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SCHOOL PHYSICS
EMBRACING THE RESULTS OF THE MOST RECENT
RESEARCHES IN THE SEVERAL DEPARTMENTS
OF NATURAL PHILOSOPHY
BY
JOHN D. QUACKENBOS, A. M., M. D. (LITERARY EDITOR)
Professor of Rhetoric, Columbia College, New York
Member of the N. Y. Academy of Sciences, Fellow of the N. Y. Academy of Medicine
ALFRED M. MAYER, PH. D. SILAS W. HOLMAN, S. B.
Professor of Physics, Stevens Institute of Associate Professor of Physics,
Technology, Hoboken, N. J. Massachusetts Institute of Technology, Boston
FRANCIS E. NIPHER, A. M. FRANCIS B. CROCKER, E. M.
Professor of Physics, Instructor in Electrical Engineering,
Washington University, St. Louis, School of Mines, Columbia College,
and President St. Louis Academy of Science and President New York Electrical Society
NEW YOKE : CINCINNATI : CHICAGO
AMERICAN BOOK COMPANY
COPYRIGHT, 1891, BY
AMERICAN BOOK COMPANY.
ptintefc b
H>. Bppteton & Company
J)orft, -d. S. H.
PREFACE.
THE present volume is intended to meet an existing demand for
a thoroughly modern text-book on Natural Philosophy, which shall
reflect the most advanced and practical laboratory and pedagogical
methods, and at the same time be adapted, in style and matter, for
use in the higher grades of our grammar-schools, our high-schools, and
our academies. In the belief that special investigators and teachers
are distinctively qualified for the purpose, the editor has assigned the
different sections of the book to educators of recognized eminence and
skill, governing his selection in each case by the peculiar qualifica-
tions of the author. The reputation of the several contributors, and
the standing of the great scientific schools which they represent, must
secure for this work a consideration accorded to few American school-
texts. The sections on motion, energy, force, the properties and con-
stitution of matter, solids, liquids, gases, and mechanics proper, were
prepared by Professor Silas W. Holman, of the Massachusetts Institute
of Technology ; those on heat, light, f rictional and voltaic electricity, by
Francis E. Nipher, Professor of Physics in Washington University, St.
Louis. Professor Alfred M. Mayer, of the Stevens Institute of Tech-
nology, Hoboken, N. J., furnished the chapter on sound ; and Francis
B. Crocker, E. M., Instructor in Electrical Engineering, School of
Mines, Columbia College, the sections relating to magnetism and the
practical applications of electricity. Numerous friends of the book
have aided the editor with valuable suggestions and criticisms ; special
acknowledgment is due to Professors Rood, Trowbridge, and "Rees, of
Columbia College, and Professor George F. Swain, of the Massachu-
setts Institute of Technology.
The attention of teachers is asked to the following specific features :
The thorough and original treatment of motion, energy, force, and
work. In the chapters on dynamics, the author has presented a mod-
ern and appliable conception of the nature, transformation, and con-
servation of energy, as well as of the relation existing between energy
and force. These subjects are treated with the greatest simplicity,
183612
j v PREFACE.
precision, and thoroughness, for it is believed that a proper under-
standing of them lies at the base of all scientific knowledge, however
far" it may be pursued.
The book is adapted to students of fourteen years and upward, but
by the occasional omission of an advanced paragraph, an algebraic
expression, or an exceptionally difficult principle, the text becomes
perfectly comprehensible to the most juvenile learners. Thus it is es-
sentially fitted to pupils of different degrees of maturity. The easier
principles may form the basis of a first year's course ; while, in the
second year, the student will find in the complete text additional mat-
ters which increased age and extended experience now enable him to
grasp and appreciate.
