The Machinery of the Universe: Mechanical Conceptions of Physical Phenomena — Reading Companion

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].

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.

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.

PROPERTIES OF MATTER AND ETHER

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.

A common conception of the ether has been that it is a finer-grained substance than ordinary matter, but otherwise so like the latter that the laws found to hold good with matter were equally applicable to the ether, and hence the mechanical conceptions formed from experience in regard to the one have been transferred to the other, and the properties belonging to one, such as density, elasticity, etc., have been asserted as properties of the other.

There is so considerable a body of knowledge bearing upon the similarities and dissimilarities of these two entities that it will be well to compare them. After such comparison one will be better able to judge of the propriety of assuming them to be subject to identical laws.

1. MATTER IS DISCONTINUOUS.

Matter is made up of atoms having dimensions approximately determined to be in the neighbourhood of the one fifty-millionth of an inch in diameter. These atoms may have various degrees of aggregation;--they may be in practical contact, as in most solid bodies such as metals and rocks; in molecular groupings as in water, and in gases such as hydrogen, oxygen, and so forth, where two, three, or more atoms cohere so strongly as to enable the molecules to act under ordinary circumstances like simple particles. Any or all of these molecules and atoms may be separated by any assignable distance from each other. Thus, in common air the molecules, though rapidly changing their positions, are on the average about two hundred and fifty times their own diameter apart. This is a distance relatively greater than the distance apart of the earth and the moon, for two hundred and fifty times the diameter of the earth will be 8000 x 250 = 2,000,000 miles, while the distance to the moon is but 240,000 miles. The sun is 93,000,000 miles from the earth, and the most of the bodies of the solar system are still more widely separated, Neptune being nearly 3000 millions of miles from the sun. As for the fixed stars, they are so far separated from us that, at the present rate of motion of the solar system in its drift through space--500 millions of miles in a year--it would take not less than 40,000 years to reach the nearest star among its neighbours, while for the more remote ones millions of years must be reckoned. The huge space separating these masses is practically devoid of matter; it is a vacuum.

THE ETHER IS CONTINUOUS.

The idea of continuity as distinguished from discontinuity may be gained by considering what would be made visible by magnification. Water appears to the eye as if it were without pores, but if sugar or salt be put into it, either will be dissolved and quite disappear among the molecules of the water as steam does in the air, which shows that there are some unoccupied spaces between the molecules. If a microscope be employed to magnify a minute drop of water it still shows the same lack of structure as that looked at with the unaided eye. If the magnifying power be the highest it may reveal a speck as small as the hundred-thousandth part of an inch, yet the speck looks no different in character. We know that water is composed of two different kinds of atoms, hydrogen and oxygen, for they can be separated by chemical means and kept in separate bottles, and again made to combine to form water having all the qualities that belonged to it before it was decomposed. If a very much higher magnifying power were available, we should ultimately be able to see the individual water molecules, and recognize their hydrogen and oxygen constituents by their difference in size, rate of movements, and we might possibly separate them by mechanical methods. What one would see would be something very different in structure from the water as it appears to our eyes. If the ether were similarly to be examined through higher and still higher magnifying powers, even up to infinity, there is no reason for thinking that the last examination would show anything different in structure or quality from that which was examined with low power or with no microscope at all. This is all expressed by saying that the ether is a continuous substance, without interstices, that it fills space completely, and, unlike gases, liquids, and solids, is incapable of absorbing or dissolving anything.

2. MATTER IS LIMITED.

There appears to be a definite amount of matter in the visible universe, a definite number of molecules and atoms. How many molecules there are in a cubic inch of air under ordinary pressure has been determined, and is represented approximately by a huge number, something like a thousand million million millions.

When the diameter of a molecule has been measured, as it has been approximately, and found to be about one fifty-millionth of an inch, then fifty million in a row would reach an inch, and the cube of fifty million is 125,000,000000,000000,000000, one hundred and twenty-five thousand million million millions. In a cubic foot there will of course be 1728 times that number. One may if one likes find how many there may be in the earth, and moon, sun and planets, for the dimensions of them are all very well known. Only the multiplication table need be used, and the sum of all these will give how many molecules there are in the solar system. If one should feel that the number thus obtained was not very accurate, he might reflect that if there were ten times as many it would add but another cipher to a long line of similar ones and would not materially modify it. The point is that there is a definite, computable number. If one will then add to these the number of molecules in the more distant stars and nebulae, of which there are visible about 100,000,000, making such estimate of their individual size as he thinks prudent, the sum of all will give the number of molecules in the visible universe. The number is not so large but it can be written down in a minute or two. Those who have been to the pains to do the sum say it may be represented by seven followed by ninety-one ciphers. One could easily compute how many molecules so large a space would contain if it were full and as closely packed as they are in a drop of water, but there would be a finite and not an infinite number, and therefore there is a limited number of atoms in the visible universe.

THE ETHER IS UNLIMITED.