LIMITS OF OUR KNOWLEDGE OF NATURE. 19 



clopsedia, 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 devel- 

 oped in some measure than in Laplace himself, inasmuch as Leibnitz 

 conceives of this mind as being endowed with senses and with tech- 

 nical powers of corresponding perfection. Bayle brought against the 

 doctrine of Preestablished 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 con- 

 struct 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 incom- 

 parably 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 Xature. To show how 

 far we are from even the beginnings of such knowledge, we need but 

 make one observation. Before our difierential equations could be 

 brought into the universal formula, all natural facts would have to be 

 reduced to the motions of a substantially undifierentiated and conse- 

 quently property-less substratum of what appears to us as heteroge- 

 neous 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. Muller calls 

 them, " sense-substances " (Si?i7isubstantzei}), a motion that is in all 

 cases ultimately identical. As in the experiment suggested by Bidder 

 and successfully made by Yulpian 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 ilerves 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-percep- 

 tion, therefore, as such, has its rise in the "sense-substances." It is 



