-Take next a glass tube, bent in the
form of the letter U, its arms being of exactly
equal length, and immerse it in water. When 
it is completely filled, close one end with the
finger and lift the tube from the liquid. Hold
it with open end downward; the water does
not run out. Close the other end and open the
first; the water still remains.
Now put the forefinger of one hand exactly  Fig. 12
under the middle of the bend so that the tube
will balance, and then very carefully take the
finger away from the end of the tube. Both
ends are now open downward (Fig. 13), but still
the water does not run out.  Notice that the
water in both arms is pressing downward —that
the air at both ends is pressing upward. Again,
see that the downward pressures, being equal,
overcome equal portions of the air pressFig. 18. ures, and thus leave equal upward ress- I
ures to keep the water from running out.
Ex. 50.-Take next a bent tube, one arm
being longer than the other. Use it exactly as
the tube was used in the last experiment. The
water will not remain in the tube balanced upon
the finger; notice it running out of the longer
arm only! (Fig. 14.)
In this case there is greater pressure of water
downward in the long arm than in the other;
it overcomes more of the air-pressure. This
leaves more of the air-pressure upward against  Fig. 14.
the water in the short arm. This stronger pressure of




36               PHYSICAL SCIENCE.
the air upward against the water in the short arm pushes
the water up through it, over the bend and out of the
longer arm. Such a bent tube, one
arm longer than the other, is called a
siphon. It is used to transfer liquids
from  one vessel into another; let
\  another experiment show how it is
used, thus:
Ex. 51.-Place an empty jar (fruitcan) or other vessel, beside another
Fig. 15.    containing water.  Fill the siphon
with water by immersing it, and close the longer arm by
holding the finger over its end, while the end of the
shorter arm is being put into the vessel of water. Let
the longer arm hang over into the empty vessel, and
open its end. (Fig. 15.) The water will continue to run
until it stands at the same height in both vessels. (See
PAilosophy, p. 73.)
The Effect of Heat. Ex. 52.-Take a bottle containing some colored water, and fit to it a cork
having a hole in its center. Take the little vial
and glass tube used in Ex. 36, and pass the tube
through the hole in the cork of the bottle down
into the colored water below. (Fig. 16.) Now
apply the heat of a lamp-flame yently to the vial,
or pour warm water over it, and notice bubbles
of air coming out of the tube and up through
the water. The vial and tube can no longer hold
all the air they did.
Ex. 53.-Press a goblet bottom upward down
into a vessel of water. See that the goblet is full Fig. 16.
of air. Pour warm water over the goblet, and notice




AIR.                    37
bubbles of air coming out through the water, showing that
the air is made larger by the warmth. These experiments
teach that the effect of heat upon air is to expand it.
Ex. 54.-If the bottle and vial, used in Ex. 52, have
now been standing some time since the heat was applied,
the air in the vial must have grown cool again. Look at
the apparatus, and see the colored water standing far in
the tube above the fluid in the bottle. Notice that the air
has been cooling and growing smaller at the same time.
Ex. 55. —Pour now upon the vial some cold water; see
the water mounting still higher, showing again that as the
air is cooled it gets smaller.
We are thus taught that air contracts when heat is
withdrawn from it.
Ex. 56.-Place a piece of candle about an inch long —
perhaps less-upon a flat block of wood. Light it, and
notice the flame burning steadily. Now put
a lamp-chimney over the flame, leaving one
edge of it projecting over the edge of the block
(Fig. 17), and notice that the flame is no longer
steady. Its flickering shows that air is coming
under the edge of the chimney against it.
Ex. 57.-Now let some bits of light cot- 
ton or feather, hanging at the end of fine
thread, be held over the top of the chimney;  Fig. 17.
they will be blown away, showing that air is coming out
of the top of the chimney.
We thus learn that heated air is pushed upward by the
colder air beside it which flows in at the bottom to take
its place.
Upon this principle the production of winds may be
explained. (Natural Philosophy, p. 141.)




'VIBRATION.
The Pendulum. Ex. 58.-Let a ball —it may be a
bullet, a ball of wood, or even an apple-be fastened to
the end of a cord, the other end of which is to be attached
to some fixed support above. This fixed support is easily
arranged by nailing a bar of wood to the window-frame,
so that it will project out some distance from the wall
into the room. A string may be bound around the bar,
and the cord of the ball may be tied into this ring. By
this means the ball is able to swing freely beneath its
support.
A body hung so as to be able to swing freely under its
support, is a pendulum.
Ex. 59.-Lift the ball several inches away to one side
and let it go. Notice it swinging back and forth over
the same path. Such a motion is called vibration.
Ex. 60.-Lift the ball again to several inches; let it
go, and catch it with the other hand just as it reaches the
point where it would turn to go back; it has swung once
over its path. This one motion over its path is called a
vibration.
Ex. 61.-Take two balls of equal length, one of lead,
another of wood, or, such not being convenient, an apple
and a potato may be used instead, only let them be as
nearly of equal size as possible. Hang them from the




VIBRATION.                  39
same bar, side by side, with cords of the same length.
Take one in each hand; pull them to the same distance,
and let them both start at the same moment. Notice
that they go over their paths and get back to the hands at
the same time, showing that:
Pendulums of different materials, other things being
equal, vibrate in the same time.
Ex. 62,-Take two balls of the same material, two
apples, for instance, of different sizes, with cords of equal
lengths. Release them at the same moment; notice that
they get back to the hand again at the same time, showing that:
Pendulums of different sizes, other things being equai,
vibrate in equal times.
Ex. 63.-Take two balls of the same material and of
the same size, but hang them on cords of different lengths.
Release them both at once, and notice the short one vibrating faster than the other.
Ex. 64.-Change the lengths of the cords, but still
have one shorter than the other, and after every change
notice that the shortest pendulum vibrates most rapidly.
We thus learn that the time of vibration depends upon
the length of the pendulum.
Ex. 65.-Take now two pendulums, one being just
four times the length of the other.*  Count the number
of vibrations each one makes in one minute by the watch.or clock. Divide 60 by these numbers, to learn how long
each one takes to make one vibration. Then notice that
* Measure from the point of support to a point a very trifle below the
middle of the ball.




40               PHYSICAL SCIENCE.
the time for the longer pendulum is just two times as
great as for the shorter.
Length = 4....... Time of a vibration = 2.
Ex. 66.-Let, next, one pendulum be nine times as
long as the other. Count and divide as before. Notice
that the longer pendulum takes three times as long to
vibrate.
Length = 9...... Time of a vibration = 3.
Now compare the lengths of pendulums and the times
of one vibration, and see that:
The time of one vibration varies as the square root of
the lengths of the pendulum.




SOUND.
Ex. 67.-Strike the prongs of a tuning-fork gently
upon the edge of a table, and then stand the other end
upon the table-top. The sound will be distinctly heard.
Repeat the operation, and while the sound is heard, bring
the edge of a knife-blade carefully alongside of one of
the prongs, and notice what a rattle it causes. The prong
is found to be in motion, bounding back and forth against
the blade.
Ex. 68.-Let a bell be struck, and while the sound is
heard, touch the bell gently with the finger, andfeel the
tremulous motion while its sound is heard.
Ex. 69.-If the bell is large, or, better still, if you have
a glass bell-jar, make a little pendulum of cork, and hang
it so that it touches the lower rim of the bell. When the
bell is struck, notice that you not only hear the sound but
at the same time see the tremulous motion of the ball
caused by the riotion of the bell.
Ex. 70.-Take a piece of violin-cord, or of piano-wire,
somewhat longer than your table. Fasten one end to a
nail in one end of the table, and let the other end of the
cord pass over a pulley, or even a projecting piece of board,
fastened to the other end of the table, and to this end of
the cord hang a heavy weight-a pail or box filled with
sand or stones. Let two bridges, like the bridge of a
violin, be placed under the cord near the ends of the
table. The arrangement is now complete.




