212 THE POPULAR SCIENCE MONTHLY. 



this circumstance, especially as it is his avowed principle that, if the 

 conclusion of an induction turns out false, it cannot have been a good 

 induction. Nevertheless, neither he nor any of his scholars seem to have 

 been led to suspect, in the least, the perfect solidity of the framework 

 which he devised for securely supporting the mind in its passage from 

 the known to the unknown, although at its first trial it did not answer 

 quite so well as had been expected. 



IV. 



When we have drawn any statistical induction such, for instance, 

 as that one-half of all births are of male children it is always possible 

 to discover, by investigation sufficiently prolonged, a class of which the 

 same predicate may be affirmed universally ; to find out, for instance, 

 to hat sort of births are of male children. The truth of this principle 

 follows immediately from the theorem that there is a character peculiar 

 to every possible group of objects. The form in which the principle is 

 usually stated is, that every event must have a cause. 



But, though there exists a cause for every event, and that of a kind 

 which is capable of being discovered, yet if there be nothing to guide 

 us to the discovery ; if we have to hunt among all the events in the 

 world without anj T scent ; if, for instance, the sex of a child might 

 equally be supposed to depend on the configuration of the planets, on 

 what was going on at the antipodes, or on anything else then the dis- 

 covery would have no chance of ever getting made. 



That we ever do discover the precise causes of things, that any in- 

 duction whatever is absolutely without exception, is what we have no 

 right to assume. On the contrary, it is an easy corollary, from the theo- 

 rem just referred to, that every empirical rule has an exception. But 

 there are certain of our inductions which present an approach to uni- 

 versality so extraordinary that, even if we are to suppose that they are 

 not strictly universal truths, we cannot possibly think that they have 

 been reached merely by accident. The most remarkable laws of this 

 kind are those of time and space. With reference to space, Bishop 

 Berkeley first showed, in a very conclusive manner, that it was not a 

 thing seen, but a thing inferred. Berkeley chiefly insists on the im- 

 possibilit}' of directly seeing the third dimension of space, since the 

 retina of the eye is a surface. But, in point of fact, the retina is not 

 even a surface ; it is a conglomeration of nerve-needles directed toward 

 the light and having only their extreme points sensitive, these points ly- 

 ing at considerable distances from one another compared with their areas. 

 Now, of these points, certainly the excitation of no one singly can pro- 

 duce the perception of a surface, and consequently not the aggregate 

 of all the sensations can amount to this. But certain relations subsist 

 between the excitations of different nerve-points, and these constitute 

 the premises upon which the hypothesis of space is founded, and from 



