[CHAPTER VII.]
CONSERVATION.—THE RELATION OF GOD TO THE WORLD.
(Continued.)
Of the various hypotheses which seek to dispense with the immediate agency of God, and to explain the conservation of the world by "secondary" or natural agencies, the second is that of active Force communicated to matter at its creation. This force being transformable, and at the same time indestructible, is regarded as adequate to the conservation of the universe.
This hypothesis must not be confounded with the Dynamical theory of matter propounded by Leibnitz, and more fully elaborated by Boscovich, which regards matter as a mere phenomenon or function of force; on the contrary, it conceives of matter as a distinct entity moving under the action of a primary impulse communicated by "the Creator's fiat at the beginning." This hypothesis in its fundamental conception and its further elaboration is purely mechanical. It represents the universe as a machine first set in motion by the Deity, and conserved by the actions and reactions of its several parts. All subsequent motions, changes, and configurations are the prolonged results of the original impulse, without any further direct action or control on the part of the Creator.
A more precise and accurate statement would require that the term "Energy" should be substituted for "Force." In the language of modern physics, Force is "that which originates or tends to originate motion or change," and "is wholly expended in the action it produces."[255] All energy has its origin in force, but force can not pass into energy except under conditions in which it is at liberty to act. For instance, the force of gravity produces the energy of motion of a falling body, but gravity can not produce motion unless there is space through which the body can fall. Energy, therefore, is defined as "the power of doing work."[256] The work done is the resistance overcome, and in overcoming resistance the energy is transformed, but not annihilated. In every case in which energy is lost by resistance, heat is generated; and we learn from Joule's investigations that the quantity of heat generated is a perfectly definite equivalent for the energy lost. It is therefore claimed that the total quantity of energy in the universe is constant, and that the material system is dynamically conservative. The universe is a self-acting and self-sustained machine, and perpetual motion is a necessary consequence.
A little reflection, however, ought to convince any one that this conception of the universe—as a machine which is kept in perpetual motion by the reciprocal action of its parts—is a false analogy. And its fallacy is apparent from this, that the moving force of every machine is not inherent in the machine, but some natural primary force distinct from the machine, such as gravity, or the primary atomic forces of attraction and repulsion; and consequently the very idea of mechanism assumes the existence of those primary forces of which it is the professed object of a mechanical theory of the universe to give an explanation. A machine "can no more create energy than it can create matter;" its sole function is "to transform energy into a kind most convenient for us."[257] "We may with the greatest ease convert mechanical work into heat, but we can not by any means convert all the energy of heat back again into mechanical work. In the steam-engine we do what can be done in this way, but it is a very small portion of the whole energy of the heat that is convertible into work, for a large portion is dissipated, and will continue to be dissipated however perfect our engine may become. Let the greatest care be taken in the construction and working of a steam-engine, yet we shall not succeed in converting one fourth of the whole energy of the heat of the coals into mechanical work."[258] It is impossible to construct a machine that can do work without parting with energy; and when the energy is all parted with, any machine whatever must necessarily cease to do any more work unless a fresh supply of energy be brought in from without. It is impossible to make a water-mill work without a constantly renewed supply of water, or to make a steam-engine work without a constantly renewed supply of fuel. "Every one who understands mechanics knows that any such inexhaustible supply of energy is impossible by means of merely mechanical arrangements; but it is equally true, though not perhaps equally so evident, that it is impossible by means of any arrangement of thermal, electric, or chemical forces."[259]
But we are told that modern science has proved that the law of the Conservation of Energy is an absolute law of the universe, and that though man can not construct a machine which will realize the dream of perpetual motion, the material universe is in reality such a machine. It becomes us to speak with some degree of diffidence in regard to a question which lies outside of our special department of study. Nevertheless we must confess that we have a growing suspicion of all so-called "absolute laws" in the domain of physical nature. And we are confirmed in this mistrust by the fact that physicists themselves are not agreed in regarding this law of conservation of energy as universally true. "That the amount of energy in the world is unchangeable, the sum of the actual or kinetic and potential energies being a constant quantity, has been by some writers overstrained. It may be taken as a postulate, and is probably true, but it is a proposition equally incapable of proof and of disproof."