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_THE ROMANCE OF SCIENCE_
THE MACHINERY OF THE UNIVERSE
MECHANICAL CONCEPTIONS OF
PHYSICAL PHENOMENA
BY
A. E. DOLBEAR, A.B., A.M., M.E., PH.D.
PROFESSOR OF PHYSICS AND ASTRONOMY, TUFTS COLLEGE, MASS.
PUBLISHED UNDER GENERAL LITERATURE COMMITTEE.
LONDON:
SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE,
NORTHUMBERLAND AVENUE, W.C.;
43, QUEEN VICTORIA STREET, E.C.
BRIGHTON: 129, NORTH STREET.
NEW YORK: E. & J. B. YOUNG & CO.
1897.
PREFACE
For thirty years or more the expressions "Correlation of the Physical
Forces" and "The Conservation of Energy" have been common, yet few
persons have taken the necessary pains to think out clearly what
mechanical changes take place when one form of energy is transformed
into another.
Since Tyndall gave us his book called _Heat as a Mode of Motion_ neither
lecturers nor text-books have attempted to explain how all phenomena are
the necessary outcome of the various forms of motion. In general,
phenomena have been attributed to _forces_--a metaphysical term, which
explains nothing and is merely a stop-gap, and is really not at all
needful in these days, seeing that transformable modes of motion, easily
perceived and understood, may be substituted in all cases for forces.
In December 1895 the author gave a lecture before the Franklin Institute
of Philadelphia, on "Mechanical Conceptions of Electrical Phenomena," in
which he undertook to make clear what happens when electrical phenomena
appear. The publication of this lecture in _The Journal of the Franklin
Institute_ and in _Nature_ brought an urgent request that it should be
enlarged somewhat and published in a form more convenient for the
public. The enlargement consists in the addition of a chapter on the
"_Contrasted Properties of Matter and the Ether_," a chapter containing
something which the author believes to be of philosophical importance in
these days when electricity is so generally described as a phenomenon of
the ether.
A. E. DOLBEAR.
TABLE OF CONTENTS
CHAPTER I
Ideas of phenomena ancient and modern, metaphysical and
mechanical--Imponderables--Forces, invented and
discarded--Explanations--Energy, its factors, Kinetic
and Potential--Motions, kinds and transformations
of--Mechanical, molecular, and atomic--Invention of
Ethers, Faraday's conceptions p. 7
CHAPTER II
Properties of Matter and Ether compared--Discontinuity
_versus_ Continuity--Size of atoms--Astronomical
distances--Number of atoms in the universe--Ether
unlimited--Kinds of Matter, permanent qualities
of--Atomic structure; vortex-rings, their
properties--Ether structureless--Matter
gravitative, Ether not--Friction in Matter, Ether
frictionless--Chemical properties--Energy in
Matter and in Ether--Matter as a transformer
of Energy--Elasticity--Vibratory rates and
waves--Density--Heat--Indestructibility of
Matter--Inertia in Matter and in Ether--Matter
not inert--Magnetism and Ether waves--States
of Matter--Cohesion and chemism affected by
temperature--Shearing stress in Solids and in
Ether--Ether pressure--Sensation dependent upon
Matter--Nervous system not affected by Ether
states--Other stresses in Ether--Transformations
of Motion--Terminology p. 24
CHAPTER III
Antecedents of Electricity--Nature of what is
transformed--Series of transformations for the
production of light--Positive and negative
Electricity--Positive and negative twists--Rotations
about a wire--Rotation of an arc--Ether a
non-conductor--Electro-magnetic waves--Induction
and inductive action--Ether stress and atomic
position--Nature of an electric current--Electricity
a condition, not an entity p. 94
CHAPTER I
Ideas of phenomena ancient and modern, metaphysical and
mechanical--Imponderables--Forces, invented and
discarded--Explanations--Energy, its factors, Kinetic
and Potential--Motions, kinds and transformations
of--Mechanical, molecular, and atomic--Invention of
Ethers, Faraday's conceptions.
