Education Library
FIRST
LESSONS IN PHYSICS.
FOR USE
IN THE UPPER GRADES OF OUR COMMON
SCHOOLS.
In Nature, all ia Motion, Life, and Labor." Lesson xrii-
BY C. L. HOTZE,
Teacher of Physic* in the Central High School, Cleveland, O.
ST. LOUIS:
HENDRICKS, CHITTENDEN & CO.
1872.
Entered according to Act of Congress, in the year 1871, by
HENDRICKS & CHITTENDEN,
In che Office of the Librarian of Congress, at Washington
qc
PREFACE.
The conviction that an elementary knowledge of some
important instruments, machines and physical phenomena
can and should be given in our Common Schools, has in-
duced the author to prepare the present little volume. Its
object is the presentation of a number of phenomena, laws,
and applications of the same, specially adapted to the per-
ceptive capacities of the pupils of the upper grades.
Inasmuch as the demand of a large amount of time might
delay the introduction of physical science into the Common
School, the book has been so prepared as to secure good
results in the minimum of time ever given any study in our
schools, viz. : one lesson a week.
Each of the thirty-nine lessons commences with a fact
familiar to the child, or an easy ', little experiment, which
serves as the basrs for the development of a natural law.
After this law, comes the application man makes of it such
as the barometer, thermometer, pump and hydrostatic press.
Costly apparatus is unnecessary. A pencil , a marble , a
piece of board, of India-rubber, of wire ; glass tubes, and
M289988
IV PREFACE.
other objects of trifling expense, are sufficient, for our pur-
poses even preferable. The steam engine and other com-
plicated machines should be examined when in actual use
at the workshop or other places, by the class in company
with the teacher, but not until after the preparatory lesson
in the school-room.
Like all instruction, instruction in physics should proceed
in concentric circles from the near to the remote. The
present volume may be considered as the first and smallest
of those circles. Its usefulness in the highest grade of our
Common Schools has been shown by practical experience ;
the author has written it, however, with a view of intro-
ducing it into the second, and even into the third.
At the end of every lesson, articles in books and popular
magazines are pointed out, where the pupil may find inter-
esting reading matter ; and where, while thus improving his
leisure time, he may collect material for composition exer-
cises in school.
Explanations regarding the practical working and experi-
ments will be given in the Teachers Guide, to be published
simultaneously with the present volume.
C. L. HOTZE.
CLBVKLAND, O., April 8, 1871
Preface to the Third Edition.
The hearty welcome given to the first edition of this work undoubt-
edly had its reason in the long-felt want of a text-book suitable for the
thousands of girls and boys whose school education ends in the com-
mon school. Among the many things there learned, there are few
things which they remember to greater advantage than the phenomena
and daily applications of the laws of gravitation, the pressure of air, the
lever, the pump, the steam-engine, and the telegraph. These realities
train the observing powers, instill a love for knowledge, form a preven-
tive against habits of superficial reasoning, and thus tend to diminish
explosions, conflagrations, and other calamities, many of which are
caused by persons ignorant of the powers of nature. The merchant,
the laborer, or the manufacturer will do his work the better for having
had his senses trained in observing nature's operations, and his mind
disciplined by scientific thought. It may safely be stated that this view
is held by most educators in this country, and that the time is fast
approaching when physical science will no longer be a stranger in our
common schools.
And yet there are a few followers of the cramming-system, who
would deny the right of nature to a share in the education of the young;
who would not teach about the things themselves, but merely their names
nd forms. These persons consider objective instruction in the lower
grades of schools as simply a transient concession to ephemeral de-
mands, although, during the last two centuries, such men as Cowley,
Milton, Locke, Rousseau, Pestalozzi, Whewell, and Macaulay have
advocated it. In the upper grades they refuse it admission altogether,
notwithstanding its introduction there is urgently pressed by the scientific
men of all countries, by the entire periodical press, and the most prom-
inent educators of the world.
These few opponents to progress in education are joined by a still
smaller class of persons who are not adverse to the introduction of
VI PREFACE.
physical science into the schools, but who fear, lest the appropriation of
time one lesson a week ! might diminish the habitual number of arith-
metical examples, geographical names, and grammatical rules, and there-
by vitiate the results of the annual examinations. So some people en-
tertain a groundless prejudice against the acquisition of a foreign
language, on the plea that the child's English might suffer. Huxley,
in his "Answers to Certain Questions by the Schools Inquiry Commis-
sion," says : " Physics lie at the foundation of all science ; and if nothing
else were taught, it -would be a great gain to have the youth of this
country soundly instructed in the laws of the elementary forces gravi-
tation, heat, light, andso forth." An English Journal, " Nature," says :
" The notion, that when a child has learned to read, write, and cipher,
he is educated, must be eradi'zted. These are at best but means, and are
only the instruments by which education is conducted." An editorial in
the "Scientific American" (January 14, 1871), ends with the following
significant words : " As object teaching is a mere handmaid of science
is of use only to give scientific habits of 'thought, and to convey a know-
ledge of scientific facts, and is worthless without science, the pnblic should
see that its introduction into our schools be carried on under the advice
of scientific experts, who shall direct what is best to be taught, and
advise with the adepts in teaching how such knowledge may best be
imparted. As a journal having the interests of science and education at
heart, desiring to see science soundly popularized, and the masses made
acquainted with its technical value, we make this suggestion, and further-
more ask: Is there any man of- scientific attainments in the present
Board of Education ? Is there any scientific authority upon its general
staff? "
Physical science was introduced into the B and C grammar classes of
this city last September ; the pupils have now been using First Lessons
in Physics for several months, and none of their other studies have been
curtailed, yet the average of the monthly examinations does not suffer
on that account, and, in the opinion of our teachers, it never will. A
peculiar feature connected with the use of this book one which we trust
will not be brought forward as an objection is, that the children ask a
great many questions more or less to the point ; and that they find no
rest until they have received a satisfactory answer, either from the
teacher's experiments or their own. The fact is truly surprising, that
PREFACE. VH
the pupils of the C grade (sixth school-year) passed a very fair examina-
tion a few days ago, on questions at the end of the book which were not
found too easy for the C grade of the High- school (the tenth school-
year). This shows what earnestness may accomplish ; and we have but
begun
It may be well to state that the modern technical sense of a word
sometimes conflicts with its preconceived English meaning, or use; and
as a book of this kind demands language both youthful and technical,
the author may be excused for having given a slightly different dress to
not a few of the laws. He has omitted several of the so-called "pro-
perties " of matter which are very puzzling to the young; and, for the
sake of simplicity, has treated the somewhat magic "impenetrability" of
air as elasticity of air. The independent terms, Force, Motion, and
Heat, are better understood by young pupils than Expansive Force,
Moving Force, and so forth. The text in fine print, as well as pages
83, 84 and 120, must be omitted in a lesson of less than aitf-hour's length.
The development of the steam-engine will find favor from those appre-
ciating the historical element in the schooL While the lessons in Optics
may claim special clearness in treatment, those in Chemical Electricity,
being very difficult for young learners, will need forbearance. A two-
fluid element was chosen, because it may be seen in actual use at the
telegraph office. The questions in fine print serve for reviews and ex-
aminations, but not as equivalents for experiments.
Even a brief perusal of the volume will show the author's intention
not to cram the pupil with meaningless facts, to be forgotten as rapidly
as they are learned. As no special scientific qualification has been re-
quired of the teacher who, to-morrow, may be called upon to impart
scientific instruction to her class, a text-book in the hand of the pupil
seems for the present a necessity. I earnestly hope that my feeble con-
triburion to so great a cause may not be judged by its shortcomings
alone, and that the day may soon come when physical science shall form
a regular branch of study in the common school.
C. L. H.
CLEVELAND, O., December I, 1871.
CONTENTS.
OF ATTRACTION.
PAOH
LESS. 1. Gravity . 9
" 3. Gravity, Specific Floating and linking.... 14
" 3. Magnetic Attraction. .--,... 17
" 4. Electric Attraction , 20
" 5. Lightning. Lightning Rods , 26
" 6. Cohesion 29
" 7. Adhesion. Capillary Attraction 83
" 8.-Eeview 36
-OF PRESSURE.
LESS. 9. Elasticity... . 39
" 10. Elasticity of Air 42
* 11. Pressure of Air ... 46
" 12. Barometer. .. ....- 48
" 13. Review. .. ,..-... . 51
" 14. Inertia 53
MOTION,
OF MASSES.
LESS. 15. Inclined Plane. ... 56
" 16. Lever. ... ........ . 59
" 17. Pendulum 63
" 18. Communicating Vessels. Hydraf'tc Press. 67
" 19. Breathing. The Bellows 71
" 20. Common Pump 74
" 21V Forcing Pump. Fire-Engine 77
" 22. Review 8J
MOLECULAR.
LESS. 23. Sound . . 86
" 24. Evaporation, Fog, Clouds, Rain, Sr ->, Hail,
Dew, Frost 88
" 25. Heat. Conduction of Heat 92
" 26. Draught 96
" 27. Expansion by Heat. Thermometr . 99
" 28. Thermometer Compared with Baro3T*ter. .. 102
*' 29. Atmospheric Steam-Engine 105
" 30. Steam-Engine Ill
" 31. Review 118
" 32. Light. Its Sources. Direction i 121
" 33. Radiant and Specular Reflection 124
34. Visible Direction. Refraction.
}. Prisms. Lenses
36. Colors
37. Chemical Electricity . . .
127
131
135
140
" 38. Electro-Magnetic Telegraph 143.
" 39. Review 150
QUESTIONS 153
APPENDIX 171
GLASS AMD CORK WORKING I
LESSON I.
GRAVITY.
i. EXPERIMENT. A stone in our hand does
not fall, because the hand supports it. But if
the hand is withdrawn, the stone falls, and con-
tinues to fall, until prevented from falling far-
10 FIRST LESSONS IN PHYSICS.
ther by another obstacle, such as the floor or the
ground.
Familiar Facts. Chalk, pencils, paper, pens,
and India-rubber, often fall from the desk upon
the floor. A stone thrown into a pond sinks to the
bottom ; a sign-board blown off by the storm falls
upon the side-walk; rain, snow, and hailstones,
descend to us from the clouds ; and large bodies
of water, when precipitated from high rocks, form
waterfalls. A cat may fall from a house-top ; a
careless child tumbles down stairs ; coals fall
through the grate ; meal falls through the sieve,
and soot through the air. Branches of fruit-trees,
hanging full with fruit, break off and fall to the
ground ; the lily, whose stem is broken, droops
its head ; the mighty oak in the Western forests,
groaning under the blows of the settler's ax, falls
with a crash to the ground. Heavy rods are at-
tached to maps and curtains, to draw them down.
Clocks are provided with weights, which move
slowly in a downward direction; the heavy
anchors of vessels plunge into the depths of the
ocean.
Having noticed these facts, you naturally in-
quire, " Why is it that all bodies near the earth
have a tendency to approach the earth ? " As
every State and every town has its laws, so
Nature has her laws, which all bodies must obey.
All the facts given above may be comprised under
GRAVITY.
11
the law: All bodies fall, if unsupported; they
are attracted to the earth. The force which
attracts them is called the Force of Gravity. 1
2. EXPERIMENT. This stone is
not supported by my hand (Fig. 1).
It is merely suspended. What pre-
vents it from falling ? The string.
When you draw the stone a little to
one side, it moves back again; it
wants to stay in one place. And,
observe, that the string is kept
straight. The string indicates the
direction in which the stone would
fall, if it were left free to do so.
This direction is vertical. Who
does not know the plumb-line used
by carpenters and bricklayers ?
The direction in which a body
falls, if moved by the force of grav-
ity atone, is vertical.
no.
I. That a body, instead of approaching the earth, may sometimes do
the opposite, that is, ascend into the air, is due to the influence of other
forces. Thus, when a boy leaps a few feet high, he succeeds in over-
coming gravity ; however, he does so only for a few moments at a time.
Birds and winged insects can overcome gravity longer by means of an
action peculiar to them, which we call flying. An ordinary fly makes
as many as five hundred beats with its wings during a second. But as
soon as the influence of other forces ceases, the body must obey the
law of gravity. The powerful eagle excels in swiftness the fastest loco-
motive ; yet, when pierced by a deadly shot, he drops like a stone to
the hunter's feet.
12 FIRST LESSONS IN PHYSICS.
3. EXPERIMENT. Place a large book upon the
hand; the hand will be pressed downward. If a
small book be taken, the downward pressure is
much less. The small book has not as much
weight as the large one.
Familiar Facts. A large stone presses itself
into the ground. The weight of a heavy wagon
makes deep ruts in a road. When ladies buy
silk robes, they lift the article on their hands.
Do you know why ?
All bodies press on their support ; this pressure
is called their weight.
4. EXPERIMENT. A rod balanced on the edge
of the hand has equal weight on each side of the
support. The direction of the rod is level, or
horizontal. Now, let a crayon be suspended from
each end. The rod will still be horizontal, because
both crayons have like weight ; they are attracted
to the earth with the same force on either side.
If a number of crayons be suspended from one
end of the rod, and a standard of weight, such as
i, or 1 lb., from the other, we have a crude form
of the scale, or balance.
A balance is an instrument for weighing. The pieces of iron, brass,
or lead, used as standards, are the weights. Instead of the edge of the
hand, a metal pivot is used. At each end of the beam a pan is sus-
pended. When a person buys a pound of sugar, why does he see that
the beam of the balance is horizontal ? Did it ever enter your mind
that, when buying a pound of sugar, you actually bought a quantity of
GKRAVITY. 13
sugar whose force of gravity amounted to a pound? That is, you
bought a mass of sugar which is attracted by the earth to the amount
of a pound. It matters not to gravity of what kind a substance is. A
pound of coffee is as heavy as a pound of lead ; a pound of feathers, as
a pound of iron.
Application. The common balance clock
weights hour glasses.
Bead p. 224 and fig. on Weight of the Earth in " Things not Gener-
ally Known," by David A. Wells. New York: Appleton & Co.
Bead chapter on "Weight of the Earth" in Bernstein's Popular
Treatise on Natural Science. New York : Chr. Schmidt, 39 Centre st.
Gravity, as we have seen, is the force which attracts all bodies to the
earth. This force is only a portion of the universal force of attraction
between all bodies on the earth as well as in the universe (planets and
fixed stars). A pound- weight has very nearly the same weight all over
the earth; but if taken to the moon it would have less weight; it would
weigh only about }/ of a pound there. On the sun, which contains
355,000 times as much matter as our earth, the pound would have the
weight of about 28 pounds. Owing to that universal force, the planets
revolve around the sun. The force with which the sun and moon attract
our earth causes the huge tide-waves on the ocean ; while the earth's
attraction for the moon causes this planet to revolve around the earth
about once every four weeks.
14 FIRST LESSONS IN PHYSIOS.
LESSON II.
SPECIFIC GRAVITY FLOATING AND SINKING
OF SOLIDS.
5. EXPERIMENT. Take two ink-wells of the
same size. Fill the one with water, the other with
oil, and place them on the pans of a balance. The
one containing the water will be found to be de-
pressed ; evidently the water has more weight
than the same bulk of oil. In common words we
say, water is heavier than oil ; but we ought to
say, that water has greater specific weight than
oil ; that is, a bulk of water has more weight than
the same bulk of oil ; or, water is denser than oil.
For is not a pound of water as heavy as a pound
of oil?
Specific Gravity is the weight of a substance
compared with the weight of a like bulk of some
other substance taken as a standard.
6. EXPERIMENT. Now first pour the oil into a
tumbler, and then the water. The latter being
the heavier, it settles in the bottom, the oil rising
above it. Thus oil floats on water, because it has
not as much weight as the same bulk of water.
Familiar Facts. Smoke rises high into the
air; balloons ascend into the clouds. Each is
lighter than a like bulk of surrounding air.
SPECIFIC GRAVITY. 15
Fluids of different specific gravity place them-
selves in the order of their specific gravity the
heaviest below, the lightest above.
7. EXPERIMENT. Drop a stone into a tumbler
filled with water; it sinks. A piece of cork
would float. Upon one pan of a balance place a
tumbler filled to the brim with water ; upon the
other place as many weights as are necessary to
establish equilibrium. Remove the tumbler and
drop a stone into it. The stone will sink and
some water will run over. The space now occu-
pied by the stone was before occupied by water,
and th.at quantity of water was borne by the
water in the tumbler. Now, if the stone had no
greater weight than a like bulk of water , it would
likewise be borne by the water. That it has, can
easily be shown by placing the tumbler with the
stone in it on the balance again ; the tumbler will
have more weight than it had before.
8. EXPERIMENT. An empty flask, closed with
a cork, floats on water. Look how little water it
displaces. It evidently has less weight than a
like bulk of water. It would float even if it con-
tained a few pebbles, while a bottle filled with
water sinks.
A body floats, if it has less weight than an
equal bulk of water ; it sinks, if it has more.
16 FIRST LESSONS IN PHYSICS.
Familiar Facts. As the flask, so do vessels
float, though they be heavily laden. The body
of a man has scarcely more weight than a like
bulk of water, and will float on water, provided
the chest remains filled with air.
QUESTIONS. I. Why is it difficult for bathers to walk in water chin-
deep?
2. In drawing water from a well, why has the bucket more weight as
it emerges from the water ?
3. Why may heavy stones be lifted in water, while on dry land they
can scarcely be moved?
Persons who can not swim, often lose their lives on falling into the
water, because, when they first sink the water closes their mouth and
nose, preventing them from inhaling air. Frightened by this, they lose
their presence of mind, and, instead of holding their breath, they exhale
the air from their lungs. Thus they diminish their volume, and are, of
course, more apt to sink. Then they foolishly extend their arms into
the air; the head then naturally sinks, and, unless rescued, they are
drowned. The danger would have been very slight if these persons, on
falling into the water, had first held their breath, spread out their limbs,
and then quietly folded their arms over the crown of the head. For,
by throwing the head slightly backward, a person is enabled to keep his
mouth and nose above water, and thus may save his life. If the waves
run high, he must, by all means, hold his breath as long as he is sub-
merged; then no water can enter his mouth.
Application. By means of specific gravity the
purity of liquids and the value of substances,
such as gold-quartz, can be ascertained.
Bead Influence of Oil on Water, p. 256, in "Things Not Generally
Known," by David A. Wells. New York : Appleton & Co.
MAGNETIC ATTRACTION. 17
LESSON III.
MAGNETIC ATTRACTION.
9. EXPERIMENT. Suspend an iron nail by a
string. The direction of the string will be verti-
cal (Lesson 2). But if we bring a magnet near
the nail, the string will incline toward the magnet ;
the more so, the nearer the magnet is brought to
the nail. On approaching it still nearer it will
attach itself to the magnet, and, if detached, con-
trary to gravity, will not fall. This is owing to
Magnetic Attraction.
Reverse the last experiment. Suspend the mag-
net at one of its ends, and lay the nail on the
table. Holding the nail with one hand so as to
keep it steady, the magnet will be seen to move
toward the nail and adhere to it in spite of
gravity. This shows that Magnets and unmag-
netic iron attract each other.
10. EXPERIMENT. If iron filings be placed on
a piece of paper or glass, they will likewise be
attracted by the magnet. The latter need not be
in contact with them ; it may be placed under the
paper, or even under the table. Magnetic attrac-
tion, like attraction of gravity, operates also
through intervening bodies.
18 FIRST LESSONS IN PHYSICS.
Let the magnet be placed lengthwise in the iron
filings and turned round several times. On with-
drawing it we find that it is covered at the ends
with long threads of the filings, while toward the
middle they become shorter, and in the center of
the magnet the attraction is so slight that no fil-
ings adhere. From this we see that the power of
a magnet resides chiefly at its ends.
11. EXPERIMENT. The ends of a magnet are
called its polls. Attach
the magnet at its center
to a string, and suspend
it from the hand. The
magnet will vibrate until
it finally takes a certain
position, which it keeps.
If disturbed, it will again
vibrate, and after many
vibrations, resume the same position. It will do
so anywhere, in the room or out-doors. Upon
examining the direction, we find that it is north
and south. That end of the magnet which points
north is called its north pole, that which points
couth, its south pole.
A freely suspended magnet points north with
one end; south, with the other.
12. EXPERIMENT. Bring the north pole of a
magnet near the north pole of a magnet freely
suspended; it will be repelled. The same is
MAGNETIC ATTRACTION. 19
seen, if the south poles are brought together. The
magnets will not come to rest before the north
pole of the one has found the south pole of the
other.
Like poles repel each other; unlike poles attract each
other.
Application The most important application
of this property of the magnet is the Magnetic
Needle, or Compass, used by surveyors and mari-
ners.
A needle may easily be rendered magnetic by means of a magnet.
Lay a needle upon the table and hold its point with the left hand.
Taking the magnet with the right, place it with its north pole upon the
center of the needle. Then pass it slowly along the right-hand part of
the needle, rubbing the needle in the direction from the center to the
eye. When arrived at the eye, the magnet must be raised from the
needle and passed through the air back to the center, there to recom-
mence the same operation with the same pole. This process must be
repeated about thirty times. After that, the magnet is reversed, taken
into the left hand, and, while the right now holds the needle, placed
upon the center of the needle. By rubbing the magnet from the middle
of the needle to the left end, returning through the air, and repeating this
the same number of times as the first process, the needle becomes a
perfect magnet. It will attract iron, and be attracted by the same ; it
will point north and south, if suspended at the middle and if left to
move freely.
Magnets have usually the form of a horse-shoe, so that the poles are
brought near together ; this more than doubles their supporting capacity.
Bead "Magnetism," in Faraday's "Six Lectures on the Various
Forces of Matter." New York : Harper & Brothers.
Bead "Terrestrial Magnetism," in Harper's Monthly, Vol. I, p. 651.
20 FIRST LESSONS IN PHYSICS.
LESSON IV.
ELECTRIC ATTRACTION.
The ancient Greeks gave amber the name of
Electron ; they knew that if amber was rubbed it
would attract small, light bodies. This attractive
power is called Electricity.
13. EXPERIMENT. Eub apiece of sealing wax,
a bar of sulphur, or a lamp-chimney, with a piece
of flannel, and bring it near light bodies, such as
tiny bits of paper, wafers, or small feathers.
They will adhere to the sealing wax, sulphur or
glass, which have become electric, and have now
the power of attracting light bodies.
14. EXPERIMENT. Heat a piece of writing
paper over a stove or lamp. Place it upon a
table, rub it several times with a piece of India-
rubber, and then bring it quickly near some light
bodies ; it will attract them. From this we see
that Friction produces Electricity, and that elec-
tric bodies attract light bodies.
15. EXPERIMENT. If, in a very warm room,
where there are but few persons, and where the
atmosphere is perfectly dry, we bring the knuckle
near electrified sulphur, glass or paper, we may
see a spark pass from the substance to the
ELECTRIC ATTRACTION. 21
hand. 1 At the same time, we also hear a crack-
ling noise, feel a slight stinging in the hand, and
smell a peculiar odor near the electrified object.
Familiar Facts. The fur of a cat sparkles
when rubbed with the hand in cold weather. The
sparks are seen best in the dark. If the electric
paper be held against one's face, a peculiar sensa-
tion is felt, as though the face were being covered
with a cobweb. The reason of this is, that the
fine hair on the face is attracted by the paper and
caused to move. Sparks a foot long are often
seen when there is strong friction between the
rubber bands and the wheels of a machine.
But what has become of the electricity uiat
passed from the sulphur, or glass, to the knuckle
while emitting a spark ? If it had remained there,
the knuckle would certainly attract light bodies ;
but this is not the case. Neither the knuckle nor
the hand shows any sign of electricity. It spread
I. As it often depends upon uncontrollable circumstances whether a
spark can be obtained by such simple means, the following contrivance
has been suggested: "Take a glass tube of j-inch bore and a little over
a foot long. Then take an iron wire, coil it spirally, and insert it into
the tube the windings should be J^-inch distant from each other, and
must rest firmly against the inner surface of the tube. One end of the
wire is to protrude from the tube, and a tin ball to be soldered on to the
protruding end. The other end of the spiral wire should not extend
farther than the middle of the tube, in order that about six inches of the
tube may be used as a handle. On rubbing the tube, a spark may be
obtained from the tin ball."
22 FIKST LESSONS IN PHYSICS.
all over the body and over the earth, and thus ix
was sensibly lost. If we bring a key near elec-
trified sulphur or glass, or a tin ball (see foot
note p. 21), a spark will likewise be seen passing
over to the key ; but the electricity which the key
receives does not stay there; it passes into the
hand, and thence through the body to the ground.
This shows that metals and the human ~body
are good conductors of electricity. If in place
of the hand and the key, we take sealing wax,
silk or glass, no spark will be seen, and they wil)
remain electric after the contact. These objects
do not conduct electricity. Hence sealing wax,
silk and glass are non-conductors of electricity.
The difference between conductors and non-con-
ductors of electricity is this : A conductor re-
ceives, and loses, electricity immediately on all the
parts of its surface. A non-conductor receives,
and loses, electricity only at the point of contact.
16. EXPERIMENT. Suspend a pith ball, 1 attached
I. " Pith balls may be obtained best yi winter from young elder-trees of
one year's growth. The stem is split open with a sharp knife, the pith
is cut into small pieces, each of which is rolled between the hands into
a ball. To suspend the balls, pierce each with a needle carrying a silk
or linen thread, make a knot on the opposite side, and then draw the
knot tight a little ways into the ball. The linen thread should be very
fine. If silk thread is used, care must be taken that it contain no metal-
lic color, as, for example, Prussic Blue, and that no cotton thread be
inside, as cotton is a good conductor. The thread to which the little
ball is attached is taken from three to five inches long ; one with a ball
at each end should, of course, have double the length. They may be
ELECTRIC ATTRACTION. 23
to a silk thread, from the
hand or some other support
(Fig. 3). On presenting it to
an electrified bar of sealing
wax, it will be seen that the
ball is attracted by the seal-
ing wax, that it comes in con-
tact with the same, and that,
after it has become electric
itself, it is repelled. If we
then slowly follow it with the
sealing wax, it is repelled
still farther. The repulsion
between the two bodies con-
tinues, until the aqueous vapor in the room, or
gome other good conductor, or the contact of our
hand, deprives the ball of its electricity.
17. EXPERIMENT. In a similar manner sus-
pend two pith balls attached to a silk thread.
On presenting electrified sealing wax, they be-
come electric themselves by contact with it, and
then repel each other. They hang no longer verti-
cally ; the attracting and repelling force of elec-
tricity may overcome gravity in the same way in
which magnetic attraction overcomes gravity.
18. EXPERIMENT Repeat the 16th Experiment
with a single pith ball ; after it becomes electric,
suspended from a strong wire bent at right angle, which may be inserted
in the cork of a bottle, so as to give it firm support."