[260] "This principle," says Sir J. Herschel, "so far as it rests upon any scientific basis as a legitimate conclusion from dynamical laws, is no other than the well-known dynamical theorem of the conservation of vis viva (or of 'energy,' as some prefer to call it), supplemented to save the truth of its verbal enunciation by the introduction of what is called 'potential energy,' a phrase which I can not help regarding as unfortunate, inasmuch as it goes to substitute a truism for the announcement of a dynamical fact. No such conservation, in the sense of an identity of total amount of vis viva at all times and in all circumstances, in fact, exists. So far as a system is maintained by the mutual actions and reactions of its constituent elements at a distance (i. e., by force), vis viva may temporarily disappear, and be subsequently reproduced between certain limits. Collision, indeed, between its ultimate particles or atoms, regarded as absolutely rigid, and therefore inelastic (for that which can not change its figure can have no resilience), can not take place without producing a permanent destruction of it, which there exists no means of repairing.... If, indeed, we could be assured à priori that the system [of the universe] is one of simple or compound periodicity, in which a certain lapse of time will restore every molecule to identically the same relative situation with respect to all the rest, we should then be sure that in the nature of things there would take place, so to speak, a winding up from a lower to a higher state of potential energy, to be subsequently exchanged for newly created vis viva. But, as we can have no such à priori assurance, can only assume such restoration to be possible, and can see no means of effecting it, if possible, otherwise than by foresight and prearrangement; the one equally with the other is an unknown function, variable within unknown limits, and susceptible of fluctuation to an unknown extent; nor can we have any, the smallest, right to assert that what is expended in one form is necessarily laid up for further use in the other. It would be very difficult, I apprehend, to show whether, in the winding up of a clock or the building of a pyramid, taking into consideration all the various modes in which vis viva disappears and reappears in the expenditure of muscular power, the evolution of animal heat, the consumption of the materials of our tissues, the propagation of vibratory motions, and a thousand other modes of transfer, the total vis viva of this our planet is increased or diminished. That it should remain absolutely unchanged during the process is in the last degree inconceivable. The amount of vis viva latent in the form of heat or molecular motion in the sun and planets in our immediate system may bear, and probably does bear, a by no means inappreciable ratio to that more distinctly patent in the form of bodily motion in the periodic circulation of the planets round the sun, and the sun and planets round their axes. The latter amount fluctuates to and fro according to laws easily calculable, but the former we have no means whatever of computing, and to what extent, or within what limits, it may be variable, we are altogether ignorant."[261]
The two dynamical laws of Conservation of Energy and Transformation of Energy can not therefore be regarded as universal and absolute laws; they are particular and derivative laws subject to limitations which are supplied by the third dynamical law—the Dissipation of Energy. The law of the conservation of energy simply asserts "that the whole amount of energy in the universe, or in any limited system which does not receive energy from without, or part with it to external matter, is invariable;" in other words, that every material system subject to no other forces than actions and reactions between its parts is a dynamically conservative system. But Sir William Thomson has shown that "in nature this hypothetical condition is apparently violated in all circumstances of motion. A material system can never be brought through any returning cycle of motion without spending more work against the mutual forces of its parts than is gained from these forces, because no relative motion can take place without meeting with frictional or other forms of resistance."[262] "There can be but one ultimate result for such a system as that of the sun and planets, if continuing long enough under existing laws, and not disturbed by meeting with other moving masses in space. That result is the falling together of all into one mass, which, although rotating for a time, must in the end come to rest relatively to the surrounding medium."[263]
The law of the transformation of energy is "the enunciation of the empirical fact that in general any one form of energy may by suitable processes be transformed, wholly or in part, to an equivalent amount in any other given form." This law, however, is subject to limitations which are supplied by the dissipation of energy. "No known natural process is exactly reversible, and whenever an attempt is made to transform and retransform energy by an imperfect process, part of the energy is necessarily transformed into heat and dissipated, so as to be incapable of further useful transformation. It therefore follows that, as energy is constantly in a state of transformation, there is a constant degradation of energy to the final unavailable form of uniformly diffused heat, and that will go on until the whole energy of the universe has taken this final form."[264] No mechanical work can be done by heat in a state of equilibrium; as a dynamical agent it is dead. "Thus the inexorable laws of mechanics indicate that the store of force in our planetary system, which can only suffer loss and not gain, must be finally exhausted."[265]
So far, then, as the conservation of energy has any scientific meaning, it is inadequate to account for the origin or explain the continuance of the existing order of nature. It is true we may conceive that every atom of matter was endowed at the Creation with a certain store of potential energy—"the potential energy of gravitation"[266]—which it has ever since given out; but as every motion which has resulted from its action has been attended with the expenditure of a certain amount of the original endowment, it must have been continually undergoing a diminution. There is, says Professor Norton, no escaping this conclusion but by taking the ground that the primary atomic forces (as gravitation, and the atomic repulsion and attraction by which atoms are aggregated into bodies of sensible magnitude) are correlated with the living forces (or various forms of energy) which are involved in the motions that have resulted from the previous operation of the primary atomic forces. "But," he says, "no evidence has been obtained of any such correlation." The primary force of attraction (if it be regarded as a primary force) may be the cause of motion in bodies which are separated in space, and part of that energy of motion may be transformed into the energy of heat or light or electricity, but the primary force of attraction is not transformed. Energy is convertible into other forms of energy, but heat, light, and electricity are not transformable into primary force. The correlation of force and energy is therefore a scientific heresy.[267]