'And now we might add something concerning a most subtle spirit
which pervades and lies hid in all gross bodies, by the force
and action of which spirit the particles of bodies attract
each other at near distances, and cohere if contiguous, and
electric bodies operate at greater distances, as well repelling
as attracting neighbouring corpuscles, and light is emitted,
reflected, inflected, and heats bodies, and all sensation is
excited, and members of animal bodies move at the command of
the will.'--NEWTON, _Principia_.
In Newton's day the whole field of nature was practically lying fallow.
No fundamental principles were known until the law of gravitation was
discovered. This law was behind all the work of Copernicus, Kepler, and
Galileo, and what they had done needed interpretation. It was quite
natural that the most obvious and mechanical phenomena should first be
reduced, and so the _Principia_ was concerned with mechanical principles
applied to astronomical problems. To us, who have grown up familiar with
the principles and conceptions underlying them, all varieties of
mechanical phenomena seem so obvious, that it is difficult for us to
understand how any one could be obtuse to them; but the records of
Newton's time, and immediately after this, show that they were not so
easy of apprehension. It may be remembered that they were not adopted in
France till long after Newton's day. In spite of what is thought to be
reasonable, it really requires something more than complete
demonstration to convince most of us of the truth of an idea, should the
truth happen to be of a kind not familiar, or should it chance to be
opposed to our more or less well-defined notions of what it is or ought
to be. If those who labour for and attain what they think to be the
truth about any matter, were a little better informed concerning mental
processes and the conditions under which ideas grow and displace others,
they would be more patient with mankind; teachers of every rank might
then discover that what is often called stupidity may be nothing else
than mental inertia, which can no more be made active by simply willing
than can the movement of a cannon ball by a like effort. We _grow_ into
our beliefs and opinions upon all matters, and scientific ideas are no
exceptions.
Whewell, in his _History of the Inductive Sciences_, says that the
Greeks made no headway in physical science because they lacked
appropriate ideas. The evidence is overwhelming that they were as
observing, as acute, as reasonable as any who live to-day. With this
view, it would appear that the great discoverers must have been men who
started out with appropriate ideas: were looking for what they found.
If, then, one reflects upon the exceeding great difficulty there is in
discovering one new truth, and the immense amount of work needed to
disentangle it, it would appear as if even the most successful have but
indistinct ideas of what is really appropriate, and that their
mechanical conceptions become clarified by doing their work. This is not
always the fact. In the statement of Newton quoted at the head of this
chapter, he speaks of a spirit which lies hid in all gross bodies, etc.,
by means of which all kinds of phenomena are to be explained; but he
deliberately abandons that idea when he comes to the study of light, for
he assumes the existence and activity of light corpuscles, for which he
has no experimental evidence; and the probability is that he did this
because the latter conception was one which he could handle
mathematically, while he saw no way for thus dealing with the other. His
mechanical instincts were more to be trusted than his carefully
calculated results; for, as all know, what he called "spirits," is what
to-day we call the ether, and the corpuscular theory of light has now no
more than a historic interest. The corpuscular theory was a mechanical
conception, but each such corpuscle was ideally endowed with qualities
which were out of all relation with the ordinary matter with which it
was classed.
Until the middle of the present century the reigning physical philosophy
held to the existence of what were called imponderables. The phenomena
of heat were explained as due to an imponderable substance called
"caloric," which ordinary matter could absorb and emit. A hot body was
one which had absorbed an imponderable substance. It was, therefore, no
heavier than before, but it possessed ability to do work proportional to
the amount absorbed. Carnot's ideal engine was described by him in terms
that imply the materiality of heat. Light was another imponderable
substance, the existence of which was maintained by Sir David Brewster
as long as he lived. Electricity and magnetism were imponderable fluids,
which, when allied with ordinary matter, endowed the latter with their
peculiar qualities. The conceptions in each case were properly
mechanical ones _part_ (but not all) _of the time_; for when the
immaterial substances were dissociated from matter, where they had
manifested themselves, no one concerned himself to inquire as to their
whereabouts. They were simply off duty, but could be summoned, like the
genii in the story of Aladdin's Lamp. Now, a mechanical conception of
any phenomenon, or a mechanical explanation of any kind of action, must
be mechanical all the time, in the antecedents as well as the
consequents. Nothing else will do except a miracle.