42               PHYSICAL SCIENCE.
Pull the middle of the cord to one side and let it go
again. Notice the sound that is heard, and the motion
that is at the same time seen.
In all these experiments we find that the sounds of
bodies are accompanied by tremulous motions or vibrations, which leads us to infer that:
Sounds are produced by vibrations.
Ex. 71.-Move one of the bridges toward the other;
this shortens the vibrating part of the cord. Make it
sound again, and notice that while the cord is shorter, the
sound it makes is higher. Shorten it more yet; the sound
is still higher.
Ex. 72.-Move the bridge gradually back to its first
position, thus lengthening the vibrating part of the cord.
Make it sound after every change in length, and notice
that while the cord is lengthening the sound is gradually
getting lower.
We thus learn that the height or pitch of sound produced by a cord or wire depends upon its length-the
highest sound being caused by the shortest cord.
Ex. 73.-Let the bridges remain stationary, and put
more and more weight into the box at the end of the cord,
to stretch it tighter. Notice the sound after every addition. It will be found to get higher and higher.
Ex. 74.-Next take off the weight gradually, so that
the cord will be stretched less and less, and notice the
sound after each loss of weight; it will be found to be
lower and lower.
From these experiments we infer that:
The pitch of the sound of a cord or wire depends upon
the weight or force which stretches it,-the higher sound
being produced when the cord is most tightly stretched.




SOUND.                    43
Ex. 75.-Take two cords of different sizes so that they
may be of different weights, and stretch them over the
table side by side. Place the bridges under both cords,
so that their vibrating parts shall be of equal lengths, and
finally hang equal weights at their ends. The lighter
cord will invariably give the higher sound. From this
we infer that:
The pitch of sounds produced by different cords depends
upon their weights. Other things being equal, the lightest
cord gives the highest sound.




LIGHT.
FoR experiments with light it is very desirable to darken
the class-room and admit a small beam of sunlight with
which to work. Choose a window into which the sunlight enters most directly at the time the experiments are
to be made, and prepare it as follows:
Let some boards be cut of the right length, and let
them be of such number and length that when fastened
together by cleets they will form a shutter fitting the inside of the window and darkening it completely. At a
convenient distance from the bottom of this shutter a hole
two or three inches in diameter should be made, through
which sunlight may come. For some experiments the
direction of the beam of light passing through the room
is a matter of importance. An addition easily made to
the shutter will help the operator to control the direction and change it at will. Let a shelf be fastened to the
outside of the shutter, just under the hole. Upon this shelf
a piece of looking-glass may be placed. Now, by propping
up the outer end of this glass, and perhaps one side of it
also at the same time, it may be given just the right position to receive the sun's rays and throw them through the
hole into the room. Any change of position of the glass
will change the direction of the light. That the glass
may be easily changed at pleasure, have a second hole in
the shutter large enough to allow the hand to pass out for




LIGHT.                   45
the purpose: this hole may be covered with black cloth
when not in use.
It will not be difficult to darken the other windows in
the room by closing shutters, or drawing curtains, or
perhaps by hanging shawls over them.
With this cheap and easily-constructed arrangement
many very beautiful experiments may be made with the
greatest ease. A looking-glass, a small concave mirror, a
convex mirror, one convex lens and another concave, and
a glassprism, are the most important pieces of apparatus.
They can be obtained from apparatus dealers at small
cost.
A little time, a little money, and a little ingenuity
spent in putting up and using this apparatus, will be
abundantly repaid in beautiful results.
Choose a day when the sun shines brightly, and while
making experiments keep the lower sash of the window
raised above the hole.
Ex. 76.-Through the hole in the shutter admit the
sunbeanm: sprinkle dust in the path by striking two dustbrushes together in front of its entrance. Notice the path.
of the sunbeam shown by the very beautiful bar of illumined dust: it is perfectly straight.
Ex. 77.-Change the inclination of the looking-glass a
little, and see the change of direction of the sunbeam in
the room. But notice that in every position the beam of
of light is straight.
We thus learn that light travels in straight lines.
Ex. 78.-Hold the convex lens in the beam of light
entering the room, and see what a curious change: Notice
that the light is brought to a point (Fig, 18) at some




46                PHYSICAL SCIENCE.
distance from  the lens, and that beyond this point it
widens out again.
A point where light is collected is called a focus.  The
cone of light going toward the
focus is called a pencil of light:
the cone going from the focus is
also a pencil. In the first case
Lp~ ^-M^^^^    the pencil consists of converging
rays; in the second the pencil
Fig. 1       consists of diverging rays.
Ex. 79.-Place a lighted lamp or candle on a table in
the darkened room. Hold a flat piece of wood, two or
three inches in width, at a convenient distance in front
of the flame and catch its shadow upon a white wall or
upon a piece of white cloth about as far from the wood
as the wood is from the flame. Notice that the shadow
is made up of two distinct parts-a dark center and a
much lighter fringe on each side.
Ex. 80.-Form shadows of other bodies in the same
way-it scarcely matters wlhat is chosen for the purpose.
The two parts of the shadow will in every case be more
or less distinct.
Now the dark center is called the umbra and the
lighter envelope is called the penumbra. Every shadow
is made up of these two parts.
Ex. 81.-Place two flames upon the table a little distance apart, and hold the fiat piece of wood in front of
them, and notice that two shadows appear upon the wall
or screen.
Ex. 82.-Then move the wood gradually toward the
screen and notice the two shadows drawing nearer to



LIGHT.                    47
gether. At length the two shadows will lie right beside
each other. Carry the wood a little farther, and the two
shadows begin to overlap each other, and we may notice.
then a single shadow made up of the two, its umbra and
penumbra very distinct.
The umbra in the last experiment is the part of the
shadow which gets no light from either of the flames; the
penumbra receives light from one or the other, and is not
so dark in consequence.
Just so the umbra in a common shadow is the part
which gets no light from any part of the flame which
casts it, while the penumbra is the part which receives
light from some part of the flame, and is not so dark on
that account.
Ex. 83.-The " dance of the witches " may be shown
by cutting fantastic figures out of heavy card-board and
hanging them by slender rubber cords from a bar of wood,
by which they can be held between the flame and the
screen. A dancing motion can be easily given to these
figures, and the motion of their shadows will present an
amusing spectacle to those sitting in front of the screen.
Two or three flames a little distance apart will multiply
the shadows and increase the amusement.
Ex. 84.-A circular disk of card-board, a triangular
piece of wood, a cubical block, a ball, and bodies of other
shapes, may be in turn held in front of a flame and their
shadows formed. Notice the shapes of the shadows: they
will change with every change in the position of the object. The disk, for example, gives a circular shadow
when its side is toward the light, but only a dark line
when turned edgewise. The ball, however, will give a
circular shadow in all positions.
The sphere is the only form which will in all positions




s8-              PHYSICAL SCIENCE.
give a circular shadow. The earth's shadow on the.-moon
in an eclipse always has a circular outline, showing that
the earth is a sphere.
Ex. 85.-Let a beam of sunlight into the darkened
room and hold a looking-glass obliquely in its path: the
light will be instantly thrown from the
glass toward the ceiling or wall of the
room.   (Fig. 19.)  If the air is well
sprinkled with dust, the bars of light
~   striking the glass and thrown from its
surface will be seen distinctly.
Ex. 86.-H-old a piece of bright tin
or of any polished metal in place of the
glass, and notice the same result.
Fig. 19.    The light which falls upon the surface
of a body is called the incident light:
that which is thrown off is called reflected light.
Ex. 87.-Place a looking-glass upon the floor with its
face uppermost, and upon a thick block of wood, or a
book on the floor, near one end of the mirror, put a
lighted candle. Standing on the other side of the glass,
move around until the image of the candle is distinctly
seen.
Ex. 88.-If the room is not darkened you may stand a
goblet partly filled with water upon the face of the
looking-glass, and then see the goblet standing upon its
image-one goblet seeming to stand erect upon another
bottom upward partly full of water.
Notice in these experiments that every part of the
image is just as far behind the looking-glass as the corresponding part of the object is in front of it, and that
the image is just as large as the object.




