14. MATTER HAS DENSITY.
This quality is exhibited in two ways in matter. In the first, the different elements in their atomic form have different masses or atomic weights. An atom of oxygen weighs sixteen times as much as an atom of hydrogen; that is, it has sixteen times as much matter, as determined by weight, as the hydrogen atom has, or it takes sixteen times as many hydrogen atoms to make a pound as it takes of oxygen atoms. This is generally expressed by saying that oxygen has sixteen times the density of hydrogen. In like manner, iron has fifty-six times the density, and gold one hundred and ninety-six. The difference is one in the structure of the atomic elements. If one imagines them to be vortex-rings, they may differ in size, thickness, and rate of rotation; either of these might make all the observed difference between the elements, including their density. In the second way, density implies compactness of molecules. Thus if a cubic foot of air be compressed until it occupies but half a cubic foot, each cubic inch will have twice as many molecules in it as at first. The amount of air per unit volume will have been doubled, the weight will have been doubled, the amount of matter as determined by its weight will have been doubled, and consequently we say its density has been doubled.
If a bullet or a piece of iron be hammered, the molecules are compacted closer together, and a greater number can be got into a cubic inch when so condensed. In this sense, then, density means the number of molecules in a unit of space, a cubic inch or cubic centimeter. There is implied in this latter case that the molecules do not occupy all the available space, that they may have varying degrees of closeness; in other words, matter is discontinuous, and therefore there may be degrees in density.
THE ETHER HAS DENSITY.
It is common to have the degree of density of the ether spoken of in the same way, and for the same reason, that its elasticity is spoken of. The rate of transmission of a physical disturbance, as of a pressure or a wave-motion in matter, is conditioned by its degree of density; that is, the amount of matter per cubic inch as determined by its weight; the greater the density the slower the rate. So if rate of speed and elasticity be known, the density may be computed. In this way the density of the ether has been deduced by noting the velocity of light.
The enormous velocity is supposed to prove that its density is very small, even when compared with hydrogen. This is stated to be about equal to that of the air at the height of two hundred and ten miles above the surface of the earth, where the air molecules are so few that a molecule might travel for 60,000,000 miles without coming in collision with another molecule. In air of ordinary density, a molecule can on the average move no further than about the two-hundred-and-fifty-thousandth of an inch without such collision. It is plain the density of the ether is so far removed from the density of anything we can measure, that it is hardly comparable with such things. If, in addition, one recalls the fact that the ether is homogeneous, that is all of one kind, and also that it is not composed of atoms and molecules, then degree of compactness and number of particles per cubic inch have no meaning, and the term density, if used, can have no such meaning as it has when applied to matter. There is no physical conception gained from the study of matter that can be useful in thinking of it. As with elasticity, so density is inappropriately applied to the ether, but there is no substitute yet offered.
15. MATTER IS HEATABLE.
So long as heat was thought to be some kind of an imponderable thing, which might retain its identity whether it were in or out of matter, its real nature was obscured by the name given to it. An imponderable was a mysterious something like a spirit, which was the cause of certain phenomena in matter. Heat, light, electricity, magnetism, gravitation, were due to such various agencies, and no one concerned himself with the nature of one or the other. Bacon thought that heat was a brisk agitation of the particles of substances, and Count Rumford and Sir Humphrey Davy thought they proved that it could be nothing else, but they convinced nobody. Mayer in Germany and Joule in England showed that quantitative relations existed between work done and heat developed, but not until the publication of the book called _Heat as a Mode of Motion_, was there a change of opinion and terminology as to the nature of heat.
For twenty years after that it was common to hear the expressions heat, and radiant heat, to distinguish between phenomena in matter and what is now called radiant energy radiations, or simply ether-waves. Not until the necessity arose for distinguishing between different forms of energy, and the conditions for developing them, did it become clear to all that a change in the form of energy implied a change in the form of motion that embodied it. The energy called heat energy was proved to be a vibratory motion of molecules, and what happened in the ether as a result of such vibrations is no longer spoken of as heat, but as ether waves. When it is remembered that the ultimate atoms are elastic bodies, and that they will, if free, vibrate in a periodic manner when struck or shaken in any way, just as a ball will vibrate after it is struck, it is easy to keep in mind the distinction between the mechanical form of motion spent in striking and the vibratory form of the motion produced by it. The latter is called heat; no other form of motion than that is properly called heat. It is this alone that represents temperature, the rate and amplitude of such atomic and molecular vibrations as constitute change, of form. Where molecules like those in a gas have some freedom of movement between impacts, they bound away from each other with varying velocities. The path of such motion may be long or short, depending upon the density or compactness of the molecules, but such changes in position are not heat for a molecule any more than the flight of a musket ball is heat, though it may be transformed into heat on striking the target.