24- FIRST LESSONS IN PHYSICS.
present it to an electrified glass rod or tube. 1 The
ball will be immediately attracted by the elec-
tricity of the glass.
19. EXPERIMENT. Repeat the 17th Experi-
ment, and after the two balls are separated by
repulsion, present electrified glass to one of them.
The glass will attract this ball and impart its
electricity to it ; after which the ball will be re-
pelled from the glass and at once fly to the other
ball.
When the two balls had the same kind of elec-
tricity, they repelled each other ; now that they
possess different electricities the one glass elec-
tricity, the other sealing-wax electricity they
attract each other.
20. EXPERIMENT. Again suspend two pith
balls. Bring electrified sealing wax near the one,
electrified glass near the other. The balls will at
first be attracted and then repelled, when they
will fly toward each other and stay together.
This is easily understood if we remember that
one ball had glass electricity, and the other seal-
I. "Glass differs greatly with respect to electrical purposes. Some
varieties are good conductors of electricity, because they contain metal.
Hard glass, and common green bottle glass, if not colored with metal,
are non-conductors, and, therefore, well adapted for that purpose. All
kinds of glass, however, are hygroscopic, that is, they draw moisture
from the atmosphere. For this reason thick glass rods are preferable
to glass tubes. Before being used, both, tubes and rods, should be
slightly heated, and should be rubbed with a warm cloth."
ELECTRIC ATTRACTION. 25
ing wax, or, as it is called, resinous electricity.
From all this it appears that there are two kinds
of electricity Vitreous or Glass Electricity r , and
Resinous Electricity. The former is also called
positive electricity, the latter negative electricity.
Like electricities repel each other ; unlike elec-
tricities attract each other. (For a similar phe-
nomenon see the preceding lesson.)
Historical. The sparks obtained by the rubbing of furs, and light-
ning, with its companion, thunder, must have been observed by the
earliest people upon the earth. Although the Greeks, about 600 years
before the Christian era, recorded the attracting property of amber, it
was not before the beginning of the lyth century, that a book was
published by Dr. Gilbert, an Englishman, who mentions many other
substances, such as glass and sulphur, as having the same property.
This author stated correctly that magnetism attracted as well as repelled,
but, curiously enough, he added that electricity only attracted.
In 1670, the first electric machine was constructed by Otto Guericke,
burgomaster of Magdeburg, the inventor of the air-pump. He also
discovered the property of electric repulsion. He excited electricity by
means of sulphur (brimstone) exposed to friction.
The distinction between conductors and non-conductors of electricity
was discovered by Mr. Stephen Grey. He wished to electrify a cord
suspended by linen threads, but was unsuccessful because the electricity,
when entering the cord, at once passed over to the threads. The
threads thus were found to be conductors of electricity. Upon the sug-
gestion of a friend he tried silken threads, and as silk is a non-con-
ductor, the experiment then met with the desired result.
Du Fay distinguished between vitreous and resinous electricity. A
number of other scientists afterward improved the electric machine, and
by continuous research added largely to the progress of the science. But
they were eclipsed by Dr. Franklin who astonished the world by draw-
ing electricity from the clouds.
26 FIBST LESSONS IN PHYSIOS.
LESSON Y.
LIGHTNING. LIGHTNING KODS.
A lamp-chimney yields only a small spark;
but the glass disk in an electrical machine, such
as is used in High Schools and Colleges, produces
a long, zigzag spark, resembling a flash of light-
ning, It had long been supposed that lightning
was an electric phenomenon, but it was not until
1752 that, through the genius of our countryman,
Benjamin Franklin, all doubts were removed.
Having long been thinking over the subject, he
one day saw a boy fly a kite, and the idea at once
struck him that he must make one himself and
send it into the clouds. Accordingly he stretched
a silk handkerchief upon two sticks, in the form
of a cross, on the top of which he fastened a
pointed iron wire. This he connected with the
hempen string holding the kite, and upon the
approach of a thunder-storm he went out, accom-
panied only by his little son. The hempen string
was attached below to a key, and the key was
insulated by silk string which Franklin held in
his hand. The clouds were passing rapidly, but
without any apparent effect upon the kite ; and
the two observers, standing below and watching
it with great anxiety, were about to abandon the
LIGHTNING LIGHTNING KODS. 27
undertaking, when suddenly the fibres of the
string bristled up, and a crackling noise was
heard. Franklin now presented his knuckle to
the key, and received an electric spark, which
was soon followed by an abundance of sparks as
the string became wet with the falling rain.
Franklin's experiment, together with many
experiments by scientific men in Europe, demon-
strated beyond a doubt, that all rain clouds are
electric.
Familiar Facts. When two such clouds
approach each other, their electricities try to
unite. In doing so, one of them leaps over the
space between them. This passage of electricity
through the air produces a great electric spark
which we call Lightning.
Familiar Facts. Lightning mostly passes
from one cloud to another. But it may also pass
from the clouds to the earth, and from the earth
upward to the clouds. It rarely happens thafc
lightning strikes that is, strikes objects on the
earth. Tall objects made of good conducting
material are most liable to be struck tall objects,
because they are nearer to the clouds ; good con-
ductors, because electricity can get to the ground
soonest through them. High houses, tall steeples,
trees or chimneys, therefore, offer a good passage
to electricity. In its onward course lightning
28 FIRST LESSONS IN PHYSICS.
always prefers the best conductors ; thus it passes
along the spouting of houses, along water-pipes,
stove-pipes and iron pillars. It melts metallic
objects ; it splits trees into fragments, and 'kills
living beings by destroying the activity of their
nerves.
The safest place during a thunder-storm is that
part of a room not too near the fire-place, stove,
chandelier, gas-pipe or bell-rope. Why is it un-
safe to seek shelter under tall trees, or in the en-
trance of a house with rain pouring down over
it? Knowing that lightning always follows the
best conductors, Franklin devised a means by
which he might direct its course, and invented
the Lightning Rod. It consists of a metallic rod,
with pointed upper ends, which protrudes several
feet above the roof, in order that on the approach
of a dense cloud the metallic point, and no part
of the building, should be struck. The rod con-
ducts the electricity into the ground, where it can
do no harm.
As lightning is an electric spark, so is on a
large scale thunder the crackling noise which
accompanies the electric spark.
Bead " Thunder and Lightning," in "Illustrated Library of Won-
ders." New York : Scribner & Co.
Bead "Lightning and its Effects,'" page 291, in Wells' "Things
Not Generally Known."
Bead " Thunderstorm," in " The Earth and its Wonders." Cincin-
nati : Hitchcock & Walden.
COHESION. 29
LESSON VI.
COHESION.
Familiar Facts. In order to cut meat, to
whittle a stick, to sharpen pencils, to split logs,
to saw wood or to plane boards, we find it neces-
sary to use instruments, such as a knife, an ax or
a saw. We see that the parts of a solid body are
not easily separated; evidently they are very
close together. They are held together by a force
which we call Cohesion. We know that it is
difficult to break a piece of iron, because iron has
a strong cohesive force ; yet a blow with a poker
sometimes may break the door of an iron stove.
Rolled or hammered iron is much stronger than
cast-iron, because, by the process of rolling or
hammering, its particles have been brought nearer
together, and hence they cohere more firmly.
The strength of our tools and building-material
depends upon this cohesive force. 1 We can break
wood more easily than iron, because it has less
cohesive force. Easier yet to break, or separate,
I. If iron be made to pass through fine openings, iron wire is ob-
tained. (What is this property of iron called ?) Iron wire of the thick-
ness of a match may support a weight of forty tons. A cable of wires,
each wire having one-third of that thickness, may support a weight of
ninety tons. Suspension bridges.
30 FIRST LESSONS IN PHYSICS.
is water, oil, or air. Place the hand in water,
now try to place it in wood. This is impossible,
for the particles of a solid body cohere more closely
than those of a liquid. How easily we can pour
water from a pitcher into a tumbler, and oil from
a can into a lamp ! And that our light- winged
songsters can divide the air so swiftly, is owing
to the fact that air has even less cohesion than
water. We can walk, run, ride or jump in air.
To do this in water is more difficult ; in molasses,
it would be next to impossible. 1
To break a body, its force of cohesion must be
overcome.
Familiar Facts. When a little child breaks
his slate, he tries to put the parts together again,
but he quickly perceives that they will not re-
main together; he must get a new slate. The
particles on the surface of the edges can not be
brought so near to each other as they were be-
fore ; that is, they cohere no longer. A broken
walking-cane, although the broken parts are
glued together again, has lost its former strength.
I. When we overcome the force of cohesion of a body, we do so by
displacing its parts ; we do not in reality penetrate the body. Thus, in
driving a nail into a board, the nail merely displaces parts of the board.
A body can not occupy the space of another body unless that other
body be first removed; that is, no two bodies can occupy the same space
at the same time. If an inverted tumbler be placed in water, the water
can not fill it, because the air in the tumbler has no means of escape.
See Lesson X.
COHESION. 31
But it is different with a liquid ; two parts of
water can readily be made to form one mass by
pouring them together.
The greater or less resistance which the body
offers when being broken, determines the degree
of its cohesive force. A solid body has more co-
hesion among its parts than a liquid. Gaseous
bodies have no cohesion at all.
Examples : Ice, water, steam.
The great enemy of cohesion is Heat.
Familiar Facts. Although solids and liquids
cohere, they contain a great number of holes,
which are called Pores. They may be of differ-
ent size in the same body, and they may be visible
or not. The pores of our skin are so minute that
they can not be detected without a magnifying
glass. Every square inch of our skin contains
about 1,000 pores. Our health depends largely
upon their activity. 1
Solid and liquid bodies are porous.
Application. (a.) Of Cohesion : Beams and
Pillars. Wire; Thread; Rope, &c., &c. (b.) Of
Porosity : The Sponge ; Blotting-Paper.
I. In the year 1661 the Academy of Florence proved that pores exist
even in gold. A thin globe of gold was filled with water, and the orifice
carefully closed. A violent pressure was then brought to bear upon it,
and the result was, that the water was forced through the pores- of
the gold, and stood like dew upon the outer surface of the globe.
32 FIRST LESSONS IN PHYSICS.
i
LESSON VII.
ADHESION. CAPILLAEY ATTRACTION.
21. EXPERIMENT. Cut two leaden bullets
with a pen-knife so as to form two bright surfaces,
and let the two faces be pressed against each
other until they are in the closest contact ; they
will be found to adhere firmly to each other.
Familiar Facts. The same takes place, if a
piece of India-rubber be cut and the two surfaces
be pressed together. Dealers in glass-ware know
that when mirrors have been placed together with
their surfaces, they are often broken in the at-
tempt to separate them. Between solid bodies,
adhesion takes place if ike surfaces are highly
polished; that is, if they are so smooth that the
parts of one surface closely approach those of
the other. If not highly polished, the surfaces
will not adhere as two bricks laid together. Nor
will adhesion take place, if thin paper is placed
between the two polished surfaces.
As a general thing, bodies which we wish to
adhere to one another, are not very smooth.
Owing to the unevenness on their surface, many
of the parts of one surface are prevented from
coming in close contact with those of the other ;
ADHESION. CAPILLARY ATTRACTION. 33
in this case there can be no adhesion. What
may be done, then, in order to make two rough
surfaces adhere? Simply put a liquid body be-
tween the two, to fill out the unevenness.
22. EXPERIMENT. Put two moistened glass
plates together, and it will require some effort to
separate them. The same may be found if two
boards are placed together with water between
them. 1
Why does the hand become wet when immersed
in water ? Why does it remain dry when drawn
out from mercury ? Because, in the first case, the
adhesive force between the water and hand is
stronger than the cohesive force of the water ; in
the other case, the cohesive force of the mercury
is stronger than the adhesive force between it
and the hand. Thus, when the hand is placed
in water, a struggle takes place, as it were, be*
tween the adhesive and cohesive force of the
water. The hand comes out victorious, for on
withdrawing, it carries off a portion of the
water.
I . Between paper we put mucilage ; between bricks, mortar ; between
the pieces of a broken dish, cement. Adhesion takes place between the
surface of these bodies and the liquid; cohesion between the parts of the
liquid. It is thus that the two surfaces of glass, paper, brick and porce-
lain are made to adhere to each other.
3
34
FIRST LESSORS IN PHYSICS.
Adhesion is the attraction between the surfaces
of bodies in contact with each other.
Application. All gilding, painting, whitewash-
ing, cementing, varnishing, gluing, writing, solder-
ing, coating of looking-glasses, plating, &c., &c.
Soot adheres to the chimney ; dust to the ceiling;
chalk, and fresh paint, to one's dress.
23. EXPERIMENT. Immerse a clean glass plate
partly in water, some
of the water will be
seen to rise on both
sides of the plate.
Evidently the adhe-
sive force between
the glass and the
water is greater than
the cohesive force of
the water. Were it
not so, the water would not rise,
another glass plate near the first and not parallel
to it (Pig. 4). Water will rise between them, and
the form of its surface will be concave. The
nearer the glass plates are brought to each other
tlie higher will the water rise between them. This
is natural, for the quantity of water between them
is in this case very small ; and the cohesive force
of the water, therefore, easily overcome by the
adhesive force. If a glass tube be immersed (see
FIG. 4.
Now immerse
ADHESION CAPILLARY ATTRACTION. 85
Pig. 5) the water will rise still higher,
because here is a small quantity of
water, surrounded on all sides by glass,
and the force of adhesion is, therefore,
comparatively of greater effect. 1
Capillary tubes are tubes so small
that nothing thicker than a horse-hair m
can pass through them. When such
a tube comes in contact with a liquid FI0 - 6 -
whose cohesive force it overcomes, the liquid is
compelled to rise in it. The finer the bore of the
tube the higher will the liquid rise in it. In a
tube 1-100 of an inch in diameter water will rise
over five inches.
Capillary attraction is the result of adhesion
operating between solid and liquid bodies.
Application. Sponge, blotting paper. Eggs
and meat may be kept fresh in sand or pulverized
charcoal, these two substances containing capil-
lary tubes which absorb any moisture that would
otherwise affect the eggs or the meat. Lamp-
wicks likewise contain capillary tubes ; these sup-
port combustion, although there may be but little
oil Grease spots in the floor may be removed by
laying earth upon them. Our clothes become wet
from the rain. In short, everything about us is
filled with fine capillary tubes.
i. But the reverse of all these phenomena takes place that is, water
is always depressed about glass surfaces, if these are greased. Grease
has no attraction for water ; the water, consequently, is left free to obey
its cohesive force, and falls below the level of the liquid surrounding
the tube.
36 FIRST LESSONS IN PHYSIOS.
LESSON VIII.
REVIEW.
LESSON i.
All bodies are attracted to the earth. The
force which attracts them is called the Force
of Gravity.
2. All bodies fall if unsupported ; if supported.
they press upon their support ; if suspended.
they pull in the direction in which they would
fall if left free to do so.
3. The direction in which a body fatts, if it ir
moved by gravity alone, is vertical.
4. The pressure of bodies upon their support is
called Weight.
6. A pound is a weight, indicating a certain
amount of that pressure taken as a standard.
LESSON ii.
6. The specific gravity of a substance is it
weight, compared with the weight of a like
bulk of some other substance taken as a
standard. When we say, mercury has a spe-
cific gravity of 13.5, we mean that any bulk
of mercury has 13.5 times as much weight as
a like bulk of water.
RKVIKW. 37
7. Fluids of different specific gravities, when
brought together, place themselves in the
order of their specific gravities, the heaviest
below.
8. A body which is lighter than a quantity of
water of equal bulk, floats on water; one
which is heavier, sinks.
LKSSON in.
9. The attraction between magnets and iron is
called Magnetic Attraction. The attraction
which the earth has for magnets, causes the
magnetic needle, or any magnet freely sus-
pended, to point north and south.
LBSSON iv.
10. Tlve attraction of electrified bodies is called
Electric Attraction.
LBSSON vi.
11. The parts of a body are kept together by
their mutual attraction. The attraction be-
tween the parts of the same body is called
Cohesion.
18. In order to separate a body, its cohesion
must first be overcome. If it is difficult to
break, we call the body tenacious ; if dim
cult to penetrate, we call it hard.
38 FIKST LESSONS IN PHYSIOS.
LESSON vii.
13 The attraction between the surfaces of bodies
in contact, is called Adhesion.
14. The adhesion between solids and liquids is
often called Capillary Attraction.
15. Gravity, Magnetism, Electricity, Cohesion,
and Adhesion, are forces of attraction The
last two are called Molecular Forces, because
they bind molecules 1 together.
16. The first three Gravity, Magnetism and Elec-
tricity act through great distances ; adhe-
sion and cohesion only at an insensible dis-
tance.
17. Instead of magnetic and electric attraction.
we may witness magnetic and electric Repul-
sion, while gravity, cohesion and adhesion,
however, exert only attraction.
Questions. What natural force is applied in the
balance the compass the lightning rod
suspension bridges blotting paper ?
I. "A molecule is the smallest particle of matter into which a body
can be divided without losing its identity." Thus, the smallest particles
of bread or of salt, which are still bread or salt, respectively, are
eules of bread or of salt
1LASTICITY 39
LESSON IX.
ELASTICITY.
Familiar Facts. More than a thousand years
ago, long before powder was invented, our ances-
tors used the cross-bow for the purpose of fighting
the enemy as well as for the pleasures of the chase,
At present, the cross-bow is used only by certain
savage tribes, and as a plaything by our children.
If you draw the string of the cross-bow, and then
let it go again, the arrow placed before the string
Hies off with astonishing rapidity. u How is it,'*
may we ask, " that a string can obtain such great
force ?" If we double a piece of India rubber be-
tween two fingers, it straightens again when the
pressure is removed. After pressing a steel pen
gently against our thumb nail to try its writing
qualities, it immediately returns to its former
shape. Steel blades and whalebones likewise
resume their former shape after having been bent.
Steel, ivory, and India-rubber, possess this prop-
I. Bodies such as lead, cotton, clay, show very little elasticity. For-
merly, it was believed that they had none ; hence they were called inelas-
tic; but even these bodies are not without elasticity ; and it may safely'
be asserted that there are no inelastic bodies. Indeed, were it not that
all bodies are more or less elastic, it would be difficult for us to live.
Were not the ground, the floor, the walls of our houses, the tables and
chairs elastic, every contact with them would hurt us. Were not our
pa;>er and pens elastic, how long would it not take us to commit our
thoughts to paper ! Were not wood elastic, every stroke of wind would
blow branches of trees down upon us.
40 FIRST LESSONS IN PHYSIOS.
erty in a high degree. Such substances are called
elastic. Stone, lead, glass and many other bodies
possess it to a small extent. Yet glass, when
drawn out in tine threads, is so elastic that tissues
have been woven from them.
23. EXPERIMENT. Take an ivory ball ; press
it with your hand upon a slab of marble that has
been blackened over a lamp. The ball will show
a black spot about as large as a pin's head. Now
lay the slab on the floor, stand on the table, and
let the ball drop upon the slab from a consider-
able height. The ball will then have a black spot
very much larger than before. Although of a
hard substance, the ball is flattened to that extent
when it strikes the slab, and in resuming its for-
mer shape, it rebounds.
Familiar Facts.- An India-rubber ball is flat-
tened still more, and therefore rebounds farther.
A soap bubble, striking against the wall, some-
times rebounds. Air, too, is elastic. This may
be seen by striking upon a bladder inflated with
air. When powder is ignited, gases are developed
whose elastic force is so great that it overcomes
everything before it.
The parts of an elastic body return to their
former position, when the external force which
displaces them ceases to act.
. Bodies, such as glass or sugar, that break if the
displacing force is beyond the limits of their elas-
ELASTICITY. 41
tieity, are called brittle Bodies, such as metals,
whose parts instead of breaking may assume a
different position, are either malleable or duc-
tile. 1 ' The malleability of iron may be seen in
sheet iron, and in the plates of gun- boats ; its
ductility, in the telegraph wire.
Questions. When are bodies said to be dense ?
rare ? soft ? hard ? brittle ? malleable ? ductile ?
Application of Elasticity. 1. To produce mo-
tion : Watch-springs ; springs in watch-cases,
boxes, and carriage-lanterns ; the ballista of the
ancients ; the cross-bow ; locks, and triggers.
2. To counteract concussion: Wagon-springs;
packing glass ware in hay or straw ; springs in
mattresses, sofas, chairs and etui-cases. 3. To
cause close contact or pressure: Springs in
pocket- inkstands: printers' cylinders; some kinds
of pen-holders. 4. For weighing : Spring-bal-
ances
i. Gold is -very- malleable. Gold leaf is hammered out so thin that it
takes 300,000 sheets, placed one upon another, to make the thickness
of an inch. Platinum is very ductile. 3,000 feet of platinum wire of a
certain thickness were found to weigh only about one grain. A single
*ilk-vrorm thread possesses a thickness equal to that of 140 such fine
threads of platinum. Now, as a foot contains 144 lines, and as the tenth
part of a line is readily visible to the naked eye, it follows that a single
grain of platinum can be drawn out into 4,320,000 parts, each of which
is distinctly visible.
42 FIRST LESSONS IN PHYSICS.
LESSON X .
ELASTICITY OF AIR.
24. EXPERIMENT. If we immerse an inverted
tumbler perpendicularly in water, only a very little
of the water will enter the tumbler, and, of course,
the air in the tumbler is compressed. If the ves-
sel is pressed down still farther,
a little more water enters it, but
it will never be entirely tilled
with water, because it contains
air. A cork previously placed
in the tumbler, will show the
position of the water-level in-
side. (See Fig. 6.) Air maintains its v place like
every other body, and presses upon bodies. Its
pressure is distinctly felt, and if you withdraw
the hand which presses the tumbler down, the
tumbler will instantly rise. The air in the glass
was compressed, and tended to expand again, be-
cause air, like other bodies, is elastic.
2r>. EXPERIMENT. If a glass funnel be im-
mersed instead of a tumbler, and if inverted
with the mouth downward, the upper end being
closed with the thumb, the air in the funnel is
compressed. As the thumb is removed, however,
water rushes into the funnel, forcing out some of
the air.
ELASTICITY OF AIR. 43
26. EXPERIMENT. Cement a funnel into the
neck of a bottle and pour water into it. Only a
small quantity of water will enter, unless the fun-
nel is placed in the bottle loosely, so that there
is a passage for the air. For, as the water is
poured into the funnel, it forces the air in the
tube of the funnel into the bottle. The air in the
bottle being thus greatly compressed, its elastic
force resists the downward pressure of the water.
27. EXPERIMENT. Another beautiful illustra-
tion of the expansive force of air may be obtained
by the " Hero's Fountain." Take a cork
which fits into a bottle, and perforate it
with a round file. The hole should
be made so as to admit with difficulty
a glass "nbe, which is now pushed
through the cork. The tube should have
a very fine opening above. This being
done, fill the bottle about half with
water and close it with the cork. Then PIQ ' *'
drive the glass tube farther down, until it nearly
reaches the bottom of the bottle. The bottle now
contains air in its upper part and water in its
lower. On blowing more air into the tube, the air
will ascend through the water (Lesson II) and col-
lect in the space above. In so doing, the air over
the water is compressed, and in trying to expand,
it forces the water upward through the tube.
The inventor of this little apparatus was Hero,
44 FIRST LK880NS IN PHYSICS.
a philosopher, who died in Alexandria, before
Christ.
Familiar Facts. The amusing toy, whose harmless missile darts off
with such rapidity, the pop-gun, becomes a wonderful object, when we
consider the powerful force it serves to illustrate. A piston moves air-
tight in the tube of the pop-gun. Let it be at one end of the tube ; then
insert, air-tight, a stopper into the other end of the tube and commence
pushing down the rod ; the air inside is now compressed, it has the ten-
dency to expand again ; but its force is not great enough, as yet, to drive
out the stopper. If the rod is pushed in farther, the air is compressed
still more, and the stopper is expelled with a loud report Another
source of amusement is the blow-pipe. It consists of a long, smooth
wooden tube, into which is fitted a sharp nail, around whose head shreds
of cotton are tied. This nail is inserted, and by blowing into the tube
at the same end, a great quantity of air is forced in, compressing the air
inside ; this causes the nail to move forward. On blowing more strongly,
the air is compressed more, and its expansive force, therefore, greatly
increased. The nail is then expelled from the tube, and its speed will
be in proportion to the force with which you have blown into the tube.
The air in a diving-bell is so compressed by the water's trying to
enter, that divers often experience great difficulty in breathing.
Air is an elastic body; the more we compress
it, the greater is its expansive force.
A useful application of this property of air is
the air chamber, used in connection with pumps.
(Comp. Less. 77, p. 78.) The Diving-bell may
also be considered an application of this force,
because it is the expansive force of the compressed
air which prevents the water from entering the
bell. (Comp. 24 exp.)
PRESSURE OF AIR.
LESSON XI.
PRESSURE OF AIR.
28. EXPERIMENT. A tumbler filled with water
to the brim, with a piece of paper
placed over it, is inverted. (See
Pig. 8.) The hand on the paper,
after pressing the latter firmly
against the tumbler, is removed,
bat the water does not flow out.
How can this be accounted for?
Notice that the tumbler contains
no air; it is entirely filled with water. The air
evidently presses upward against the paper. It
is this upward pressure of the air, which supports
the water in the tumbler. Were it not for the
paper, the air would force its way into the water,
by rushing up along a part of the inner side of
the tumbler, leaving the water to fall down on the
opposite part.
29. EXPERIMENT. Immerse a tumbler, hori-
zontally, into a bowl of water, and press it down
gradually. It will fill with water, and afterward
be entirely below the surface of the liquid. Now
turn it to the vertical position, and without, how-
ever, raising its mouth above the surface, lift it
as high as possible. The whole tumbler is still
filled with water, and will remain filled, although
46
FIRST LBS8ON8 IN PHYSICS.
the water in two communicating vessels ought to
have the same height (Lesson XVIII). The tum-
bler contains no air, while a large amount of air is
over the remaining water, pressing downward upon
the water. It is this downward pressure of air
which supports the column of water in the tumbler.
30. EXPERIMENT. Let a vessel be filled with
water; then take a narrow glass
tube, open at both ends, and im-
merse it perpendicularly in the
vessel. The tube will partly fill
with water; if taken out, the
water will flow through the tube
and fall, because attracted to the
earth. Place the tube again in the
water, but so that no air remains in
it, and take it out again, keeping
the upper opening closed with th<j
thumb. No water will flow from
the tube, because air presses
against the lower opening and thus
supports the column of water in
the tube. On removing the thumb
the water will flow out, because, in
that case, the air presses as strong-
ly above as it does below; the
water, consequently, obeys the
force of gravity and falls. Hold-
ing the glass tube more and more
PRESSURE OF AIR. 47
obliquely, until it is in a horizontal position the
water will still remain in the tube.
This shows that air presses not only upward,
downward^ and laterally, but in all directions.