It has been the aim of the authors of this volume not to teach
results merely, but to show how these results have been reached as
well as what practical use is made of them, and thus to inspire the
learner with enthusiasm in his work of questioning Nature. Prece-
dence is everywhere given to the practical. The steam-engine, the
electric motor, the telephone, and the telegraph, even the simplest
tools, are shown to be machines or devices by which energy of some
form is made to do work useful to man. The experiments, especially
those described in the chapters on dynamics, etc., are largely intended
as illustrations, and not as proofs ; hence the pupil is not led to draw
extended inferences from insufficient evidence a habit antagonistic
to proper and symmetrical mental development. Further, the signifi-
cance of the algebraic formulae is immediately impressed upon the
learner by solved numerical examples. This feature is of special
importance in the earlier discussions, where the abstract or general
statements are rendered much more intelligible because accompanied
with concrete forms.
Instructive diagrams and illustrations have been introduced wher-
ever it was thought they would relieve the text ; suggestive questions,
not intended to supersede minute examination by the teacher, but
rather to exercise the reasoning faculties of the pupil, are inserted at
such intervals as mark convenient and logical divisions into lessons ;
problems are appended to the several sections, to test the student's
understanding of the principles therein explained; and applications
of these principles in every-day experience render them delightful to
learn and easy to remember.
The illustrations not only reproduce the more complicated appa-
ratus usually found in the school laboratory, but also elucidate the
descriptions of simple experiments that can be successfully attempted
by young people with home-made appliances. At the beginning of
PREFACE. v
each principal section is pictured a suggestive group of such apparatus
as will be found necessary to the performance of the experiments de-
scribed in the chapter following ; and, throughout the book, minute
instructions are given for the cheap manufacture of essential pieces of
apparatus.
The publishers feel assured that the many valuable features of this
new School Physics must recommend it to teachers as a singularly
practical and authoritative text-book on the subjects of which it treats.
NEW YORK, March 2, 1891.
TABLE OF CONTENTS.
PAGE
Introduction and Preliminary Definitions V . . , 1
Kinematics *.-.-... 13
Energy . . . . . . . . 28
Force 43
Properties and Constitution of Matter 60
Measurement of Mass, Force, Energy, and Work .... 76
Action of Forces . . . '. . . , . . . 105
Gravitation and the Pendulum 119
Friction and Machines . 138
Three States of Matter .166
Solids 167
Liquids 173
Gases , 200
Heat 230
Light 293
Sound 370
Magnetism 419
Electricity 435
Practical Applications of Electricity 505
PHYSICS, OR
NATURAL PHILOSOPHY.
PRELIMINARY STATEMENTS AND DEFINITIONS.
The Fundamental Things about which we have to
learn in Physics are Matter and its Motion matter, out of
which everything is built up ; motion, which gives to matter
the possibility of form, structure, phenomena, and laws, and
which is everywhere and unceasing.
Matter in motion possesses Energy that which not only
does all the work of the universe, but which holds every
particle to its neighbor and yet keeps it apart from that
neighbor.
Physical Science deals only with the phenomena and
laws of matter, and of matter in motion. It does not at-
tempt to determine whence matter and its motion came,
what matter is, or how it acquired motion. It does not
deny that other things than matter in motion are essential
to the universe. Whatever such things there are, lie out-
side the scope of Physical Science.
We are everywhere surrounded by objects which form a part of
what we call the physical universe. In studying them we proceed
upon the suppositions or beliefs
1. That they exist independently of ourselves, or, as we say, have
objective existence.
2. That we perceive them and become acquainted with them solely
by the aid of our senses.
2 PHYSICS, OR NATURAL PHILOSOPHY.
3. That we are liable to misinterpret the indications of our senses.
4. That the continued exercise of Reason enables us gradually to
sift the truth from the error in our interpretation of these indications.
Phenomena. As we examine and consider the ob-
jects about us, we perceive that they differ as to size, shape,
color, hardness, position, and many other characteristics or
qualities. We also perceive that they are concerned in cer-
tain events or occurrences which are going on naturally, Or
can be made to take place. Thus, we observe that objects
when dropped fall to the ground, that water on a sloping
surface runs downward, that an object held up in the sun-
shine casts a shadow, that the sun appears to rise in the
east and set in the west. These and a multitude of other
events are what we call Phenomena.
Science. But a mere examination and cataloguing
of objects and phenomena would never give us a science.