LIGHT.                    49
It is the light going from the object to the glass, and
being reflected from its surface to our eyes, that enables
us to see the image.
Ex. 89.-Take two looking-glasses of considerable size
and stand them upon their edges at right angles to each
other on the table, the room not being darkened. Let a
vase of flowers or any other convenient object be placed
between the two glasses. Three distinct images of the
object will be seen.
Ex. 90.-Make the opening between the glasses much
less than a right angle, and then put your face halfway
between their ends and laugh, as few ever fail to do, at
the circle of faces which is seen in the mirrors-a " surprise party,' every member of which will laugh with
you.
Ex. 91.-Take a bowl or basin in the dark room, and
at a little distance from it put a candle-flame, so that its
light may pass over the top
and strike the opposite side
just at the bottom. (a, Fig.
20.)  The whole bottom
will then be in the shade, 
and will look much darker             \ 
than the side on which the          Fig. 20.  b  a
light shines. Then pour water into the bowl until it is
nearly filled. Notice that the light now covers a part of
the bottom (a b) of the vessel.
We see that in this case the light is bent out of the
straight line on entering the water. Such a bending of
light always occurs when light passes from one substance
into another: it is called refraction.
3




50               PHYSICAL SCIENCE.
Ex. 92. —The room being light, put a penny at the
bottom of the empty bowl, so that as you look over the
edge of the vessel it is
/     just out of sight (at a,
Fig. 21).  Now   poui
water into the bowl
carefully, so as not to
[7.,'7   ~     disturb the penny. The
\ r^' \j  /           penny will very soon
b  a      Fig. 21.      come into view (at b),
no change having occurred in the position of the vessel,
penny, or eyes.
Remember that we see the penny just as we see every
thing else, by light that comes from it to our eyes. Without the water, this light, coming up over the edge of the
bowl, goes above the eye; for this reason we do not see
the penny. But when it has to come up out of water the
light is bent where it enters the air, and then, coming
over the edge of the bowl, can enter our eyes and enable
us to see the penny.
Ex. 93.-Let a convex lens-a spectacle glass can be
used with success-be placed in the opening in the
shutter of the dark room. The hole should be no larger
than the lens: it can be made smaller, if need be, by cutting a hole of the right size in a piece of card-board, and
then tacking this card over the larger hole in the shutter.
Let a screen be made of thin white muslin stretched over a
wooden frame. Place this screen near the lens, and move
it back and forth until the best effect is found. A beautiful inverted picture in miniature of all things outside
the window will be seen upon the screen. A sheet of
white paper may be used instead of the muslin screen; the
picture will then be best seen on the side toward the lens.




HEAT.
Production of Heat. Ex. 94.-Rub a metallic button upon a smooth board briskly; it soon will become
quite hot.
Ex. 95.-Let the finger of the right hand be pressed
upon the coat-sleeve of the other arm, or upon a piece of
woolen cloth fastened to the desk or table, and then
rubbed briskly back and forth. An inconvenient heat is
soon felt.
We thus learn that heat is produced by friction.
Ex. 96.-Let a nail be laid upon some hard surface, a
smooth stone, or a flat-iron, for example, and then let it be
struck several blows with a hammer in quick succession.
On feeling the nail, it will be found to be considerably
warmed. Indeed, it call, in this way, be made too hot to
be handled conveniently.
We thus learn that heat is produced by blows.
Ex. 97.-Upon some large fragments of quick-lime
lying on a plate, pour some water. After a few minutes,
notice the lime swelling and crnmbling to powder, while
large volumes of steam are escaping. Let the hand be
held in this steam only for an instant, or be laid upon the
plate when the action has ceased, and great heat will be
discovered.




52               PHYSICAL SCIENCE.
The action of the lime and water is called a chemical
action, because the nature of these bodies is changed.
Ex. 98.-Into a cup put a small quantity of cold water,
and then add about one-fourth as much oil of vitriol.
The mixture will become intensely hot. There is a chemical action between the two fluids.
From these experiments we learn that heat is produced
by chemical action. The heat of all our lamp-flames and
furnaces is produced by chemical action.
Conduction of Heat. Ex. 99. —Take an iron wire
and press a bit of wax against one side of it at a distance.... of a few inches from one end. Place
this end in the flame of a lamp. (Fig.
U D)       22.) After a few minutes the little
bit of wax, all this time clinging to
Fig. 22.  the wire, will fall off. ]Now, the beat
must have travelled from the flame gradually along the
wire until it reached the wax, and then, by melting it,
caused its fall.
Ex. 100.-Hold one end of a brass rod, a few inches
long, in the lamp-flame. After a little waiting the rod in
the fingers at the other end feels warm. In this case the
heat has evidently travelled gradually from the flame
through the rod to the fingers.
When heat travels from particle to particle gradually,
as in these experiments, it is said to be conducted. The
body in which it travels is called a conductor.
Ex. 101.-Take the stem of a tobacco-pipe and a rod
of iron as nearly of the same size as possible, and place
their ends together, lapping them about an inch, and
binding them firmly with small wire. Next fasten a ball
of wax to the under side of each of the rods, equally




HEAT.                    53
distant from the middle point of their junction. Now, if
this arrangement is held with the junction in a lamp
flame (Fig. 23), it will not be     - -.  - -
long before the ball of wax is 
melted from the iron, but it
will take a long time indeed
to melt the ball from  the         Fig. 23
pipe-stem. We learn thus that the iron conducts heat
better than the pipe-stem.
Ex. 102.-Take two wires of different metals, brass
and copper, for example, of the same size and length.
Hold one wire in each hand, the other end of the wire
being in the lamp-flame. The heat will be found to reach
tlhe fingers through one of the wires quicker than through
the other. The two metals teach us that they do not
conduct heat alike.
Ex. 103.-Let two spoons, one of German silver, the
other of silver, be put into the same cup of hot water,
with their handles projecting. Feel of the upper ends
from time to time, and notice that the silver spoon is
heated quickest.
From these experiments we learn that all bodies do not
conduct heat alike.
Convection of Heat.-Ex. 104.-Fill a glass flask
two-thirds full of water, and place it upright in a shallow
basin of sand standing on a hot stove. Very soon one
who looks closely at the water will see delicate currents
moving upward from the bottom. Drop a bit of blue
litmus into the water. It falls to the bottom and slowly
dissolves. Blue clouds appear, which, wafted upward by
the currents of water, enable us to see their motion distinctly. These upward currents are of warm water, and




54               PHYSICAL SCIENCE.
the heat is being distributed throughout the water in the
flask by their motion.
When heat travels by means of currents in the body
receiving it, the process is called convection.
Radiation of Heat.-Ex. 105.-Heat an iron ball
or a piece of stone in the stove until nearly or quite redhot. Let it be brought out into tlhe room by means of a
pair of tongs. Hold the hand at a little distance above it,
on one side of it and on another, and below it. Notice
that instcantly, no matter in what direction, the lieat of
the ball is felt. The air is a very poor conductor, but we
find heat going throug'h it in all directions more swiftly
than it can go tllrough the very best conductor.
Heat that is thrown through poor conductors in all
directions is said to be crdiated, and the process of distributing heat in this way is called radiation.
Expansion by Heat. Ex. 106.-Take a bottle having a ground stopper. When the stopper is out, warm
the neck of the bottle yentl?/ by wrapping a cloth wet
with warmn water around it, and afterward put the stopper
in-not too tightly-just so that it fits the neck nicely.
Let the neck cool again, and when cold try the stopper.
lotice that it is tightly held-perhaps it will not come
out at all, because the neck of the bottle is so small as to
grasp it too closely. Nlow wrap the neck again in the
warm clotl, and after a little try tlle stopper; notice tlat
it comes out easily. The heat seems to have made the
neck larger, so as to let the stopper out.
Ex. 107.-Let a hole be bored throulgh a piece of hard
wood, just large enonghl to allow a bullet or other metallic
ball to pass through, closely touching its sides. An iron




