I need hardly point out that the hypothesis that Aether is gravitative, is bound to play a most important part in the consideration and development of this phase of the study of the universal aetherial medium. It is not my intention, however, at this stage of the work to go fully into the development of this aspect of the subject.
The application of this principle will be considered at the right time, and in the right place. It is, however, generally a.s.sumed, that the Aether is at rest in s.p.a.ce, and that the earth, the planets, and the sun and all stars, move through it with varying velocity, although, as Lord Kelvin points out, such an a.s.sumption is covered with a cloud which up to the present is "as dense as ever." Of course, if the Aether be at rest, and the planets and other heavenly bodies move through it with varying velocity, then the only a.s.sumption regarding the Aether is, that it is frictionless, but, as I have shown in Art. 45, this is opposed to all philosophical reasoning, and therefore to experience and observation.
We have, therefore, to postulate for the Aether such motions as shall fulfil all the Rules of Philosophy, that is, shall be simple in conception, shall be in harmony with our experience and observation, and which shall satisfactorily account for the phenomena sought to be explained, that is, the universal Law of Gravitation; for it is by the properties, combined with the motions of the Aether, that the physical cause of Gravitation is alone to be explained.
Let us revert to the question of a stationary Aether for a moment or two, and let us ask ourselves, where is the evidence for such an a.s.sumption? Has the sun ever ceased to shine, or to send its light-waves with their enormous velocity speeding through the solar system? So far as experience and observation go, I have never read of any record of such a fact, or that light-waves have ceased to proceed from the sun and fill the solar system with Aether-waves.
Not only is this true of the sun, but it is equally true of every planet and satellite, every meteor or comet, every star and sun that exist or dwell in this aetherial medium; for, as has already been shown (Art.
49), every body emits Aether-waves, and these waves spread out in all directions in a spherical form.
The truth is, that the universal Aether is in eternal motion, and that motion forms the physical life of the universe. If it were possible to destroy the motion, then the whole fabric of the universe would fall to pieces, and the beauty, order, and harmony of the celestial mechanism would be replaced by disorder, confusion, and ultimate ruin. Take any a.n.a.logy of Nature, and see what such an a.n.a.logy teaches us. Look at any planet, sun, or star. Do we find any one of these stationary or at rest?
Why from the smallest meteorite or satellite, to the largest star that shines in the firmament of heaven, there is nothing but motion; each satellite, planet, sun, and star moving on and on, ever and ever through the countless ages of time until its course is run and its existence ended. But rest, never! Such a thing as rest is unknown in the entire universe, whether it be in the atomic systems of matter, or the systems of stars and suns that form the universe of worlds.
Take another ill.u.s.tration--that of the ocean! Is that ever at rest, with its unceasing wave and tidal motion? Has the reader ever stood on the sh.o.r.e and seen the ocean when it has been absolutely still, or when the tide has ceased to flow? Such a possibility is almost absurd to contemplate. The same argument applies to the air with its regular flow of winds. Now in regard to the aetherial and universal medium, there are just as regular motions as the flowing of the tide round the earth, or the revolving of a satellite round a planet, or a planet round the sun.
And what is as important, all the motions can be as satisfactorily explained and accounted for from the physical standpoint, as the flow of the tide, or the revolution of a planet.
Year in and year out, the motions of the Aether remain the same, governed by the same laws and producing the same effects. Age after age, the Aether has been moving, producing by its various motions the continuity of that beauty, order, and harmony that govern the universe as a whole.
I have already indicated in Art. 45 the effect of Gravitation on the Aether surrounding each satellite, or planet, or star, or sun. As each satellite, or planet, or star moves through the universal Aether, it takes with it its surrounding Aether as indicated in Art. 45, in the same way that each planet or sun takes with it its own a.s.sociated atmosphere, which is held in contact with it by the self-same force of Gravitation.
In addition to this motion of the aetherial atmosphere through s.p.a.ce, there are other motions of this same gravitating Aether that have to be taken into consideration, before a complete and adequate conception of all the motions of the Aether can be arrived at.
I do not intend, however, at this stage to go fully into such motions, but rather wish to lead up to them from a consideration of hypotheses put forward by such men as Rankine, Challis, Maxwell, Lord Kelvin, McCullagh, and Helmholtz, and from a consideration of such hypotheses in the realm of heat, light, and electricity to be able to form a scientific conception of the proper motions of the Aether, as well as a philosophical one.
CHAPTER V
ENERGY
ART. 51. _Energy._--In the days of Newton, and for a long time afterwards, all energy went by the name of "Force." Thus Newton in his Laws of Motion refers to the action of forces on stationary or moving bodies, and shows how the motion of any body is effected by the impressed force.
(Art 13.)