This conception of heat as the rapid change in the form of atoms and molecules, due to their elasticity, is a phenomenon peculiar to matter.
It implies a body possessing form that may be changed; elasticity, that its changes may be periodic, and degrees of freedom that secure space for the changes. Such a body may be heated. Its temperature will depend upon the amplitude of such vibrations, and will be limited by the maximum amplitude.
THE ETHER IS UNHEATABLE.
The translatory motion of a mass of matter, big or little, through the ether, is not arrested in any degree so far as observed, but the internal vibratory motion sets up waves in the ether, the ether absorbs the energy, and the amplitude is continually lessened. The motion has been transferred and transformed; transferred from matter to the ether, and transformed from vibratory to waves travelling at the rate of 186,000 miles per second. The latter is not heat, but the result of heat. With the ether constituted as described, such vibratory motion as constitutes heat is impossible to it, and hence the characteristic of heat-motion in it is impossible; it cannot therefore be heated. The space between the earth and the sun may have any assignable amount of energy in the form of ether waves or light, but not any temperature. One might loosely say that the temperature of empty spaces was absolute zero, but that would not be quite correct, for the idea of temperature cannot properly be entertained as applicable to the ether. To say that its temperature was absolute zero, would serve to imply that it might be higher, which is inadmissible.
When energy has been transformed, the old name by which the energy was called must be dropped. Ether cannot be heated.
16. MATTER IS INDESTRUCTIBLE.
This is commonly said to be one of the essential properties of matter.
All that is meant by it, however, is simply this: In no physical or chemical process to which it has been experimentally subjected has there been any apparent loss. The matter experimented upon may change from a solid or liquid to a gas, or the molecular change called chemical may result in new compounds, but the weight of the material and its atomic constituents have not appreciably changed. That matter cannot be annihilated is only the converse of the proposition that matter cannot be created, which ought always to be modified by adding, by physical or chemical processes at present known. A chemist may work with a few grains of a substance in a beaker, or test-tube, or crucible, and after several solutions, precipitations, fusions and dryings, may find by final weighing that he has not lost any appreciable amount, but how much is an appreciable amount? A fragment of matter the ten-thousandth of an inch in diameter has too small a weight to be noted in any balance, yet it would be made up of thousands of millions of atoms. Hence if, in the processes to which the substance had been subjected, there had been the total annihilation of thousands of millions of atoms, such phenomenon would not have been discovered by weighing. Neither would it have been discovered if there had been a similar creation or development of new matter. All that can be asserted concerning such events is, that they have not been discovered with our means of observation.
The alchemists sought to transform one element into another, as lead into gold. They did not succeed. It was at length thought to be impossible, and the attempt to do it an absurdity. Lately, however, telescopic observation of what is going on in nebulae, which has already been referred to, has somewhat modified ideas of what is possible and impossible in that direction. It is certainly possible roughly to conceive how such a structure as a vortex-ring in the ether might be formed. With certain polarizing apparatus it is possible to produce rays of circularly polarized light. These are rays in which the motion is an advancing rotation like the wire in a spiral spring. If such a line of rotations in the ether were flexible, and the two ends should come together, there is reason for thinking they would weld together, in which case the structure would become a vortex-ring and be as durable as any other. There is reason for believing, also, that somewhat similar movements are always present in a magnetic field, and though we do not know how to make them close up in the proper way, it does not follow that it is impossible for them to do so.