During the fifty years, from about 1820 to 1870, a somewhat different
kind of explanation of physical events grew up. The interest that was
aroused by the discoveries in all the fields of physical science--in
heat, electricity, magnetism and chemistry--by Faraday, Joule,
Helmholtz, and others, compelled a change of conceptions; for it was
noticed that each special kind of phenomenon was preceded by some other
definite and known kind; as, for instance, that chemical action preceded
electrical currents, that mechanical or electrical activity resulted
from changing magnetism, and so on. As each kind of action was believed
to be due to a special force, there were invented such terms as
mechanical force, electrical force, magnetic, chemical and vital forces,
and these were discovered to be convertible into one another, and the
"doctrine of the correlation of the physical forces" became a common
expression in philosophies of all sorts. By "convertible into one
another," was meant, that whenever any given force appeared, it was at
the expense of some other force; thus, in a battery chemical force was
changed into electrical force; in a magnet, electrical force was changed
into magnetic force, and so on. The idea here was the _transformation of
forces_, and _forces_ were not so clearly defined that one could have a
mechanical idea of just what had happened. That part of the philosophy
was no clearer than that of the imponderables, which had largely dropped
out of mind. The terminology represented an advance in knowledge, but
was lacking in lucidity, for no one knew what a force of any kind was.
The first to discover this and to repudiate the prevailing terminology
were the physiologists, who early announced their disbelief in a vital
force, and their belief that all physiological activities were of purely
physical and chemical origin, and that there was no need to assume any
such thing as a vital force. Then came the discovery that chemical
force, or affinity, had only an adventitious existence, and that, at
absolute zero, there was no such activity. The discovery of, or rather
the appreciation of, what is implied by the term _absolute zero_, and
especially of the nature of heat itself, as expressed in the statement
that heat is a mode of motion, dismissed another of the so-called forces
as being a metaphysical agency having no real existence, though standing
for phenomena needing further attention and explanation; and by
explanation is meant _the presentation of the mechanical antecedents for
a phenomenon, in so complete a way that no supplementary or unknown
factors are necessary_. The train moves because the engine pulls it; the
engine pulls because the steam pushes it. There is no more necessity for
assuming a steam force between the steam and the engine, than for
assuming an engine force between the engine and the train. All the
processes are mechanical, and have to do only with ordinary matter and
its conditions, from the coal-pile to the moving freight, though there
are many transformations of the forms of motion and of energy between
the two extremes.
During the past thirty years there has come into common use another
term, unknown in any technical sense before that time, namely, _energy_.
What was once called the conservation of force is now called the
conservation of energy, and we now often hear of forms of energy. Thus,
heat is said to be a form of energy, and the forms of energy are
convertible into one another, as the so-called forces were formerly
supposed to be transformable into one another. We are asked to consider
gravitative energy, heat energy, mechanical energy, chemical energy, and
electrical energy. When we inquire what is meant by energy, we are
informed that it means ability to do work, and that work is measurable
as a pressure into a distance, and is specified as foot-pounds. A mass
of matter moves because energy has been spent upon it, and has acquired
energy equal to the work done on it, and this is believed to hold true,
no matter what the kind of energy was that moved it. If a body moves, it
moves because another body has exerted pressure upon it, and its energy
is called _kinetic energy_; but a body may be subject to pressure and
not move appreciably, and then the body is said to possess potential
energy. Thus, a bent spring and a raised weight are said to possess
potential energy. In either case, _an energized body receives its energy
by pressure, and has ability to produce pressure on another body_.
Whether or not it does work on another body depends on the rigidity of
the body it acts upon. In any case, it is simply a mechanical
action--body A pushes upon body B (Fig. 1). There is no need to assume
anything more mysterious than mechanical action. Whether body B moves
this way or that depends upon the direction of the push, the point of
its application. Whether the body be a mass as large as the earth or as
small as a molecule, makes no difference in that particular. Suppose,
then, that _a_ (Fig. 2) spends its energy on _b_, _b_ on _c_, _c_ on
_d_, and so on. The energy of _a_ gives translatory motion to _b_, _b_
sets _c_ vibrating, and _c_ makes _d_ spin on some axis. Each of these
has had energy spent on it, and each has some form of energy different
from the other, but no new factor has been introduced between _a_ and
_d_, and the only factor that has gone from _a_ to _d_ has been
motion--motion that has had its direction and quality changed, but not
its nature. If we agree that energy is neither created nor annihilated,
by any physical process, and if we assume that _a_ gave to _b_ all its
energy, that is, all its motion; that _b_ likewise gave its all to _c_,
and so on; then the succession of phenomena from _a_ to _d_ has been
simply the transference of a definite amount of motion, and therefore of
energy, from the one to the other; for _motion has been the only
variable factor_. If, furthermore, we should agree to call the
translatory motion [alpha], the vibratory motion [beta], the
rotary [gamma], then we should have had a conversion of [alpha]
into [beta], of [beta] into [gamma]. If we should consider
the amount of transfer motion instead of the kind of motion, we should
have to say that the [alpha] energy had been transformed into
[beta] and the [beta] into [gamma].