Familiar Facts. From an open faucet in a
full barrel with its bung-hole closed, the liquid
does njt flow, because the air presses against the
openi ig in the faucet. To draw vinegar, or any
other liquid from a barrel, plunge a long tube into
the liquid ; close the upper end with the thumb
and withdraw the tube. The liquid in the tube
will not flow out (why not ?) as long as the thumb
closes the upper end. Oil- cans must be opened
on the top in order to obtain a ready flow
Application. The Barometer (see next lesson).
Pneumatic Railway.
Give an example of each of the four applica-
tions of Elasticity (Lesson IX).
Bead ''Impenetrability," p. 3, in Pepper's "The Boy's Playbook
of Science." Routledge & Sons, London.
48 FIRST LESSON9 IN PHYSIOS.
LESSON XII.
THE BAROMETER.
The instrument before you is a Barometer.
It consists of a glass tube with its upper end
closed, and its lower end open (terminating in an
open bulb). This end of the tube may be straight,
or bent in a curve. The frame is not an essential
part of the instrument. Inside the glass tube and
bulb is mercury. The mercury does not extend
quite up to the closed end ; there is a vacant space.
Let us examine this space by placing the barome-
ter cautiously in a horizontal position. The mer-
cury will rise to the highest point of the tube.
No air could have been in the vacant space; if
there had been any, it would not have allowed
the liquid to penetrate so far (Lesson X). Let
the instrument be put slowly into a vertical posi-
tion again. The vacant place over the mercury
contains no air ; it is called a vacuum.
Raise the window, and set the barometer in the
open air. Our atmosphere is a great many miles
in height. The column of air above the bulb
presses upon the mercury ; for air presses in all
directions (Lesson XI). The cause of the mercury's
standing so high in the open air is the p, Assure
of air. The mercury may be in a leather bag,
BAROMETER. 49
enclosed in a wooden or metallic case. The
pressure of air, like magnetic attraction and
attraction of gravity, is strong enough to act
through intervening substances.
Since the pressure of air is so great as to sup-
port a column of mercury about 29 inches high, it
is evident that the amount of this pressure is equal
to the weight of the column. When the atmos-
pheric pressure decreases, the mercury in the tube
falls (why ?); when it increases, the mercury in
the tube rises (why ?). Hence the Barometer is
used for measuring the pressure of air.
Take the barometer back into the* room. You
will notice that the mercury stands as high as it
did in the open air ; yet the column of air from
the ceiling down, which presses on the bulb, is
much shorter. The air out-doors is pressed upon
by the layers of air above it ; it is compressed,
consequently it tends to expand (Lesson X).
Now, were the air in the room less compressed,
the outer air would rush in, until the air in-doors
and that out-doors would be equally compressed.
Thus both masses of air exert like pressure ; the
pressure of the air out-doors is the same as that
of the air in the room ; and we can measure it
with the barometer in the room or out of the
room.
The height of the column of Mercury in the barometer is not
always the samej it varies as the mercury rises or falls. This shows
4
50 FIRST LESSONS IN PHYSIOS.
that the atmospheric pressure constantly varies. The reason of this
rariation is intimately connected with the temperature of our atmos-
phere. If we always had the same temperature on our planet, the
atmospheric pressure (at the same elevation above the ocean's level)
would be the same all over the earth. But let any portion of a column
of atmospheric air become warmer than its surrounding parts, then its
specific gravity (Less. II.) is diminished; it rises, as warm air always
does, and passes away to other regions of the atmosphere. Now, the
pressure of this column of air has been diminished because the density
(Less. II.) of the column is less than before; and, accordingly, the mer-
cury in the barometer falls. When any portion of a column of air
becomes cooler it becomes denser, and its pressure is increased ; the
mercury in the barometer then ritet.
Winds that are hot, and therefore light, make our atmosphere less
dense, and thus cause the barometer to fall. If, as is usually the case,
they are charged with moisture, they bring us rain. Colder winds,
however, will make our atmosphere denser, and thus cause the barome-
ter to rise.
Violent disturbances of the atmosphere, such as storms, cause the
mercury to fall suddenly. At present, by means of the electric tele-
graph, we can anticipate these atmospheric disturbances, and guard
against losses to shipping.
Hence the use of the barometer as a weather prophet But as our
weather depends, also, upon other circumstances, the prophecies of the
barometer are not very reliable.
The average amount of pressure of air at a temperature of 60 degr. F.
is 15 pounds to the square inch. Supposing the surface of an adult to
be about 2,000 square inches, the pressure of air continually exerted
upon him is about 30,000 pounds.
REVIKW. 51
LESSON XIII.
REVIEW.
LESSON ix.
1. Bodies tend to resume their former shape after
their parts have been displaced. This ten-
dency is called ELASTICITY.
2. If the displacing force is WITHIN the limit of
their elasticity, bodies resume their former
shape.
3. If BEYOND, bodies change their former shape.
4. On changing their former shape, bodies may
retain their cohesion, and are then said to be
either MALLEABLE or DUCTILE ; or they may
lose it, and are then said to be BRITTLE.
LESSON x.
5. Air is an elastic body ; and the more we com-
press it, the greater is its expansive force.
LESSON xi.
6. The air about us is constantly pressed upon
by the higher strata of air; therefore, it
tends to expand continually ; and, being a
fluid, it exerts a constant pressure in all
directions.
52 FIRST LESSONS IN PHYSICS.
LESSON xn.
7. An empty space which contains no air is called
a VACUUM.
8. The pressure of the air is measured by means
of an instrument called a Barometer.
9. When the air of our atmosphere becomes less
dense, its pressure is diminished. The mer-
cury in the barometer then falls.
10. When the air of our atmosphere becomes
denser, its pressure is increased. The mer-
cury in the barometer then rises.
What force of nature is illustrated by the watch-
spring? by gold leaf? by iron wire? by the div-
ing-bell? pop-gun? barometer?
INERTIA. 53
LESSON XIV.
INERTIA.
31. EXPERIMENT. Place a piece of chalk upon
a book, and move the book quickly sideways.
The chalk drops to the floor without participating
in the motion of the book, because the book is
withdrawn from under it.
Familiar Facts. A coin laid upon a card on
the mouth of a bottle, drops into the bottle if the
card is snapped off quickly. It falls, because its
support, the card, has been removed from under
it. Persons in a 7iorse-car are thrown backward
if it starts suddenly. These, and numerous other
facts, attest that a body at rest remains at rest
until it is set in motion by some force.
32. EXPERIMENT. The motion given to the
book, and to the card, was so sudden that there
was not sufficient time for it to be communicated
to the chalk and coin. Hence it was that these two
bodies did not participate in the motion, but drop-
ped, simply because they were left unsupported
(Lesson I). Now move the book and the card
slowly; the two objects upon them will partici-
pate in the motion, and not fall. This shows that
for a body to be set in motion, time is necessary.
54 FIRST LESSONS IN PHYSICS.
Familiar Facts. A. person running down hill,
a railroad train in motion, can not stop sud-
denly. Take up your book with the chalk on it,
move the book until it strikes against the wall ;
the chalk will continue to move after the book
has ceased moving. So do persons in a car which
stops suddenly. A bell continues to ring for a
time after it has been pulled.
A boat moves on a little if the action of the oars
has just ceased. After stirring the coffee it will
revolve in the cup, although the spoon has been
removed. Do you recollect how, when sleigh-
riding last winter, you came flying down hill on
your sleigh, and immediately went up the opposite
hill a short distance ? A rabbit can not run as
fast as a hound ; but if pursued by the hound, he
may, by suddenly changing his course to the
right or left, gain considerable advantage over the
hound, who, not being prepared for the change,
must first overcome his inertia before he can turn.
From this we see that a body once in motion, re-
mains in motion until stopped by some force or
resistance. To stop the motion of a body, time
is necessary.
Familiar Facts. If a moving body meet with resistance so sudden
as not to have sufficient time to stop, the consequences may be terrible.
They are terrible to the body moving, if it can not overcome the resist-
ance. A rider, galloping, whose horse stops suddenly, flies over the
horse's head, and is violently thrown to the ground. A frightful disas-
ter is caused when, in its dashing speed, the locomotive of a train k
INERTIA. 56
suddenly arrested by an obstacle on the track. A boy who in run-
ning strikes his feet against a stone, falls with his face to the ground ;
for the upper part of his body continues moving after his feet have been
stopped. For the same reason it is dangerous to leap from a train when
it is in motion.
If the body moving can overcome the resistance, the consequence*
will be borne by the resisting body mainly. A stone thrown break-
through a window. An arrow plunges deep into the side of a horse ;
*nd a rifle ball whizzing through the air pierces the person against
whom it strikes.
Inertiavmay be said to be the indifference of
matter ^as to motion or rest.
Application. Fly-wheels. The switching-off
of trains without a locomotive.
The story goes, that once there was a prince of one of the South Sea
Islands who, when he first saw himself in a looking-glass, ran round
the glass to see who was standing behind it. So we all would like to
know the cause of everything. The cause of Inertia lies clearly before
us, when we consider that it is the most natural thing for a body to
lie perfectly still as long as it is undisturbed ; and, also, that it is quite
natural for a body, if once set in motion, to move on forever, if there is
no force acting on it so as to disturb that motion. Thus a bullet in a
rifle would remain there forever if not acted upon by any disturbing
force ; the cause of this state of rest is commonly called the Inertia of
the ball, and in former times people thought that the ball possessed a
special "property" of Inertia. Now, let the rifle be fired off; the ball
will shoot forth, and there is no reason why it should not fly on without
stopping, like the earth or the moon, provided there be no disturbing
force,
56 FLBST LESSONS IN PHTSIOS.
LESSON XV.
THE INCLINED PLANE.
33. EXPERIMENT. A ball lying on a book
upon a table will not fall as long as the book lies
in a horizontal position. But let the book be
raised on one side, and the ball rolls down. It
rolls down the faster the higher the book is raised.
The ball presses with its whole weight upon the
book ; but when the book is raised a little on one
side the ball presses less, and begins to fall. The
higher we raise the book the less will the ball
press upon the book, and the more rapidly will it
descend. The surface of the book, when raised
on one side, is an inclined plane.
Familiar Facts. A wagon descending a steep
hill need not be drawn by the horses ; it is checked
rather, in order to prevent it from rolling down
too rapidly. When ascending a hill, the horses
have a more difficult task than on a level road.
It is tiresome for us to ascend steep stairs. In
loading wagons the skid is used, It saves much
labor, if it is not placed too steep. If the wagon
is very high, the skid must be quite long. The
steeper an inclined plane, the greater the velocity
of a body descending on it; and the greater the
force required to ascend it.
THE INCLINED PLANE.
57
FIG. 10.
34. EXPERIMENT. Let an inclined plane be
formed by a board. (See Fig. 10.) Now it makes
a great difference whether the ball is rolled down
from the middle, or from
the top of the inclined
board. Try both. The
result will be that the
ball, when rolling down from the top, acquires a
greater velocity. A 'body increases in velocity as
the space increases through which it descends.
35. EXPERIMENT. Before the lower end of
a grooved board place a ball. Then let another
ball be rolled down the inclined plane, so that it
strikes the first ball. Mark the place to which
the latter moves, and put it in its former position
again. Repeat the experiment, having the upper
FIG. 11.
end of the board raised a little higher ; that is,
having the inclined plane a little steeper (Fig. 11).
The ball rolling down will then cause the first ball
to move farther, perhaps to a, and will strike it
with greater force. This is owing to the greater
steepness of the plane. We have seen that the
velocity of a body increases with the inclination
of the plane. The last experiment shows that
58 FIRST LESSONS IN PHYSIOS.
the greater the velocity of a body the greater Us
striking force.
Familiar Facts A bullet thrown with the
hand inflicts less harm than one lired from a gun.
A boy running slowly against a tree scarcely feels
the shock ; while by running against it quickly,
he might be seriously injured. We throw a mar-
ble in the air and catch it again without being
hurt, but we should experience pain, if the mar-
ble were thrown up very high. Hailstones may
strike with force sufficient to break glass, and
to destroy standing grain. A boy jumps easily
from a fence, but would scarcely dare to jump
from the top of a house.
The descent of bodies on the inclined plane
shows that they are not supported by it with
their whole weight; if they were, they would not
descend. To say they are not wholly supported
means: An inclined plane overcomes a portion
of the. weight of bodies upon it. Hence its
Application I. To overcome weight: A road
winding up a hill. A skid ; an obliquely-placed
plank ; wedges and axes.
2. To exert strong pressure : Wedges used in
oil-wells, sugar- mills, &c., to press out the juice.
3. To overcome cohesion. Our knives, axes,
hatchets, scissors, needles, nails, swords, bay-
onets, saws, files, chisels, planes, plows, &c., &c.
THE LEVER. 59
LESSON XVI.
THE LEVER.
36. EXPERIMENT. Balance a rod horizontally
on a slate, supported between two heavy books.
The rod is in a state of equilibrium, because on
each side of the point of support there is an
equal amount of matter. Now, place the rod in
such a manner that on one side of the support it
shall be twice as long as on the other. The longer
arm will descend, because it contains more mat-
ter. Let us repeat this slowly. Observe, that
in lifting the end of the long arm with the hand,
it moves through a greater space than is passed
through by the end of the short arm. The lengths
of the two arms of the lever are in the ratio of 1
to 2 ; and the space passed through by the end
of the long arm is twice as great as that passed
through by the other. Notice, also, that the ends
describe these unequal spaces in the same length
of time ; therefore, the end of the long arm of a
lever lias greater velocity than the end of the
short arm.
But it was stated before (Less. XV), that, owing
to their great velocity, hailstones, although small
bodies, could acquire great power. So will any
small weight or object, if it be given great veloc-
ity. Apply this to the present case :
60 FIRST LESSONS IN PHYSIOS.
37. EXPERIMENT. Place a heavy weight on
the short arm of a lever. The greater the length
of the other arm, the smaller may be the weight
upon it requisite to lift the large weight on the
short arm. The weight or pressure to be applied
to the long arm for that purpose is called the
Power. Thus the small power, with the great
velocity of the long arm, counterbalances the
large weight with the small velocity of the short
arm. A stiff* bar made to turn on one point is
a lever.
The greater the length of one arm of a lever,
the less power needs be applied to that arm to
lift the load on the other arm.
Question. What power is needed in a lever to
counterbalance the load on the short arm ? The
amount of power depends, evidently, upon the
length of the long arm. If, as in the above case,
it has twice the length of the short arm, the power
needed to lift and counterbalance the load is one-
half the weight of the load. Thus, if a burden
of 100 pounds is to be lifted by means of a lever
whose long arm has twice the length of the short
arm, a power of 50 pounds is required ; if four
times, a power of one-fourth, or 25 pounds. To find
the power necessary to lift a load by means of a
lever, divide the product of the load into its dis-
tance from the point of support by the distance
from the point of support to the place where the
THE LEVER. 61
power is to be applied. The qnotent = the power
required.
The important points in a lever: 1. The point
of support, or Fulcrum. 2. The load (or weight)
to be lifted. 3. The power applied.
In the lever illustrated above, as well as in the
applications given below, the order of these three
points is: Load Fulcrum Power. Levers ar-
ranged in this order are called Levers of the First
Class.
Application. The Steelyard; Crowbars ; Pump-
handles ; children teetering ; scissors and shears.
If, in order to lift a load, a laborer supports his
crowbar on a stone upon the ground, and enters
the short arm of the lever thus formed under the
weight , his lever is one of the first class ; why ?
But if he does not use the stone ; if he simply
rests his crowbar with one end on the ground, so
that the load comes to lie between him and the
fulcrum (the ground), then the order of his lever
is : Fulcrum Load Power ; and this constitutes
a Lever of the Second Class.
Application. The nut-cracker; where its limbs
are riveted together, is the Fulcrum ; the nut re-
presents the load (in this case the load, or resist-
ance, is to be crushed, not lifted); the power is
where the hands are applied. We have here two
levers combined. The cTiopping-Tcnife is a lever
62 FIRST LESSONS IN PHYSIOS.
of the same class. Where the knife is fastened
is the Fulcrum. The object to be cut is the Load ;
the Power is at the handle (in this case, too, the
resistance is not a load to be lifted, but cohesion
to be overcome). Lemon-squeezers ; Cork-squeez-
ers ; the Wheel-barrow ;* the oar of a boat. 8
The great progress of our age does not lie so
much in the introduction of new forces of nature,
of which there are but a few, but in the ingenious
application of those few forces, and in their skill-
ful combination into machines. One of the offices
of machines is to communicate the effect of a force
to bodies which otherwise could not be acted upon
by that force. Thus, without the locomotive, the
expansive force of steam could not communicate
its effect upon a train of cars.
The Lever is the simplest of all machines ; and
probably, also, the most ancient. By means of a
very long arm, it becomes a most powerful instru-
ment. It is told of Archimedes, a Syracusan
philosopher (about 250 years before Christ), that
he offered to move the earth itself, if the king
would give him a place to stand on.
Bead on Levers, and The Art of Walking, in "Things Not Generally
Known."
1 . The Fulcrum is where the wheel rests on the ground.
2. The Fulcrum is where the oar rests in the water ; the Load is the
boat.
THE PENDULUM. 63
LESSON XVII.
THE PENDULUM.
38. EXPERIMENT. (a.) The string by which a
stone is suspended has a vertical direction (Less.
I). If the stone is drawn a little to one side, the
direction of the string will be slanting. On letting
the stone go now, it will begin to move. Since all
bodies are drawn to the earth (Less. I), it will
approach the earth as near as possible. When
nearest the earth, it has again the vertical direc-
tion. But the weight does not stop there; its
inertia (Less. XIV) carries it onward , being held
by the string it does not fall to the ground ; it
ascends, until gravity finally stops it. Gravity
not only stops it, but also pulls it down again.
Noticing its downward course more closely, we
see that it descends with increasing velocity.
Inertia causes it again to pass by the lowest point
of its path ; it ascends on the other side, stops an
instant of time, and is then forced back again by
gravity. Thus it swings back and forth for a
certain time. Each swinging in one direction is
called a vibration. The vibrations grow shorter,
and observation shows us. that, finally, they cease
altogether.
If, while the pendulum is vibrating, we beat
time, it will be found that the same length of time
is necessary for the shorter vibrations toward the
64 FIEST LESSONS IN PHYSIOS.
close of the experiment as for the earlier longer
ones. Thus if the pendulum at first made sixty
vibrations a minute, it will continue to make the
same number during the same time, although it
afterward passes through shorter arcs.
The vibration of the same pendulum, whether
its space is quite short or not, takes place in the
same length of time.
39. EXPERIMENT. (b.) Cut off three-fourths of
the string. The pendulum is now shorter than it
was before; it has only one-fourth the former
length. After it is set to vibrating, count the num-
ber of its vibrations during a minute ; the number
will be greater than that of the former pendulum.
The reason of this is easily seen, if we suspend
the shorter and longer pendulum, both, from the
same point. The shorter one descends on a shorter,
but steeper, incline than the other, and, therefore,
takes less time to descend. This shows that a
short pendulum vibrates more quickly than a
long one. 1
I. A pendulum whichjs four times as long as another will need
twice as much time to perform one vibration; that is, it will vibrate
twice as slowly as the other. Let one pendulum be nine times as long
as the other, it will need three times as much time (it will vibrate three
times as slowly); or, it will vibrate once while the other vibrates three
times. Hence the times of vibrations of pendulums are to each other as
the square roots of their lengths. Thus, if one pendulum has a length
of 4, and another the length of 36, the former will vibrate faster than the
latter ; the square roots being 2 and 6, the latter will require three times
as much time as the other to perform one vibration that is, if it vibrates
once every three seconds, the former will vibrate once every one second;
or, the longer pendulum will vibrate once in the same length of time
that the shorter one vibrates three times.
THE PENDULUM.
65
The principal application of the pendulum
is its use for the
regulation of
clocks. A clock is
required to keep
good time. From
the preceding, it is
evident that a pen-
dulum, by its vi-
brations, whether
it moves fast or
slowly, gives us
equal portions of
time. But a pen-
dulum will cease
vibrating after a
short time ; what,
then, must be done
to meet this diffi-
culty? Everybody
r]G 12 knows that the
pendulum stops when the clock has " run down ;"
that is, when the weight has descended so far
that it can descend no farther. The downward
tendency of the weight, then, is sufficient to meet
that difficulty ; for while the pendulum alone
would very soon cease vibrating, the descent of
the weight lasts at least 24 hours. (What is
meant by winding up a clock ?) But the weight,
after commencing to fall, increases in speed (Les-
son XV), and as the cord from which it is sus-
5
66
FIRST LESSONS IN PHYSICS.
pended, passes round an axle which causes the
hands to move, the accelerated velocity would
cause the hands to move faster and faster. To
obviate this, the axle is connected with a wheel
of saw-shaped teeth (Fig. 12), whidi revolves with
it, and above which swings a curved hook, A. A.,
called an escapement, whose two teeth work al-
ternately in the saw-shaped teeth of the wheel.
At every vibration of the pendulum, one of these
two teeth stops the revolution of the wheel, and
thus interrupts the descent of the weight. Now,
since the pendu-
lum vibrates in
equal portions of
time, the weight
descends through
equal spaces in
equal times. And
since the weight
descends through
equal s p a c e s in
equal times, it
turns the axle, the
work, and the
hands with uni-
form velocity.
Hence clocks are
moved by the de-
scent of the weights, and regulated by the vibra-
tions of the pendulum. (See Fig. 13.)
FIG. 18.
COMMUNICATING VESSELS. 67
LESSON XVIII.
COMMUNICATING VESSELS HYDRAULIC PRESS.
40. EXPERIMENT. Fit a piece of thin board
into a tumbler, so that it forms a partition divid-
ing the inside of the tumbler into two spaces.
The board should not touch the bottom of the
glass, but be a little above it. Now pour water
into the tumbler, and there will be two horizontal
surfaces of water, each having the same height.
Remove the board, and in place of it immerse a
wide glass tube. The two surfaces of water will
again be of the same height.
Familiar Facts. The same may be seen in
two glass tubes of unequal
width (Fig. 14) which are ce-
mented into a base made of
tin, and connected with each
other by means of a tin tube
(a). Also in a teapot. The tea
PIG. 14. r i ses as high j n t j ae S p OU t ^ i n
the body of the pot, and if the body were higher
than the spout the tea would flow from the spout.
Hence, in pouring out tea, we lift the pot and
lower the spout
41. EXPERIMENT. Take a tube made of glass
or tin and bend it so that one limb be very short,
perhaps, only one- twentieth as long as the other,
68 FIRST LESSONS IN PHYSIOS.
and let the opening of the short limb be drawn
out fine (Fig. 15). Then ponr water into the
long tube, holding the short one closed with
the finger. On removing the finger, water
will jet forth. Thus we have a fountain on
a small scale. If the short tube were tall
enough, the water would rise until it stood
at a level with the water in the other tube.
There being no more tube, however, the ! jj
water rises in a jet, but not to that level,
because there is friction, and because the
returning drops depress the rising jet.
Familiar Facts. Cisterns, offices, dwel-
ling-houses and factories are supplied with
water from large elevated reservoirs.
Vessels connected with each other, so that a
liquid can pass freely from one into the other,
are called Communicating Vessels.
Why may water pipes under ground be said to
be communicating tubes ?
42. EXPERIMENT. Take a cylindrical tin ves-
sel (about five inches high), with a
neck, B, perfectly cylindrical (Fig. 16),
into which a cork can be fitted tightly,
and with small holes in the sides of
the vessel as well as in the upper
(tapering) part. These openings are
carefully closed with beeswax, the
vessel filled with water to the very
HYDRAULIC PRESS. 69
edge of B, and the cork set on the neck. If the
cork is then driven in by a sudden blow with the
hand, the water jets forth from all the openings
simultaneously. This will not take place, if the
vessel be filled with fine sand. The pressure
which we gave to the water in the neck was com-
municated to the larger body of water in the ves-
sel. The effect of that pressure was great, much
greater than the original pressure upon the liquid
in the neck ; it was as many times as great as the
surface of the water in the neck is contained
number of times in the cross- surf ace of the large
body of water.
The force of a pressure brought to bear upon a
small portion of a liquid, is transmitted equally
(or undiminished) to all parts of the liquid (in
all directions).
Supposing, now, the bottom of the tin vessel
had merely been telescoped in the vessel. The
pressure given to the water in B, would evidently
have forced the bottom out; and the bottom
would then have exerted a pressure upon any
resisting object in its way.
Application. Advantage has been taken of
this in a machine called the " Hydraulic Press,"
invented in 1796 (Fig. 17). By means of a lever
(of the second kind) a pressure is exerted upon
the water in the narrow tube, A. This pressure
is communicated to the water in the wide tube, c,
70
FIRST LESSONS IN PHYSICS.
forcing the movable cylinder, J9, to ascend. Bales
of cotton, or any other object to be compressed,
lying on the plate, and prevented from yielding
by the fixed plate, P, are thus compressed with
FIQ. 17.
enormous force. For if the surface of the water
in the cylinder be 100 times that of the water in
the narrow tube, and if the pressure applied to
the liquid in the tube amount only to 50 pounds,
the pressure exerted upon the bale of cotton will
amount to 5,000 pounds But since the power
applied by the hand may be increased tenfold
with the advantage gained by a longer lever, the
amount of pressure may easily be raised to
50,000 pounds It can be farther increased by
steam-pressure so that the force of pressure may
amount to over a million pounds.
BREATHING. THE BELLOWS. 71
LESSON XIX.
BREATHING. THE BELLOWS.
43. EXPERIMENT. If a glass tube be placed
with one end in water, we can cause the water to
rise in the tube by sucking it up with the mouth.
This is the reason for it : We draw the air which
is in the tube, into the mouth ; a vacuum (Lesson
XIII) is thus created, and the pressure of the ex-
ternal air* upon the water forces water into the
tube.
Familiar Facts. Instead of water we may
draw up air alone ; this is done in breathing. We
enlarge our lungs and the cavity in our chest
(Lesson II, p. 16) ; by this, the air in the chest is
rarefied, and the external air, by the pressure of
the layers of air above it, forced to rush into the
chest. This process is called Inhalation. During
the process of Exhalation we contract the chest,
and the air must rush out. If we immerse a pail
in a pond, and fill it with water, the moment the
pail is drawn out again, the water rushes in and
occupies the space where the pail was before. In
the same way.
Air rushes into a vacuum, or into any space
containing rarefied air.
72 FIRST LESSONS IN PHYSIOS.
^L very useful application of the pressure of
air is the Bellows, an instrument for blowing fire.
