Modern physicists have laughed at a philosopher of the old school (Arriaga), who, as late as 1639, "was troubled to know how, when several flat weights lie upon one another on a board, any but the lowest should exert pressure on the board." It would have been more prudent on their part to ask themselves whether the question was one which the modern school could answer at all. If we ask how two equal weights can exert equal pressures on the board from unequal distances, what can they answer? If they wish to be consistent with their notions, they can only answer that "the actions are transmitted from one weight to another till they meet the board." Now, this is a great philosophical blunder; for actions are accidents, and therefore cannot travel from one subject to another. Neither action nor active power are ever transmitted; not even movement is properly transmitted, but only propagated by a series of successive exertions from molecule to molecule. Were we to admit in philosophy any such transmission, we would soon be entangled in innumerable contradictions.
Mechanical work also is often styled a force, though it is nothing but the process by which a force is exhausted. The notion of work is very simple. A body moving through space against a continuous resistance is said to do work. Work is therefore so much the greater according as a greater mass measures a greater space under a greater resistance; and thus the work which a given body can perform may be represented by the product of three factors, viz., the mass, the mean resistance, and the space measured. This is the philosophical and analytical expression of work; and mathematicians show that this expression in all cases (viz., whether the resistance be constant or variable) is equal to half the product of the mass into the square of its initial velocity. Now the question comes: Is work a force? It is not difficult to anticipate the answer. Since the adoption of the so-called "living forces," or vires vivæ, of Leibnitz, physicists have called vis viva the sum of the works of two conflicting bodies; and consequently the work done by either of the two was said to be one-half of the vis viva. But, with all the respect due to the memory of Leibnitz, I would say that neither the work nor the so-called vis viva is a force in the philosophical sense of the word. When a mass, M, animated by a velocity, V, encounters a resistance and begins its work, its momentum is MV. This momentum, while the work is being done, is gradually reduced till it is finally destroyed by the resistance. The resistance is, therefore, equal to the momentum MV. But the resistance, according to the law of impact, is always equal to the exertion of the impinging body. And therefore the amount of the exertion of the impinging body is also equal to MV; that is to say, the force by which the work is done is an ordinary dynamical force represented by the usual dynamical momentum, and not by the amount of the work done.[273]
And here I must close this rather long excursion into the field of mechanics. But I cannot conclude without calling the reader's attention to the reckless tendency of the phraseology which I have above criticised. It seems as if the object of a class of scientific writers in these late years has been to banish from science all secondary causes, no doubt as a preliminary step (in the intention of the most advanced among them) for the banishment of the First Cause itself. The words cause, power, force, and others of the same kind, have indeed been maintained, as they could not be easily dispensed with; but they receive a new interpretation: they have become "kinds of motion," and have been identified with the phenomena—that is, with the effects themselves. Thus "movement" is now everything; its boasted "indestructibility" makes it independent of all secondary causes; and we are told that the existence of "essential causes" can no longer be proved by the phenomena, and that "science" has the right to reject them as metaphysical dreams. Let us hear Mr. Grove again:
"Though the term (force) has a potential meaning, to depart from which would render language unintelligible, we must guard against supposing that we know essentially more of the phenomena by saying that they are produced by something, which something is only a word derived from the constancy and similarity of the phenomena we seek to explain by it" (p. 18).
And again: "The most generally received view of causation—that of Hume—refers to invariable antecedence—i.e. we call that a cause which invariably precedes, that an effect which invariably succeeds" (p. 10).
And again: "It seems questionable not only whether cause and effect are convertible terms with antecedence and sequence, but whether, in fact, cause does precede effect.... The attraction which causes iron to approach the magnet is simultaneous with, and ever accompanies, the movement of the iron" (p. 13). Yet he adds: "Habit and the identification of thoughts with phenomena so compel the use of recognized terms that we cannot avoid the use of the word 'cause,' even in the sense to which objection is taken; and if we struck it out of our vocabulary, our language, in speaking of successive changes, would be unintelligible to the present generation" (ib.)
And lastly: "In all phenomena, the more closely they are investigated, the more are we convinced that, humanly speaking, neither matter nor force can be created or annihilated, and that an essential cause is unattainable. Causation is the will, creation the act, of God" (p. 218).
It is not Mr. Grove alone that entertains such views; I might quote other English authors, and many German, Italian, French, and American writers whose opinions are even more extravagant. But a theory which pretends to ignore efficient causality, no matter how loudly trumpeted by scientific periodicals, no matter how pompously dressed in scientific books, no matter how constantly inculcated from professorial chairs, in the long run is sure to fail. It bears in itself and in its very phraseology its own condemnation. It is vain to pretend to explain away its inconsistencies by alleging that "the habits of the present generation compel the use of recognized terms;" the simple truth is that the abettors of modern thought reap in their inconsistencies the reward of their vanity. Mankind will never consign created causality to the region of dreams, and we would remind our scientific friends who have not received a thorough philosophical training of the old adage, "Let the cobbler stick to his last."
A Friend of Philosophy.