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]
What a given amount of energy will do depends only upon its _form_, that
is, the kind of motion that embodies it.
The energy spent upon a stone thrown into the air, giving it translatory
motion, would, if spent upon a tuning fork, make it sound, but not move
it from its place; while if spent upon a top, would enable the latter to
stand upon its point as easily as a person stands on his two feet, and
to do other surprising things, which otherwise it could not do. One can,
without difficulty, form a mechanical conception of the whole series
without assuming imponderables, or fluids or forces. Mechanical motion
only, by pressure, has been transferred in certain directions at certain
rates. Suppose now that some one should suddenly come upon a spinning
top (Fig. 3) while it was standing upon its point, and, as its motion
might not be visible, should cautiously touch it. It would bound away
with surprising promptness, and, if he were not instructed in the
mechanical principles involved, he might fairly well draw the conclusion
that it was actuated by other than simple mechanical principles, and,
for that reason, it would be difficult to persuade him that there was
nothing essentially different in the body that appeared and acted thus,
than in a stone thrown into the air; nevertheless, that statement would
be the simple truth.
[Illustration: FIG. 3.]
All our experience, without a single exception, enforces the proposition
that no body moves in any direction, or in any way, except when some
other body _in contact_ with it presses upon it. The action is direct.
In Newton's letter to his friend Bentley, he says--"That one body
should act upon another through empty space, without the mediation of
anything else by and through which their action and pressure may be
conveyed from one to another, is to me so great an absurdity that I
believe no man who has in philosophical matters a competent faculty of
thinking can ever fall into it."
For mathematical purposes, it has sometimes been convenient to treat a
problem as if one body could act upon another without any physical
medium between them; but such a conception has no degree of rationality,
and I know of no one who believes in it as a fact. If this be granted,
then our philosophy agrees with our experience, and every body moves
because it is pushed, and the mechanical antecedent of every kind of
phenomenon is to be looked for in some adjacent body possessing
energy--that is, the ability to push or produce pressure.
It must not be forgotten that energy is not a simple factor, but is
always a product of two factors--a mass with a velocity, a mass with a
temperature, a quantity of electricity into a pressure, and so on. One
may sometimes meet the statement that matter and energy are the two
realities; both are spoken of as entities. It is much more philosophical
to speak of matter and motion, for in the absence of motion there is no
energy, and the energy varies with the amount of motion; and
furthermore, to understand any manifestation of energy one must inquire
what kind of motion is involved. This we do when we speak of mechanical
energy as the energy involved in a body having a translatory motion;
also, when we speak of heat as a vibratory, and of light as a wave
motion. To speak of energy without stating or implying these
distinctions, is to speak loosely and to keep far within the bounds of
actual knowledge. To speak thus of a body possessing energy, or
expending energy, is to imply that the body possesses some kind of
motion, and produces pressure upon another body because it has motion.
Tait and others have pointed out the fact, that what is called potential
energy must, in its nature, be kinetic. Tait says--"Now it is impossible
to conceive of a truly dormant form of energy, whose magnitude should
depend, in any way, upon the unit of time; and we are forced to conclude
that potential energy, like kinetic energy, depends (even if unexplained
or unimagined) upon motion." All this means that it is now too late to
stop with energy as a final factor in any phenomenon, that the _form of
motion_ which embodies the energy is the factor that determines _what_
happens, as distinguished from how _much_ happens. Here, then, are to be
found the distinctions which have heretofore been called forces; here
is embodied the proof that direct pressure of one body upon another is
what causes the latter to move, and that the direction of movement
depends on the point of application, with reference to the centre
of mass.