The bearing of all this upon the problem of the transmutation of elements is evident. No one now will venture to deny its possibility as strongly as it was denied a generation ago. It will also lead one to be less confident in the theory that matter is indestructible. Assuming the vortex-ring theory of atoms to be true, if in any way such a ring could be cut or broken, there would not remain two or more fragments of a ring or atom. The whole would at once be dissolved into the ether. The ring and rotary energy that made it an atom would be destroyed, but not the substance it was made of, nor the energy which was embodied therein. For a long time philosophers have argued, and commonsense has agreed with them, that an atom which could not be ideally broken into two parts was impossible, that one could at any rate think of half an atom as a real objective possibility. This vortex-ring theory shows easily how possible it is to-day to think what once was philosophically incredible. It shows that metaphysical reasoning may be ever so clear and apparently irrefragable, yet for all that it may be very unsound. The trouble does not come so much from the logic as from the assumption upon which the logic is founded. In this particular case the assumption was that the ultimate particles of matter were hard, irrefragable somethings, without necessary relations to anything else, or to energy, and irrefragable only because no means had been found of breaking them.
The destructibility or indestructibility of the ether cannot be considered from the same standpoint as that for matter, either ideally or really. Not ideally, because we are utterly without any mechanical conceptions of the substance upon which one can base either reason or analogy; and not really, because we have no experimental evidence as to its nature or mode of operation. If it be continuous, there are no interspaces, and if it be illimitable there is no unfilled space anywhere. Furthermore, one might infer that if in any way a portion of the ether could be annihilated, what was left would at once fill up the vacated space, so there would be no record left of what had happened.
Apparently, its destruction would be the destruction of a substance, which is a very different thing from the destruction of a mode of motion. In the latter, only the form of the motion need be destroyed to completely obliterate every trace of the atom. In the former, there would need to be the destruction of both substance and energy, for it is certain, for reasons yet to be attended to, that the ether is saturated with energy.
One may, without mechanical difficulties, imagine a vortex-ring destroyed. It is quite different with the ether itself, for if it were destroyed in the same sense as the atom of matter, it would be changed into something else which is not ether, a proposition which assumes the existence of another entity, the existence for which is needed only as a mechanical antecedent for the other. The same assumption would be needed for this entity as for the ether, namely, something out of which it was made, and this process of assuming antecedents would be interminable.
The last one considered would have the same difficulties to meet as the ether has now. The assumption that it was in some way and at some time created is more rational, and therefore more probable, than that it either created itself or that it always existed. Considered as the underlying stratum of matter, it is clear that changes of any kind in matter can in no way affect the quantity of ether.
17. MATTER HAS INERTIA.
The resistance that a mass of matter opposes to a change in its position or rate and direction of movement, is called inertia. That it should actively oppose anything has been already pointed out as reason for denying that matter is inert, but inertia is the measure of the reaction of a body when it is acted upon by pressure from any source tending to disturb its condition of either rest or motion. It is the equivalent of mass, or the amount of matter as measured by gravity, and is a fixed quantity; for inertia is as inherent as any other quality, and belongs to the ultimate atoms and every combination of them. It implies the ability to absorb energy, for it requires as much energy to bring a moving body to a standstill as was required to give it its forward motion.
Both rotary and vibratory movements are opposed by the same property. A grindstone, a tuning-fork, and an atom of hydrogen require, to move them in their appropriate ways, an amount of energy proportionate to their mass or inertia, which energy is again transformed through friction into heat and radiated away.
One may say that inertia is the measure of the ability of a body to transfer or transform mechanical energy. The meteorite that falls upon the earth to-day gives, on its impact, the same amount of energy it would have given if it had struck the earth ten thousand years ago. The inertia of the meteor has persisted, not as energy, but as a factor of energy. We commonly express the energy of a mass of matter by _mv_^{2}/2, where _m_ stands for the mass and _v_ for its velocity. We might as well, if it were as convenient, substitute inertia for mass, and write the expression _iv_^{2}/2, for the mass, being measured by its inertia, is only the more common and less definitive word for the same thing. The energy of a mass of matter is, then, proportional to its inertia, because inertia is one of its factors. Energy has often been treated as if it were an objective thing, an entity and a unity; but such a conception is evidently wrong, for, as has been said before, it is a product of two factors, either of which may be changed in any degree if the other be changed inversely in the same degree. A cannon ball weighing 1000 pounds, and moving 100 feet per second, will have 156,000 foot-pounds of energy, but a musket ball weighing an ounce will have the same amount when its velocity is 12,600 feet per second.
