Page:Popular Science Monthly Volume 16.djvu/651

 Let us take, again, the simple case of magnetic attraction. A man who knows nothing of magnetism sees a piece of iron, brought within a certain distance of what looks looks like a horseshoe bar of the same metal, suddenly jump toward its approximated ends; and might, as before, correctly express the fact in "terms of motion." But let him take the piece of iron in his hands, so as to feel the "pull" upon it when brought sufficiently near the magnet, and he then becomes conscious, through his force-sense, of a power of which he was before utterly ignorant.

Thus, as it seems to me, an analysis of those physical experiences on which all our cognitions of the physical universe around us are really based irresistibly lands us in the conclusion that, as Herbert Spencer expresses it, "All the sensations through which the external world is known to us are explicable by us only as resulting from certain forms of force"; the direct derivation of our conception of force from our own experience of muscular tension (or, as I should myself say, from our own sense of effort) being "a fact which no metaphysical quibbling can set aside." In the words of the able American writer I have already quoted, "The conception of force is one of those universal ideas which belong of necessity to the intellectual furniture of every human mind." By no one has the principle for which I am contending, been more clearly and more authoritatively expressed than by Sir John Herschel, a philosopher who united to his wonderful grasp of Nature-phenomena a profound insight into the action of the mind of man in the interpretation of them:

Whatever attempts have been made by metaphysical writers to reason away the connection of cause and effect, and fritter it down into the unsatisfactory relation of habitual [unconditional] sequence, it is certain that the conception of some more real and intimate connection is quite as strongly impressed upon the human mind as that of the existence of an external world, the vindication of whose reality has, strange to say, been regarded as an achievement of no common merit in the annals of this branch of philosophy. It is our own immediate consciousness of effort, when we exert force to put matter in motion or to oppose and neutralize force, which gives us this internal conviction of power and causation, so far 'as it relates to the material world.—(Treatise on "Astronomy" in Lardner's "Cyclopædia," p. 232.)

Man's position as the "interpreter of Nature" may be not inaptly likened (as it seems to me) to that of an intelligent observer of the working of a cotton-factory, with whose mechanical arrangements he is entirely unacquainted, and of whose moving power he knows nothing whatever. He is taken into a vast apartment, in which he is at first utterly bewildered by the number and variety of the movements going on around him; but, by directing his attention to the several