As science advanced, and scientific research was carried into the fields of heat, light, and electricity, we find that the various forces began to be particularized, with the result that such terms as electrical force, magnetic force, chemical force, etc., became common and familiar terms. As gradually it became known that one particular kind of force was the outcome of another kind, there was given to the world such terms as the Correlation of Forces (Grove), in which he proved that whenever one kind of force appeared as heat or light, it was at the expense of another kind of force, as electricity.
Of later years, however, another term has crept into Philosophy, and instead of the term Force, which is very indistinct and indefinite in character, there appeared the term Energy, although Force and Energy are not exactly synonymous terms. Thus electricity, heat, and light are forms of energy, and are convertible into one another, in the same way that the forces were convertible. Thus we get transformations of energy in the same way that we had transformations of force, and conservation of energy in the same way that we had conservation of force.
Even the term Energy, however, is being replaced in the present times by something more definite and simple, and instead of the term Energy, we shall find, in the development of this phase of natural phenomena, that that term is being replaced by the simple idea of motion, or modes of motion, and that all forms of energy, as light, heat, magnetism, and electricity, and even Gravitation itself, are due to motion of some kind or other. We will, however, lead up to this truth by looking briefly at the term Energy, and see what it implies and embodies.
Energy, therefore, is that property which a body possesses, by which it is capable of doing work. Thus our ideas of work give us our conception of energy. For example, when a weight is lifted, work is done, and a certain amount of energy is expended in the process. Further, the amount of work done is proportionate to the weight lifted, and the height to which the body is raised. Work is done against resistance, so that whenever resistance is overcome, then work is the result. For example, suppose one pound is lifted one foot high, in opposition to the force of gravity, then work is done, and this amount of work is known as a foot-pound.
If a body weighs ten pounds, and is lifted ten feet, the work done is equal to ten pounds multiplied by ten feet (10 10 equals 100), so that one hundred times the amount of work has been done in comparison with the lifting of the one pound one foot high.
As all weight is essentially a gravitational measure, depending upon the intensity of gravity at the place, then, whenever a body is raised or lifted, the work so done is done against the gravity of the earth.
Work is also done, as Newton points out in the first and second laws, whenever we apply force to any body, either stationary or already in motion. The results of all observation and experiments prove, that whenever we have two bodies upon which work is being done, the amount of work is determined by the amount of energy transferred from one body to the other, and that the actual amount of energy gained by one is equal to the amount of energy lost by the other.
Energy is always found in a.s.sociation with matter, so that matter has sometimes been termed the Vehicle of Energy. Wherever, therefore, we find energy of any kind or sort, there we find matter also, as the two are inseparably connected together. Thus, wherever we have heat, we have matter in a particular state of motion, generally understood as vibratory motion Wherever we have light, which is also a form of energy, we also have matter in motion, that is the Aether, in a state of periodic wave-motion; and wherever we have electricity, we have again matter possibly in a state of rotatory motion, as we shall see later on.
Energy, therefore, is the power which a body possesses to do work.
ART. 52. _Conservation of Energy._--The principle of the Conservation of Energy was first enunciated by Mayer in 1842. The principle may be defined as follows: The total amount of all the energy, as light, heat, electricity and magnetism, Gravitation, etc., in Nature is unchangeable; so that, according to this law, the universe possesses a store of energy which is unchangeable in quant.i.ty throughout all time. The energy may pa.s.s from one form to another, yet the total amount ever remains the same. It is almost unnecessary to say, that this is a principle which, like the conservation of matter, is incapable of absolute proof, but its a.s.sumption has greatly helped scientific thought and speculation from time to time. Clerk Maxwell says (_Theory of Heat_) on this point: "The total energy of any body is a quant.i.ty which can neither be increased nor decreased by any mutual action of the bodies, though it may be transformed into those forms of which energy is susceptible."
The conservation of energy is inseparably connected with the conservation of matter (Art. 30). They cannot be divided, because, if energy is only to be found in a.s.sociation with matter, then if the law of the conservation of matter falls to the ground, the principle of the conservation of energy falls with it. Energy, therefore, like matter, cannot be destroyed or created by any process known to man. As there is no process known, either in the chemical or in the physical world, by which new matter may be created by man, so, in relation to energy of any kind or sort, there is no process known by which man can create or even destroy the smallest form of energy that exists. If energy appears in any body or in any particular form, it is solely because of the loss of energy in some other body, or in some other form.
All changes of energy, therefore, are simply changes due to the difference in form in which the energy is manifested. At one time it will be manifested in the form of light, then of heat, then in mechanical motion, and so on. Joule gave us some good ill.u.s.trations of this principle of the conservation of energy. He showed us how electricity could be changed into heat, and the heat into work. When light, which is a form of energy, is absorbed by any opaque body, it is found that the body which has absorbed it has become hotter. The energy of light has not been destroyed, but as its energy cannot pa.s.s through the opaque body, it has been employed in agitating the particles and atoms of that body, which becomes hotter in consequence.