It is needful now to look at the other term in the product we call
energy, namely, the substance moving, sometimes called matter or mass.
It has been mentioned that the idea of a medium filling space was
present to Newton, but his gravitation problem did not require that he
should consider other factors than masses and distances. The law of
gravitation as considered by him was--Every particle of matter attracts
every other particle of matter with a stress which is proportional to
the product of their masses, and inversely to the squares of the
distance between them. Here we are concerned only with the statement
that every particle of matter attracts every other particle of matter.
Everything then that possesses gravitative attraction is matter in the
sense in which that term is used in this law. If there be any other
substance in the universe that is not thus subject to gravitation, then
it is improper to call it matter, otherwise the law should read, "Some
particles of matter attract," etc., which will never do.
We are now assured that there is something else in the universe which
has no gravitative property at all, namely, the ether. It was first
imagined in order to account for the phenomena of light, which was
observed to take about eight minutes to come from the sun to the earth.
Then Young applied the wave theory to the explanation of polarization
and other phenomena; and in 1851 Foucault proved experimentally that the
velocity of light was less in water than in air, as it should be if the
wave theory be true, and this has been considered a crucial experiment
which took away the last hope for the corpuscular theory, and
demonstrated the existence of the ether as a space-filling medium
capable of transmitting light-waves known to have a velocity of 186,000
miles per second. It was called the luminiferous ether, to distinguish
it from other ethers which had also been imagined, such as electric
ether for electrical phenomena, magnetic ether for magnetic phenomena,
and so on--as many ethers, in fact, as there were different kinds of
phenomena to be explained.
It was Faraday who put a stop to the invention of ethers, by suggesting
that the so-called luminiferous ether might be the one concerned in all
the different phenomena, and who pointed out that the arrangement of
iron filings about a magnet was indicative of the direction of the
stresses in the ether. This suggestion did not meet the approval of the
mathematical physicists of his day, for it necessitated the abandonment
of the conceptions they had worked with, as well as the terminology
which had been employed, and made it needful to reconstruct all their
work to make it intelligible--a labour which was the more distasteful as
it was forced upon them by one who, although expert enough in
experimentation, was not a mathematician, and who boasted that the most
complicated mathematical work he ever did was to turn the crank of a
calculating machine; who did all his work, formed his conclusions, and
then said--"The work is done; hand it over to the computers."
It has turned out that Faraday's mechanical conceptions were right.
Every one now knows of Maxwell's work, which was to start with Faraday's
conceptions as to magnetic phenomena, and follow them out to their
logical conclusions, applying them to molecules and the reactions of the
latter upon the ether. Thus he was led to conclude that light was an
electro-magnetic phenomenon; that is, that the waves which constitute
light, and the waves produced by changing magnetism were identical in
their nature, were in the same medium, travelled with the same velocity,
were capable of refraction, and so on. Now that all this is a matter of
common knowledge to-day, it is curious to look back no further than ten
years. Maxwell's conclusions were adopted by scarcely a physicist in
the world. Although it was known that inductive action travelled with
finite velocity in space, and that an electro-magnet would affect the
space about it practically inversely as the square of the distance, and
that such phenomena as are involved in telephonic induction between
circuits could have no other meaning than the one assigned by Maxwell,
yet nearly all the physicists failed to form the only conception of it
that was possible, and waited for Hertz to devise apparatus for
producing interference before they grasped it. It was even then so new,
to some, that it was proclaimed to be a demonstration of the existence
of the ether itself, as well as a method of producing waves short enough
to enable one to notice interference phenomena. It is obvious that Hertz
himself must have had the mechanics of wave-motion plainly in mind, or
he would not have planned such experiments. The outcome of it all is,
that we now have experimental demonstration, as well as theoretical
reason for believing, that the ether, once considered as only
luminiferous, is concerned in all electric and magnetic phenomena, and
that waves set up in it by electro-magnetic actions are capable of being
reflected, refracted, polarized, and twisted, in the same way as
ordinary light-waves can be, and that the laws of optics are applicable
to both.