SIR JAMES JEANS 245 



thought of what, for want of a wider word, we must 

 describe as a mathematical thinker. 



In the stately and sonorous diction of a bygone age, 

 Bishop Berkeley summed up his philosophy in the 

 words : 



"All the choir of heaven and furniture of earth, in 

 a word all those bodies which compose the mighty 

 frame of the world, have not any substance without 

 the mind. ... So long as they are not actually per- 

 ceived by me, or do not exist in my mind, or that of 

 any other created spirit, they must either have no 

 existence at all, or else subsist in the mind of some 

 Eternal Spirit." 



Modern science seems to me to lead, by a very 

 different road, to a not altogether dissimilar conclu- 

 sion. Because of our different line of approach we 

 have reached the last of the above three alternatives 

 first; and the others appear unimportant by compari- 

 son. It does not matter whether objects "exist in my 

 mind, or that of any other created spirit," or not; 

 their objectivity arises from their subsisting "in the 

 mind of some Eternal Spirit." 



This may suggest that we are proposing to discard 

 realism entirely, and enthrone a thoroughgoing ideal- 

 ism in its place. Yet this, I think, would be too crude 

 a statement of the situation. If it is true that the 

 "real essence of substances" is beyond our knowledge, 

 then the line of demarcation between realism and 

 idealism becomes very blurred indeed. It is little more 

 than a relic of a past age in which reality was believed 

 to be identical with mechanism. Objective realities 