Science involves a study of the relations between different
objects and between phenomena. These relations must be
analyzed and expressed in general statements, which are
called Laws. The whole body of truth thus gained, namely,
the knowledge of material objects, phenomena, and relations
or laws, constitutes the science called Physics, or Natural
Philosophy.
Law. Let us look a little more closely at what is meant
by physical laws. If almost any object whatever be held up
from the earth's surface and then be released, it will fall to
the ground. From our own experience and that of others
in the past, we know that every object tested in this way
has fallen except where for some well-understood cause it
was prevented from so doing, as, for instance, a balloon by
the buoyancy of the air or a feather by the resistance of the
air. We may, therefore, say that every object tested has
shown a tendency to fall toward the earth.
But this statement is merely a summary of the facts or
phenomena for all bodies tested, and is not a law. How
PHYSICAL LAW. 3
must it be changed to become one ? Simply by being made
general that is, it must be expressed so as to apply to all
bodies. If, then, we say every body near the earth possesses
a tendency to fall, that is, has weight, we shall have a state-
ment of the class which we call laws. This statement in-
cludes every body near the earth, whether it has been tested
or not.
Now, how do we know that this law is true ? "We do not know that
it is true in the same sense that we know the truth of the first state-
ment. We can not even have the same certainty that a given object
which has weight to-day will have weight to-morrow. How, then, can
we have any confidence in general statements or predictions based
upon past experience H And if these laws are an essential part ol
science, how much reliance is to be placed upon them ? There cer-
tainly is such a thing as too great confidence in science, and there is a
wide difference between the degrees of confidence to be given to differ-
ent scientific laws. These laws are being continually developed and
corrected, and the measure of confidence to which they are entitled
depends on the thoroughness with which the underlying facts were
examined, and in the exactness with which subsequently observed
facts and phenomena have been found to coincide with the law.
The chief reason why we are disposed to put confidence in laws
and predictions is our belief in the proposition that " the same causes
will always produce the same effects." This is a generalized statement
of our own and all past experience, viz., that the same causes have
always produced the same effects, and our belief in it is measured by
the breadth of experience upon which it rests.
It must be remembered that laws do not " govern " events
in the sense of causing them. A law is merely the general
ized statement of what has been observed to occur.
Cause and Effect. What do these terms mean ? Push
a book lying on the table. It moves. Try the experiment
under a variety of conditions as to time, place, temperature,
and so on. You will find that the push, unless neutral-
ized in some obvious way, always produces the motion, and
that the motion does not occur without a push. You con-
clude, then, that it appears not to be simply a matter of
4 PHYSICS, OR NATURAL PHILOSOPHY.
chance that the push and the motion occur at the same
time, but that they necessarily occur together, and that the
motion appears to result from the push. The push is then
said to be the cause of the motion, and the motion the effect
of the push.
We should feel a considerable degree of confidence, then,
in making the generalized statement that the push, unless
neutralized, always will produce the motion ; but we should
not pretend to say that this statement is absolutely true, for,
besides the liability to some imperfection in our observa-
tions, we are not certain of the truth of the proposition,
" the same causes always produce the same effects " ; and
this is an essential part of the process by which we have ar-
rived at the general statement.
In the application of this proposition, we must bear in mind that if
the cause be not precisely the same (except with respect to time), the
effect will not be precisely the same ; it may be extraordinarily differ-
ent. For instance, a burnt-out match may be repeatedly thrust into
gunpowder, with always the same effect of merely pushing aside the
grains ; but, if the match differs only by being slightly hotter on some
occasion, the effect may be strikingly changed.
Chance. A multitude of events which take place
around us occur at times or places or in ways which, so far
as we can see, are without any order or any apparent law or
reason. We speak of such events as occurring by Chance ;
but, the more broad and accurate knowledge becomes, the
more it is evident that events are orderly occurrences and
capable of prediction. They appear to occur by chance,
only because we do not know their causes or the laws which
represent their actions. With infinite knowledge, all thought
of chance would disappear.