Thus from the principle of the conservation of energy, which is in operation not only in our planetary world, but throughout the whole of the solar and stellar s.p.a.ce, and indeed throughout the whole universe, we arrive at the conclusion that the total quant.i.ty of energy throughout the universe is unchangeable. In the evolution and development of worlds, and in the destruction of those worlds after long periods of time, throughout all the varied manifestations of heat, light, electricity, and magnetism, a.s.sociated with the development and destruction of each globe, the sum-total of the energy of the universe remains the same. Meteors may rush into the atmosphere of planets, and be dissolved into Aether through the friction, comets may be dissolved into their component gases as they near the sun, water may be changed into vapour by the heat of the summer sun, vegetation may be produced from apparently dead matter, and then that vegetation may itself decay and return to the dust by which it had been built up, but throughout all these processes of birth and death, of evolution and devolution, the sum-total of active living energy which is a.s.sociated with all the phenomena, remains unalterable and unchangeable. Such is the teaching of the great principle of the Conservation of Energy as enunciated by Mayer and Helmholtz.
ART. 53. _Transformation of Energy._--One of the chief characteristics of energy is, that we can transform it, and it is chiefly of use to us because of its capability to be transformed, but in all its transformations, the total quant.i.ty of energy remains the same. The transformation of energy renders it necessary to the existence of all life, and to all physical change in the universe. Mayer showed us that all energy in the solar system primarily derives its existence from the sun, and that all plant life and physical life owe their continued existence to the energy which is poured out from the sun upon the planetary worlds. So that energy is always flowing from the sun into the surrounding s.p.a.ce in the form of light, heat, and electricity, the medium of its pa.s.sage being the universal Aether.
This principle of transformation teaches us, that heat may be converted into electricity; that light may be converted into heat, or electricity may be converted into either heat or light or both. This principle of transformation naturally follows from the principle of the conservation of energy; because, if energy cannot be destroyed in any way, but is made to disappear by any process, it must reappear in some other form, and therefore has been transformed from its original state. So that, whenever one kind of energy disappears, then it is absolutely necessary, according to the principle of conservation of energy, that some other kind shall be produced. There cannot be any real loss or destruction.
That leads us to the next point regarding this principle of transformation, which is that all transformations of energy take place in fixed proportions. When a certain quant.i.ty of coal is burned, a certain quant.i.ty of heat, or thermal energy as it is sometimes called, is produced, and the quant.i.ty of heat so produced is definitely proportionate to the quant.i.ty of coal consumed.
If a certain quant.i.ty of coal were burned in a perfect steam-engine, that is one in which there would be no loss of heat, then also a definite amount of mechanical work would be done, which would be strictly proportionate to the heat generated by the consumption of the coal. So that when coal is put into an engine, the potential energy of the coal is transformed into kinetic energy of the steam, and that is again transformed into actual mechanical energy of the engine itself, by which work is done in driving or pushing or pulling the train along, and the amount of work done is proportionate to the coal consumed.
Ill.u.s.trations of transformation are common, and may be seen by any person living in a large town. Thus at any electrical station or electric tram terminus, these transformations of various forms of energy are very familiar sights. We have first the transformation of the coal in the furnace into heat. This heat converts water into steam, whose motion is communicated by proper machinery into a dynamo, the product of which is electricity. That electricity is then conveyed along wires, and work is done by it, by moving trams along the connected tram system, or it may be converted into heat in the carbon filament in the car itself, which, if heated enough, will then produce the electric light. So that starting from the coal, we have several transformations therefrom into the forms of heat, light, motion, and finally mechanical energy, which results in Work. The question arises as to what is the law of equivalence in regard to the transformation of energy. That is, if we have a certain amount of energy of a given sort, how much of any other sort can be produced by it? The answer is partly to be found in a statement made by Joule in 1843, which practically embodies what is known as the first law of Thermo-dynamics, and is as follows: "When equal quant.i.ties of mechanical effects are produced by any means whatever, from purely thermal sources, or lost in purely thermal effects, then equal quant.i.ties of heat are put out of existence or are generated, and for every unit of heat measured by raising a pound of water one degree F. in temperature, you have to expend 772 foot-pounds of work." From this law we learn that heat may be used to do work, but that a certain amount of heat is always used up in the process. It can also be demonstrated that electric currents can do work, but to generate the currents a certain amount of work must be done.
This equivalence and transformation prevail in all forms of energy, whether it be mechanical energy, thermal or heat energy, or electrical energy.
