Page:Popular Science Monthly Volume 5.djvu/29

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LIMITS OF OUR KNOWLEDGE OF NATURE.

clopædia, expressed it, giving utterance to the germ of Laplace's thought, "the universe would be one single fact and one great truth."

In Leibnitz, too, we find Laplace's thought, and even better developed in some measure than in Laplace himself, inasmuch as Leibnitz conceives of this mind as being endowed with senses and with technical powers of corresponding perfection. Bayle brought against the doctrine of Preëstablished Harmony the objection that it supposes the human body to be like a vessel that makes for its harbor by means of its own forces; Leibnitz replied that this is not so impossible as Bayle holds it to be. "There is no doubt," says he, "that a man might construct a machine that could for some time move about in a city, and turn accurately at certain street-corners. An incomparably more perfect, though still finite mind, might foresee and obviate an incomparably greater number of obstacles. So true is this, that if the world is, as some suppose, only a compound of a finite number of atoms, which move in accordance with the laws of mechanics, it is certain that a finite mind might be elevated sufficiently to comprehend and to foresee with mathematical certitude whatsoever is to occur therein within a given time. And thus this mind could not only construct a ship capable of making a given port by itself, provided the proper force and direction were supplied, but it could even construct a body capable of imitating the actions of man."

It need not be said that the human mind will ever remain very remote from this degree of acquaintance with Nature. To show how far we are from even the beginnings of such knowledge, we need but make one observation. Before our differential equations could be brought into the universal formula, all natural facts would have to be reduced to the motions of a substantially undifferentiated and consequently property-less substratum of what appears to us as heterogeneous matter: in other words, all quality would have to be explained by the arrangement and the motion of this substratum.

This is entirely in accord with what we know of the senses. It is universally conceded that the sense-organs and the sense-nerves carry to their appropriate cerebral regions, or, as Job. Müller calls them, "sense-substances" (Sinnsubstantzen), a motion that is in all cases ultimately identical. As in the experiment suggested by Bidder and successfully made by Vulpian on the nerves of taste, and those of the muscles of the tongue, the sensory and motor nerves, on being cut across, so heal together that excitation of the one class of fibres is transmitted by the cicatrix to the other class; in like manner, were the experiment possible, fibres from different sets of nerves would blend perfectly together. With the nerves of vision and of hearing severed, and then crossed with each other, we should with the eye hear the lightning-flash as a thunder-clap, and with the ear we should see the thunder as a series of luminous impressions. Sense-perception, therefore, as such, has its rise in the "sense-substances." It is