HEAT.                    55
rod may be used instead of a ball often more conveniently.
Heat the ball or rod, and before it gets hot enough to
burn the wood, try to pass it through the hole. If it has
been warmed enough you will notice that the hole is no
longer large enough to let the body pass.
These experiments teach us that heat expands or enlarges solid bodies.
Ex. 108.-Fill a bottle with cold water. Pass a piece
of glass tube, a few inches long, through a cork fitting the
neck of the bottle nicely, and press the cork into
the neck. If the bottle was brimfull of water, as
it ought to be, the water will stand some distance
up in the tube when the cork is inserted (Fig. 24).
Tie a string around the tube to mark the height
of the water in it. Now plunge the bottle into a
vessel of warm water. Notice the water quickly 
beginning to rise up the tube, and continuing to  |
do so while the heat is applied.
We see that the water is getting larger as it 
becomes hotter.                             Fig. 24.
Ex. 109.-Another bottle, used in the same way, with
some other liquid, as oil or alcohol, will show the same
effect; the liquid will get larger as it gets warmer.
From these experiments we learn that heat expands
ligqid bodies.
Ex. 110.-Fit the neck of a bottle with a cork, and
through this cork put the end of a glass tube several
inches long. Into another bottle put some water, which
may be colored with ink, or cochineal, or litmus. Turn
the first bottle bottom upward, and put the open end of
its tube down into the colored water of the second.




i6               PHYSICAL SCIENCE.
Notice, before going farther, that the upper bottle and'ts
tube are full of air. Next pour warm water upon the
upper bottle, and notice numerous bubbles of air escaping
through tle fluid from the lower end of the tube. Tile
air is expanded by the heat.
Ex. 111.-After a little time, the colored water will
rise some distance up the tube in the arrangement used in
the last experiment. When this is the case, notice that
the tube, above the water, and the bottle are full of air.
Now pour some warm water again over the bottle, and
see the water quickly driven down by the expanding air.
We thus learn that heat expands air, and when similar
experiments have been made with other gases, the general
truth is found that heat expands gaseous bodies.
Contraction by Cooling. Ex. 112.-The hot rod
of iron (Ex. 107) was too large to go through the hole in
the hard wood, but now that it is cold again, try it, and
notice that it goes through easily again. It ]as given
off its heat; and at the same time grown smaller.
Ex. 113.-Take the bottle and tube with water, used
in Ex. 108; mark the height of the water in the tube,
and then place the bottle in a vessel of cold water. Notice
the water falling in the tube, showing that as the water in
the bottle cools it grows smaller.
If this does not show distinctly the desired result, then
first warm the bottle of water, and afterward put it into
the vessel of cold water.
Ex. 114.-Take the apparatus used in Ex. 52, the colored water now standing some distance up in the tube,
the space in the tube above the water and in the bottle
being filled with air. Pour cold water upon the upper
bottle, and notice the colored water quickly rising higher




HEAT.                     5T
in the tube. The air is cooled by the water, and we see
that it at the same time gets smaller.
From these experiments we learn that the withdrawal
of heat f'rom bodies causes them to contract. We thus
find that the hotter a body is the larger it is, and the contrary-the colder it is, the smaller.
Curious effects in Water. Ex. 115.-Into a common bowl or basin put a considerable quantity of snow, or
ice shaved fine with a large knife, and add about half as
mTuch common salt. Stir the mixture thoroughly; it will
become nearly fluid and be intensely cold. It is called
afreezing mixture. Fill a thimble with water, or a pipebowl, with the hole in its bottom closed with wax, and
stand this little dish in the freezing mixture. The water,
after a few minutes, will be frozen.
Ex. 116.-Now take the bottle and water (Ex. 108),
the fluid standing some distance up the tube, and place it
in the freezing-mixture.
Notice first, that the fluid sinks in the tube, showing
that as the water cools it contracts.
Notice next, after a little time the fluid stops sinking,
showing that as water goes on cooling more yet the contraction stops.
Notice again, that the water begins to rise in the
tube again, showing that the cooling water is now expanding.
Notice finally, that ice begins to form in the bottle, and
that while the water is freezing, the water in the tube
continues to rise, showing that water expands while
freezing.
Ex. 117.-Take now the bottle containing ice from




08               PHYSICAL SCIENCE.
the freezing-mixture, and put it into a vessel of water
slightly warm.
Notice the water sinking in the tube while the ice is
melting, showing that heat contracts the ice while it
melts it.
Notice afterward, that the water continues to sink in
the tube for a little time, showing that heat applied to icecold water contracts it.
Notice finally, that the water in the tube begins to rise
again, showing that after water has reached a certain
degree of temperature, heat expands it. (See Natural
Philosophy, p. 240.)




ELEOTRICITY.
THE successful performance of experiments in electricity
demands a dry atmosphere and dry material: dampness in
either may cause annoyance and even complete failure.
The winter season is generally more favorable than the
summer, and an unventilated room, in which the air is
loaded with moisture from the lungs of many individuals,
is to be especially avoided. In a long, cold winter evening, wihen the family are gathered around the cheerful
sitting-room fire, electrical experiments are most likely to
succeed admirably. And in a school-room, which has
been thrown open and well-ventilated during recess, and
in which a brisk fire is rapidly heating the atmosphere
again, or, better still, in the morning before the pupils
have had time to load the air with dampness, electrical
experiments may be tried with the best assurance of
success.
The following experiments are simple enough for a
child to perform, and will furnish children not only, but
older students as well, with much amusement and instruction.
Electricity produced by Friction. Ex. 118.Take a piece of thin and tough brown paper, about an
inch wide and six inches long; heat it thoroughly by
holding it over a hot stove or the flame of a lamp, and then
holding it in one hand by the end, quickly pull it between




60               PHYSICAL SCIENCE.
the thumb and fingers of the other hand, thus rubbing it
vigorously. After two or three such rubbings bring the
paper near to the wall, and it will instantly fly into contact with it, and perhaps if you let go of it you will see
it clinging to the wall. It will thus remain sometimes'for several minutes as if pasted.
Ex. 119.-Rub the paper a second time, and, holding
it by one end in one hand, bring the other hand alongside
of it  Notice how quickly the paper flies against the
fingers, and how strongly it is inclined to stay there.
Ex. 120.-Procure a glass tube several inches in
length,-a lamp-chimney, if one can be found of convenient shape to rub easily; procure also a piece of flannel
cloth. Both should be thoroughly dry. Iolding the glass
in one hand, bring it up very near to the face; you will
be able to notice no effect. Next rub the glass vigorously
with the flannel held in the other hand, and bring it afterward near to the face as before. A sensation will now be
felt like what would be caused by drawing spiders' webs
over the face.
Ex. 121.-Rub the glass again vigorously, and afterward bring it near to the knuckle of your hand; a crackling sound will be heard, and in the dark little sparks of
light are often seen.
Ex. 122.-Place some very small and light bits of
cotton upon the table. Thoroughly rub the glass again,
and bring it near to the bits of cotton; notice how quickly
they leap up to meet it.
Ex. 123.-Let a bit of cotton or downy feather be
floating in the air; bring the glass, which has been vigorously rubbed, near to it. The cotton or the feather will
instantly dart against the glass through considerable distance.