Explanation of Phenomena and Laws. A physical
phenomenon or law is said to be explained or accounted for
when it is shown to be a particular case of some more funda-
mental law or group of laws. By way of illustration, we
EXPLANATION OF PHENOMENA. 5
find that objects tend to fall toward the earth. We ask
why that is, we seek an explanation. Sir Isaac Newton,
by a study of the motion of bodies, including that of th&
moon and planets, was led to deduce the law known as that
of universal gravitation, viz., that every particle of matter
tends to approach every other particle, the amount of the
tendency depending on the amount of matter in the parti-
cles and on their distances apart. The tendency of objects
to fall toward the earth is, then, a particular case of universal
gravitation, and is therefore explained.
But we do not know why every particle tends to ap-
proach every other that is, we have as yet no explanation
of universal gravitation ; we do not know any more funda-
mental law to which to ascribe it. Thus explanation in any
case only carries us a step farther back; but that step is
often of great service. Without it, knowledge would be
fragmentary and disconnected.
Theory. Hypothesis. There are many phenomena
and laws which we are not yet able to show to be special
cases of more fundamental known laws that is, to explain ;
but in the effort to find explanations we are continually
forming suppositions and testing them to see whether they
appear to afford the explanations desired. These supposi-
tions in their earliest stages are often very crude and im-
perfect, and are then called Hypotheses. As they are more
and more completely developed, and are shown to be more
trustworthy or more probable, hypotheses are called Theories.
A hypothesis is developed into a theory by continued
comparison with new facts, and by being corrected if neces-
sary to correspond with them. The theory is verified and
developed in the same way, and may eventually become so
well confirmed as to be regarded as a highly probable law.
One of the best tests of a theory or law is to predict what would
occur under certain new conditions or at a certain future time if the
theory or law proves true, and then to bring about those conditions or
6 PHYSICS, OR NATURAL PHILOSOPHY.
wait for that time and see whether the event occurs as predicted. If
it does, the theory will be strengthened. If it does not, and we can
show that the prediction was correctly made, the theory is thereby
proved to be incorrect or incomplete, and should be amended. Thus
the verification of the prediction of eclipses, of the apparently very
irregular path of the moon among the stars, and especially of the
existence of the planet Neptune, all based on the law of gravitation,
greatly strengthens our belief in that law.
Theories and even crude hypotheses are often of very great service,
even when they ultimately prove to be incorrect, for they aid in direct-
ing investigation and thus lead up to truth. It is hardly to be sup-
posed that any theory now held will eventually prove to be an abso-
lutely correct expression of the truth to which it relates ; but theories
are at present none the less indispensable.
QUESTIONS. What are the fundamental things about which we learn in the study
of Physics ? Does physics have anything to say as to the origin of matter ?
of motion ? of life ? What forms the physical universe ? Does this universe
exist outside of our own thoughts ? How do we perceive it ? What are our
senses ? What enables us to separate truth from error in our observations f
Define qualities ; a phenomenon.
What constitutes the science of Physics ? How does a science differ from a
mere catalogue of facts and phenomena ? What has been observed in regard
to the tendency of objects to fall ? Why is this not a law ? State the law de-
rived from this observed fact. Are any physical laws supposed to be certainly
true ? Why ? For what reason do we have any confidence in them at all ?
Illustrate cause and effect. What do we mean by saying that an event occurs
by chance ? To a mind knowing everything, could there be such a thing as
chance ? How, then, can any one believe it possible that the whole universe
exists as a matter of chance ? What do we mean by explanation ? Does ex-
planation explain ? What is the relation between theory and hypothesis ?
DEFINITIONS CONTINUED.
Physics, or Natural Philosophy, is that branch of
human knowledge which deals with all objects, phenomena,
and Jaws of the material or physical universe.
In the physical universe we come to recognize two, and
only two, things which seem to be indestructible, and thus
to exist entirely independently of us or of any operation of
our senses or reason. These two things are Matter and
Energy. Hence, Physics has been also called the science of
matter and energy.
