The conservation of vis viva is, within certain limits, that is with regard to ponderable bodies impinging on one another,[269] an established fact; but its interpretation as given by advanced physicists is a huge blunder. "It is very generally believed," says Mr. Grove, "that if the visible motion of one body be arrested by impact on another body, the motion ceases." Of course, it is believed; and, what is more, it is demonstrably true, whatever Mr. Grove may say to the contrary. Yet it is not true, nor is it very generally believed, that "the force which produces it (the motion) is annihilated." When the movement of a body is arrested, its velocity is extinguished; but that velocity was not the force which produced the movement. When a stone falls to the ground, its movement is produced, not by its velocity, but by the action of the earth on it. Velocity is only the formal principle of movement, and is itself included in movement as a constituent, not as an efficient power. To say that velocity produces movement is, therefore, to confound formal with efficient causation, and to admit that movement produces itself. This is one of the conclusions for which I hope, as I said, physicists will blush hereafter.
But the force, we are told, "is not annihilated, but merely subdivided or altered in direction or character." This cannot be. The word force here means a quantity of movement, which is nothing but the product of the velocity into the mass of the body. Now, the velocity of a body is not subdivided when the movement is arrested, but is really extinguished. I say extinguished, not annihilated; because annihilation, as well as creation, regards substances, not accidents. Velocity is an accident; it is therefore neither created nor annihilated, but originates in a determination produced by an agent, and ends by exhaustion or neutralization under the influence of an antagonistic agency. I say, then, that the movement of the body, though not annihilated, is extinguished and not subdivided. It is impossible to conceive of divisions where there is nothing divisible. On the other hand, nothing is divisible which has no extension and no material parts. Now, where are the material parts or the extension of velocity? Velocity in each primitive particle of a body is a simple actuality, which can increase or decrease by degrees of intensity, but cannot be taken to pieces in order to be apportioned among the other particles of the body, and therefore the pretended subdivision of velocities is a mere absurdity.
Nor does it matter that force can be "altered in direction or character." We must not forget that force is here a sum of velocities, and accordingly cannot change direction or character unless such velocities are intrinsically changed. But they cannot be changed with regard to either character or direction without some new degree of velocity being produced or extinguished by some efficient cause. For the character of velocity is to actuate the extension of the movement in proportion to its own intensity. This, and no other, is its character; and, therefore, velocity cannot be altered in character without its intensity being increased or diminished by action. And the same is to be said of the change of direction, which cannot be conceived without action. Now, if action can modify motion, and diminish to any extent its velocity, it remains for our scientists to explain how a certain action cannot stifle movement and velocity altogether.
They will say that the "indestructibility of force" is the only hypothesis consistent with the theory of the conservation of vis viva, and consequently that the two must stand or fall together. But the truth is that the conservation of vis viva needs no such hypothesis, since it depends on a quite different principle, viz., on the equality of action and reaction.
When two billiard-balls impinge on one another, they act and react. Their molecules urge one another (by their mutual actions of course, not by their velocity), and become compressed. All the work they do up to the maximum of compression is styled action. But reaction soon follows; for, as compression brings the neighboring molecules into an unnatural position where they cannot settle in relative equilibrium, the molecular exertions tend now to restore within the bodies the original molecular distances; which work of restoration is properly called reaction.[270] And since reaction must undo what the preceding action had done, hence the amount of the reaction must equal the amount of the action, and thus no energy is lost; for the same quantity of movement is produced in one ball as is extinguished in the other.
I do not wish to enlarge on this topic, which is of a physical rather than metaphysical nature. I only repeat that the mistake of our physicists lies in supposing that the quantity of movement which is lost by one body still exists in nature, and passes identically into another body; whilst the fact is that the quantity of movement lost by the first body is altogether extinguished, and the quantity acquired by the second body is a new production altogether. To send an accidental mode, such as velocity, travelling about from one substance to another without support, as an independent and self-sufficient being, may be a bright device of modern progress; but when the time comes for repenting of other scientific blunders, this bright delusion will, I am sure, be reckoned among the most grievous philosophical sins that science will have to regret and to atone for in sackcloth and ashes.
These remarks go far to show that the terminology of our modern scientists concerning physical causation is philosophically incorrect. I have more to say on this same subject; but to make things plainer I wish to give beforehand what I consider to be the true distinction between cause, power, action, and force, as implied in the causation of natural phenomena. To do this in the most simple and intelligible manner, I lay down the following propositions:
I. It is a principle philosophically certain that the substance of all natural things has been created by God for his extrinsic glory—that is, for the manifestation of his power and other perfections. Accordingly, every created substance has received a natural aptitude and fitness to manifest in some manner and in some degree the power and perfection of its Creator.
II. Therefore, every creature naturally, per se, not accidentally, but by the very fact of its creation, is destined to act; for manifestation is action, and consequently possesses permanently and intrinsically such an active power as is proportionate to the kind and degree of the intended manifestation. In other terms, every created substance is destined to be the efficient cause of determined effects.
III. The power of created substances is finite, and its exertion is subject to definite laws. All finite power, according as it is exerted under more or less favorable conditions, gives rise to effects of greater or less intensity. Hence different effects may proceed from one and the same cause, and equal effects from different causes, acting under different conditions.