Nevertheless, another body acting upon either bullet or cannon ball, tending to move either in some new direction, will be as efficient while those bodies are moving at any assignable rate as when they are quiescent, for the change in direction will depend upon the inertia of the bodies, and that is constant.
The common theory of an inert body is one that is wholly passive, having no power of itself to move or do anything, except as some agency outside itself compels it to move in one way or another, and thus endows it with energy. Thus a stone or an iron nail are thought to be inert bodies in that sense, and it is true that either of them will remain still in one place for an indefinite time and move from it only when some external agency gives them impulse and direction. Still it is known that such bodies will roll down hill if they will not roll up, and each of them has itself as much to do with the down-hill movement as the earth has; that is, it attracts the earth as much as the earth attracts it. If one could magnify the structure of a body until the molecules became individually visible, every one of them would be seen to be in intense activity, changing its form and relative position an enormous number of times per second in undirected ways. No two such molecules move in the same way at the same time, and as all the molecules cohere together, their motions in different directions balance each other, so that the body as a whole does not change its position, not because there is no moving agency in itself, but because the individual movements are scattering, and not in a common direction. An army may remain in one place for a long time. To one at a distance it is quiescent, inert. To one in the camp there is abundant sign of activity, but the movements are individual movements, some in one direction and some in another, and often changing. The same army on the march has the same energy, the same rate of individual movement; but all have a common direction, it moves as a whole body into new territory. So with the molecules of matter. In large masses they appear to be inert, and to do nothing, and to be capable of doing nothing. That is only due to the fact that their energy is undirected, not that they can do nothing. The inference that if quiescent bodies do not act in particular ways they are inert, and cannot act in any kind of a way, is a wrong inference. An illustration may perhaps make this point plainer. A lump of coal will be still as long as anything if it be undisturbed. Indeed, it has thus lain in a coal-bed for millions of years probably, but if coal be placed where it can combine with oxygen, it forthwith does so, and during the process yields a large amount of energy in the shape of heat. One pound of coal in this way gives out 14,000 heat units, which is the equivalent of 11,000,000 foot-pounds of work, and if it could be all utilized would furnish a horse-power for five and a half hours. Can any inert body weighing a pound furnish a horse-power for half a day? And can a body give out what it has not got? Are gunpowder and nitro-glycerine inert?
Are bread and butter and foods in general inert because they will not push and pull as a man or a horse may? All have energy, which is available in certain ways and not in others, and whatever possesses energy available in any way is not an ideally inert body. Lastly, how many inert bodies together will it take to make an active body? If the question be absurd, then all the phenomena witnessed in bodies, large or small, are due to the fact that the atoms are not inert, but are immensely energetic, and their inertia is the measure of their rates of exchanging energy.
THE ETHER IS CONDITIONALLY POSSESSED OF INERTIA.
A moving mass of matter is brought to rest by friction, because it imparts its motion at some rate to the body it is in contact with.
Generally the energy is transformed into heat, but sometimes it appears as electrification. Friction is only possible because one or both of the bodies possess inertia. That a body may move in the ether for an indefinite time without losing its velocity has been stated as a reason for believing the ether to be frictionless. If it be frictionless, then it is without inertia, else the energy of the earth and of a ray of light would be frittered away. A ray of light can only be transformed when it falls upon molecules which may be heated by it. As the ether cannot be heated and cannot transform translational energy, it is without inertia for _such_ a form of motion and its embodied energy.
It is not thus with other forms of energy than the translational. Atomic and molecular vibrations are so related to the ether that they are transformed into waves, which are conducted away at a definite rate.