THE IDEA OF TIME. 7
While physics neither denies nor affirms that there is
something in the universe other than matter and energy,
no complete discussion of such questions is possible without
an adequate knowledge of the laws of this science.
Physics, as thus defined, is given its broadest scope. It includes al-
most all branches of science except mental science ; but the term is
generally employed in a much more limited sense. Those sciences
which deal with classification only (as most of the natural history sci-
ences), with phenomena where substances undergo changes in their
properties (chemistry), or with phenomena which occur in living be
ings (biology) are usually understood to be excluded when the term
physics is employed.
There are also certain branches of physics proper which are more
or less distinctly separated, or are not usually treated in text-books
upon physics. Such are astronomy, which deals with the stars, sui\
planets, nebulae, comets, etc., their positions, motions, and laws ; dy-
namical geology, which treats of the structure of the earth ; etc.
The relations between physics, even in the more limited sense, and
chemistry and biology, are extremely close. Many chemical and bio-
logical phenomena are almost purely physical, and this is true to such
an extent that, without a knowledge of a large part of physics, little
progress can be made either in chemistry or biology.
Time. The earliest idea of Time probably comes from
the recognition of the fact that one event occurs after an-
other. If your memory were perfect, you could mentally
place all events in your own experience in the order in
which they followed one another in time ; but it would be
impossible for you to compare correctly two intervals of
time between different events. By experience, however, you
have found that there are certain natural processes which
appear to go on in a uniform or rhythmical manner, such as
the succession of night and day, of winter and summer, the
apparent motions of the sun, stars, and moon, the swings of
a pendulum, the flow of water through an orifice. By re-
ferring events to such processes, you can arrange a system
by which the order of succession of all events and the rela-
tive intervals between them can be expressed.
8 PHYSICS, OR NATURAL PHILOSOPHY.
In the actual measurement of time, we make use of the period of
the earth's revolution around the sun to mark the longer interval of a
year, the rotation of the earth on its axis to mark the day, and the
beats of the pendulum to divide the day into parts.
Space. We are accustomed to think of material objects
as occupying definite positions with reference to one another
that is, as being at certain distances apart in certain direc-
tions. We understand that this is what is meant when we
refer to the relative positions of bodies in Space.
In thinking of the distance between bodies, we do not
conceive it as depending upon any material thing between
them. Our idea of their distance apart would not be
changed if we thought of them as separated by no material
medium like air or water. This abstract idea of distance,
or, as we may express it, of length, breadth, and depth,
without any regard to the presence of matter, forms the
basis of our idea of space.
" Absolute space is conceived as remaining always similar to itself
and immovable. The arrangements of its parts can no more be altered
than the order of the portions of time. To conceive them to move
from their places is to conceive a place to move away from itself."
Relative Character of our Knowledge of Time and
Space. There is nothing to distinguish one portion of time
from another except the different events which occur in
each. Similarly, there is nothing to distinguish one part
of space from another except their relation to the places of
material bodies. We can not describe the time of an event
without referring to some other event, or the place of a body
except by reference to some other body. All our knowledge
of both time and space is therefore essentially relative.
Think, for instance, of our method of stating the time of an event.
We say that something occurred in 1776 A. D., on the 4th of July. We
mean, first, that it occurred after the birth of Jesus Christ ; secondly,
that it occurred after that event by an interval measured by 1,776
whole revolutions of the earth about the sun and by a certain fraction
of another revolution. Thus we ordinarily reckon the time of events
MATTER DEFINED. 9
relatively to another (or standard) event, the birth of Christ, and by
means of an event which is being continually and regularly repeated,
viz., the revolution of the earth about the sun.
In locating bodies in space, no such universal point of
reference is used as in time. Bodies or places upon or near
the earth's surface are described as being at a certain distance
in a certain direction from any convenient starting-point.
The exact location of any point of the earth's surface for precise
work in geod'esy, geography, and astronomy, is given by latitude, longi-
tude, and height above the sea-level. Latitude is measured by angular
distance north or south of the equator ; longitude, by angular distance
east or west from a meridian chosen at will, as that passing through