ELECTRICITY.                 61
Ex. 124.-Any one of the preceding experiments may
be made with a stick of sealing-wax in place of the glass
tube. The same effect will be produced.
In these experiments we see that by rubbing the paper,
the glass, or the sealing-wax, a new power seems to be
developed in them. All the effects noticed are due to
electricity, and this electricity is in such cases produced
by rubbing, or, as it is called, by friction.
Attraction and Repulsion. Ex. 125.-Untwist a
silk thread, and take one of its fine fibres; tie to the end
of this a very small and light piece of cotton. Let another
person hold the cotton by taking hold the other end of the
thread, while you rub the glass tube vigorously. Then
bring the tube near to the bit of cotton. You will see
the cotton fly quickly toward the glass, sometimes through
a distance of several inches. The cotton is attracted by
the glass.
Ex. 126.-Rub the glass thoroughly again, and again
bring it near the cotton; the cotton will doubtless be
attracted as it was before. If so, let it cling to the glass
for some time; then rub the tube again and present it to
the cotton as before. If the cotton is again attracted, let
it stay in contact with the glass for a time, and then go
over the same work again. After a few,-sometimes only
one of these trials, the cotton will refuse to again come in
contact with theglass.  As often as the tube is moved
toward it, the cotton darts away. Not until it has first
touched some other body can the cotton be made to touch
the glass.
In this experiment we find the cotton driven away from
the glass tube; it is said to be repelled.
Ex. 127.-Sometimes the electricity may be made so




62              PP tSICAL SCIENCE.
strong on the glass that placing it on one side of the suspended cotton and the hand or piece of iron on the other
side of it, the little pendulum will fly quickly back and
forth between them many times, being first attracted and
then repelled by the electrified glass.
We learn from these experiments that electricity shows
its presence in two ways, viz.: by attraction and repulsion.
Ex. 128.-Let a long silk ribbon, warm and dry, be
hung over the forefinger of the left hand; the two parts
will hang down side by side together. Now put the forefinger of the other hand between the two parts of the
ribbon and press them tightly against it with the thumb
and other fingers. Pull the ribbon out quickly, rubbing
the whole length of its parts between the fingers; repeat
this operation three or four times, and then notice that
the two parts of the ribbon will no longer be willing to
touch each other. They repel each other. Put the hand
between them, and both quickly fly toward it; remove
the hand, and they as quickly fly back again.
Ex. 129.-Let one person rub the ribbon, as in the
last experiment, while another rubs the stick of sealingwax with the dry flannel. When both are well electrified, let the sealing-wax be brought between the parts of
the ribbon. They will fly still farther apart. The electrified sealing-wax repels the electrified ribbon.
Ex. 130.-Now rub a glass tube, a lamp-chimney, if
of convenient shape, and bring it between the electrified
branches of the ribbon. Both parts instantly fly toward
the glass; the electrified glass attracts the electrified
ribbon.
We see that the ribbon acts differently toward the




ELECTRICITY.                 63
electrified glass and toward the electrified sealing-wax.
It flies toward the first, andfrom the second.
Ex. 131.-Hang a little ball of cotton to the end of a
silk fibre, as in Ex. 125. Rub the glass, and then bring it
in contact with the ball until the latter flies away, being
repelled by the electrified glass. Rub the sealing-wa:with flannel, and bring it toward the ball; the ball will
quickly fly to meet it, being attracted by it.  Again, we
see that electrified glass and electrified sealing-wax act in
different ways; when the cotton is repelled by glass it is
attracted by sealing-wax.
Now whenever the electricity is like that produced by
rubbing glass it is called positive electricity, and when it
is like that produced by rubbing sealing-wax with flannel
it is called negative electricity.
The Electroscope. Ex. 132.-Rub the glass tube
or stick of sealing-wax vigorously, and observe whether
any visible change whatever is produced. None: then,
without somefarther trial, it is not possible to tell whether
electricity has been developed or not.
It may be brought near to the face or hand, and the
feeling of cobwebs, or a snapping sound, may show that
the tube or wax is electrified, or bringing it near to liglht
bodies, as cotton, on the table, electricity will show its
presence by attracting them. But neither of these ways
is always quite convenient.
Ex. 133.-Now take a slender rod of some dry wood,
several inches long; make a little ball of the dried pith
of corn-stalk or elder, of cork, or even of cotton; fasten
it to one end of a silk fibre, and tie the other end of the
fibre to the other end of the wooden rod. Next place tle
rod upon the table, so that the end carrying the ball shall




64               PHYSICAL SCIENCE.
project some inches beyond the edge, or, what is better
yet, put the wood up on a pile of books, or some other
support, above the table, so that the little ball may swing
clear.
Now notice that whenever the electrified glass tube or
sealing-wax is brought near to this little pendulum, the
electricity is at once shown by the motions of the ball,
which, if the electricity is well developed, will fly toward
the tube or wax, and, after a moment's hesitation, will
as quickly fly away again.
Ex. 134.-Or, take tinfoil, -a piece one-half inch
long and one-quarter inch wide, and hang it in place of
the ball in the preceding experiment, and it will be found
to show the presence of electricity as well as the other.
Here then notice these simple and convenient arrangements by which to show the presence of electricity. Any
such instrument is called an electroscope.
Ex. 135.-Rub the glass tube vigorously, and then
bring it in contact with the ball of the electroscope; this
ball, remaining in contact only a moment, if the tube is
well electrified, flies away again. We have seen this
action in former experiments, but what we wish to notice
now is that the ball in contact with the glass takes electricity from it, so that it is electrified in the same way as
the glass, or in other words, positively, and that when this
is the case, the two bodies separate, showing that they
repel each other.
In this experiment we see that two bodies, electrified
with positive electricity, repel each other.
Ex. 136.-Next rub the sealing-wax vigorously with
flannel, and hold it in contact with the ball of the elec* The thin metallic wrapping found on some kinds of packages at the
grocery store.




ELECTRICITY.                 65
troscope until it flies away, as it will do after one or more
trials. Now what we must notice here is that the electricity of the sealing-wax is negative, and that the little
ball must have the same kind of negative electricity also
inl it when it flies away from the wax.
In this experiment we see that both bodies, electrified
with negative electricity, repel each other.
We see from these two experiments that when bodies
are electrified in the same way, they repel each other.
Call this the 1st dLaw.
Ex. 137.-Rub the glass tube again, and electrify the
ball of the electroscope with it. Notice that the little
ball is positive, because electrified from glass. Then rub
the sealing-wax with flannel, and bring it near to the
little ball. The ball darts instantly against the wax. The
wax is negative, the ball is positive, and the two attract
each other.
Here we see that two bodies, electrified with opposite
kinds of electricity, attract each other. Call this the 2d
Law.
Ex. 138.-Repeat the experiment with the silk ribbon
(Ex. 128). Notice its two branches repelling each other.
Now, are these branches electrified with the same or with
op)posite kinds of electricity? (1st Law.)
Ex. 139.-Can we find out which kind of electricity
we have in the silk?
Rub the glass tube, and hold it in contact with the ball
of the electroscope until it flies away. We know that the
ball is positive. Bring the silk ribbon, whose branches
are repelling each other, near to the positive ball, and see
how quickly the two fly together! The positive ball is