It consists of a space enclosed by two boards
opposite each other, which are united around the
edges by a wide strip of leather. In front, this
spaco opens in a narrow tube. In one of the
boards is a hole closed by a valve. A valve is a
lid over an opening which admits a fluid into a
space, but prevents its return. When the bel-
lows is drawn out, the air inside is rarefied. The
external air now seeks to rush in, but it finds no
other way than through the valve ; this it opens
and instantly fills the extended bellows. When
the bellows is drawn in, the air inside is com-
pressed, and its expansive, or elastic, force (Les-
aon X) being greatly increased, it presses against
the inner sides of the bellows, and, in doing so,
closes the valve. There being no other egress,
the air passes through the tube in front into the
fire.
On the same principle yon may explain Drink-
ing and Smoking.
REVIEW. 73
REVIEW.
LESSON xv.
1. The steeper an inclined plane, the greater the
velocity of bodies descending on it ; and the
greater the force required to ascend it.
2. A body increases in velocity as the space in-
creases through which it descends.
3. The greater the velocity of a body, the greater
its striking force.
LESSON xvi.
4. A lever is an inflexible bar made to turn about
a fixed point
5 When moving, the end of the long arm (where
the power is applied) has greater velocity
than the end of the short arm where the load
is attached.
6. The greater the length of the long arm of the
lever, the greater becomes its velocity ; and,
consequently, the less power needs be ap-
plied to lift the load.
7. To find the power required to lift a load by
means of a lever, divide the product of the
load into its distance from the point of sup-
port by the distance between the point of
support and the place where the power is to
be applied. The quotient is the Power.
74
FIRST LESSONS IN PHYSIOS.
LESSON XX.
COMMON PUMP.
44. EXPERIMENT. Instead of immersing the
end of a glass tube, as we did in the preceding
lesson, let us dip a syringe into water. On draw-
ing up the piston, by means of the piston-rod, the
liquid is seen to rise in the
syringe. This is explained
by the law given in the pre-
ceding lesson, for the piston
being air-tight, it leaves, as
it rises, a vacuum below it,
which is eagerly filled by
the water. But what causes
the water to rise ? The answer
is : The pressure of air on the
surrounding water.
Application. Our pumps.
They act on the same princi-
ple. When we look at a
pump (Fig. 18), the first thing
that strikes our eye is the
cylinder, or barrel, C, the
spout, S, and the lever, or
Jiandle, H. The lower part
of the barrel, P, is called the
COMMON PUMP. 75
suction-pipe ; it is submersed in the water per-
pendicularly. Inside of the barrel works a piston
0, which fits air-tight, and can be moved up and
down by means of the piston rod to which it is
attached. It is pierced with a hole, and the hole
is covered with a valve, 0, which moves upward.
The piston-rod is connected at the top with the
lever H
When the handle of the pump is drawn out,
and has arrived at its highest point, the piston is
at its lowest, near the water. If, then, the handle
is moved to the left (See Fig. 18), the piston is
raised; the valve is now closed, because the air
above it presses down upon it, and because a par-
tial vacuum has been created below the piston.
We must now turn our attention to another
valve, A^ which is situated between the piston
and the surface of the water in the reservoir (in a
manner such that the piston, when at its lowest,
rests upon it), and which, also, opens upward.
When the piston rises, this valve is opened, be-
cause the air below it that is, the air between it
and the water expands in order to fill the
vacuum caused by the withdrawal of the piston
(Less. XIX, p. 71). The air ascends into the space
between the lower valve and the piston, and, ac-
cordingly, is now rarefied air But the air below
that valve is likewise rarefied, and as such (Less.
XIX) it has lost a large portion of its expansive
76 FIRST LESSONS IN PHYSICS.
force, and does not press upon the water in P &A
much as the air over the water outside of ths
suction-pipe, at F F. As a consequence of thia,
the water within P is forced to ascend. Then the
piston is lowered. The valve A now closes of itu
own weight; a portion of air escapes throixgb
valve v. On raising the piston-rod the second
time, more air is withdrawn from the suction-
pipe ; water commences rushing up, and enters
through valve A. On lowering the piston a^ain,
it descends into the water, and from thia mo-
ment all the air below the piston is expelled.
Some water is now above the piston, and the
lower valve again falls of its own weight. Hence-
forth, whenever the piston descends, a large quan-
tity of water passes through the piston-valve /
whenever it rises, that quantity of water remains
on top of the piston-valve. Afterward, at every
rise of the piston, the water above it flows out
through the spout.
The great principle of the pump is the fact,
that the pressure of air upon a body of water,
forces the water to rush up into a vacuum that
has been formed above the water in a tube com-
municating with that body of water.
Theory of Pump ^ p. 267, in "Things not Generally Known."
PUMP. FIRE-ENGINE.
77
LESSON XXI.
FORCING PUMP. FIRE-ENGINE.
A common pump will not raise water higher
than about 32 feet. The reason of this is, the air
over the water can not exert a greater pressure.
In order to elevate it to a greater height, the Forc-
ing Pump is used (Fig. 1 9). It is constructed OR
78 FIRST LESSONS IN PHYSIOS.
the same principle as the Common Pump ; it dif-
fers from the latter in the following three points :
1. The piston of the Forcing Pump is not pierced.
2. In place of the spout there is a tube at the
lower part of the barrel, which leads to the place
where the water is to be carried. 3. That tube
contains a valve, a 2 , which opens outwardly.
When the piston P is raised this valve is closed;
thus the air below the piston becomes rarefied, and
water is forced through the lower valve t) 1 , the
same as in the common pump. When the piston
descends, the lower valve is closed on account of
"its own weight; the water above the valve v l is
then forced through valve tf into the tube, from,
which it can not flow back. (Why not?)
The Fire-Engine
Consists of a Herorts Fountain (Lesson X) and
of two Forcing Pumps to pump water into it.
Both pumps stand in a large box filled with
water. Two iron levers (called brakes) L and L\
work the iron piston-rods P and P', A wide
cylinder, N, stands between the two pumps. It
contains water, and a metallic tube which nearly
reaches to the bottom and is open at the top
This cylinder acts like a "Hero's Fountain," but
in the Fire-Engine, and in other pumps, it is
called Air-chamber. The tubes of the Forcing
Pump enter the air-chamber; each has a valve
opening outwardly.
FORCING PUMP. FIRE-ENGINE.
79
When A, one of the pistons -, rises, the valve of
tube B is closed by the pressure, which the air
over the water in the air-chamber exerts. Water,
at the same time, enters from the box through
the lower valve C into the barrel of the pump.
Why? When the piston E descends, the lower
valve D closes of its own weight, and water is
forced into the air-chamber through the valve
of the tube F. After continued pumping, the
water in the air-chamber has risen so high that
it has concentrated and compressed the air into
a much smaller space. But from Lesson X we
see that the more we compress air, the greater its
expansive force. Hence it is evident that the jet
80 FIE8T LESSONS IN PHYSICS.
of water sent forth from the metallic tube is sent
forth by the expansive force of the compressed
air in the air-chamber. There being two pumps,
the jet is continuous.
Give the difference between the Common Pump
and the Forcing Pump.
Also, between a Hero's Fountain and the Air-
Chamber of a Fire-Engine.
The Common Pump and Barometer Compared.
Four points in common :
1. Both have a tube or cylinder.
2. Both have a vacuum.
3. In both the liquids rise in consequence of
tTie pressure of air.
4. In both, the liquids can not rise higher than
the capacity of that pressure permits.
Seven points of difference :
1. The Barometer has a glass tube; pumps
usually have iron cylinders.
2. The barometer-tube is closed above the vacu-
um ; while in pumps there is a valve above the
vacuum.
3. The vacuum in the pump can never be tmade
as perfect as that in the barometer.
COMMON PUMP AND BAROMETER. 81
4. In the pump, the vacuum must first be pro-
duced ; in the barometer, the vacuum, once estab-
lished, remains.
5. Tho liquid in the barometer is always mer-
cury ; in the pump it may be water, oil, vinegar,
&c., &c.
6. In the barometer neither spout nor lever is
required.
7. No graduated scale is attached to the pump.
8. The liquid column in the barometer usually
stands no higher than 30 inches. The liquid col-
umn in the pump stands higher than that in the
barometer as many times as its specific gravity
is smaller than that of mercury. Let the specific
gravity of water be one- thirteenth that of mer-
cury ; then will a common pump raise a column
of water 13 X 30 = 390 inch. =32^ feet high ; how-
ever, it never does so in reality, for it is impossi-
ble to obtain a perfect vacuum in a pump.
82 FIRST LESSONS IN PHYSIOS.
LESSON XXII.
REVIEW .
LESSON xvn.
1. The vibration of a pendulum, whether its space
be quite short or not, takes place in the same
length of time.
2. A short pendulum vibrates more quickly
makes a greater number of vibrations in the
same length of time than a longer one.
.3. In Clocks the motory force is the force of
Gravity ; in Watches (and in clocks without
weights), the motory force is the force of Elas-
ticity.
4. In Clocks the motion is regulated by the Pen-
dulum ; in Watches by the Balance-spring.
LESSON xvni.
5. Vessels connected with each other, so that a
liquid can pass freely from one into the other,
are called Communicating Vessels.
6. The force of pressure upon a small portion of
any liquid is transmitted equally and undi-
minished to all the parts of the liquid in all
directions.
LESSON xix
7. Air rushes into a vacuum, or into any space
containing rarefied air.
REVIEW. 83
LESSON xx.
8. If there is a Fluid between a vacuum and
the air, the pressure of air will force the
Fluid into the Vacuum. Thus water or mer-
cury rushes into a vacuum formed over a part
of its surface, because the pressure of air
upon the remaining portion of its surface
forces both to do so. (Pumps and Barometer.)
9. A stone on a support, a weight suspended by
a cord, are at rest. They may remain at rest
during thousands of years. The force of
gravity in them is also at rest. But as soon
as the support is withdrawn, or the cord
lengthened but the hundreth part of an inch,
they begin to move. Then the force of gravity
in them may be said to do work. That work
is called Motion.
10. An elastic spring may be compressed, and
may remain so for thousands of years. Dur-
ing this time the force of elasticity in it does
no work. But withdraw the pressure, and
the spring commences moving. Its motion is
the work done by the Force of Elasticity.
11. Motion is a manifestation of the work done
by a Force, and is always accompanied by a
change of place.
12. a. A body on an incline (Fig. 10) will not fall ;
b. A pendulum (Fig. 13) will not vibrate ;
c. The long arm of a lever will not move ;
84 FIRST LESSONS IN PHYSICS.
d . The water in the wide tube of a communi-
cating vessel (if by means of a stop- cock
shut-off from the narrow tube) will not flow
into the narrow tube (Fig. 14);
e. The air outside the bellows will not enter ;
/. The air over the cistern of a pump will not
force the water up (Figs. 18 and 19) ,
So long as the force of gravity (in e and /
the force of elasticity) does no work. But
from the moment that the rope at the top of
the incline, to which the body is fastened, is
cut; from the moment that the pendulum-
weight be drawn to one side ; that the long
arm of the lever be provided with additional
weight ; that the stop-cock in the communi-
cating-tube be opened ; % that the bellows be ex-
tended ; that the piston of the pump be moved ;
From that moment Work is done and Mo-
tion produced.
13. The effect of the Force of Gravity is Pull. It
pulls all bodies to the earth. The effect of
the Force of Elasticity is Push (pressure).
These effects disappear when work is being
done by the forces ; the forces are then con-
verted into Motion.
14. The motion of masses is produced by the
work which their forces perform. The mo
tions of the human body are work which its
forces perform. When its forces cease to labor,
Death takes place. In nature all is Motion,
Life and Labor.
SOUND. 85
LESSON XXIII.
SOUND.
Familiar Facts. When an electric spark
leaps over, its passage is followed by a crackling
noise, and the passage of lightning through air
is followed by thunder. The blow of a whip in
the air is also accompanied by a crackling noise ;
and a pencil, when it falls upon the table, pro-
duces a sound which we hear. So does a stone
thrown into the water, a book dropped upon the
floor, or the hand rapping at the door. Now, if
the whip had not moved through the air, nor the
pencil upon the table, nor the stone into the water,
nor the book on the floor, nor the hand against
the door, no sound would have been produced.
Sound is caused by the motion of a body (or
mass).
45. EXPERIMENT. Insert the Blade of a knife
between the horizontal joints on the side of a
desk, or table ; take the free end of the handle,
press it downward as far as convenient, and then
let go : a noise will be heard, and the knife will
be seen to move up and down very fast until it
comes to rest. This is a swinging, vibratory
motion, similar to that of the pendulum of a clock.
46. EXPERIMENT. Let a few drops of water
fall into a tumbler filled with water. After first
striking the surface, each drop will rise and then
86
FIRST LE680NS IN PHYSIOS.
fall again. This vibratory motion is communi-
cated to the remaining water. The water shows it
in the circular elevations (rings) round the point
of contact. Thus the motion of the knife, as well
as that of the water, is a vibratory one.
Familiar Facts. A vibratory motion may be
heard and felt, when a door is slammed or a gnn
fired off. A body is first set to vibrate, then it
communicates its own vibrations to the air around
it, and the air in turn transmits its vibrations to
FIG. 20.
the ear. In water, the vibrations are rings ; in
air, hollow spheres of compressed air, alternating
with hollow spheres of rarefied air. No sound is
heard if the vibrations are too faint, or too far off
to reach the ear ; or if one is deaf.
Familiar Facts. That the sounding-board
of a piano vibrates while the instrument is being
played, may be seen if a pin or other small bodj
be placed on it. Blowing into a pipe sets the air
SOUND. 87
vibrating. In windy weather the church-bells of
a city may be heard farther off than usual, at a
place which lies in the direction of the wind;
while at a place nearer by, but in an opposite di-
rection, they may not be heard at all.
Sound is caused by, the vibratory motion of a
body.
If a cannon is fired off at a distance of about
1100 feet, the flash is seen instantaneously, but
the report will be heard a second later. At twice
that distance, the report will be heard two sec-
onds later. From the time which elapses between
the flash of a gun on a vessel in distress, and
the hearing of the report on the shore, the dis-
tance of the vessel may be found. Thus, if ten
seconds have elapsed, the vessel is about 11,000
feet, a little over two miles, distant. The distance
of a thunderstorm may be ascertained in a like
manner, by counting the seconds that elapse be- '
tween the lightning and the thunder following it
i'ii . c <
Sound moves at the rate of about 1100 feet, a
second.
Question. I What causes the noise when a
piece of paper is torn ? 2. "What, when a piece
of wood is broken? 3. What, when a whip is
cracked ?
Bead "Wonders of Acoustics," in Illustrated Library of Wonders.
Bead "The Ear," in "Human Body" Illust. Library of Wonders. '
Bead "Sound- and Echoes" y. 268, in Things not Generally Known,' ;i
88 FIKST LESSONS IN PHYSICS.
LESSON XXIV.
EVAPORATION FOG CLOUDS RAIN SNOW '
HAIL DEW FROST.
Water is one of the most necessary elements in
human life. By the Hindoos and other pagan
nations, it was revered as a Deity; and the
masses of bleached bones lying around the few
wells in the desert, show that during great heat
the want of water may be death to the traveling
caravans.
Familiar Facts. Moisture on a slate or on
a piece of paper will disappear very soon.
Water in a tumbler, exposed to the air, constantly
diminishes, until finally none is left. The water
in streets, cisterns, ponds, and rivers gradually
disappears. When water thus passes off into
the air, we say it evaporates. Evaporation takes
.place only at the surface of liquids.
By evaporation water is changed into aqueous
-vapor (the aeriform state of water) .
Familiar Facts. In summer our breath is in-
visible; not so in winter, because it cools off
immediately after leaving the mouth. In warm
weather the vapors rising from rivers, swamps
and lakes, are invisible. There may be a great
quantity of vapor in the atmosphere, and yet the
FOG CLOUDS RAIN. 89
vapor not be seen. When the air near the earth
is cool, the vapor becomes visible, and then we
call it Fog. Aqueous vapor (warm, moist air)
coming in contact with cool air, forms Fog.
The vapor may not be perceived below, but
become visible higher up in the atmosphere.
This takes place especially when the warm, moist
winds (south or southwest winds) come in contact
with colder (north or northeast) winds. The va-
por then forms clouds.
Fog is clouds near the earth. Clouds are fog
in the upper regions of the air.
Familiar Facts A piece of chalk, a piece of
earth, a lump of coal, drop quickly ; but dust,
soot and finely powdered chalk, descend very
slowly. The minute water-bubbles of which
clouds and fog are composed, may float in the
air for a length of time. Being filled with air,
their specific gravity permits them to do so.
Remember that soap-bubbles may do the same.
But when aqueous vapor comes in contact with
cold air, its bubbles collapse. Then they form
drops and descend as rain. On their passage
through the air, these drops, small at first, in-
crease in size, because they meet with more aque-
ous vapor in the air, which condenses upon them.
The higher up the clouds, the greater the rain-
drops. (Why ?) Rain is condensed aqueous vapor.
90 FIRST LESSONS IN PHYSICS.
In winter, the aqueous vapor in the atmosphere,
instead of condensing, freezes and forms minute
crystals These increase in size on their passage
through the air, because more of the frozen vapor
settles upon them, and reach us as snow-flakes.
Snow is frozen aqueous vapor.
On stormy summer-days, stones of ice some-
times fall from dense clouds, having an opaque
kernel and a transparent rind. They may be dis-
astrous to green-houses and to the crops They
are called Hail-stones. But it is not known why,
in summer, such cold can be produced as to freeze
water, for If ail is, perhaps, frozen rain.
Familiar Facts. Inhabited rooms contain
much aqueous vapor. A part of it is exhaled
from our lungs. If, in summer, a tumbler is filled
with cold water, it becomes cold ; the aqueous
vapor in the air around it cools, off, condenses,
and forms drops of water all over the glass. If r
in winter, a cold tumbler is brought into a warm
room, the vapor around the glass condenses, and
forms, likewise, moisture on the glass. Axes,
iron safes and soda-fountains are vulgarly said to
" sweat." Moisture is deposited when a person
breathes against a window-pane. The aqueous
vapor of heated apartments condenses on the cold
window-panes and may run down as water.
Aqueous vapor is condensed into water when
in contact with cold bodies.
DEW FROST. 91
Familiar Facts. Those glistening dew drops
which you have so often admired in the early
morning-sun, originate in the same manner. In
clear weather, the objects on the ground cool off
during the night ; and at the same time the aque-
ous vapor in the air about them is condensed.
Grass and leaves, in general all pointed objects,
cool more quickly, hence they have the most dew.
If the sky is cloudy, the clouds act like a screen ;
they throw the heat back to the earth. Then the
objects do not become sufficiently cold and no dew
is formed. Sometimes there is no dew, and yet
the sky is serene ; this is owing to winds, which
bring warmer air to the objects so that they can
not cool off sufficiently. As rain is aqueous va-
por condensed in the air, so Dew is aqueous vapor
condensed on solid bodies. If, during the night,
objects cool off to a greater extent, the dew which
is formed, freezes. We call it then Frost.
frost is frozen dew
Bead "Lakes, Springs, Rain, Dew, Ice," in "The Earth and its
Wonders."
Bead "Atmosphere, Ocean, Rivers, Waterfalls, in "The Sublime ia
Nature." Illustrated Library of Wonders.
Bead "Dew and Water vapor,'''' in "The Phenomena and Laws of
Heat. "Illustrated Library of Wonders.
92 TIBST LESSONS IN PHYSIOS.
LESSON XXV.
HEAT. CONDUCTION OF HEAT.
47. EXPERIMENT. Strike a piece of flint and
steel together; sparks will fly off.
Familiar Facts. On a stone pavement, at
dusk, sparks may be seen when we are walking,
or when a horse is galloping. In these cases,
iron (the nails) has forcibly struck against stone.
The sparks which we see, are minute particles of
iron, or steel, which have been heated to redness
by friction.
48. EXPERIMENT. Rub a key, or a copper coin,
on the floor. It will soon become heated.
49. EXPERIMENT. Try to ignite a match by
rubbing one gently on a piece of smooth glass.
It will not burn, because there is insufficient fric-
tion; it merely glides over the smooth surface.
But if rubbed against a rough surface, such as
the floor or a brick, the match presses against the
projecting parts of the rough surface and, owing
to the friction thus produced, it becomes heated
and ignites.
Familiar Facts. Wagon wheels have so much
friction at their axles, that unless properly
greased, they may be set on fire. He that lets him-
self down by a rope has his hands blistered. On
a cold day, we sometimes rub our hands together.
HEAT. CONDUCTION OF HEAT. 93
Saws and augurs, after being used, feel hot; a
piece of India-rubber, warm. This shows that
Friction produces heat. It shows, also, that Mo-
tion may be converted into heat ; for friction is
motion arrested.
Familiar Facts. "By holding our hands near
to a heated stove they become warm. Heat of
the stove passes first to those parts of the hands
nearest the stove, then it gradually passes to
the parts next ; and so on, until all the parts of
the hand are heated.
50. EXPERIMENT. Hold a short wire in the
flame of a burning lamp. It will be felt, that
even the part of the wire which is not in the
flame, is heated; and that the heat increases so
that we must soon drop the wire. It is plain
that the heat of the flame was imparted first to
one end of the wire, and that it was communi-
cated successively to the remaining parts of the
wire. This shows that Heat may be communi-
cated by passing successively from any part of a
body to the remaining parts. This communica-
tion is called Conduction of Heat.
51. EXPERIMENT. Hold a taper, a straw, or a
thread in the flame. It may burn quite near your
fingers without hurting them.
52. EXPERIMENT. Take up the wire again
(50 Exp.), but wrap a strip of paper, or cloth,
around the end in the hand. If held into the
04 FIRST LESSONS IN PHYSICS.
flame again, there is scarcely any heat felt. Tea-
pots and soldering-irons have usually wooden
handles. Why ?
Metals are good conductors of heat. Paper,
wood, cotton, wool, fur, feathers, ashes, snow, ice,
xtraw, and air, are bad conductors of heat.
53 EXPERIMENT. Place a wire and a piece of
wood upon a heated stove, and let them remain
there for a while. Both receive the same amount
of heat ; yet, if touched with the hand, the wire
seems to be the warmer. This is owing to the fact
that, being a good conductor, it instantly imparts
all its heat to the hand. If you touch a cold iron
bar, it instantly takes heat from the hand, and,
therefore, seems cold.
Questions. 1. Why may ice be kept as well
in a feather bed as in an ice-chest?
2. Why do mittens keep the hands warmer than
'gloves with fingers ?
3. Why does iron feel cold in winter, and warm
in summer?
4. Why are steam-chests and steam-cylinders
often covered with wood ?
5. Why are the walls of safes often filled with
fine ashes ?
6. Why do wide garments keep us warmer than
tight ones ?
7. Why are frame houses warmer than stone
houses?
CONDUCTION OF HEAT. 95
Application of Conducting Substances.
/. Good Conductors. They conduct heat very rapidly, and, therefore,
they are applied in order to diffuse heat quickly. Thus, to boil water
and roast meat, iron vessels are used. Iron stoves are heated in very
little time.
//. Bad Conductors. They conduct heat very slowly, but they also
part with it slowly ; for this reason we apply them to retain heat.
They serve to prevent a warm body from cooling off^ and a cold body
from becoming heated.
Familiar Facts. If we wish to warm a tumbler on a heated stove,
a piece of paper should be placed between the gla. c s and stove; other-
wise the glass may crack. In winter, pieces of heated wood are laid in
sleighs to keep the feet warm. Boards are placed on pavements, and
horsemen like to have wooden stirrups, because wood does not withdraw
the warmth from the foot.
Cotton quilts, woolen garments, blankets and furs keep the body
warm in winter ; they neither allow the warm air surrounding the body
to pass off, nor do they permit the cold external air to enter. In cold
countries animals have very thick /#r/ some in our latitude have thicker
fur in winter than in summer. Northern birds have thick feathers.
Feather beds are in favor with persons fond of sleeping very warm.
Blast-furnaces are sometimes provided with double walls, and the space
between is filled with ashes. A cover of snow retains the heat of the
earth ; thus it protects the winter grain from the cold. The Esquimaux
build themselves huts of snow and ice. Tender trees, vines and pumps
are covered with straw in winter to protect them against the cold. Ice-
houses are thatched with straw, and their walls filled with saw -dust, to
prevent heat from entering. Double windows are used in some houses,
becanse the layer of air between them prevents the cold air from enter-
ing and the heated air from going out.
Bead "Heat," by J. Abbott. Harper & Brother.
Bead " Sources of Heat," in The Phenomena and Laws of Heat.
Bead " Good and Bad Conductors," in The Phen. and Laws of Heat.
Bead " Woolen Clothing," p. 296, in Things not Generally Known.
96 FIRST LESSONS IN PHYSICS.
LESSON XXVI.
DR A UGH T.
54. EXPERIMENT. Shreds of cotton, or small
strips of paper, held over a heated stove or regis-
ter, or over a lamp flame, will move upward, and,
if let go, they will ascend. The air above the
source of heat is heated. From the fact that boil-
ing water runs over, and from a great many othe*
facts (Less. XXVII), we know that heat expands
bodies, and that heated air is expanded, and thus
takes up more space than before, and, therefore,
has less specific gravity (Less. II) than it had
when cold. Now, as air rises in bubbles through
water, so does heated air ascend in currents
through the colder air.
55. EXPERIMENT. Insert one end of a rod
upright in a cork, and stand the whole on a
heated stove or register. Suspend from the top a
band of paper, cut in the shape of a spiral , the
upward current of hot air will cause it to revolve.
56. EXPERIMENT. Bring a thermometer near
the floor of a room; then, near the ceiling. It will
be seen that near the ceiling the air is warmer
than below. Heated air rises.
Why do balloons, smoke and steam rise I (See
Lesson II.)
DRAUGHT. 97
57. EXPERIMENT. If a window in a heated
room be opened above and below, the flame of a
burning candle, held in the opening above, will
be blown from the room ; if held in the opening
below, into the room.
Familiar Facts. The same may be observed
with cotton shreds in place of the flame. This
shows that the colder air from out-doors rushes
into the room from below, while the heated air of
the room flows out above. The colder air is con-
fined to the lower parts of a room, because it
has greater specific gravity than heated air.
Wherever a fire is burning, a current of air, or
draught, is produced. A draught is also noticed
when passing from the sun into the shade, for
where the sun shines, warmer air ascends, and is
replaced by the colder air from below. Chimneys
serve to increase the draught, because they en-
close a tall column of heated air, which has less
specific gravity than the outer, colder air. The
latter presses in with increased force proportion-
ate to the height of the chimney. If a handker-
chief be tied around the small openings under
the burner of a lighted lamp, the flame will be
extinguished. The same happens, also, if the top
of the chimney is covered with a piece of glass ;
in this case the draught is stopped because the
heated air can not pass out, and consequently no
fresh air come in.
7
98 FIRST LESSONS IN PHYSICS.
Heated air rises ; colder air flows in to take its
place.