ART. 54. _Potential Energy._--Energy has been divided into two cla.s.ses, which are termed respectively Potential Energy and Kinetic Energy. We will look at the former first.
_Potential Energy_ may be briefly defined as energy of position.
Thus if we lift a body from the ground, the energy which has been imparted to it is energy of position, or potential energy. A glacier high up the mountain possesses potential energy, because of its position. By the mere fact that it is situated high up the mountain, it has a capacity for doing work by its descent, and if that descent be very sudden, the work done will be destructive work, as it may sweep away all houses and villages in its sudden descent. Thus, by the mere fact of its elevation, it possesses a power of doing work, which it has lost when it has descended. Again, work done in winding up the spring of a clock is stored up in the form of potential energy, and gradually runs out in the form of motion or kinetic energy.
Potential energy is really the complementary principle of kinetic energy. That is to say, the amount of potential energy lost by any body, is equal to the amount of kinetic energy gained by the other body, to which the energy has been transferred. In the case of a body falling, as the potential energy diminishes, the kinetic energy increases, but the total amount of the two combined always remains the same. This is well ill.u.s.trated in the case of a swinging pendulum. When a pendulum is at the highest point of its swing, its velocity or kinetic energy is zero, but at that point its potential energy is greatest. As it descends, the potential energy decreases, but the kinetic energy increases. When the pendulum is at the lowest point its energy is wholly kinetic, the potential energy being zero at that point, while it has sufficient kinetic energy to raise it to the highest level again. Throughout the cycle of these operations, the sum-total of the two energies always remains the same.
Professor Tait points out, in his _Recent Advances in Physical Science_, that the available sources of all potential energy may be divided into four cla.s.ses--
1st. Fuel.
2nd. Food of Animals.
3rd. Water-power.
4th. Tidal Water-power.
All these are different forms of potential energy. Under the head of fuel he includes not only wood, coal, but also all forms of matter that may be used or burnt up by heat, or dissolved by chemical agencies. Thus zinc and lead, which are used in batteries, are merely forms of fuel.
That potential energy resides in such things as wood and coal is a matter of common experience. All our coal-fields are stores of energy, which received their energy when in plant form, ages ago, from the sun, and this energy is now being used to drive our machinery, to warm our houses, and to give light to our homes and our cities. It has been calculated that a pound of coal would give out 14,000 heat units, which is equal to 11,000,000 foot-pounds of work, which is also equal to the amount of work a horse can do in five hours. Again, all food, whether it be the food of animals, as vegetables and plants, or of man, as bread, meat, etc., are all forms of potential energy, or energy which is stored up in matter. All forms of food have a certain amount of energy in them, which is used up in the body in building up waste tissue and imparting energy to the physical frame.
Again, all forms of water-power, whether it be in the form of the flowing river or the tidal motion of the sea, possess a large amount of potential energy which may be used up to do mechanical work. They also possess kinetic energy, or energy of motion. We find ill.u.s.trations of the possession of potential energy by rivers and tides, in the fact that by their fall from a higher to a lower level they may be made to do mechanical work, as in the case of the turning of the water-wheel by the fall of the water, which motion is communicated to machinery, and various forms of work are the result. In Switzerland and America advantage is being taken of the energy of falling water to generate electricity, by means of which villages and towns are being supplied with electric light at a very small cost.
ART. 55. _Kinetic Energy._--Kinetic energy may be defined as energy of motion, and is the energy which a body possesses in consequence of its motion. A body in motion thus possesses kinetic energy, which it must impart to some other body before it can be brought to a state of rest.
The body may be simply an atom, as a vortex atom, but if it be in motion, as all atoms are, then it must possess kinetic energy, which may be transferred to another atom by collision, or by some other method. As has already been pointed out in previous articles, kinetic and potential energy are complementary to one another, the sum-total of the two combined always remaining the same in any cycle of work, according to the principle of the conservation of energy. We get a good example of this oscillation from kinetic to potential, and _vice versa_, in the planetary system. When the earth is farthest from the sun, its velocity, and consequently its kinetic energy, is at its lowest point; but there the potential energy is at its greatest. As the earth turns round in its...o...b..t, however, and begins to approach the sun again, its potential energy decreases, while its kinetic energy increases with its increased velocity. So that by the time it has reached the nearest part of its...o...b..t to the sun, its velocity, and consequently its kinetic energy, is at a maximum, while the potential energy is at a minimum. Then as the earth pa.s.ses round its perihelion, the kinetic energy is used up in a.s.sisting the earth to overcome the attraction of the sun. Thus there is this oscillation from kinetic to potential, and from potential to kinetic, year in and year out, as the earth performs its cycle round its central body the sun.