66               PHYSICAL SCIENCE.
attracted, and hence (2d Law), the silk must be negative.
We see then that our little "electroscope" not only
helps us to detect the presence of electricity; it also
helps us to tell which kind a body is electrified with.
Let us try it.
Ex. 140.-Take a piece of thin but strong brown
paper; cut from it a strip an inch wide and sixteen or
twenty inches long; thoroughly dry and warm it, and
then use it just as the silk ribbon was used (Ex. 128).
After the branches of the paper have been drawn through
the fingers once or twice, they repel each other strongly.
Now what kind of electricity have they? Electrify the
ball of the electroscope from the sealing-wax rubbed with
flannel; the ball is then negative. Bring near the ball
the paper, and see how strongly they repel each other,
showing (1st Law) that they are in the same condition;
the paper is negative.
Ex. 141.-Electrify the ball of the electroscope from
glass: it is positive. Now rub the sealing-wax withflannel, and notice that it attracts the ball, showing the wax
to be negative.
Pass the hand over the surface of the sealing-wax to
remove the electricity from it, and then rub it vigorously
with a piece of silk. Electrify the ball of the electroscope from the glass again; it is positive.  Bring the
electrified wax near to it, and then notice that it now
repels the ball, showing the wax to be positive. It appears that the electricity of sealing-wax, when rubbed
with flannel, is positive, but, when rubbed with silk, is
negative!
Ex. 142.-See whether the electricity of glass is different when the rubber is flannel from that when the rubber




ELECTRICITY.                67
is silk. To do this electrify the little ball from the
sealing-wax, rubbed with fannel, and bring the electrified glass near to it.
Ex. 143.-Take two pieces of brown paper, each
about ten inches long by five inches wide; make them
quite hot by holding them over a heated stove or the
flame of a lamp. Place them on the table, or, still
better, on a tea-tray, one above the other, and rub them
vigorously with the palm of the hand. If now you take
hold of one corner and lift them from the table, you will
find them clinging to each other. If you try to separate
them you will see how strongly they attract each other,
and sometimes you may hear also a crackling sound on
pulling them apart.
Notice that the upper one only was rubbed but that
both are electrified. And more, since they attract each
other they are electrified in different ways.
Ex. 144.-Take two fiesh sheets of paper, such as
described in Ex. 143, and, having heated them thoroughly,
put one above the other on a pane of glass. Rub the
upper sheet vigorously with the hand. Taking hold of
one end, lift them from the glass, and notice that they
now repel each other.
If Experiments 143 and 144 are repeated, it will be
found that the papers whenever rubbed while lying upon
the tea-tray will attract, but if rubbed while lying upon
the glass they repel each other.
Now the upper one only is electrified by the rubbing;
the lower one is electrified from the upper one. When
they lie upon glass the lower one becomes electrified in
the sanme way as the upper one, and lience they repel (1st
Law), but when they lie upon the tea-tray the lower one




68               PHYSICAL SCIENCE.
becomes electrified in the opposite way, and hence they
attract (2d Law).
When one electrified body electrifies another body near
to it, and puts it into a condition opposite to its own, it is
said to act by induction. The upper strip of paper, when
they were rubbed on the tea-tray, electrified the lower
one by induction.
The full explanation of induction, or, as it is now generally called, polarization, may be left for a higher course
of study.
Ex. 145.-Having electrified the two sheets of paper,
show that they are in opposite conditions by testing them
with the electroscope.




EASY EXPERIMENT$S
IN
CH1EMISTRY.








CHEMISTRY.
THE following simple experiments in Chemistry are
pretty and instructive, but, as a general thing, the materials needed are not so conveniently obtained as those
needed for the experiments in Natural Philosophy. They
are not expensive, however, and what cannot be found at
the village stores can be sent from dealers in larger towns
on application.
Chemical Action. Ex. 146.-Put some strong vinegar into a goblet-enough to fill it about one-quarter full.
Take some common " baking soda," as much as will lie
upon the end of a case-knife blade, and sprinkle it into
the vinegar. A violent foaming will occur, continuing
for a time, and when it stops the " soda " will have disappeared. Add more "soda," little by little, until the
fluid refuses to foam; the "soda" last added will then
remain in the bottom. Now notice: the soda has disappeared from view in this action, while the vinegar (touch
it with the tongue) is so changed as to be no longer sour.
Here then we find a violent action going on between
the vinegar and the soda, by which the natures of both
these substances are changed.
Ex. 147.-Into a common bottle put a few small
pieces of copper, and then pour in upon them nitric acid
enough to cover them.   iYotice that a violent action
quickly begins. The fluid appears to boil. Its color be



72              PHYSICAL SCIENCE.
comes deep blue. Cherry-red vapors fill the bottle above
the fluid, and perhaps run over the top of it into the
room. The copper is, in the mean time, being slowly
used up: it will finally disappear altogether if there is
acid enough used for the purpose; and when the action
ceases, there will remain the quiet blue liquid in the
bottle, with some of the red vapors remaining in the air
above.
In this experiment we again find a violent action, by
which the nature of the substances used is changed.
Ex. 148.-Into one goblet put three or four drops of
hydrochloric acid: into another put as much ammonia.
Now turn one of these goblets right bottom side up
over the mouth of the other. Both will be quickly filled
with white fumes. The acid and the ammonia are liquids
nearly or quite colorless: they form, when put together, a
vapor which is white.
Here also we notice an action which changes the nature
of substances.
Ex. 149.-Mix together a half-teaspoonfull each of
sugar and potassic chlorate, both powdered, and put the
mixture upon a common card. The card may well be
laid upon the top of a goblet for support to keep it off the
table.  Now put two or three drops of sulphuric acid
upon the mixture. A curious combustion will quickly
follow, in which tongues of purple flame will shoot up
some distance with considerable noise.
When the burning is over, look for the sugar and the
chlorate: both have disappeared, and nothing but a black
coal-like mass remains upon the card instead.
We notice that this combustion is an action by which
the natures of the burning bodies are changed.
Now, all such acticns as have been shown in these ex



CHEMISTRY                   73
perimrents are called Chemical Actions. We therefore
mean by the term  chemical action any action among
bodies of matter by wlich their natures are changed.
Combination and Decomposition. Ex. 150.Into a small vial-a long and narrow one is best for the
purpose-put some water, and then add oil enough to
cover the water well. Being the lighter liquid, the oil
of course floats upon the water. Now pour in a little
ammonia and shake the mixture thoroughly. A soapy
liquid will appear instead of the oil and water. Indeed,
the oil and the ammonia have joined themselves together
and made a kind of soap which mixes with the water.
Notice that this new substance, the soap, is a very different thing from  either the ammonia or the oil which
make it.
Now, when two or more substances disappear to form
a new one different from themselves, they are said to
combine.  The new substance made is called a compound.   The ammonia and the oil have combined to
form the soap, which is a compound.
Ex. 151.-Add to the soapy liquid just made in Ex.
150, a little strong sulphuric acid.  Shake them well
together. The soapy liquid will in part or wholly disappear, while the oil will be brought back again and will
be seen floating upon the water as before. Now we see
that the sulphuric acid must have taken the ammonia
away from the oil, for the soapy substance is broken up,
the oil in it coming back again.
When a substance is separated into the different materials which compose it, as the soap has been in this
experiment, it is said to be decomposed. The substances
into which it is separated are called its constituents. The




74               PHYSICAL SCIENCE.
soap was decomposed; oil is one of its constituents, ammonia is another.
Acids. Ex. 152.-Crush one or two small pieces of
blue-litmus and put the powder into a goblet of water.
The litmus will dissolve and give a deep blue color to the
water. Now add a little strong vinegar, and notice the
curious change in color: the blue turns to red.
Ex. 153.-Into another goblet of water, colored blue
with litmus, put a few drops of sulphuric acid: the blue
is quickly changed to red.
Ex. 154.-Into another solution of blue litmus put a
few drops of nitric acid, and notice how quickly the red
color appears.
Ex. 155.-Take another goblet of litmus, and add
hydrochloric acid: the blue instantly gives place to red.
We find that there is a class of substances which are
able to turn the color of blue litmus to red. Should you
taste these substances you would find them all to be sour.
They have other characters in common, but the one most
conveniently tested is their power to turn the blue color
of litmus to red. These substances are called acids.
Alkalies. Ex. 156.-Take a goblet containing litmus,
the color of which has been changed to red by an acid,
and put into it a little ammonia. Notice that the red
color changes back again to blue.
Ex. 157.-Take a common glass or tin funnel, stop its
neck by crowding some unsized paper (blotting paper)
into it, and then pack the funnel nearly full of wood-ashes.
Pour some warm water upon the ashes, and as it runs
through them and out of the stem of the funnel catch it
in a bottle, through whose neck the funnel-stem passes