This shows that such property of inertia as is possessed by the ether is selective and not like that of matter, which is equally "inertiative"
under all conditions. Similarly with electric and magnetic phenomena, it is capable of transforming the energy which may reside as stress in the ether, and other bodies moving in the space so affected meet with frictional resistance, for they become heated if the motion be maintained. On the other hand, there is no evidence that the body which produced the electric or magnetic stress suffers any degree of friction on moving in precisely the same space. A bar magnet rotating on its longitudinal axis does not disturb its own field, but a piece of iron revolving near the magnet will not only become heated, but will heat the stationary magnet. Much experimental work has been done to discover, if possible, the relation of a magnet to its ether field. As the latter is not disturbed by the rotation of the magnet, it has been concluded that the field does not rotate; but as every molecule in the magnet has its own field independent of all the rest, it is mechanically probable that each such field does vary in the rotation, but among the thousands of millions of such fields the average strength of the field does not vary within measurable limits. Another consideration is that the magnetic field itself, when moved in space, suffers no frictional resistance.
There is no magnetic energy wasted through ether inertia. These phenomena show that whether the ether exhibits the quality called inertia depends upon the kind of motion it has.
18. MATTER IS MAGNETIC.
The ordinary phenomenon of magnetism is shown by bringing a piece of iron into the neighbourhood of a so-called magnet, where it is attracted by the latter, and if free to move will go to and cling to the magnet. A delicately suspended magnetic needle will be affected appreciably by a strong magnet at the distance of several hundred feet. As the strength of such action varies inversely as the square of the distance from the magnet, it is evident there can be no absolute boundary to it. At a distance from an ordinary magnet it becomes too weak to be detected by our methods, not that there is a limit to it. It is customary to think of iron as being peculiarly endowed with magnetic quality, but all kinds of matter possess it in some degree. Wood, stone, paper, oats, sulphur, and all the rest, are attracted by a magnet, and will stick to it if the magnet be a strong one. Whether a piece of iron itself exhibits the property depends upon its temperature, for near 700 degrees it becomes as magnetically indifferent as a piece of copper at ordinary temperature. Oxygen, too, at 200 degrees below the zero of Centigrade adheres to a magnet like iron.
In this as in so many other particulars, how a piece of matter behaves depends upon its temperature, not that the essential qualities are modified in any degree, but temperature interferes with atomic arrangement and aggregation, and so disguises their phenomena.
As every kind of matter is thus affected by a magnet, the manifestations differing but in degree, it follows that all kinds of atoms--all the elements--are magnetic. An inherent property in them, as much so as gravitation or inertia; apparently a quality depending upon the structure of the atoms themselves, in the same sense as gravitation is thus dependent, as it is not a quality of the ether.
An atom must, then, be thought of as having polarity, different qualities on the two sides, and possessing a magnetic field as extensive as space itself. The magnetic field is the stress or pressure in the ether produced by the magnetic body. This ether pressure produced by a magnet may be as great as a ton per square inch. It is this pressure that holds an armature to the magnet. As heat is a molecular condition of vibration, and radiant energy the result of it, so is magnetism a property of molecules, and the magnetic field the temporary condition in the ether, which depends upon the presence of a magnetic body. We no longer speak of the wave-motion in the ether which results from heat, as heat, but call it radiation, or ether waves, and for a like reason the magnetic field ought not to be called magnetism.
THE ETHER IS NON-MAGNETIC.
A magnetic field manifests itself in a way that implies that the ether structure, if it may be said to have any, is deformed--deformed in such a sense that another magnet in it tends to set itself in the plane of the stress; that is, the magnet is twisted into a new position to accommodate itself to the condition of the medium about it. The new position is the result of the reaction of the ether upon the magnet and ether pressure acting at right angles to the body that produced the stress. Such an action is so anomalous as to suggest the propriety of modifying the so-called third law of motion, viz., action and reaction are equal and opposite, adding that sometimes action and reaction are at right angles.
There is no condition or property exhibited by the ether itself which shows it to have any such characteristic as attraction, repulsion, or differences in stress, except where its condition is modified by the activities of matter in some way. The ether itself is not attracted or repelled by a magnet; that is, it is not a magnetic body in any such sense as matter in any of its forms is, and therefore cannot properly be called magnetic.
It has been a mechanical puzzle to understand how the vibratory motions called heat could set up light waves in the ether seeing that there is an absence of friction in the latter. In the endeavour to conceive it, the origin of sound-waves has been in mind, where longitudinal air-waves are produced by the vibrations of a sounding body, and molecular impact is the antecedent of the waves. The analogy does not apply. The following exposition may be helpful in grasping the idea of such transformation and change of energy from matter to the ether.