Familiar Facts. Near heated ground, the
air ascends and is replaced by colder air. This
causes our atmosphere to be in constant motion.
The currents thus produced are called Winds.
Application. Chimneys (in lamps, stores, fac-
tories, &c., &c.) Ventilation of rooms and halls.
Bead "Draught and Ventilation," p. 269, in Things not Generally
Known.
Read " Winds and Currents" p. 279, in Things not Generally Known.
Bead "Does the Sun Influence a Fire," p. 267, in Things not Gen-
erally Known.
REVIEW.
LESSON xxiv.
1. Heat changes liquids into Vapors. Vapor of
water is called Aqueous Vapor. The process
is called Evaporation.
2. Aqueous vapor coming in contact with cool
air, forms Fog. Fog is clouds near the earth.
Clouds are fog in the higher regions of air.
3. Aqueous vapor, in contact with cool air, forms
Fog ; in contact with cold air, Rain; with
cold, solid bodies, Dew ; with intensely cold
air, Snow. Hail is, perhaps, frozen rain.
Frost is frozen dew.
EXPANSION BY HBAT. 99
LESSON XXVII,
EXPANSION BY HEAT. THERMOMETER.
58, EXPERIMENT. Hold a fine glass tube,
partly filled with water, over a flame of a lamp ;
the water will be seen to rise as it becomes heated.
Warm water takes up a larger space than cold.
Familiar Facts. A. cold tumbler placed on a
heated stove will crack at the bottom. The heat
expands the glass ; but glass is brittle (what is
meant by "brittle?" Lesson IX), and so the tum-
bler must break. How may it be prevented from
cracking? (Lesson XXY, p. 95.) A bladder, filled
with air and tied up at the end, expands if near a
hot stove or register. The air inside becomes
heated, and heated air takes up a greater space
than cold air. A flask with ground glass-stopper
is sometimes difficult to open; if it be gently
heated around the neck the stopper may be taken
out without difficulty. The rails on a railroad-
track are laid so that their ends shall be at a
slight distance from each other ; in summer their
ends are very nearly together ; in winter they are
farther apart. Tires are heated red-hot before
they are placed on the wheels, for they are then
wider, and, on cooling, fit tight to the wheels.
Chestnuts and pop -corn, when exposed to heat,
100 FIRST LESSONS IN PHYSIOS.
burst open; the heated air inside expanding,
forces its way through. Heavy rocks, and the
walls of houses, may crack. The reason is this :
They expand in summer and contract again in
winter.
All bodies are expanded by heat ; they contract
again by cold.
Here is an instrument called "Thermometer."
The silvery substance in it is one of the few
metals which have the liquid state at ordinary
temperature ; at an intense degree of cold such
as Arctic explorers experience it freezes into a
solid mass. Its name is Mercury, or Quicksilver
If the mercury is heated, it expands, and rises in
the tube, simply because it has no other place to
which to go. On cooling, it contracts and falls.
It may be heated by our atmosphere, that is, by
the sun ; or by hot water ; by steam ; by heated
oil, or merely by the natural warmth of our hand
placed upon it. On examining the thermometer,
you notice that it consists of a glass tube with a
bulb below. Both tube and bulb are closed.
The bulb and a portion of the tube are filled with
mercury. Above the mercury is a vacuum. The
vacuum is obtained by heating the mercury to a
very high degree ; while it then stands very high,
THERMOMETER- 101
the tube is fused at the highest point of the mer-
cury. This closes the tube so that no air can get
in. As the source of heat is removed, the mer-
cury falls slowly, leaving a vacuum behind. The
frame is not an essential part of the thermometer.
A little above the bulb is a point, marked Freez-
ing Point. Everywhere on the earth, ice melts at
the same degree of temperature. So, after the
tube is sealed and cooled off, it is placed in melt-
ing ice. Immediately the mercury sinks, because
the cold contracts it. It occupies now a much
smaller space, and when it has settled, its low-
est point is carefully marked, either on the
frame or by etching it on the glass tube. This
point is called the " Freezing Point." It has also
been found that all over the earth, water, in low
countries, boils at the same temperature. So the
thermometer is now held upright in the hottest
steam issuing from boiling water. Heat expands
all bodies ; hence the mercury expands and is
seen to rise in the tube. The point to which it
ascends is carefully marked ; it is the "Boiling
Point" The space between the two points has
been divided into degrees. By means of these
degrees, we are enabled to indicate the tempera-
ture which a body has acquired.
" Expansion Thermometer," in " The Phenomena and Laws
102 FIRST LE88ONS IN PHY8IOB.
LESSON XXVIII.
THERMOMETER COMPARED WITH BAROMETER.
59. EXPERIMENT. If the palm of the hand,
after being rubbed a little so as to be perfectly
dry, is held to the thermometer-bulb, the mercury
will rise to a point which marks the Blood-heat
of the human body. It happens to be indicated
on our thermometers by the number 97. This is
owing to the fact, that in our country, and also in
England, the space between the freezing and the
boiling points is measured by very small degrees,
of which there are 180 between those two points.
Fahrenheit, a philosophical instrument maker,
divided that space into 180 degrees. He com-
menced counting, however, not at the Freezing-
point, but at a point below, which is the zero
point. The freezing-point thus happens to be at
32; this causes the boiling-point to be marked
212. On the continent of Europe, the Freezing-
point is marked 0; the Boiling-point 80. That
is, the space between the two points is divided
into only 80 degrees. Each degree of this kind is
much larger (how many times as large ?) than one
of the former kind, the Fahrenheit. From the
name of the French philosopher who arranged
THERMOMETER BAROMETER. 103
this scale, its degrees are called degrees Reau
mur. Thus 80 R. is equivalent to 180 F. Far
more convenient than either of the two preceding
scales is the one of Celsius. He divided the space
between the freezing and the boiling points into
100 degrees. The use of this division is gradually
spreading. According to it, 100 C=18Q C F=8Q G R.
Explain the following table :
JReaumur. Centigrade (Celsius). Fahrenheit.
80 100 212
40 50 122
20 25 77
O 32
I4f 17J O
40 50 58
The healthiest temperature for any room ie
about 65 F. Our rooms should not be heated
beyond that in winter. Thermometers should be
placed at equal distance from stove, or fireplace,
and the windows, so as to show the mean tem-
perature of the air.
Questions. If in New York the mercury stands
at 80 above zero, how would the same tem-
perature be indicated in Paris (according to C.
degrees)? How in Berlin (according to R. de-
grees) ? By what numbers would the blood-heat
point be indicated according to those scales ? By
what number is the point of healthiest tempera-
ture indicated in C. and R. degrees ?
104 FIRST LE88ON8 IN PHYSICS.
Thermometer and Barometer Compared.
Four points in common :
1. Both instruments consist of a glass tube.
2. Both have mercury in their tube.
3. Both have a vacuum.
4. Both have a graduated scale.
Four points of difference :
1. The thermometer -tube is closed above and
below ;
the barometer tube is closed above but open
below, so that the pressure of air may reach
the mercury within it.
2. In the thermometer-tube, the mercury rises
and falls on account of the effects of heat
and cold ;
in the barometer- tube, the mercury rises and
falls on account of the increase or decrease
of air-pressure.
8. The thermometer haa a scale of degrees
whose -size is arbitrary and may be differ-
ent in different thermometers ;
the barometer has a scale of inches, and frac-
tions of inches ; its scale is of less extent,
and only at the upper part of the tube.
4. Mercurial Thermometers may have any
length ;
mercurial Barometers have uniform length.
ATMOSPHERIC ENGINE. 106
LESSON XXIX.
THE ATMOSPHERIC ENGINE.
1. If we look at a sewing-machine while it is
in motion, our attention is immediately called to
a long, upright rod, made to move up and down
by the stroke of the foot. The rod being fastened
to a wheel, it is evidently its up and down motion
that causes the motion of the wheel and with it,
that of the machine. You need but fasten a rod
to the edge of a toy- wheel, and you may demon-
strate the same. Motion in a straight line rec-
tilinear motion is thus converted into circular
motion.
2. This was known thousands of years ago;
but, strange to say, the principle upon which the
steam-engine is founded, was not thought of until
about 1690, A. D. At that time, Professor Papin,
an exiled Frenchman living in Germany, pub-
lished a little work, in which he says : " There is
a property peculiar to water, owing to which a
small quantity of that liquid, if heated and con-
verted into steam, acquires a force of elasticity
which much resembles that of air. When cooled
down, it returns to the liquid state, and loses its
elasticity, I am, therefore, inclined to believe
106 FIRST LESSONS IN PHYSICS.
that machines may be constructed which are
moved by the application of heat to water."
3. These words laid the foundation for the
greatest change which human society ever ex-
perienced. The machine that effected this change
has benefited humanity more than all the gold
mines in the world. The steam-engine not only
reveals to us the hidden treasures of the earth ;
" it can engrave a seal ; crush masses of obdurate
metal like wax before it; draw out, without break-
ing, a thread as fine as a gossamer, and lift a ship
of war like a bauble in the air. It can embroider
muslin and forge anchors ; cut steel into ribands
and impel loaded vessels against the fury of the
winds and waves." And when it flies with the
rapidity of a bird, over land and water, hurling
dense masses of steam and smoke into the air,
does it not look like some gigantic monster that
contains the strength and the power of thousands
of men ? Well may we admire the genius of man
that can turn one of Nature's simplest forces to
such wonderful account.
4. The simplicity of Papin's statement is demon-
strated by his own application. Knowing that
steam was elastic like air (Lesson X), he immedi-
ately proceeded to the construction of an appar-
atus which, although its practical usefulness was
impeded by its slowness, was the first steam-
engine ever built.
THE ATMOSPHERIC ENGINE. 107
60. EXPERIMENT. Papin's apparatus may be
illustrated by a test- tube (one of tin is preferable
inasmuch as glass breaks easily,) as shown
in Fig. 22. A small disk of wood, with a
packing of thread around it to make it fit
tight, is made into a piston, P, moving in a
tube nearly air-tight, and attached to a rod.
The tube is then filled with water about
an inch high, which is made to boil over a
flame after the piston is carefully placed
in the tube. The generation of steam causes
the piston to rise. The steam escapes FIG. .
through a small hole, E, made in the upper part
of the tube. Between the water, when boiling,
and the piston there is no air ; the space is filled
with steam. On immersing the tube in cold water,
the rod descends again, because the steam below
the piston is condensed by the cold, and because
a vacuum is thus formed between the piston and
the surface of the heated water. What is it that
forced the piston down ? The answer is : " At-
mospheric Pressure." (Lesson XI.)
5. In place of the small tube of this experiment,
Papin used a large iron cylinder, with proper
piston and piston-rod. We can readily imagine
how, by throwing, at regular intervals, a stream
of cold water on the cylinder, he produced an
up-and-down motion of the rod ; and how his ma-
chine must needs have been slow too slow to be
108 FIRST LB88ON8 IN PHYSIOS.
practically applied. A steam-engine built upon
the principle of Papin's that is, one not worked
by the expansive force of steam, but merely by
atmospheric pressure is not a steam-engine. It
is an " Atmospheric Engine."
6. Captain Savery, an Englishman, constructed
at about the same time, an apparatus in which
the steam served the purpose of raising water.
The steam was generated in a separate boiler,
and thence led into a chamber where it was con-
densed by cold water flowing over the chamber.
The apparatus, however, was very imperfect, and
used only for pumping water. Still, his was
the merit of having constructed the first Atmos-
pheric Steam -Engine that received practical ap-
plication.
7. Thomas Newcomen, a hardware man, and
John Cowley, a glazier, both Englishmen, by their
brilliant invention, completely eclipsed Savery's
engine. They improved upon Papin's plan in
this, that they generated the steam in a boiler
not in the cylinder and that they condensed
it, not by cooling the boiler from without, but
by forcing a jet of cold water into the steam.
The machine was put to immediate use in the
coal-mines of England; and it is sometimes used
even at present, in places where a great mass of
water is to be pumped out. Its construction is
very simple.
THE ATMOSPHERIC ENGINE.
109
8. It consists of the boiler, A (Fig. 23), where the
steam is generated, and the cylinder, Z?, which is
PIG. 23.
connected with the boiler by means of the pipe,
F. When steam has entered the cylinder and
the piston, #, is raised, the stop-cock, a, is closed.
This shuts off the connection between the boiler
and the cylinder. The stop-cock, 6, is then
opened, and a jet of cold water from the small
reservoir, (7, is thrown into the cylinder. This
110 FIRST LESSONS IN PHYSIOS.
condenses the steam in the cylinder ; a vacuum
is formed below the piston, and atmospheric
pressure forces the piston down. The water
from the condensed steam flows off through the
pipe, d, into a reservoir with water. (At the
end of d is a valve opening outward.) By means
of an iron chain, the piston-rod, H, is attached to
a working-beam, which swings on the pivot, J9,
and which is connected at the other end with the
rod E. This rod is raised when the piston de-
scends. When the stop-cock, a, is opened again,
the steam rushes again into the cylinder ; but as
the force of pressure of the steam scarcely ex-
ceeds that of the air over the piston, the piston
would not rise, were it not for the heavy weight
attached to the rod, E. This weight falls when-
ever steam is let in under the piston, Q; and in
falling, forces one arm of the working- beam
down, causing, at the same time, the piston at
the other arm to rise. The rod P is the piston-
rod of a pump, and is fastened to the weight.
In tJie Atmospheric Engine the piston is raised
by Gravity, and lowered by Atmospheric Pressure.
State the principal points of Papin's engine;
of Savery's ; and Newcomen's.
Head "H. Pottes" in "Inventions and Discoveries/' by Tetuple,
London: Groombridge.
STBAJt-BNGltfB, 111
LESSON XXX.
THE STEAM-EtfGUNE.
1. Half a century had passed away. New-
couien's engine had been introduced into most of
the coal-mines of England, when, in the winter of
1763, a young mechanic, James Watt, in Glasgow,
was employed by the University of that city to
repair one of Newcomen's engines, The task
which this man of uncommon mind was about to
undertake, marks a new era in the history of
steam-power, an era that finally resulted in the
perfection of a machine which is an element of
modern civilization. On trying the engine after
he had repaired it, young Watt perceived that it
was very imperfect. The principal defect con-
sisted in this, that the machine used a great deal
more steam than was needed for the motion of
the piston. For when the stream of cold water
was thrown into the cylinder, the steam was con-
densed ; but at the same time, the cylinder was
cooled down to such an extent, that when fresh
steam was admitted again, a great quantity of it
was wasted in reheating the cylinder ; and thus
there was a loss of money in direct proportion to
the amount of fuel necessary for producing the
quantity of steam equivalent to the quantity
112 FIRST LESSONS IN PHYSICS.
wasted. On calculating the loss, it was found
that I of all the fuel used was wasted ; that is,
employed in reheating the cylinder. The question
with Watt now was, How can the cylinder, in-
stead of being cooled, be kept permanently hot ?
In other words, How can the steam be condensed
without at the same time cooling the cylinder ?
2. Watt's genius solved the problem by an in-
vention of surprising simplicity. He condensed
the steam in a separate chamber, the condenser.
It stood in a chest filled with water, and was con-
nected with the cylinder by means of a pipe.
Thus the steam could be condensed without cool-
ing the cylinder, by simply leading it off. The
immediate result was the saving of I of the fuel.
3. But Watt did not stop here. He noticed that
the air entering the heated cylinder as the piston
went down, also cooled the cylinder. This caused
a waste of steam, as the cylinder, in order not to
condense the fresh steam entering, had first to be
reheated to 212. To remedy this, he dispensed
with the air entirely, in providing the cylinder
with a cover pierced in the center so as to admit
the piston-rod air-tight. The air (atmospheric
pressure) could now no longer act upon the piston ;
how then was the piston to descend? It was
made to descend by allowing steam from the
boiler to enter above the piston, through a pipe
connecting the boiler with the upper part of the
STEAM-ENGINE. 113
cylinder ; and to pass out again through a pipe
connecting the cylinder with the condenser.
Thus while there was a vacuum established in
the lower part of the piston, steam was admitted
into the upper part ; the upper part then being
made a vacuum by leading the steam off into the
condenser, fresh steam was admitted into the
lower part and forced the piston up. By this im-
provement, the steam not only served as a ready
means for obtaining a vacuum, as in Newcomen's
engine, but its expansive force was also made use
of, and from that time Watt's engine was no
longer an atmospheric, but a steam-engine.
4, The atmospheric engine was "Single Act-
ing ; " it did work only while the piston descend-
ed ; the rise of the piston, as we remember from
the preceding lesson, was effected by gravity.
The power obtained by this machine was so small
that it could not overcome the resistance of a
wheel, and, therefore, it was used mainly for
pumping water out of coal -mines.
5. It will now be readily understood, that by
admitting the steam alternately above and below
the piston, Watt made the steam-engine "Double
Acting," and this was, perhaps, the most impor
tant of all his improvements. For now, circular
motion could be produced, without which no lo-
comotive or steamboat could ever have been
thought of.
8
114 FIRST LESSONS IN PHYSICS.
Watt died in 1819, honored and admired by all
who knew him. Within a short time after his
death, five large statues were erected to his
memory.
6. In all the engines constructed by Watt, the
power of the steam was low ; it amounted scarcely
to more than li atmospheres (li as much as the
pressure of our atmosphere ; that is li times 15
pounds to the square inch of surface). The alter-
nate condensation of steam on either side of the
yiston was, therefore, the only means of obtaining
the up-and-down motion of the piston; for the
feeble expansive force of the steam was totally
insufficient to overcome the counter- pressure of
the atmosphere. But by employing steam of
greater expansive force that is, steam capable
of exerting a higher pressure one might dispense
with the condenser. It was reserved to an Ameri-
can, Oliver Evans, in Philadelphia, to introduce
steam of a higher pressure as motive power.
Engines usually having a steam-pressure of from
3 to 15 atmospheres (45 to 225 pounds of pressure
to the square inch), are called High Pressure
Engines; those working with a lower pressure,
Low Pressure Engines.
STEAM-ENGINE.
115
7. The admission of steam into the cylinder
is now accomplished by means of a sliding-valve.
Ste 101 Chest.
Cylinder.
It is enclosed in a square box, called the steam-
chest (See Fig. 24), which is attached to one side
of the cylinder. When the steam from the boiler
reaches the steam-chest through the opening, o,
it fills the chest at once, and, as the sliding-valve
keeps the opening, 5, closed, it presses through
the opening a into the cylinder. There it fills the
upper part and forces the piston down. This it
does because a vacuum has been formed on the
other side of the piston, or, as is the case in High
Pressure Engines (see Fig. above), by the immense
expansive force of the steam. At the same time,
however, the sliding-valve (which rises when the
piston-rod descends, and descends when the pis-
116
FIRST LESSONS IN PHYSIOS.
ton-rod rises,) has moved upward, and shuts off
the steam from a (see Fig. 25) ; the steam must
8M*m -Chesv PIO. 35. Cy Under
now enter through the opening b and force the
piston up. Meanwhile the old steam above the
piston passes through a and e into a tube lead-
ing to the condenser. In a steam-engine which
has no condenser, as, for example, the loco-
motive, the old steam passes through e into the
air. After the piston has arrived above, the
process is renewed, owing to the sliding-valve
having a motion opposite to that of the piston ;
thus steam is admitted alternately above and be-
low the piston which, as every one knows, movee
in a vacuum, or rather, in a space filled with steam.
Steam-engines with steam of very high pressure
usually have no condensing apparatus.
STEAM-ENGINE. 117
8. When we look at a locomotive rushing past
us at full speed, we notice a horizontal iron rod
moving back and forth. The rod connects two
large wheels, and runs at one end in a wide brass
cylinder. Next to this cylinder is the steam-chest,
a small square box. It is in the cylinder that
the motory power is imparted to the engine. In
addition to these things, we see a great many
wheels, pipes and rods; but they mostly serve
minor purposes. The main parts of the locomo-
tive are the steam-chest, cylinder, piston, piston-
rod, the large wheels, and the boiler.
9. The steam, by means of the sliding- valve,
causes the back-and-forth motion of the piston in
the cylinder ; by this, it causes the back-and-forth
motion of the piston-rod ; and by this, the revolu-
tion of the large wheels. The wheels roll on
the track ; they cause the locomotive to move on-
ward, and the locomotive pulls the cars attached
to it.
Bead "James Watt," in "Pursuit of Knowledge," Vol. II. New
York: Harper & Bros.
Bead "The Locomotive Engine^" by C. Colburn. H. C. Balrd, Phila.
Bead "The Steam- Engine," by David Read. Hurd & Houghton,
New Vork.
Bead " The Railway and its Cradlt " " The Youth of Janus
Watt" in "Inventions and Discoveries." Groombridge & Sons,
London.
118 FIRST LESSONS IN PHYSICS.
LESSON XXXI.
REVIEW.
LESSON xxin.
1. The motion of a body produces vibrations in
the air which, it 1 they impress the ear, give us
the sensation of sound. Sound, therefore, is
merely the effect of a vibrating motion upon
our ear.
LESSON xxv.
2. Heat may be communicated by passing suc-
cessively from one part of a body to the other
parts. This mode of communication is called
Conduction of Heat.
LESSON xxvi.
3. Heated air rises, because it has less specific
gravity than cold air. This fact causes
Draught and Winds.
LESSON xxvn.
4. All bodies are expanded by heat; and con-
tracted by cold.
5. What we call " Heat," is merely a vibrating
motion among the minute invisible parts
(molecules) of a heated body. We can not
see that vibrating motion, but we can feel it.
6. What we call "Sound," is merely a vibrating
motion of masses. We can neither see nor
feel that vibrating motion, but we can hear it.
BE VIEW. 119
7. As sound is the effect of vibratory motion upon
the ear, so heat is the effect of vibrating mo-
tion upon our nerves.
LESSON xxix.-
8. In the Atmospheric Steam-Engine, the piston
is raised by Gravity; and forced down by
Atmospheric Pressure.
LESSOX xxx.
9. Low Pressure engines have a steam -pressure of
not mor than \\ atmospheres. The steam-
pressure in High Pressure-engines may go as
high as 15 atmospheres.
10. In the locomotive, steam causes (by means of
a sliding- valve) the back-and-forth motion of
the piston in the cylinder ; and by this mo-
tion, the back-and-forth motion of the piston-
rod ; and by this, the revolution of the large
wheels. The wheels roll on the track ; this causes
the locomotive to move onward and draw the cars
attached to it.
11. On dropping a stone to the floor, the floor and
the air over the floor, commence vibrating.
This shows that Force (Force of Gravity in
this case) may be converted into Motion.
12. The motion of a train of cars heats the axles
and wheels of the cars. This shows that
Motion is convertible into Heat.
120 FIRST LESSONS IN PHYSIOS.
13. Heat expands all bodies (Less. XXVII); and
as expansion (the work done by heat) ia mo-
tion, we may say that Heat is also converti-
ble into Motion. (Thermometer.)
14. Heat expands water into steam. Steam ex-
pands still farther. The particles of steam,
therefore, are in continual motion. The ef-
fect of this motion is the Expansive Force of
Steam. This shows that Motion is convertible
into Force. (Compare Less XXII, Review.)
15. The Expansive Force disappears as soon as
the steam has moved the piston of the engine.
The motion of the piston is the work done by
the steam. Thus, in this case, Force is con-
verted into Motion. (Compare No. 14, above,
and Less. XXII, No. 13.)
16. Force of Pressure is convertible into Motion
of Masses. (Wind Barometer Pumpa.)
17 From all the preceding, we see that
a. Force is convertible into Motion. (The
pump.)
. b. Motion is convertible into Heat. (Friction.)
c. Heat is convertible into Motion. (Thermom-
eter.)
d. Motion is convertible into Force. (Expau-
sive Force of Steam )
LIGHT ITS SOURCES DIRECTION.
LESSON XXXII.
LIGHT ITS SOURCES DIRECTION.
Familiar Facts. While the sun shines that
is, during the day it is light; we can see objects
at a distance. But we can not see objects at
night, for then it is dark ; the sun is on the other
side of the earth. The light of the stars, or flashes
of lightning, may somewhat relieve the darkness
of night ; glow-worms may feebly illuminate our
immediate vicinity. If we rub a match in the
dark against the hand, the phosphorus will shine
on the hand. This property is called Phosphor-
escence. Glimmers of light are also noticeable in
decaying animal and vegetable substances. Two
pieces of sugar, after being rubbed together, also
emit light. Candles, oil and gas, at times, also,
torch-lights, are our usual means of illumination.
But our greatest luminary is the sun.
1. The Sun and the Fixed Stars, Electricity ',
Phosphorescence and Burning Substances are
Sources of Light. The sun, stars, lightning,
phosphorus, glow-worm and flame are Self-lu-
minous Bodies.
Familiar Facts. The moon sends light to us ;
so do other planets. But this light is not her own ;
122 FIKST LESSONS IN PHYSICS.
she receives it from the sun, the same as the other
planets do. She is invisible to us, except when
the sun's light falls upon her. When the room is
dark, a book upon the table can not be seen;
neither can the table, nor the desks, nor the streets,
nor anything else. None of these objects is self-
luminous; that is, in order to be seen, these ob-
jects need light from a self-luminous body.
2. Neither the planets, nor most of the objects
surrounding us, are self-luminous bodies.
Familiar Facts. If we close our eyes we can
not see. Nor can persons who were born blind,
or have become blind from accident or disease.
In order to see objects behind us, we must turn
around ; to see things above us, we must turn our
eyes upward.
3. Bodies not self-luminous are visible only
when they receive light from a self-luminous
'body; and then only, if a part of that light
forms an impression on our eye.
Pencils, crayons, glass, water, ice, trees, houses, .and all other ob-
jects are seen by us, because when light falls upon objects, a portion of
the light is diffused from their surface in all directions, and because a
small portion of that diffused light enters our eye and forms an im-
pression on the retina. From our room we see objects out-doors very
clearly; but when looking from without, objects in the ibom are not
seen so well. The amount of light diffused in a room is much smaller
than that diffused out-doors. It is light in daytime, although it may be
rery cloudy. The clouds receive all the light from the sun, and diffuse
a portion of it.
LIGHT ITS SOURCES DIRECTION. 123
61. EXPERIMENT. Place a large paste-board
(with a small hole in it) a few inches from the
blackboard. Light a candle and place it in front
of the hole in the pasteboard. A bright spot will
be seen on the blackboard. It is a spot illumined
by the rays of the light that pass from the flame
through the opening. The direction from the flame
through the hole to the illumined spot is that of a
straight line. Let the flame be moved about, the
spot will move also.
Familiar Facts. Through the cracks in the
shutter of a darkened room, rays of light are ob-
served to enter in straight lines. The hunter levels
his gun at a squirrel in the direction in which the
rays of light diffused from the squirrel enter his
eye. Opera-glasses and telescopes have straight
tubes.
4. I/igTit emanates from self-luminous bodies
in all directions^ and travels in straight lines.
