150 THE PRINCIPLES OF SCIENCE. [CHAP. 



tion that new events will conform to the conditions detected 

 in our observation of past events. No experience of finite 

 duration can give an exhaustive knowledge of the forces 

 which are in operation. There is thus a double uncertainty ; 

 even supposing the Universe as a whole to proceed un- 

 changed, we do not really know the Universe as a whole. 

 We know only a point in its infinite extent, and a moment 

 in its infinite duration. We cannot be sure, then, that our 

 observations have not escaped some fact, which will cause 

 the future to be apparently different from the past ; nor 

 can we be sure that the future really will be the outcome 

 of the past. We proceed then in all our inferences to 

 unexamined objects and times on the assumptions 



1 . That our past observation gives us a complete know- 



ledge of what exists. 



2. That the conditions of things which did exist 



will continue to be the conditions which will 



exist. 



We shall often need to illustrate the character of our 

 knowledge of nature by the simile of a ballot-box, so often 

 employed by mathematical writers in the theory of proba- 

 bility. Nature is to us like an infinite ballot-box, the 

 contents of which are being continually drawn, ball after 

 ball, and exhibited to us. Science is but the careful 

 observation of the succession in which balls of various 

 character present themselves; we register the combina- 

 tions, notice those which seem to be excluded from occur- 

 rence, and from the proportional frequency of those which 

 appear we infer the probable character of future drawings. 

 But under such circumstances certainty of prediction 

 depends on two conditions : 



1. That we acquire a perfect knowledge of the com- 



parative numbers of balls of each kind within 

 the box. 



2. That the contents of the ballot-box remain unchanged. 

 Of the latter assumption, or rather that concerning the 



constitution of the world which it illustrates, the logician 

 or physicist can have nothing to say. As the Creation of 

 the Universe is necessarily an act passing all experience 

 and all conception, so any change in that Universe, or, it 

 may be, a termination of it, must likewise be infinitely be- 

 yond the bounds of our mental faculties. No science no 