CHEMISTRY.                  75
and upon whici it rests. (Fig. 25.) When enough of
this liquid has been caught, pour it into a goblet of litmus
whose color has been changed to red by an acid
and notice that the blue color of the litmus is 
restored. (If too much acid has been added to 
the litmus it will be difficult to make it blue  i 
again.)
We see in these experiments that some sub- | I"
stances have the power to bring back the blue
color of litmus after it has been turned red by Fg. 20.
acids. Now, the most common substances of this kind
are called alkalies. Ammonia is an alkali, so are potash
and soda.
Acid or Alkali? Ex. 158. —Iaving a bottle and a
cork which fits its neck, take a wire and run one end of
it through the cork, so that when the cork is put into the
neck of the bottle the wire will hang down some distance
inside. Now take the cork in the hand and hold the
other end. of the wire in the fire until it is very hot.
Plunge this hot wire into a vessel of sulphur. By this
means considerable sulphur will cling to the wire. Now
again hold the end of the wire in fire to inflame the
sulphur upon it, and then plunge the burning sulphur
into the bottle. It will continue to burn for a little while,
filling the bottle with white funmes. These whllite fumes
are quite different from either the sulphur or the air: a
new compound has been fobrmed by the burning sulphur.
Remove the cork and wire and pour a little blue-litmus
water into the bottle. Shake it well, putting thle hand
over the mouth of the bottle to keep the contents from
escaping, and notice the change of color. Is the new
compound an acid or an alkali 




76                PHYSICAL SCIENCE.
The name of this new substance is sulphurous acid. The
same white fumes are made when a match is lighted.
Ex. 159.-Put some water into a goblet, and mix with
it just enough blue litmus to give it a distinctly blue color.
Then take a glass tube: put one end into the colored
water, the other into the mouth, and breathe the air from
the lungs out through it in bubbles through the water.
After a little while notice the change in the color of the
water: it turns to red.
This experiment shows that an acid is contained in the
breath as it comes from the lungs: it is called carbonic acid.
Nitrogen and Oxygen. Ex. 160.-Prepare a bottle, with cork and wire, just as was done in Ex. 158; the
bottle may be in this case a large one. Cover the end of
the wire with sulphur, and let it burn in the bottle, as in
the other experiment. Have a second cork fitting the
bottle: take the cork and wire out, putting the other cork
quickly in. Cover the wire a second time with sulphur,
and burn it in the bottle. Repeat this until the sulphur
quite refuses to burn in the bottle. Then turn the bottle
cork downward: plunge its neck into a basin of water:
take the cork out, being careful to let no air get in, and
leave the bottle thus inverted in the water. After some
considerable time, notice that the white fumes in the bottle are not as dense as they were. We see that the water
is taking them out.  Finally, they will all disappear.
Notice then that the water has risen in the bottle a ways,
and that the air (as it seems to be) above the water is
again clear."  Now cork the bottle again, and afterward
remove it from the water and stand it upon the table.
* If the teacher will perform this part of the experiment beforehand, he
need not wait for the water to take the fumes out. He can tell the pupils




CHEMISTRY.                   77
Next take a bit of candle; fasten it to the lower end of
a wire (which may be bent upward for the purpose) (Fig.
26), and having lighted it, take the cork from the
bottle and plunge the candle in. The flame is extinguished as if it had been plunged into water. If it
were air in the bottle the candle would continue to
burn, so that what seems to be air in the bottle is not.
Now, this gas is what is called nitrogen.      A
From  this experiment several things may be
learned: 
First.-The sulphur, burned in air, left only nitro-ig 26.
gen: then nitrogen is a constituent of air.
Second.-We look at the bottle and see that nitrogen is
a gas, colorless, and transparent as air itself.
Third.-Nitrogen extinguishes flame as quickly as
water would.
Fourth.-The burning sulphur took something out of
the air of the bottle to leave the nitrogen. This something combined with the sulphur to form the new compound-the white fumes.
Now this substance taken out of the air by the burning
sulphur is what is called Oxygen. So that we learn:
Fifth.-That oxygen is another constituent of the air.
The sulphur took the oxygen out of the air while burning; now, it is a fact that when any substance burns in
air the oxygen of the air is being used up. If it were not
for the oxygen in the air there would be no such thing as
fire known upon the earth.
Ex. 161.-Now light the candle and again plunge it
that he did the same thing with the other bottle, and that now, after standing so long, the fumes are all gone, and then go on with the work. Always
let the bottle which they have been using, stand, that they may see the air
clear in it also afterward.




T8               PHYSICAL SCIENCE.
into the bottle which held the nitrogen (Ex. 160), and
which has been left, standing open, on the table. Notice
that the flame is not quickly extinguished, as it was before.
The nitrogen has left the bottle, we see: it must have
gone up out of the open bottle into the air of the room.
This experiment teaches us that nitrogen is ligh/ter than
air.
Hydrogen. Ex. 162.-Put some clippings of zinc
(sheets of zinc are used under stoves) into a wide-mouth
bottle.  Let the bottom of the bottle be more than
covered with them, and then pour water in to more than
cover the zinc. Next pour a little sulphuric acid into the
bottle. In a few moments the liquid will begin to foam:
if. not, then add a little more acid, for the "boiling"
should be violent enough to make the foaming fill the
bottle half full. After this violent chemical action has
gone on for a few minutes, and while still violent, bring a
lighted match to the mouth of the bottle. An explosion
will be heard, and a flame will at the same time appear
at the mouth of the bottle-sometimes running down
into it.
We see that a gas is produced in this experiment which
is combustible. This combustible gas is called IHydrogen.
Ex. 163.-Wrap a towel around a bottle containing
zinc and water, as in the last experiment. Pour in the
acid as before, but touch the match to the mouth of the
bottle very soon after the action begins. The explosion
may be more noticeable in this experiment.
The object of the cloth is to prevent the glass from
flying and causing injury if, as very rarely cccurs, the
explosion should be strong enough to break the bottle.
Another proper caution is to tie the match to the end of




CHEMISTRY.                  9
a wire or stick, so that the hand would be at a distance
when the explosion occurs.
Now notice that in this experiment the hydrogen has
not had time to drive the air all out of the bottle, so that
there is a mixture of air and the gas when the explosion
occurs.
We see that hydrogen and air form an explosive mixture.
On this account great care should be taken, in all
experiments with hydrogen, to expel all air from the
apparatus before using the gas.
Ex. 164.-Prepare a cork for the bottle in which
hydrogen is to be made, by making a hole through the'
middle of it and inserting the end of the stem of a tobaccopipe, so that when the cork is put into the neck of tlhe
bottle it shall fit air-tight-the pipe-stem reaching above
it. The zinc and water being put into the bottle, add
enough sulphuric acid, and then quickly insert
the cork. Wait until you are sure that the air
has been driven out by the hydrogen, and then
bring a lighted match to the upper end of the
pipe-stem. The hydrogen takes fire as it issues, K 
and burns with a steady flame (Fig. 27)..L
Notice the flame, and you will see that it gives 
a feeble light, but:
Ex. 165.-Insert a small wire in the flame and rig. 2T.
you will find it quickly glowing with a red heat.
The flame of burning hydrogen is the source of little
light, but of very intense heat.
Carbonic Acid. Ex. 166.-Cover tle bottom of a
glass jar (it may be a common fruit-can) with "baking
soda," and pour upon it-a little at a time-some strong