Bead " Sun, Moon and Stars," in "The Wonders of the Heavens"
Illustrated Library of Wonders.
Bead "Light and Color," in "The Earth and its Wonders."
Bead "The Eye," m "The Human Body " Illustrated Library of
Wonders.
\
124 FIRST LESSONS IN PHYSICS.
LESSON XXXIII.
RADIANT AND SPECULAR REFLECTION.
During the daytime, sunlight is diffused in the
atmosphere as well as in the air of our rooms,
whether the sun is visible or not. Some of this
light in the air falls upon the walls and upon the
objects in the room ; and the walls, as well as the
objects, reflect (throw back) that light in all di-
rections. They reflect it thus: Every point of
their surface radiates the light in all directions ;
hence any point of this surface may be seen by a
person in the room, whatever part of the room he
may be in, provided that a portion of that reflected
light strikes his eye.
Familiar Facts. Here is a pencil. What ena-
bles us to see it? It is not a self-luminous body ;
but there is diffused light in the room, and as the
pencil has a more or less rough surface, every
point on that surface receives some of this dif-
fused light, and in turn reflects some of it. It
does so by radiating the light in all directions.
Of this radiated light, a portion enters our eye,
and we say " we see the pencil," and may then
describe it.
We see a looking-glass, owing to the light which
is reflected from it by radiation. True, its surface
LIGHT, CONTINUED.
is smoother than that of the pencil, or of most
objects; yet even in a looking-glass there are very
many uneven places, from every point of which
light is reflected by radiation. Were it not for
that, we would not see the glass at all. The sur-
face of a perfect mirror is invisible.
All bodies reflect light ~by radiation. We call
this Radiant Reflection of Light.
62 EXPERIMENT. If an India-rubber ball be
thrown upon the floor in the direction in which a
ray of light would pass through a crack on the
floor of a darkened room, the ball will rebound,
and may be made to strike the wall opposite the
craok. Let the place where it strikes the wall
be marked. Now lay a looking-glass upon the
bright spot on the floor of the darkened room
(the spot is caused by the rays of light entering
through the crack), and it will be seen that the
rays, like the India-rubber ball, rebound to where
the ball struck the wall. Evidently the rays are
reflected by the looking-glass. Any other highly
polished surface would have caused the same re-
flection.
All this shows that there are objects which not
only reflect light by Radiant Reflection in all
directions, but which, in addition, reflect an
extra amount of light in certain definite direc-
tions. We call this Specular (mirror-like) Re-
flection of Light.
126 FIRST LESSONS IN PHYSICS.
Familiar Facts. Burnished metal plates, pol-
ished wood, the surface of water or mercury, the
coating of mercury in looking-glasses, and even
common glass plates when viewed in a very ob-
lique position, exert both, "Radiant" and "Specu-
lar" reflection of light. Objects with polished
surface reflect light radiantly and specularly.
Light reflected Radiantly compared with Light
reflected Specularly.
Four points in common :
1. Both have emanated first from a self-lumin-
ous body.
2. Both have been thrown back from the sur-
face of bodies not self-luminous.
3. Both have their rays travel in straight lines,
4. Both may enter the eye.
Three points of difference :
1. Radiantly reflected light proceeds from the
surface of all bodies ;
Specularly reflected light only from the sur-
face of highly polished objects.
2. Radiantly reflected light is thrown back from
a surface in all directions;
Specularly reflected light is thrown back
from a surface only in certain directions.
3. Radiantly reflected light enables us to see
objects ;
Specularly reflected light enables us to see
images of objects.
LIGHT, CONTINUED. 127
LESSON XXXIV.
VISIBLE DIRECTION. REFRACTION.
Familiar Facts. I. When a person is hit
with a stone he does not seek the person who
threw the stone, in the direction in which the stone
flies, but in the direction from which it comes.
Thus, he whose forehead has been struck by a
stone in a downward direction, looks upward for
the perpetrator ; he supposes him to be in the di-
rection from which the stone came. If struck by
a stone in an upward direction, he will look down-
ward to find the evil-doer.
It is the same with a ray of light.
2. A boy looking at a steeple, receives its top-
most ray of light in downward direction. Imagine
Image Inverted.
this ray to be extended after passing through the
opening in his eye (Fig. 26).
128 FIRST LESSONS IN PHYSIOS.
Since light travels in straight lines (Lesson
XXXII), the ray crosses the lower part of his eye
in a downward direction. The lowest ray coming
from the foot of the steeple would, if extended,
traverse the upper part of his eye in upward di-
rection. But if, turning round and then bending
his head down to his knees, he looks at the
steeple from between his knees (Pig 27), th
Eye Inserted.
F16. T Image Cprifkt.
topmost ray will, if extended, pass downward
through the upper part of his eye ; and the lowest
ray, upward through the lower part of his eye. In
this case he would see the steeple inverted, were it
not for the fact that the eye sees an object, or any
part of an object, in the direction from which the
rays of the object come. All bodies appear to be
situated in the direction from which their ray*
enter the eye.
63. EXPERIMENT. Immerse a pencil in water
perpendicularly; it looks as straight as before.
But when immersed obliquely, it appears bent, or
broken. Oars, when partly immersed, present
129
the same appearance. When the pencil is out of
the water, we see it by means of the light diffused
from it (Lesson XXXIII). Consequently, when
the pencil is partly immersed, we see the portion
above the liquid for the same reason. The light
diffused from the immersed portion, however,
must first travel through the water, and then
through the air. Now, since the immersed por-
tion seems to be bent, it follows that the rays dif-
fused from it are bent; that is, they travel in
straight lines through the liquid, but on entering
the air, they are made to deviate from their
straight course. But the eye is in the habit of
following the direction of the rays, and must see
the pencil bent simply because the rays coming
from it are bent.
Let a b be the pencil partly immersed ; the part
immersed, a c, appears to be at d c, because the
ray coming from a, which ought to
pass out in the direction of a 6, is
made to deviate from its course
when leaving the water at c, and
enters the eye in the direction of d
e. The eye, believing the point a to
Fio.28. be in the direction from which its
ray comes, sees the point a actually as being at d.
The same takes place with the other rays entering
the eye ; hence the whole part a c is seen as being
at dc.
9
130 FIRST LESSONS IN PHYSICS.
64. EXPERIMENT. A coin placed on the bottom
of a filled tumbler, is seen in its
true direction if viewed perpendicu-
larly; but if viewed obliquely, it
will be seen in a more elevated
place.
FIG. 29.
Familiar Facts Owing to refraction of light.
the bottom of clear waters appears to be more
elevated than it really is ; that is, water often ap-
pears less deep than it in reality is. This must be
taken into account by persons bathing, so that
they may not go beyond their depth.
Rays of light, on passing obliquely through
substances of different densities (such as air
and water, or glass and water), deviate from
their straight course; they are bent. This de-
viation is called Refraction of Light.
PRISMS LENSES.
131
riQ. so.
LESSON XXXV.
PRISMS. LENSES.
65. EXPERIMENT. On a blackboard make a
mark in the shape of
an arrow, and look
IX e jjM a t i fc through a glass
Jil>^ P rism > which sh ld
be held so that only
one edge of it is di-
rected upward (Fig.
30). The arrow will
then be seen as being above its true place. The
reason is this : Rays of light, a e we take but
two for the sake of simplicity diffused from the
arrow, strike the surface, b c, obliquely, and are,
therefore, refracted to / (Less. XXXIV). On pass-
ing from the glass prism at /", they are again re-
fracted, and enter the eye which is stationed at g.
But the eye follows the direction of the refracted
rays (Less. XXXIV);
consequently it sees
the arrow as being
at h.
66. EXPERIMENT.
^ w Now look at the
4 f ' f '' arrow on the black-
no, n. board through the
132
FIRST LESSONS IN PHYSICS.
prism inverted (Fig. 31); that is, placed so as to
present two edges upward. The arrow will then
be seen below its true place. The reason of this
is the same as before. The rays a e are refracted
to// consequently the arrow is seen as being at A:.
If now we place two prisms together, as in
Fig. 32, rays diffused from the arrow and entering
the glass surface, a be, will, in like manner, be
refracted twice, and meet each other in several
PRISMS LENSES.
133
points behind the prism. In order that the eye
of a person situated at /, might receive all these
refracted rays, and thus be able to see the whole
arrow through the prisms, it would be necessary
to have these rays blend into a common point.
To do this, we must have the surface, a b c, curved
(Fig. 33) ; that is, we must have a curved glass in
place of the prisms. Such a curved glass is a
convex Lens, commonly called a Burning -glass.
For it not only brings rays of light to a common
point, the Focus, but at the same time it blends
rays of heat into a focus. In consequence of this,
a match ignites, and a hole is burnt in a piece of
paper, if either of these objects be held in the
focus.
FTOM.
The arrow, as viewed through a lens, is seen
larger (Fig. 34) ; that is, it is magnified, because
134 FIRST LESSONS IN PHYSICS.
taking the two extreme rays for the sake of illus-
tration the rays, d e and f g, refracted to the
eye, are seen as coming from the points h i.
(Why? Lesson XXXIV, p, 130.) The common
Burning glass, therefore, is also called Magnify-
ing- Glass.
An object in front of a convex lens is seen mag-
nified by an eye placed behind it.
Application. The lenses in spectacles ; opera-
glasses and telescopes ; all magnifying glasses.
Bead "Magnifying and Burning Glasses," in "Pursuit of KnowL
edge," Vol. II. Harper & Bros.
Bead "Ltnses,"'m "The Wonders of Optics" Illustrated Library of
Wonders.
Bead "How to View Pictures," p. 248, in "Spectacles," p. 250 m
"Things not Generally Known."
COLOKS. 135
LESSON XXXVI.
COLOR.
66. EXPERIMENT. If a large pasteboard with
a small hole be placed facing the sun ; or if a
room be darkened and only a few rays of light
admitted through a crack in the shutter, these
rays will pass to the floor and there form a spot
of white light. But if a prism 1 be held before
the crack or before the hole in the pasteboard,
the rays of light will be refracted (Less. XXXIV),
and spread out in the form of a long band. In-
stead of being white, this band will be colored.
The colors of the rainbow may be distinguished
in it ; viz. : Violet, indigo, blue, green, yellow,
orange and red. The colored band is called the
Solar Spectrum ; and this spreading out of light
1. A prism which is to show the refraction of light, may be of solid
glass, or, if such a one can not be had, it may be constructed in the fol-
lowing manner : Procure two strips of common
glass, having the shape of a rectangle, each of the
same size, about 5 inches long by ij inches wide.
FIG. 35 One of the long edges of each is heated over an
alcohol flame; both edges are then cemented together with sealing-wax,
allowing a distance of i^ inches between the two remaining long edges.
The ends of the vessel thus formed are closed by triangular pieces of
thin board, measuring \}/ z inches on each side, and which are likewise
cemented to the glass. Water is then put in, and when used, the prism
is held so as to have the long cemented edge below.
136 FIRST LESSONS IN PHYSICS.
is called Dispersion. If the spectrum be made to
fall upon a mirror, it will be reflected in straight
lines like ordinary light.
67. EXPERIMENT To convince ourselves that
ordinary sunlight contains the seven colors of
the rainbow, let the spectrum produced by one
prism fall upon a second
prism of the same size
as the first, but placed
as shown in the figure
annexed The rays of light, dispersed by the first
prism, have been collected by the second and have
produced white light again.
68 EXPERIMENT. The same may be shown if
a top, painted with the seven colors of the rain-
bow, is set spinning rapidly. The impressions
made in the eye by these different colors are
mixed together, and thus produce a mixture of
the colors which is nearly white.
All this shows that white sunlight is composed
of the seven colors of the rainbow.
69. EXPERIMENT. Between the crack, or the
hole in the pasteboard, and the prism insert a
piece of red glass. The spectrum will then be
almost entirely red, and the other colors be found
wanting Insert a piece of green glass in place of
the red ; the spectrum will be almost exclusively
green ; with blue glass it will be nearly blue, &c.
It is manifest, that white light falls upon each
COLORS. 137
piece of colored glass ; and that only one color at
a time falls upon the prism. Thus when the red
glass is inserted, only red light falls upon the
prism, and consequently there can be but a spec-
trum of red light. The question now is, what
becomes of the remaining light or colors which
fall on the red glass ? Evidently the red glass
absorbs all the light except the red, and this it
throws out. The same takes place with each of
the other colored glasses ; the green absorbs all
the light it receives except the green light ; this it
throws out. The blue absorbs all the light it re-
ceives save the blue, which it throws out, &c.
White glass, however, transmits nearly all the
light, and absorbs very little or scarcely any.
70. EXPERIMENT. If a sheet of red colored
paper be held facing the sun, and a sheet of
white paper before ^it, so as to form an oblique
angle with it, the portion of the white paper
which is near the red, will appear red. In this
case red rays are diffused from the red body and
fall upon the white. But the red paper receives
white light from the sun, hence it must have ab-
sorbed all of the white light save the red ; this it
throws out.
Familiar Facts. Objects near a blue curtain
often have a bluish hue. The curtain receives
white light, and absorbs it all except the blue,
which it reflects. Objects near the foliage of
138 FIRST LESSONS IN PHYSICS.
trees and bushes often have a greenish hue, be-
cause green leaves absorb all the light that falls
upon them save the green ; this they diffuse in all
directions, and thus send green light to the ob-
jects near by.
A body is colored when it reflects only a por-
tion of white light. A body is white when it re-
flects all the white light; and a body is black
when it reflects (almost) no light, that is, when it
absorbs all the light.
Questions. What causes a piece of red cloth
to appear red? It sends only red rays to the eye,
the other rays it absorbs. What causes a sheet
of white paper to appear white ? It absorbs no
light, but rejects nearly all of it. Some of this
rejected or reflected light enters the eye and thus
produces the sensation of white in us.
What causes a black coat to be black ? It ab-
sorbs nearly all the light, consequently it sends
scarcely any to the eye. The eye receives just
enough light from it to become aware of its pres-
ence, but not sufficient to perceive any color.
Why is every thing black in a dark night?
Because, when there is no light, objects receive
none, and, therefore, they can not send any to the
eye. But if no light enters the eye, we see
nothing (Lesson XXXHI).
Color is not a quality inherent in bodies.
COLORS. 139
Application. The application of colors is so
manifold, that it is impossible to mention each.
They serve to enliven the scenery aronnd us , to
improve our own appearance , to indicate joy or
mourning. We imitate the thousand delicate
hues and tinges of the colors in nature in our
paintings, artificial flowers, and in many different
contrivances Colors also serve as signals to be
seen from afar; hence their use in lighthouses,
on railroads (colored lights), and with the mili-
tary (flags), &c., &c.
Bead " Color- Blindness," p. 242, and "Principles of Harmony and
Contrasts in Color," p. 244, in " Things Not Generally Known." W
Bead " Color," in "The Earth and its Wonders."
140 FIRST LESSONS IN PHYSICS.
LESSON XXXVII.
CHEMICAL ELECTKICITY.
-
71. EXPERIMENT. Take a plain glass tumbler,
and place in it a porous cup of earthenware (un-
glazed) in a manner such, that between the cup
and the tumbler there is a finger's width of space
left. Next have a small sheet of zinc cut as high
as the cup. Then bend it into a cylinder wide
enough to encircle the porous cup freely. This
cylinder is open above and below, with a slit
through its whole height. On the top, and oppo-
site the slit, about a square inch of zinc is left
higher than the rest. To this piece, one end of a
copper wire about a foot long is soldered. The
zinc cylinder is put into the space between the
tumbler and the cup ; the space is then filled with
diluted sulphuric acid (a table-spoon full of the
acid mixed with ten times the quantity of water).
The cup is filled with strong nitric acid. In the
acid place a plate of carbon, to the top of which
the end of another copper wire is soldered. If no
carbon plate can be had, a narrow strip of pla-
tinum may be used, and another wire soldered on
it. If that, too, can not be obtained, fill the cup
with crushed coke. 1 Thus prepared, the cup is
I. The filling with coke must be done in the following manner : Coke
is pulverized in a mortar, then a small quantity is first put in the cup
CHEMICAL ELECTRICITY. 141
placed inside the zinc cylinder ; the diluted acid,
of course, surrounding it. Such an apparatus is
called a cell or element ; if two or more cells are
connected with each other, the apparatus is called
a battery.
The free end of the wires must be scraped clean
with a file or knife. If, then, they are brought
quite near to each other, a small, bright spark
is produced. If the tongue is held between the
two ends, a thrilling sensation is felt /J JK ,
In the first place, the diluted acid acts upon
the zinc; this action may be seen by the minute
bubbles rising from the zinc; it may also be
heard. They are bubbles of a gas called hydro-
gen. In the second place, we have carbon, or
platinum, in contact with nitric acid; the action
which takes place here is invisible. Thirdly, the
two liquids penetrate the porous cup, and, there-
fore, meet with each other. This action is in-
visible also.
The mutual contact of two different metals
(or of zinc and carbon), each* placed in a certain
liquid, produces Chemical Electricity.
This electricity is also called " Galvanic Elec-
and a little nitric acid mixed with it, so that the powder may be soaked
with acid. This is repeated several times, until the cup is nearly filled
with saturated coke. On top of the coke a lump of coke is placed,
around which a copper wire is wound several times, so that about a foot
length of wire remains free. That the coke lump may stand firmly,
surround the lower part of it by coke powder.
142 FIRST LESSONS IN PHYSICS.
tricity," because it was discovered by Galvani,
an Italian physician, toward the end of the last
century.
The electric spark is seen only when the free
ends of the wires are brought together. The zinc
is in contact with the diluted acid; electricity
passes from the zinc to the acids, and thence to
the carbon, and from the carbon, electricity, that
is the invisible electric current, passes along the
copper wire, returns to the zinc, then to the diluted
acid again, and so forth, in the same manner as
above, forming an uninterrupted current of Elec-
tricity. If the metals (wires) are not very near
to each other, no spark is seen, and the current is
interrupted. If the end of one of the wires be
attached to a pair of scissors, the spark will be
seen at the point of the scissors on bringing it
very near to the other wire. Nor would it make
any difference if the wires had greater lengthy
THE ELECTRO-MAGNETIC TELEGRAPH. 143
(c
LESSON XXXVIII.
THE ELECTRO-MAGNETIC TELEGRAPH.
Next to the steam-engine the telegraph forms
the wonder of our age. Its eminent usefulness
and, more yet, the incredible rapidity with which
it communicates messages from one place to an
other, is something so new, so extraordinary, that
we are tempted to believe there is nothing which
the human mind is not capable of penetrating.
The fire-signals of the ancients were no longer
sufficient for the increasing demands of civiliza-
tion. Toward the end of the last century, so-called
u optical" telegraphs, consisting of high poles
erected upon high buildings or hills were used in
France. By means of moveable arms attached to
them, signs could be made which in clear weather
were visible at great distances. But when, in 1820,
it had been discovered by Oerstedt, a Danish pro-
fessor, that the electric current running along a
wire, exerted a certain influence upon iron, it was
at once proposed to apply that influence to the
telegraph.
The first electric wire by which messages were
sent, was put up by Steinheil, between his place
of residence in Munich and the astronomical
observatory near that city. England soon fol-
144 FIRST LESSONS IN PHYSICS.
lowed the example ; so did America. As is
always the case with new inventions, a great
many improvements were made in rapid succes-
sion. It was an American, Morse, who, by a very
simple but ingenious improvement, brought the
telegraph to its present degree of perfection.
The principle of Morse's telegraph may be
illustrated easily by the following experiment :
72 EXPERIMENT. A cylindrical rod of soft
iron is bent into the shape of a horse- shoe. The
rod may be J inch in diameter and 10 inches long.
Its two ends must be filed smooth ; the whole is
then covered with clay and placed in a coal fire.
There it is left for a time and allowed to cool
gradually, until the fire has gone out. After this
the clay is removed, and the two ends filed smooth
again. Then take a coil of copper wire of about
-5*2 of an inch diameter, heat it red* hot and cool
it in water. Silk ribbon is then
wound around it (old silk rags
sewed together and cut into strips,
will serve the purpose very well),
in a manner such that the ribbon,
about \ inch in width, shall com-
pletely envelop it. The wire thus
covered, is wrapped round the
iron in close windings. (See Fig. 37.) When
beginning to wrap, leave about two feet of
wire free, wind then closely near to the bend ;
ELECTRO-MAGNETIC TELEGEAPH. 145
leave the bend uncovered, and stretch the wire
across to the other arm. Then proceed down-
ward to the other end, and leave the last two feet
of the wire again free. Both ends of the wire are
to be scraped clean, and afterward connected with
the wires of the galvanic element, so that the wire
starting from the carbon (or platinum) be con-
nected with one of the wires of the horse-shoe ;
and the wire of the zinc cylinder, with the other
wire of the same. 1
If now a piece of soft iron, smooth on one
side, or a nail, be held at a small distance from
the ends of the bent rod, it will be attracted by
them, and adhere. TTie electricity flowing around
the iron rod, has rendered the rod magnetic ; its
ends are now magnetic poles. (See Lesson III.)
The galvanic current now travels from the car-
bon along the wire, passes through the place
where the wires are fastened together, and enters
the wire leading to the horse- shoe. Then it runs
through all the windings of the two coils, and, in
doing so, constantly flows around the iron rod.
Leaving the iron rod at the other end, it passes
along the copper wire, enters the (zinc) wire where
the two wires are connected with each other, and,
finally, arrives again at the zinc, whence it starts
again to make the same travel anew.
i. The connection may be effected either by holding the two respective
wire-ends firmly together with both hands, or by twisting them closely
together.
IO
146 FIRST LESSONS IN PHYSICS.
Disconnect one of the wires, either by withdraw-
ing one hand, or by untwisting the wire ends; if
the iron rod is of the right kind, the piece of soft
iron attached will drop instantly. If held up
against the poles again, it will not be attracted
so long as the wires remain disconnected. The
iron rod shows no trace of magnetism. Evidently
it was magnetic only as long as the electric cur-
rent flowed around it. 1
Iron becomes magnetic when an electric current
passes around it in many windings. When the
current is interrupted, it ceases to be magnetic.
Such an iron rod has usually the shape of a
horse-shoe, or hair-pin, and is called an Electro-
Magnet. The piece of soft iron applied to its
poles is called the Keeper.
Principles of the Electric Telegraph.
I. According to Lesson III, magnets have the
power of attracting iron ; by means of alternately
closing and breaking the electric current, the
electro-magnet renders apiece of soft iron alter-
nately magnetic and unmagnetic.
n. The length of the wires connecting the gal-
vanic battery with the electro-magnet is imma-
I In most cases some electricity is left after the current has been in-
terrupted. It lasts, however, but a short time.
ELECTRO-MAGNETIC TELEGRAPH.
147
terial ; it may be thousands of miles. Thus a
battery may be in the city of New York, while
the electro-magnet with which it is connected is
set up in St. Louis, a distance of 1200 miles of wire.
III. A person stationed at the battery, may,
by disconnecting and connecting the wires, "break
and close the current at his pleasure.
The three principles can be demonstrated
by a simple apparatus shown in Fig. 38. Two up-
right pieces of board, M N, are fastened to a table
so as to admit the
wooden piece, #,
between them. The
horse-shoe rod, A,
is made an electro-
magnet whenever
the wires are pro-
p e r 1 y connected
with the galvanic
element. A piece
of soft iron, d e, on
which thin paper
has been pasted, is
attached to a one
armed lever, b c> FIG. as.
whose fulcrum is at D. When the electric cur-
148 FIRST LESSONS IN PHYSICS.
rent passes through A, the poles of the Electro-
magnet attract the Keeper d e; but on breaking
the current by disconnecting one of the wires, the
Keeper will drop. To prevent its dropping too
far, there is a wooden support, g, which does not
allow the Keeper to separate from the poles of the
Electro -magnet more than perhaps 1-10 of an inch.
A piece of wire previously wound around a lead-
pencil, serves to draw the lever promptly down-
ward. The paper pasted on the Keeper immedi-
ately disconnects the latter from the poles of the
magnet when the current is broken. Lastly, a
wooden point, f, writes the message upon an end-
less band of paper, which is unwound from a
cylinder above it. This cylinder is not repre-
sented in the drawing.
When the keeper is attracted by the magnet,
the point f makes a mark or indentation, on the
paper. But when the current is interrupted, the
Keeper drops, and the point drops at the same
time ; consequently no mark is then made. To
represent the letter a, for example, a sign : ,
is impressed upon the paper ; the operator at the
delivery station closes the current for an instant
only, this produces the small line ; then he
breaks it, but immediately afterward closes it
again, and keeps it closed three times as long as
before. This produces the other line, , and
now the letter a is on the paper of the operator
ELECTRO -MAGNETIC TELEGRAPH. 149
In the receiving station. To write the word table,
the following signs are necessary :
t a . b I e
Experienced operators are able to write down
the messages merely from the clicking of the lever.
Magnet and Electro-Magnet Compared.
Five points in common :
1. Both attract iron.
2. Each has usually the form of a horse-shoe.
3. Each has two poles.
4. In both the power resides chiefly at the ends.
5. Both are eminently useful to man : the mag-
netic-needle as a guide upon the ocean ;
the electro-magnet as a carrier of messages.
Three points of difference :
1. A magnet has no wire coil (helix) around it ;
an electro-magnet has.
$. A magnet always attracts iron ;
an electro-magnet, only when an electric
current passes around it.
3. By means of a magnet, a needle may be ren-
dered a permanent magnet ;
with an electro-magnet a needle is magnetic
only during contact with the electro-magnet.
Read " The Old Telegraphs," p. 69" The Laying of tht Atlantic
Cable," p. 193, in "Inventions and Discoveries," by Temple. Groom-
bridge. London.
150 FIRST LESSONS IN PHYSICS.
LESSON XXXIX.
REVI EW .
LESSON xxxn.
1. The Sun, the Fixed Stars, Electricity, Phos-
phorescence, Luminous Animals, and Burning
Substances, are Sources of Light.
2. Neither the plants nor most of the objects
around us, are self-luminous bodies.
3. Bodies not self-luminous are visible only when
they receive light from a self-luminous body,
and when a portion of that light forms an im-
pression upon our eye.
4. Light emanates from a self-luminous body in
all directions, and travels in straight lines.
LESSON xxxni.
5. All bodies reflect light radiantly.
6. Objects with polished surface reflect light, both,
radiantly and specularly.
7. All bodies appear to be in the direction whence
their rays enter the eye.
8. Rays of light, on passing obliquely through
substances of different densitj 7 ", such as glass,
water, or air, deviate from their straight
course ; they are refracted.
LESSON xxxv.
9. An object before a convex lens, appears mag-
nified to the eye situated behind it.
REVIEW. 151
LESSON XXXVI.
10. White sunlight is composed of the colors of
the rainbow.