Consider a straight bar permanent magnet to be held in the hand. It has its north and south poles and its field, the latter extending in every direction to an indefinite distance. The field is to be considered as ether stress of such a sort as to tend to set other magnets in it in new positions. If at a distance of ten feet there were a delicately-poised magnet needle, every change in the position of the magnet held in the hand would bring about a change in the position of the needle. If the position of the hand magnet were completely reversed, so the south pole faced where the north pole faced before, the field would have been completely reversed, and the poised needle would have been pushed by the field into an opposite position. If the needle were a hundred feet away, the change would have been the same except in amount. The same might be said if the two were a mile apart, or the distance of the moon or any other distance, for there is no limit to an ether magnetic field.
Suppose the hand magnet to have its direction completely reversed once in a second. The whole field, and the direction of the stress, would necessarily be reversed as often. But this kind of change in stress is known by experiment to travel with the speed of light, 186,000 miles a second; the disturbance due to the change of position of the magnet will therefore be felt in some degree throughout space. In a second and a third of a second it will have reached the moon, and a magnet there will be in some measure affected by it. If there were an observer there with a delicate-enough magnet, he could be witness to its changes once a second for the same reason one in the room could. The only difference would be one of amount of swing. It is therefore theoretically possible to signal to the moon with a swinging magnet. Suppose again that the magnet should be swung twice a second, there would be formed two waves, each one half as long as the first. If it should swing ten times a second, then the waves would be one-tenth of 186,000 miles long. If in some mechanical way it could be rotated 186,000 times a second, the wave would be but one mile long. Artificial ways have been invented for changing this magnet field as many as 100 million times a second, and the corresponding wave is less than a foot long. The shape of a magnet does not necessarily make it weaker or stronger as a magnet, but if the poles are near together the magnetic field is denser between them than when they are separated. The ether stress is differently distributed for every change in the relative positions of the poles.
A common U-magnet, if struck, will vibrate like a tuning-fork, and gives out a definite pitch. Its poles swing towards and away from each other at uniform rates, and the pitch of the magnet will depend upon its size, thickness, and the material it is made of.
Let ten or fifteen ohms of any convenient-sized wire be wound upon the bend of a commercial U-magnet. Let this wire be connected to a telephone in its circuit. When the magnet is made to sound like a tuning-fork, the pitch will be reproduced in the telephone very loudly. If another magnet with a different pitch be allowed to vibrate near the former, the pitch of the vibrating body will be heard in the telephone, and these show that the changing magnetic field reacts upon the quiescent magnet, and compels the latter to vibrate at the same rate. The action is an ether action, the waves are ether waves, but they are relatively very long. If the magnet makes 500 vibrations a second, the waves will be 372 miles long, the number of times 500 is contained in 186,000 miles. Imagine the magnet to become smaller and smaller until it was the size of an atom, the one-fifty-millionth of an inch. Its vibratory rate would be proportionally increased, and changes in its form will still bring about changes in its magnetic field. But its magnetic field is practically limitless, and the number of vibrations per second is to be reckoned as millions of millions; the waves are correspondingly short, small fractions of an inch. When they are as short as the one-thirty-seven-thousandth of an inch, they are capable of affecting the retina of the eye, and then are said to be visible as red light. If the vibratory rate be still higher, and the corresponding waves be no more than one-sixty-thousandth of an inch long, they affect the retina as violet light, and between these limits there are all the waves that produce a complete spectrum. The atoms, then, shake the ether in this way because they all have a magnetic hold upon the ether, so that any disturbance of their own magnetism, such as necessarily comes when they collide, reacts upon the ether for the same reason that a large magnet acts thus upon it when its poles approach and recede from each other. It is not a phenomenon of mechanical impact or frictional resistance, since neither are possible in the ether.
19. MATTER EXISTS IN SEVERAL STATES.
Molecular cohesion exists between very wide ranges. When strong, so if one part of a body is moved the whole is moved in the same way, without breaking continuity or the relative positions of the molecules, we call the body a solid. In a liquid, cohesion is greatly reduced, and any part of it may be deformed without materially changing the form of the rest.