SO                 PHYSICAL SCIENCE.
vinegar. Watch the violent boiling, or, as it is properly
called, effervescence, which occurs. Take a bit of candle;
fasten it to the lower end of a wire, which is bent upward
to support it. Light the candle and pass it down into
the jar: the flame will be put out as it enters the gas
given off by this chemical action.
Notice also that the gas in the jar is colorless and
transparent.  Is it nitrogen? We will see in another
experiment.
Ex. 167.-Let the jar containing the gas stand for
some time open upon the table after the effervescence has
stopped. Insert the lighted candle again: it is seen to be
again extinguished,-showing that this gas is heavier
than air, and hence is not nitrogen.
This colorless gas, which extinguishes flame and is
heavier than air, is called Carbonic acid.
Ex. 168.-Take a piece of candle, an inch in length,
and fasten it upon a cork. This may be done by dropping
some melted tallow upon the middle of the cork and
pressing the lower end of the candle down upon it, until
it hardens. Light the candle, and put it into a jar, or very
wide-mouthed bottle. Cover the jar with a plate. The
candle standing upon the bottom of the jar goes on burning for a little while, but begins to grow dim, and finally
expires. Take the plate from the jar. A stiff wire which
has been sharpened with a file may now be stuck down
into the cork, and by this means the candle may be lifted
out. Next pour a little lime-water* into the jar, and
notice that on shaking it about it becomes milky. What
* Lime-water may be prepared by taking a little slacked lime, putting it
into a bottle, filling the bottle with water, and then shaking it thoroughly.
Let the lime afterward settle, and then pour off the clear water above into
another vessel for use.




CHEMISTRY.                  81
makes this change?  Air will not do it, Nitrogen would
not stay in the open jar, so that it cannot be nitrogen;
much less can it be hydrogen. The gas which was in the
jar, to turn the lime-water milky, was colorless; it put
out the flame of the candle, and it was heavier than air.
It seems to have been carbonic acid gas. As a matter of
fact, this gas is the only one which will turn lime-water
milky.
But what produced this gas in the jar? It must have
been the burning candle.
All common flames like this one produces carbonic
acid gas.
Ex. 169.-Put a little lime-water into a goblet, and,
taking a glass tube, or even a straw, put one end into-the
water, the other into the mouth, and breathe the breath
out through the liquid. After a breath or two, the limewater will be seen to be milky, thus showing the presence
of carbonic acid gas.
We learn from this experiment that carbonic acid is
one of the things given off from the lungs in breathing.
Ex. 170.-Breathe into a clean and dry glass jar: its
sides are instantly covered with dew.  Showing that
water-vapor is another thing given off from the lungs in
breathing.
Carbonic acid and water are constantly being produced
in the process of breathing. The first of these is made
up of carbon and oxygen: the second of hydrogen and
oxygen. The oxygen for both is furnished by the air
taken into the lungs: the carbon and the hydrogen are
furnished by waste particles or impurities of the system.
The oxygen from the lungs enters the blood-vessels, and
goes throughout all parts of the circulation, meeting these
waste particles in its course. It decomposes them: com



82              PHYSICAL SCIENCE.
bines with their carbon and hydrogen, and then, as carbonic acid and water, goes back to the lungs, from which
these substances are thrown out into the air. In this way
the blood is purified.
Flame. Ex. 171.-Spread the wick of an alcohol
lamp, so that, lighting it, a large flame may be obtained.
Plunge the sulphur end of a match into the dark center
of this flame, and notice that while the wood burns in the
edge of the flame, the more combustible end of the match
does not burn in the center of it.
Ex. 172.-Take a long splinter or rod of pine wood,
freshly smoothed, that its surface may be white, and lay
it horizontally across the alcohol flame, just above the
wick. When the stick begins to burn remove it, and
notice that it is scorched in two places. The part which
was over the center of the flame is unharmed.
Ex. 173.-Press a piece of white paper, held horizontally, quickly down into the flame of the alcohol lamp, to
a place just above the wick. As soon as the scorching
begins to be seen through the paper take it quickly away.
The paper will be burned in the shape of a ring. That
part which was directly over the wick is unburned.
Ex. 174.-The following experiment may be added to
this list, provided great care is taken to follow directions:
otherwise accident might happen.
A common dinner-plate, when inverted, gives us a very
shallow dish, the bottom of a plate being, as you will see,
surrounded with a slightly elevated rim. Put a plate upon
the table, bottom upward, and pour alcohol into the shallow dish thus obtained, being very careful that none of the
fluid runs over upon the table or even upon the sides of
the plate. Take a cork, about an inch in diameter: put a




CHEMISTRY.                  83
little gunpowder upon top of it, and stand it right in the
center of the alcohol on the plate. Take a lighted match
and touch the alcohol at one edge of the plate; it will take
fire: the flame will instantly spread all over the top of
the plate, and, if no breeze waft it against the cork, the
gunpowder will remain some time, in the center of t/e
flame, unharmed!
These experiments clearly teach us that the interior of
the alcohol flame is not in a state of combustion. Tile
same experiments, except the last one, may be made with
a candle-flame with much the same results. The interior
of all ordinary flames are, like that of the alcohol-lamp,
not burning. This central part of a flame consists of
combustible gas, and is surrounded by the burning envelope.
Ex. 175.-Repeat Experiment 164 with apparatus
shown in Fig. 27. Having thus obtained a hydrogenflame, remember that it is being produced by the hydrogen from the bottle and the oxygen in the air. Now, hold
over this flame a clean and thoroughly dry glass jar. Its
sides will be seen to become instantly covered with dew.
Now, this water is the result of the action between
hydrogen and oxygen in the flame, and hence the experiment teaches that water is made up of the two substances,
hydrogen and oxygen.
Ex. 176.-Now hold a clean and dry jar in the same
way over the flame of the alcohlol-lamp: its sides are soon
dimmed with dew also. Let the same thing be done with
a candle and with other flames. Water will be, in every
case, deposited upon the sides of the jar.
But, since water consists of hydrogen and oxygen, these
results show that these two substances take part in the




84               PHYSICAL SCIENCE.
production of the flames.  Water is a product of all
ordinary combustion in flames: the oxygen is furnished
from the air: the hydrogen from the body burning.
Ex. 177.-Press the bottom of a cold dinner-plate
down upon the flame of a candle. A moment afterward
take the plate from the flame, and notice the black soot
which is collected where the flame burned against it.
There is something beside hydrogen and oxygen, we see,
taking part in the production of this flame. The black
soot is carbon. The flame of a burning stick, and indeed
almost any common flame, will furnish carbon upon a
solid body held in it. And yet no carbon is seen when a
flame burns freely. Why?
Ex. 178.-Fix a bit of candle upon a cork, by dropping a little of the melted wax or tallow upon its top and
pressing the bottom of the candle upon it until cold.
Light the candle and stand it on the table, and bring an
inverted glass-jar down over it. The candle will burn
freely for a little while, but at length it will burn more
dimly, and finally go out. Turn the glass-jar right side
up and pour into it a little lime-water. After shaking it
about a little, the lime-water will become whitish, showing the presence of carbonic acid.
Now, carbonic acid consists of oxygen and carbon, and
it has been formed in the flame. Its oxygen has been
furnished by the air, but its carbon must have come from
the candle. And now we see what becomes of the carbon
when a flames burns freely. It combines with oxygen of
the air, and forms carbonic acid gas, which, being invisible, passes unseen off into the air.
We see from these experiments that water and carbonic gas are produced by the combustion in ordinary
flames. The hydrogen and the carbon for these are fur



CHEMISTRY.                 85
nished by the fuel which burns, while the oxygen comes
from the air. Combustion in all common instances is
nothing but a chemical action between the oxygen of the
air and the elements of the fueL




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