11. A body is colored when it diffuses only a por-
tion of the white light it receives ; a body is
white when it diffuses all the white light it
receives ; a body is Hack when it absorbs all
the white light it receives.
12. Color is not a quality inherent in bodies.
LESSON XXXVII.
13. The mutual contact of two different metals
(or of zinc and carbon), each placed in a
certain liquid, produces chemical electricity.
14. Chemical electricity travels in a circuit from
its source and back again.
LESSON xxxvin.
15. Soft iron is magnetic, when an electric current
passes around it.
When the current is interrupted, it ceases to
be magnetic.
16. The principles of the Electric Telegraph are :
1. A piece of soft iron may be rendered alter-
nately magnetic and unmagnetic by means
of an electro-magnet.
2. The electric current travels over any length
of wire.
3. A person stationed at the electric battery,
may close and ~break the current at Ma
pleasure.
QUESTIONS.
(Questions preceded by a = are of a more difficult character.)
LESSON 1. GRAVITY.
PAG* 9.
I. Why does a stone in our hand
not fall ?
2 Why does it fall when drop'd?
PAG* 10.
3. Why does a pencil roll down
from the desk ?
4 Whither does a stone thrown
into a pond fall ? and why ?
5 Whither does a sign-board
blown off by the storm ? and
why?
6 Whence does rain, snow and
hailstones come ? and why ?
7 When does water form water-
falls ?
8. Why do coals fall through the
grate ?
9. Why does soot, through the
air?
10. To what purpose are heavy
rods attached to maps and
curtains ?
11. To what purpose are clocks
provided with weights ?
12. Why is it that all bodies near
the earth have a tendency to
approach the earth? (Text
p. 10.)
13. Give the law of gravity.
PACE II.
14. Why is a string, with a weight
attached, drawn straight?
15. What prevents the weight
from falling ?
1 6. What does the string indicate?
17. Define vertical.
1 8. What is a plumb-line ?
19. Give the law of Direction of
Force of Gravity.
PAGE 12.
20. Why does a large stone press
itself partly into the ground?
PAGE 12.
21. Why do heavy wagons make
ruts?
22. In what manner do ladies
judge of silk robes ?
23. Define weight.
24. What is a balance ?
25. What are the weights ?
PAGE 13.
26. How does it come that a pound
of coffee has as much weight
as a pound of lead ?
27. a pound of feathers as
much as a pound of iron ?
28. Of what force of Nature is the
Balance an application of?
29. Clock weights ?
30. Hour-glasses?
31. Why is a large drop of mer-
cury lying upon the table
never entirely round ?
32. Why do wagons, unless
checked, roll down hill with
great rapidity ?
33. Why do light bodies, such as
feathers, bits of paper, &c.,
fall to the ground more slow-
ly than heavy bodies, such as
stones and the like ?
34. Where must a rod be support-
ed to be evenly balanced ?
35. How can the weight of a body
be found by means of a bal-
anced rod ?
36. Has a body the same weight
on different heavenly bodies?
37. What will a pound of tea
weigh on the moon ?
38. What, on the sun ?
39. What, in the center of the
earth ?
40. What, half way between cen-
ter and surface ?
INDEX.
PAGE.
Lenses 133
Level 12
Lever 59
Light, Direction 124
Light, Sources 122
Light, Radiant and Specular
Reflection 125
Light, Radiant and Specular
Reflection Compared 127
Lightning 26
Lightning- Rod 27 38
Locomotive 117 118
Low Pressure 115
Magnetic Attraction 17
Magnet 18
Magnet compared with Elec-
tro-Magnet 150
Malleable 41
Metals, Conductors of Heat . . 94
Morse's Telegraph 145
Needle, How rend. Magnetic. 19
Newcomen's Engine 108
Nui-Cracker . . .. 6"
Papin's Apparatus 105
Pendulum 63
Persons Drowning 1 6
Pith-balls, How made 22
Plumb-line n
Poles of Magnets 19
Pop-gun 43
Pores 31
Pressure of Air 46 50
Pressure, Downward 12
Prisms 132, 136, 137
PAGE.
Pump, Common 74
Pump, Forcing 77
Pull .. 84
Push . x 84
Radiation of Ligfit 125
Rain 89
Reflection of Light 125
Refraction of Light 129
Refraction of Light, Law 131
Repulsion, Electric 23
Self-luminous 123
Sliding-valve 115
Snow .. 90
Sound 85
Spark, Electric 21
Steam-Engine, Atmospheric . . 105
Steam-Engine, Newcomen's.. 108
Steam-Engine, Papin's 105
Steam-Engine, Savery's 108
Steam-Engine, Watt's 112
Telegraph '. 144
Telegraph, Principle of, . .... 147
Telegraph, Prin. Demonst'd. 148
Thermometer 100, 102
Thermometer compared with
Barometer f 104
Vacuum * . . . 49
Vertical II
Visible Direction 1 28
Watt, James 112
Weight 12
Winds, Cause of 98
Work done by forces . . , 83
154
FIRST LESSONS IN PHYSICS.
41. Would it weigh more, or less,
if at a considerable distance
above the surface ?
42. What causes the tide-waves ?
43. What, the revolution of the
moon around the earth ?
LESSON II. SPECIFIC GRAVITY.
FLOATING AND SINKING SOLIDS.
PAGE 14.
44. What is meant by the state-
ment "Water is heavier than
oil ?"
45. How should the statement be?
46. Prove that a pound of water
is as heavy as (better: has
the same weight as) a pound
of oil.
47. Why does a pint of mercury
weigh more than a pint of
water ?
48. Why has a solid rubber-ball
more weight than a hollow
one ?
49. Have all solids the same
weight ?
50. Have all liquids ?
51. Define Specific Gravity.
52. What makes oil float on water?
(Answer: The fact that oil,
&c., &c.)
53. How does it come that smoke
rises, while soot falls?
(Quest. 9.)
54. Why does oil rise thro' water ?
55. Why do balloons rise through
the air?
PAGE 15.
56. Give law about Fluids of dif-
ferent specific gravity.
57. Why does a piece of wood
float, while a stone sinks,
when thrown into water ?
58. Prove that liquids have
weight.
59. Will the weight of a pail of
water be increased when a
fish is thrown in ?
60. Why does an empty flask float
on water ?
61. Why does it not also in air ?
PAGE 15.
62. Why does a bottle filled with
water sink in water ?
63. Why does it float on mercury ?
64. Under what circumstances
does a body float ? sink ?
65. Why do iron-clads float ?
66. When will the body of man
float?
67. Why is it difficult for bathers
to walk in water chin deep?
(In text.)
68. In drawing water from a well,
why has the bucket more
weight as it emerges from
the water? (Same.)
69. Why may heavy stones be
lifted in water, while on dry
land they can scarcely be
moved? (Same.)
70. What should persons who can
not swim, do on falling in
the water ?
71. Why does ice float on water ?
72. Why does a full tumbler run
over when a stone is thrown
in, and not when a piece of
, sponge?
73. Why does wood saturated with
water, sink ?
74. Vhy do some bodies, floating
on water, sink in it more
than others; thus oak wood
more than pine wood ?
75. Why can persons float on
water by means of life-pre-
servers or bladders filled
with air?
QUESTIONS.
155
77
Why do we often see a sedi-
ment on the bottom of ves
sels containing liquids, after
they have been standing for a
time?
Why do drowned persons,
after having lain under water
for a time, rise to the sur-
face ?
78. Why do ships sink deeper in
river water than in the ocean?
79. Why does a hen's egg float on
water strongly salted, while
it sinks in fresh water ?
80. Why does water in a vessel
rise higher on dropping into
it a pound of iron than it
does when a pound ot lead
is dropped hi ?
81. Why must a dog sometimes
drop a heavy stone (after hav-
ing fetched it Jrom the bot-
tom of a water) when he
reaches the surface ?
82. What enables fish to move up
and down in the water at
pleasure ?
LESSON III. MAGNETIC ATTRACTION.
PAGE 17.
83. Under what circumstances
will a plumb-line change
from the vertical direction ?
84. Will it also change if its weight
is a stone ?
85. Mention a force which may
overcome gravity.
86. Show that magnets and un-
magnetic iron attract each
other.
87. Give a property common to
both, magnetic attraction and
gravity-attraction.
PAGE 1 8.
88. Where does the power of a
magnet chiefly reside ?
89. What is the difference between
a magnet and a piece of un-
magnetic iron ?
90. What is the name of the ends
of the magnet ?
91. Where do these ends point ?
92. In what position must the
magnet be in that case ?
97-
PAGE 1 8.
93. State the law of direction of a
magnet.
94. What action is seen in two
magnets whose like ends
are brought together ?
PAGE 10..
95. Give law for it.
Whence the application of
magnets ?
Is a magnetic needle liable to
deviate more on a wooden
vessel than on an iron ?
98. How may a magnet be made ?
99. Why have magnets usually
that form ?
100. Describe a magnet.
101. Does the earth act like a mag-
net ?
Give reasons for your answer.
102. What reason have the French
for calling the north pole of
a magnet its "South Pole,"
and the south pole its ' 'North
Pole?"
LESSON IV. ELECTRIC ATTRACTION.
PAGE 20. PAGE 2O.
103. Whence the term "Electri- 105. Same, regarding paper.
city ?" I0 g tate the source O f electricity.
104. What power may sealing- wax,
sulphur and glass acquire; IO 7- What peculiar property do
and on what condition ? electric bodies manifest
156
FIRST LESSORS IK PHYSICS.
PAGE 21
1 08. What phenomena may accom-
pany electrified bodies ?
109. Why the peculiar sensation
felt on holding electrified
paper against one's face ?
PACK 22.
1 10. What becomes of electricity
after it has left the sulphur,
or the glass ?
in. Mention two good conductors
of electricity.
112. Three non-conductors.
113. Give difference between good
conductors and non-conduc-
ors.
Can electricity be produced
upon both classes of bodies?
PAGE 23.
114. \Vhat phenomena take place
when electrified sealing-wax
is presented to a suspended
pith ball?
115. When, only, do they take
place?
1 1 6. Did you notice anything simi-
lar in magnets ?
117. In gravity ?
no. What phenomena, when elec-
trified sealing-wax is pre-
sented to two pith balls f
119. What force is overcome hi that
case?
120. Was that same force ever
overcome before ? (Comp.
question 85.)
PAGE 23.
121. What phenomena, if first seal-
ing-wax and then glass is
presented to the single pith
ball?
122. How do you explain your
answer ?
PAGE 24.
123. W r hat phenomena if first seal-
ing-wax and then glass is
presented to one of the two
pith balls ?
124. What phenomena if to one of
the two pith balls you pre-
sent sealing-wax, and at the
same time, glass to the other?
PAGE 25.
125. How many kinds of electri-
city? Name them.
126. Give law of electricity.
127. Explain principle and action
of Lightning Rods.
128. On rubbing glass on flannel,
do you produce only one
kind of electricity, or both
kinds?
129. Why does an electrified bar
of sealing-wax gradually lose
its electricity ?
130. Why do small pith balls upon
a table jump up and down,
if a sheet of electrified paper
be held over them.
LESSON V. LIGHTNING. LIGHTNING-RODS.
PAGE 26.
131. What was Franklin's merit
regarding the explanation of
lightning ?
132. Give an account of Franklin's
experiment.
Why the pointed iron
wire on top of his kite ?
133. Could he have taken a silk
string instead of a hempen
one ?
134. What was the purpose of the
the key?
PAGE 27.
135. What made the fibres of the
string bristle up ?
136. What does Franklin's experi-
ment demonstrate ?
137. What is the cause of light-
ning?
138. Give three paths which light-
ning may follow ?
139. What objects are most liable
to be struc!; ? and why ?
QUESTIONS.
157
PAGE 27.
140. Why should you not stand
under a tall tree during a
thunderstorm ?
PAGE 28.
141. Which is the safest place in a
room during a thunder-
storm ?
PAGE 28.
142. Give an account of the light-
ning-rod.
143. On what conditions may a
lightning-rod be called good?
144. What becomes of the light-
ning after passing down
along the rod ?
LESSON VI. COHESION.
PAGE 29.
145. Why is it that meat must be
cut, while bread may easily
be broken ?
146. Why is water easily divided,
while ice is not ?
147. What is the name of the force
which causes the parts of a
solid to remain together ?
148. Why is rolled iron stronger
than common iron ?
149. To what purpose does a
knowledge of the cohesive
force serve ?
150. Could birds fly in water ?
PAGE 30.
151. Why would it be difficult for
us to walk through molasses?
152. What must be done to break
a body?
153. Why has a walking-cane lost
its strength if after being
broken, the parts are glued
together ?
PAGE 31.
154. What is the great enemy of
cohesion ?
155. Why does oil form larger
drops than water ?
156. What are pores ?
157. Why is a dry sponge smaller
than a wet one ?
158. What makes blotting-paper
remove fresh ink ?
159. Why do doors, window-frames
and drawers often swell in
damp weather ?
1 60. Plow is it that mercury can be
pressed through a leather
bag?
161. What causes wooden tubs to
leak in summer ?
162. What may be done to prevent
this ?
163. Define tenacious, (p. 37> No.
12.)
164. Define hard. (Ibid.)
LESSON VII. ADHESION CAP. ATTRACTION.
PAGE 32.
165. How can two leaden bullets
be made to adhere ?
1 66. Why do not two bricks ad-
here in the same manner ?
167. When, only, does adhesion
take place ?
;V.GE 33.
1 68. How may two rough surfaces
be made to adhere ?
169. Why does the hand become
wet when immersed in
water? (Given in text.)
1 70. Why does it remain dry when
drawn out of mercury ?
PAGE 33
171. What two forces are in strug-
gle with each other when the
hand is placed in water ?
172. Define adhesion.
173. Why are two smoothly pol-
ished plates separated with
great difficulty, if laid to-
gether and firmly pressed ?
174. Why does fresh paint adhere
to one's dress ?
PAGE 35.
175. What is a capillary tube
176. Define capillary attraction.
158
FIRST LESSONS IN PHYSICS.
PAGE 35.
177. What causes the sponge to
absorb water? (Comp. 157.)
1 78. Why may eggs and meat be
kept fresh in sand ?
179. Explain the action of oil in
lamp- wicks.
1 80. How, and why, may grease
spots be removed from the
floor?
181. Why do two papers pasted
together adhere firmly ?
183. Why may the hand be drawn
out of the water dry, if, be-
fore immersed it was cover'd
with Lycopodium powder?
183. Why is a greased glass not
moistened when immersed
in water ?
184. Why does a small drop of
water on a board remain tho*
the board be inverted?
185. Why does a drop of mercury
fall when the board is in-
verted ?
1 86. Why does a small drop of
mercury on a tin plate re-
main when the plate is in-
verted ?
187. Why do figures drawn with
the finger upon a window-
pane, become visible if we
breathe on them ?
LESSON IX. ELASTICITY.
PAGE 39.
188, What makes an arrow, shot
from a cross-bow, fly a great
distance ?
189, What makes steel, ivory and
India-rubber resume their
former position after being
bent?
190. Define elastic.
PAGE 40.
191. Why is the spot which an
ivory ball receives upon fall-
ing on a blackened surface,
larger if the ball has fallen
PAGE 40.
from a considerable height,
than if it has merely been
pressed with the hand upon
that surface ?
192. Why does an India-rubber
ball rebound on striking ?
PAGE 41.
193. How may the elasticity of air
be shown ?
194. Define brittle.
195. Define malleable and ductile.
196. Give examples of brittle, mal-
leable and ductile bodies.
LESSON X. ELASTICITY OF AIR.
PAGE 42.~
197. Show that air, like every other
body, maintains its place.
PAGE 43.
198. Why does not water enter a
bottle in the neck of which
a funnel is cemented ?
199. Describe the action of the pop-
gun.
200. What is its principle ?
201. Principle of the blow-pipe?
202. Principle of the Diving-bell ?
PAGE 43.-
203. What causes the air inside a
Heron's Fountain to be com-
pressed ?
204. Describe the action of a
Heron's Fountain.
205. Give the law on elasticity of air.
206. What is an air-chamber ?
207. Describe its actio
208. Why do fire-wheels turn?
209. Why do sky-rockets ascend?
210. Why do cannons recoil whet.
fired off?
QUESTIONS.
159
LESSON XL PRESSURE OF AIR.
PAGE 46.
211. Why does the water not flow
from a filled inverted tum-
bler, with a piece of paper
pressing against it ?
212. Show that air presses down-
ward.
PAGE 47.
213. Show that air presses in all
directions.
PAGE 48.
214. Why does not vinegar flow
from a barrel whose bung-
hole is closed ?
215. Explain the action of the
"Thief."
216. Why do we not feel the
pressure of air exerted upon
us?
217. Why are travelers more easily
fatigued on high lands than
on low lands ?
218. What makes us feel tired dur-
ing excessive heat, or before
a thunderstorm ?
219. Whv is it that, when a bottle
filled with air in the low
land is taken up on high
land, the air will escape with
violence when the bottle is
opened ?
LESSON XII. BAROMETER.
PAGE 49.
220. W hat is a vacuum ?
221. Describe the barometer.
222. What supports the column of
mercury *
PAGE 50.
223. Why does not the bulb need
to be open ?
22^ What do force of pressure,
magnetic attraction, and
gravity-attraction have in
common ?
225. Give the amount of air-press-
ure.
226. What causes the mercurial
column to rise?
227. What causes it to fall?
228. What is its use ?
229 Whence the use of the bar-
ometer ?
230. Show that the air-pressure
out-doors is the same as that
inside the house.
PAGE <;i.
531. Why may the barometer in-
dicate rain?
PAGE 51.
232. Why, fair weather ?
233. Are its prophecies reliable ?
234. What influence does moisture
in the atmosphere exert upon
the barometer ?
:,35- To what extent may wind in-
fluence the barometer?
(Remember that wind is air
in motion.)
236. Why does the mercury in the
barometer fall when carried
up on the mountains ?
237. Does atmospheric pressure in-
crease or decrease, as we go
away from the earth?
238. Supposing the moon to have
a terrestrial atmosphere,
how high would the mercu-
rial column stand there ?
239. How high on the sun ?
240. At the center of the earth ?
160
FIRST LESSONS IN PHYSICS.
LESSON XIV INERTIA.
PAGE __
241. Show that a body at rest re-
mains at rest until set in
motion by some force.
242. Show that for a body to be
set in motion, time is neces-
sary.
PAGE 54.
243. Show that a body once in mo-
tion remains in motion until
stopped.
Show that for the motion of a
body to stop, time is neces-
sary.
244. Define inertia.
245. Why is a fly-wheel an applica-
tion of inertia.
246. Why may the loose handle of
a hammer be fastened again
by knocking the end of the
handle against a hard object?
247. Why may a stopped-up pipe
be cleaned again by forcibly
knocking against one of its
ends?
248. Why must good bridges have
a great mass ?
249. Why may a candle be shot
from a great distance thro'
a board ?
250. Why do cannon or rifle balls
make a circular hole if fired
at a window-pane ?
LESSON XV. INCLINED PLANE.
PAGE 56.
251. What is an Inclined Plane ?
252. Why does a ball on it fall ?
253. Give three familiar instances
of an inclined plane.
PAGE 57.
254. Show that the steeper an in-
clined plane is, the greater
is the velocity of a body fall-
ing on it.
Show that in that case the
force required to ascend it is
greater.
256. Show that a body increases in
velocity as th> space in-
creases through which it
falls.
257. Show that the greater the ve-
locity of a body, the greater
its striking force.
255-
PAGE 58.
258 Why does a bullet thrown
with the hand inflict less
harm than one fired from a
gun ?
259. Why may hailstones destroy
standing grain, ?
260. What does the falling of bodies
on an inclined plane show ?
261. Whence the practical applica-
tion of the inclined plane ?
262. What is the principle of the
wedge ?
263. of the ax ?
264. of the skid ?
265. Why are roads leading np
steep mountains made in
windings ?
266. What is meant by the length
of an inclined plane ?
267. What, the height?
PAGE 59.
268. When is a balanced rod in a
state of equilibrium ?
269. Why then ?
270. Why will the longer arm of a
rod fall?
LESSON XVI. LEVER.
PAGE 59.
271. What is to be noticed in lift-
ing the end of the longer
arm with the hand ?
272. What, if the lengths of the
two arms have the ratio of
I to 2 ?
QUESTIONS.
161
PAGE 59.
273. What characterizes the end
of the long arm of a lever ?
PAGE 60.
274. What have hailstones in com-
mon with a small weight at
the end of the long arm ?
275. Define the lever.
276. Give a general law about it.
277. What does the amount of
power needed to lift a load
by means of a lever, depend
upon?
278. How may it be found ?
PAGE 61.
279. Give the three important
points in a lever.
PAGE 61.
280. What is a lever of the first
class ?
281. Give three examples, and ex-
plain.
282. What is a lever of the second
class ?
283. Give three examples, and ex-
plain.
284. To which class of -levers does
the oar belong ? and why ?
285. The wheel -barrow ?
286. How may a heavy stone be
lifted ?
287. What is the stone then called?
288. Why are levers used only for
moving loads through short
distances ?
LESSON XVII. THE PENDULUM.
PAGE 66.
297. What is the office of the
PAGE 63.
189. What is a vibration ?
290. Explain the vibration of a
pendulum.
291. How many forces act upon it,
and what are they?
PAGE 64.
291. Show that the vibration of the
same pendulum, whether
quite short or not, takes
place in the same length of
time.
293. Show that a short pendulum
vibrates more quickly than
a long one.
PAGE 65.
294. What is the principle applica-
tion of the pendulum ?
295. Explain its action.
296. What is meant by winding up
a clock ?
crutch ?
298. Explain how it comes that
weight in a clock causes the
hands to move with uniform
velocity.
299. What is the motory force of
clocks ?
300. What the regulating force? -
301
Would a pendulum placed
high up above the earth's
surface, vibrate more quickly
or more slowly than on
earth?
302. How on the moon ? .
303. How on the sun?
304. Midway between the earth's
surface and center?
305. At the center of the earth?
LESSON XVIII.-COMMUNICATING VESSELS-HYDRAULIC
PRESS.
PAGE 67. PAGE 68.
306. Show that the surface of quiet 309. Explain fountains.
310. What causes fountain -jets to be
shorter than they ought to be?
311. How does it come that our
water-pipes can lead water
to the upper part of houses,
307-
water is always level.
How does water stand in a
tea-pot ?
PAGE 68.
308. Show that your statement
must be true.
II
contrary to gravity ?
162
FIRST LESSONS IN PHYSICS.
PAGE 68.
312. Define Communicating Ves-
sels.
313. Why may water-pipes under
ground be said to be com-
municating tubes? (Text) PAGE 70.
314. Give law about pressure of 317. Explain the action of the hy
liquids. draulic press.
LESSON XIX. BREATHING BELLOWS.
PAGE 70.
315. Demonstrate it.
316. Give name and date of its ar>
plication.
PAGE 71.
318. Why can we, with a tube, suck
up water with the mouth ?
319. Explain the process of Inhala-
tion.
320. That of Exhalation.
321. What is meant by breathing?
322. What is a vacuum ?
323. What takes place when air has
access to a vacuum?
PAGE 72.
324. Explain the action of the bel-
lows.
325. What is a valve ?
PAGE 72.
326. Compare the action of the bel-
lows with the action of
breathing.
327. Explain the act of smoking.
328. That of drinking.
329. Could we breathe in a vacu'm?
Give reasons for your answer.
330. Would the bellows work in a
vacuum ?
Give reasons.
331. Would the bellows work in
water ?
LESSON XX. COMMON PUMP.
PAGE 74-
332. Explain the action of the sy-
ringe.
333. What causes the water to rise
in it ?
334. Would it rise if water and
syringe, both, were in a
vacuum ?
335. What are the principal parts
of a common pump ?
PAGE 75.
336. Where is the piston when the
handle is drawn "out farthest?
PAGE 76.
337. When is the piston at its
highest ?
338. In that case, what is below
the piston ?
339. When the piston commences
rising, which of the two
valves is opened ?
340. Why ?
341. When the piston is at its high-
est, which valve is closed ?
PAGE 76.
342. What is meant by rarified air?
343. Why does the water in the
suction-pipe rise?
344. What is the position of the
valves when the piston is
being lowered?
345. What do you pump out first ?
346. What causes the water to flow
out through the spout ?
347. What causes the lower valve
to close ?
348. What, the higher?
349. Give the principle of the com-
mon pump.
350. What is a pump ?
351. To what purpose is the lower
valve ?
352. The upper?
353. Is there any similarity between
the common pump and the
bellows ?
354. Explain your statement.
QUESTIONS.
163
355. Since the one serves to pump 356. Comparing the common pump
out water, and the other to th the barometer, give
T. i. <, *i* A four P omts which they have
pump out air, why has the in co ^ lmon<
latter but one valve ? 357. Eight points of difference.
LESSON XXL FORCING PUMP FIRE-ENGINE.
PAGE 77-
358. How high (theoretically speak-
ing) may water be lifted with
a common pump?
359. Give reason.
360. To elevate water to a greater
height, what must be used ?
PAGE 78.
361. Give three points in which it
differs from the common
362.
pump.
What are the principal parts
of the forcing pump ?
363. Where is the piston when the
handle is at its lowest ?
When at its highest?
364. When the piston is at its high-
est what is the position of
the valves ?
365. When does the lower valve
close ? and why ?
366. When is the upper valve
opened?
367. Why does it close ? and when?
368. Are both valves ever open at
the same time?
Closed at the same time ?
369. Why not ?
370. When the piston rises, why
does which valve open?
PAGE 78.
371. When the piston is at its low-
est which valve is open?
372. Why does not the water flow
back from the tube ?
373. Explain the action of the forc-
ing pump.
374. Why is it that, by means of
this pump, water may be
raised higher than by the
other ?
PAGE 79.
375. Give the parts of the Fire-
Engine.
376. Why does it not have com-
mon pumps?
377. Explain its action.
PAGE 80. .
378. What causes the flow?
379. What makes the flow continu-
ous?
380. Give the difference between a
Heron's fountain and an air-
chamber ?
381. Which of the two would work
better in a vacuum ?
382. How long will either of the
two "run"?
LESSON XXIIL SOUND.
PAGES 85 AND 119.
383. What causes sound ?
384. What is sound?
385. What makes us hear the crack
of a whip ?
386. Would we hear it if there were
no air?
387. Show that sound is the effect
of a vibrating motion.
PAGES 86 AND 1 2O.
388. What are sound-waves ?
PAGES 86 AND 120.
389. Do we hear all sound-waves?
390. Give velocity of sound.
391. What causes the noise when
paper is torn? (Text)
392. When wood is broken ?
393. When a whip is cracked?
394. Why do we not hear the alarm
of a clock in an exhausted
receiver (in a vacuum) ?
164
FIRST LESSON'S IN PHYSICS.
395. Why is music heard mOre dis-
tinctly when near than at a
great distance ?
396. Why do some bodies give a
louder sound than others ?
(Because they have a different
degree of elasticity.)
397. Why is the ax of a wood-chop-
per, at a distance, seen to
fall before the blow is heard?
398. Why may distant cannon-
thunder, be heard better by
putting the ear on the
ground?
399. Why do deaf persons not hear?
400. Why are the bells of a neigh-
boring place heard ringing
at times, and not at other
times ?
401. Why is it so quiet on the
mountains ?
402. Why need we not speak so
'loud on a calm lake as on
land?
LESSON XXIV.-EVAPORATION, FOG, CLOUDS, RAIN,
SNOW, HAIL, &c., &c.
PAGE 88.
403. Define evaporate.
404. When does evaporation take
place ?
405. What change does it effect?
406. Why is the breath visible in
winter ?
407. Is all aqueous vapor visible?
PAGE 89.
408. When is it visible?
409. What name has it then?
410. Under what circumstances
does it become visible higher
up in the atmosphere ?
411. What name has it then?
412. Why do clouds stay in the
air?
413. Why do soap-bubbles?
414. Why is it that the higher up
the clouds, the greater the
rain -drops ?
415. What is rain?
PAGE 90.
416. What is snow?
417. What is hail (probably)?
418. Whence the drops on the out-
side of a tumbler with cold
water, in summer ?
419. Why do iron safes "sweat "?
420. Whence the moisture on a
window-pane when a person
breathes against it?
PAGE 90.
421. When is aqueous vapor con-
densed?
422. What is meant by condense?
PAGE 91.
423. What is dew ?
424. Why is there no dew in cloudy
nights ?
425. Why none sometimes, al-
though the sky is serene ?
426. What is frost?
427. Why do we not have frost in
summer ?
428. Why does it rain in moun-
tainous countries more than
on low land ?
429. Has the direction of the water-
sheds anything to do with
the quantity of rain ?
430. When does it rain more, in
daytime or at night ?
431. Give your reasons.
432. Why does it not rain every
cold night?
433. Is snow useful ? Why ?
434. Upon what does the solid
state of water, its liquid
state and its gaseous state
depend ?
435. Will it do to compare the at-
mosphere to a boiler?
436. Give your reasons.
QUESTIONS.
165
LESSON XXV. HEATCONDUCTION OF HEAT.
PACK 92.
437. Whence the sparks which we
see when flint and steel are
struck together?
438. When a horse is galloping?
439. What effect is produced by
rubbing a copper coin on
the floor?
440. Why does not a match ignite
by being rubbed against
glass ?
441. Why does it ignite on a brick ?
442. Why has he his hands blis-
tered who lets himself down
along a rope ?
443. Why does a saw feel warm
after use?
PAGE 93.
444. How is heat produced?
445. What may motion be con-
verted into? (Were you to
ask " Into what may motion
be converted?" the pupil
would be inclined to answer
merely a word or two. )
446. Why do the hands get warm
on holding them to a heated
stove ?
447. What sensation is felt on keep-
ing the end of a wire in a
flame? Why?
448. What is conduction of heat ?
449. Why is it that that wire (Ques-
tion 447) may be held longer,
if the end in the hand is en-
veloped in paper ?
PAGE 94.
450. Why have teapots and solder-
ing-irons usually wooden
handles? (Text.)
451. What class of bodies are good
conductors of heat?
452. What is a good conductor of
heat?
453- What is a non-conductor (or
bad conductor) of heat?
454. Mention six non-conductors
of heat?
PAGE 94.
455. When a wire and apiece of
paper that have been lying
on a heated stove, are touch-
ed, the wire feels the warm-
er. Why?
456. Why do iron stoves heat well?
457. Why may ice be kept as well
in a feather bed as in an ice-
chest?
458. Why do mittens keep the
hands warmer than gloves
with fingers?
459. Why does iron "feel cold" in
winter and "warm" in sum-
mer?
460. Why are steam -chests and
steam-cylinders often cover-
ed with wood?
461. Why are the walls of safes
often filled with fine ashes ?
462. Why do wide garments keep
us warmer than tight ones ?
463. Why are frame houses warm-
er than stone ones ?
PAGE 95.
464. Whence the use of good con-
ductors of heat ?
465. Why are metallic vessels used
for boiling water and other
liquids ?
466. Whence the use of bad con-
ductors of heat?
467. Give their effect upon warm
and cold bodies ?
468. How should a tumbler be
heated? Why?
469. Why is less heat given out by
a stove when its inner sur-
face is covered with soot?
470. What advantage in a long
stove pipe ?
471. Why is a glowing coal rapidly
extinguished if placed on
iron?
472. Why do double windows keep
the room warm?
166
FIRST LESSONS IN PHYSICS
473. Whv does cold wind chill us
all through ?
474. Why does fruit ripen quicker
against a dark wall than
when isolated?''
475- What advantage in air being
a bad conductor ?
476. Does fanning us make the air
around us cool ?
477. Give reason for your state-
ment?
478. Why does drawing the cur-
tains down make a room
warmer ?
479. Why does snow protect the
ground from freezing?
LESSON XXVI. DRAUGHT.
PAGE 96.
480. Why will paper 'strips held
over a heated stove, move
upward ?
481. Why will they rise if let go?
482. What is the universal effect of
heat upon bodies ?
483. Why does heated air rise?
484. Explain the revolving of a
spiral paper owing to heat.
485. Prove that the air is warmer
near the ceiling.
486. Why do balloons, smoke and
steam rise ? (Text. )
PAGE 97.
487. When is a flame, held in the
upper opening of a room,
blown from the room ?
488. How about a flame held in the
lower opening ?
489. Give reasons for your state-
ments.
PAGE 97.
490. What is draught ?
491. What is the cause of draught?
492. Why is a lamp extinguished
if the draught is stopped
below ?
493. Why, if its chimney is closed
above ?
494. Compare this with Experiment
26, p. 43.
495. Show that heated air rises, and
that colder flows toward the
source of heat.
596. What is the cause of winds
497. How long does wind last?
498. What is ventilation ?
499. Is it sufficient for the ventila-
tion of a room to simply
admit fresh air ?
500. Prove your statement by a
previous experiment.
LESSON XXVIL EXPANSION BY HEAT- THERMOMETER.
PAGE 99.
501. Why does boiling water often
run over ?
502. Why does a cold tumbler crack
if placed on a heated surface?
503. How may the cracking be
prevented ?
504. What is the effect of heat upon
air?
505. Why are rails placed on the
track with space between?
$06. How are tires placed on
wheels?
507. Why does pop-corn pop ?
PAGE 100.
508. Give the law of expansion and
contraction of bodies.
509. Give the parts of the ther-
mometer.
510. Why the vacuum?
511. Why could not the glass tube
be open above ?
512. Can you heat the vacuum?
and what will be the effect
upon the mercury ?
513. Why does the mercury ex-
pand from heat ?
514. Why does the mercury rise ?
Why does it fall?
QUESTIONS.
167
PAGE 1 01
515. How are thermometers made?
516. How are the freezing and
boiling points obtained?
517. What advantage in dividing
the space between those two
points into degrees?
PAGE 100.
518. Why are the plates of metallic
roofing not nailed tqgether ?
519. When, and why, will hot water
crack a cold tumbler ?
520. What advantage in thermom-
eters ?
LESSON XXVIII. THERMOMETER COMPARED WITH
BAROMETER.
PAGE 102.
521. How is the blood-heat point of
the thermometer obtained?
522. How is it marked?
523. How did Fahrenheit divide
the space between the freez-
ing and boiling points?
524. Where did he not commence ?
525. Where did he commence?
PAGE 103.
526. How did Reaumur divide that
space ?
527. How, Celsius?
528. What are the equivalents of
80 R?
529. What of 50 C ?
530. What of 77 F?
531. What of 32 F?
532. What of 17 7-9 C?
533. What of 40 R ?
PAGE 103.
534. What is the healthiest tem-
perature of a room ?
535- Where should thermometers
be placed?
536. If in New York the mercury
stands 85, how would it
stand in Paris (according to
C. )? (Text.)
537. How in Berlin (R. )? (Text.)
538. According to those scales,
what numbers would indi-
cate the blood-heat point?
(Text.)
539. Indicate the point of healthiest
temperature in C. and R.
degrees. (Text.)
PAGE 104.
540. Give four points which the
thermometer and barometer
have in common.
541. Give four points they differ in.
LESSON XXIX. ATMOSPHERIC STEAM-ENGINE.
PAGE 105.
542. How is a sewing-machine
made to work?
543. What is rectilinear motion ?
544. Circular motion?
545. Give two instances of each ?
546. Who was Papin, and why is
he celebrated?
PAGE 1 06.
547. Mention five diff. kinds of work
done by the steam-engine.
PAGE 107.
548. Describe Papin's apparatus.
549. Describe the experiment with
the same.
550. What causes the piston to
rise ?
PAGE 105.
551. What to sink?
PAGE 1 08.
552. What is meant by an atmos-
pheric steam-engine?
55.3. Describe Savery's apparatus.
554. Compare it with Papin's.
555. Give Newcomen's improve-
ments on Papin's apparatus.
PAGE III.
556. Explain Newcomen's atmos-
pheric steam-engine.
557. What causes the piston in it
to rise? Explain.
558. What causes it to sink ? Ex-
plain.
168
FIKST LESSONS IN PHYSIOS.
PAGE III.
559. State the principal points of
Papin's engine. (Text.)
560. Of Savery's. (Text.)
561. Of Newcomen's. (Text.)
PAGE III.
562. Compare Savery's apparatus
with Newcomen's engine.
563. Compare Fapin's with New-
comen's.
LESSON XXX. STEAM-ENGINE.
PAGE 112.
564. Who was Watt?
565. Whence his familiarity with
the defects of Newcomen's
engine?
566. What was its principal defect ?
5671 What was the cause of this
defect?
PAGE US-
568. How great a loss was caused
thereby ?
569. What question arose?
570. What was Watt's first im
provement ?
571. Explain.
572. What did Watt's next im-
provement consist in ?
573. What defect did it overcome?
574. What caused now the piston
to rise and sink?
PAGE 114.
575. Did henceforth the steam
merely serve to produce a
vacuum ?
576. Why was Newcomen's ma-
chine a single -acting engine?
577. Why was it used only for
pumping water ?
578. What constitutes a double-
acting steam-engine ?
PAGE 115.
579. When did Watt die?
580. What is meant by steam of low-
pressure ? of high pressure ?
581. What are high and low press-
ure engines ?
582. What is the use of the sliding
valve ?
PAGE 1 1 6.
583. Explain action of high-press-
ure engine.
LESSON XXXI L LIGHTITS SOURCES DIRECTION.
P" AGE 122.
584. What are our sources of light?
585. Mention six self-luminous
bodies.
586. What is a self-luminous body?
(One which makes its own
light.)
PAGE 123.
587. Are the planets self-luminous?
Are they luminous ?
588. What, then, is the difference
between luminous and self-
luminous ?
PAGE 123.
589. When, only, are bodies not
self-luminous, visible ?
590. Show that light emanates from
self-luminous bodies in alt
directions.
PAGE 124.
591. Show that it travels in straight
lines.
592. Why have opera-glasses
straight tubes ?
LESSON XXXIII. --RADIANT AND SPECULAR REFLECTION.
PAGE 125.
593. What makes our rooms light
in the daytime ?
594. How do all objects reflect
light? :..-.-...
595. What enables us to see a pencil?
596. A looking-glass ?
PAGE 126.
597. What is radiant reflection of
light ?
598. Show that there are objects
which reflect light also in
certain directions.
QUESTIONS.
169
PAGE 126.
599. What is this kind of reflection
called?
PAGE 127.
600. What class of objects reflect
light, both, radiantly and
specularly ?
PAGE 127.
60 1. Compare light reflected radi-
antly with light reflected
specularly by
(a.) Giving four points in com-
mon.
(.) Three points of difference.
LESSON XXXIV. VISIBLE DIRECTION REFRACTION.
PAGE 128.
602. Whither does a person hit
with a stone, look?
603. Show that a boy looking at a
steeple does somet'ng sirmTr.
PAGE 129.
604. On page 128 the two images
have opposite directions ;
why does the person, never-
theless, see the object in
only one direction ?
605. Give general statement of the
case. (All bodies appear to
be situated &c., &c.)
PAGE 129.
606. Why do oars, when immersed
obliquely, appear bent ?
PAGE 130.
607. Why does the eye see the oar
bent?
608. When is a coin on the bot-
tom of a filled tumbler not
seen in its true place and
direction ?
PAGE 131.
609. Why do clear waters appear
more shallow than they are?
6 10. What is refraction of light?
LESSON XXXV. PRISMS LENSES.
PAGE 132.
6n. Show the passage of rays (of
an arrow) through a prism
with edge upward
PAGE 133.
6 1 2. With the edge downward.
613. What is a prism ?
614. Show the path of rays of an
arrow through two prisms
with their bases adjacent (as
on page 133).
615. Why the use of a curved glass
in place of the prisms ?
PAGE 134.
6 1 6. What two names are given to
this?
PAGE 134.
617. What is the Focus ?
6 1 8. Why the term Burning-glass ?
619. What effect has such a lens
upon objects ?
620. Is your answer true in every
sense of the word ?
PAGE 135-
621. Give the general statement
true of such a lens.
622. Does a telescope really mag-
nify distant objects ?
623. Upon what, then, is its use
based ?
PAGE 136.
624. What is dispersion of light ?
625. How can it be shown ?
626. What effect has it upon white
light ?
627. Give the principal colors of
the rainbow.
LESSON XXXVI. COLOR.
PAGE 136.
628. What is the whole series of
colors called ?
PAGE 137.
629. How can you prove that ordi-
nary sunlight contains these
colors ?
170
FIRST LESSONS IN PHYSICS.
PAGE 137.
630. Is color a substance ?
PAGE 138.
631. Why does white glass look
white ?
632. Why does blue glass look
blue?
633. Why do objects near a blue
curtain have a blueish tinge?
PAGE 139.
634. When is a body said to be
colored ?
635. When white ?
PAGE 139.
636. When black?
637. What causes a piece of red
cloth to appear red ? (Text. )
638. What, a sheet of paper to ap-
pear white? (Text.)
639. A black coat to appear black?
(Text.)
640. Why is everything black on
a dark night? (Text.)
641. Is color a quality inherent in
bodies ?
642. Is it a property of a body ?
LESSON XXXVII. CHEMICAL ELECTRICITY.
PAGE 141.
643. What constitutes a galvanic
element, or cell?
644. What is a galvanic battery ?
645. How is a coke-cell prepared ?
646. Why must the cup used be
unglazed ?
(The two liquids pass each
other through its pores.)
647. Why must the wire ends be
entirely clean !
(The electric current does not
leap over. )
PAGE 141.
648. Whence the thrilling sensation
if the current passes through
the tongue ?
PAGE 142.
649. Explain the action of such a
galvanic cell.
650. How is chemical or galvanic
electricity produced?
651. Whence the name galvanic ?
652. Explain the uninterrupted cur-
rent of electricity
653. Is the length of the wires of
importance ?
LESSON XXXVIIL THE ELECTRO-MAGNETIC TELE-
GRAPH.
PAGE 144.
654. What is next to the steam-
engine the wonder of our
, age, and why ?
655. Who discovered the effect of
the galvanic current upon
iron?
656. Who put up the first telegr'ph?
PAGE 145.
657. Who perfected the telegraph?
658. How may the principle of
Morse's telegraph be illus-
trated ?
PAGE 146.
659. What renders the horse-shoe
rod magnetic?
660. Describe the path of the elec-
tric current of the cell, when
passing around the rod.
PAGE 147.
66 1. What effect has the interrup-
tion of the current upon the
rod?
662. What is an Electro- Magnet
663. What is the keeper ?
PAGE 148.
664. What are the principles of the
electric telegraph?
665. Describe the apparatus by
which they may be demon-
strated.
666. Compare the Magnet with the
Electro- Magnet, giving
(a.) Five points in common.
(.) Three points of difference.
APPENDIX.
I. REMARKS.
LESSON III. To preserve their magnetism, the poles of magnets
should constantly be kept in contact with iron.
LESSON IV. Bar-sulphur, or a solid glass rod, is often preferred to
a lamp-chimney. The surfaces to bs electrified should be dry and clean.
LESSON V. May be used as a reading lesson, or as one in which the
unfinished part of any previous lesson can be brought up.
LESSON VII. Time is gained if the bullets are flattened with a
hammer ; then scrape one of the flattened surfaces of each with a knife ;
press the two surfaces together by a few strokes of a hammer.
The glass plates, and tubes, must be free from grease.
The pores of a body may be compared to the open ends of capillary
tubes ; the capillary tubes may be compared to glass tubes of very fine
bor
LESSON IX. Instead of an ivory ball, which is expensive, a large
marble gives the same result The round spot may be shown also on
the slab.
LESSON X. A piece of India-rubber tubing around the tube of the
funnel will do as well as sealing-wax, or any other cement. Any kind
of tube, about ^ inch in diameter and about 3 feet long, may serve as a
blow-pipe.
LESSON XI. A tumbler with a brim curved outward is best.
LESSON XVI. A square wooden beam about 20 inches long for a
lever, with the sharp edge of a ruler, paper knife or knife-blade as a
fulcrum. The fulcrum must be firmly fixed.
LESSON XVIII. The bees-wax must be put on very thin, or else
the water cannot force its way through. Draw Fig. 1 7 on the board.
The small triangular valve, when lowered, is just large enough to close
the right hand side of the short horizontal tube.
LESSONS XX AND XXI. Draw the Fig. on the board.
LESSON XXV. Copper being a better conductor than iron, copper
wire is preferable.
LESSONS XXIX AND XXX. Draw the Fig. on the board.
LESSON XXXV EXPERIMENT 65. Draw an arrow on the board,
place the prism in proper position, and sufficiently elevated for each
scholar to see the arrow through the prism. As this requires but a few
seconds, it may be found convenient to let the class slowly file past the
prism*
172 FIRST LESSONS IN PHYSICS.
II. GLASS AND CORK WORKING.
The following is taken nearly literally from Vernon Harcourt's excel-
lent work, "Exercises in Practical Chemistry, Clarendon Press,
Oxford:"
1. To CUT A GLASS TUBE. Take glass tubing about # -inch external
diameter ("hard glass " is preferable). For a Hero's fountain (Lesson
X, Experiment 27, and also frontispiece), it should reach from within half
an inch of the bottom of the flask to about eight inches above the cork.
As mercantile tubing is much longer, a piece of that length should be
cut off. To do this, lay the tube on a table, hold it between the thumb
and forefinger of the left hand, placed close to where it is to be cut.
Take a triangular file, press your left thumb and forefinger firmly against
the tube, put the edge of the file upon the tube so as to touch and lean
against the thumb, which will thus prevent the file from slipping over
the glass, and make a notch on the glass by a few short, energetic
strokes in a forward direction. While in the act of cutting, do not bear
down too heavily with the left hand; rather have your left thumb yield
a little as the file passes forward, so that the tube may turn a little in
the direction of the advancing file. To guard against injury, in case the
tube should yield, put on a glove. Now take up the tube, holding it so
that the thumb-nails are opposite to each other, with the notch between
them, and that you tightly press the tube (where the notch is) with
thumb-nail and forefinger of each hand, and with a resolute grasp break
the tube (moving your hands in a direction front you) as you would
break a stick. The edges of the new end will be sharp and rugged; to
prevent their tearing the cork, pass the file lightly over them; then hold
them a few seconds in the tip of an alcohol (or gas) flame.
For a Hero's fountain like the one in the frontispiece a more con-
venient form than that in Lesson X you should have a bent glass tube.
2. To BEND A GLASS TUBE. If the external diameter of the tube
does not exceed half an inch, a common gas flame is very suitable ; but
if the gas is not at hand, a spirit lamp with a large flame may be used.
Light the gas, or spirit lamp ; then holding the piece of tube by its ex-
tremities, bring it a little above the flame, turning it constantly around
and moving it laterally so as to heat about two inches of it equally on
both sides. After a few seconds lower it gradually into the flame, still
constantly turning it round.
If the gas burner be used, the glass will become covered with soot
when immersed in the flame ; but this is of no consequence, as the heat
of such a burner is never high enough to incorporate the carbon with
the glass. When the heated portion becomes soft and yielding, which
will take place even before it has acquired a visible red heat, withdraw
it from the flame, and gently bend it to a right angle, avoiding the use
of much force. When the proper bend is completed, lay the tube on a
bit of glass in such a position that the heated portion does not come into
contact with any cold surface, and leave it to cool slowly.
3. T.o MAKE A GLASS JET. Take the straight tube, previously ob-
tained; heat the tube two inches from one of its ends by holding it to
GLASS AND CORK WORKING. 173
the extent of half an inch in the upper part of a flame. The thumb and
forefinger of each hand should hold the glass about an inch from the
heated part. The heated part will soon become soft and a little narrower.
Then withdraw it from the flame, and draw the heated part out by pul-
ling the two ends of the glass apart. But pull very gently or else the
tube will be drawn out too thin; the jet should have about j^-inch
external diameter. Gently place the whole on the table before you and
allow it to cool ; then make a fine notch at the middle of the drawn-out
part, and break the tube there. The long part is the jet for a Hero's
fountain. If the aperture is too wide, hold it for a second or two in the
flame.
4. To PERFORATE A CORK. It now remains to fit these tubes the
bent tube and the jet to the bottle by means of a cork having two holes.
Take a good, sound cork, about an inch in diameter, squeeze it until it
becomes soft and elastic (a pair of pliers or nut-crackers will serve the
purpose of a regular cork-squeezer), then take it up between the second
finger and the thumb of the left hand, and place the sharpened end of
the smallest cork-borer against it, one end of the cork midway between
the center and the edge. Urge the cork-borer into the cork with a twist-
ing motion, as if you were using a cork screw. Some care will be re-
quired to make the hole straight through the cork, so that it may be
truly central. Of the proper direction the eye will be the best judge.
And when the cork-borer has penetrated some little way, it will be advis-
able to turn the cork a quarter round in order that it may be seen
whether the axis of the cork-borer and of the cork are still in the same
straight line. If not, a slight pressure on the cork-borer in one direc-
ti'm or the other will set it straight. When the borer has penetrated
^aite through the cork, it may be withdrawn with a twitching motion,
and will bring with it a cylindrical plug of cork, leaving a hole, the sides
of which should be smoothed with a round file. In the same manner
make the other hole midway between the center and the circumference.
Take a cork-borer rather smaller than the tubing which you have ; see
that the holes do not run into each other, or pierce the side of the cork.
The holes should next be smoothed and slightly enlarged by a rat-tail
file, until the end of one of the tubes will just enter them when some
little pressure is used. (If much pressure is used, the tube is not un-
likely to break, and the splinters of glass may cause injury. The hole
should never be so much smaller than the tube as to make it necessary
to use much force in passing the latter through it. It is a good plan,
also, to wrap the tube in a cloth or handkerchief while it is being inserted
in the cork. ) Now pass the longer of the two tubes through the cork,
with moderate pressure and a twisting motion, until it projects so far as
to reach, when the cork is fitted into its place, nearly to the bottom of
the bottle. When this is done pass the other tube through the other
hole in the cork," until it projects one or two inches on the other side.
INDEX.
>
PAGE.
Academy of Florence 31
Adhesion 32
Attraction, Capillary 35
Attraction, Electric 20
Attraction, Magnetic 17
Balance
Barometer
Barometer comp. with Pump.
Barometer compared with
Thermometer
Bellows
Blotting-paper
Blo\v-pipe
Breathing
Burning-glass
Cell, Galvanic
Clock Weights
Clocks
Clouds ;..
Cohesion
Color
Compass
Communicating Vessels
Condenser
Conductors of Electricity
Conductors of Heat
Contraction by Cold.
Conversion of Force, Motion,
Contents, Table of
Current, Electric
104
H
43
7i
134
141
I
89
:<6 9
87
"3
22
94
100
121
7
142
Dew
Direction, Visible.
Diving-bell
Draught
Drowning
Ductile
Ductility ."
9'
128
44
96
16
29
PAGE.
Elasticity . 39
Elasticity, Application of 41
Elasticity of Air 42
Electricity, Pos. and N eg 25
Electricity, Chemical 140
Electric Attraction 20
Electric Repulsion 23
Electro- Magnet 150
Element, Galvanic 141
Evaporation 88
Exhalation 71
Expansion by Heat 99
Fire-Engine 78
Fly-Wheels 55
Fog gq
Force, into Motion
Franklin's Experiment
Frost 91
Fulcrum 6l
Glass for Electric Purposes. . . 24
Glass for Prism 136
Gravity, Direction of 1 1
Gravity, Force of 9
Gravity, Specific 14
Hail 90
Heat 92
Heat, Conduction of. 93
Heron's Fountain 44
High Pressure 115
Horizontal 12
Hour-glass 13
Hydraulic Press 67
Impenetrability 30
Inclined Plane 56
Inertia 53
Inhalation 71
INDEX.
PAGE.
Lenses 133
Level 12
Lever 59
Light, Direction 1 24
Light, Sources... 122
Light, Radiant and Specular
Reflection 125
Light, Radiant and Specular
Reflection Compared 127
Lightning 26
Lightning- Rod 27, 38
Locomotive 117, 118
Low Pressure 115
Magnetic Attraction 17
Magnet 18
Magnet compared with Elec-
tro-Magnet 150
Malleable 41
Metals, Conductors of Heat.. 94
Morse's Telegraph 145
Needle, How rend. Magnetic. 19
Newcomen's Engine 108
Nut-Cracker 61
Papin's Apparatus , 105
Pendulum 63
Persons Drowning 1 6
Pith-balls, How made 22
Plumb-line n
Poles of Magnets 19
Pop-gun 43
Pores 31
Pressure of Air 46, 50
Pressure, Downward 12
132, 136, 137
PAGE.
Pump, Common 74
Pump, Forcing 77
Pull 84
Push 84
Radiation of Light
Rain _ .
Reflection of Light ,
Refraction of Light ,
Refraction of Light, Law
Repulsion, Electric ,
Self-luminous
Sliding-valve
Snow
Sound
Spark, Electric
Steam-Engine, Atmospheric. .
Steam-Engine, Newcomen's. ,
Steam-Engine, Papin's
Steam-Engine, Savery's
Steam-Engine, Watt's
125
89
125
129
131
23
123
"5
90
85
21
112
Telegraph 144
Telegraph, Principle of 147
Telegraph, Prin. Demonst'd. 148
Thermometer 100, 102
Thermometer compared with
Barometer 104
Vacuum 49
Varelcit n
Visible Direction 128
Watt, James 112
Weight 12
Winds, Cause of. 98
Work done by forces. .... 83
U77O
M289988
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