258 



SCIENCE. 



[N. S. Vol. XX. No. 504. 



world, a spot with which have been con- 

 nected, either by their training in youth, 

 or by the labors of their maturer years, so 

 many men eminent as the originators of 

 new and fruitful physical conceptions. I 

 say nothing of Bacon, the eloquent prophet 

 of a new era; nor of Darwin, the Coper- 

 nicus of biology; for my subject to-day is 

 not the contributions of Cambridge to the 

 general growth of scientific knowledge. I 

 am concerned rather with the illustrious 

 line of physicists who have learned or 

 taught within a few hundred yards of this 

 building— a line stretching from Newton in 

 the seventeenth century, through Cavendish 

 in the eighteenth, through Young, Stokes, 

 Maxwell, in the nineteenth, through Kelvin, 

 who embodies an epoch in himself, down to 

 Rayleigh, Larmor, J. J. Thomson, and the 

 scientific school centered in the Cavendish 

 laboratory, whose physical speculations bid 

 fair to render the closing years of the old 

 century and the opening years of the new 

 as notable as the greatest which have pre- 

 ceded them. 



Now what is the task which these men, 

 and their illustrious fellow-laborers out of 

 all lands, have set themselves to accom- 

 plish? To what end led these 'new and 

 fruitful physical conceptions' to which I 

 have just referred? It is often described 

 as the discovery of the 'laws connecting 

 phenomena.' But this is certainly a mis- 

 leading, and, in my opinion, a very inade- 

 quate, account of the subject. . To begin 

 with, it is not only inconvenient, but con- 

 fusing, to describe as 'phenomena' things 

 which do not appear, which never have ap- 

 peared, and which never can appear, to 

 beings so poorly provided as ourselves with 

 the apparatus of sense perception. But 

 apart from this, which is a linguistic error 

 too deeply rooted to be easily exterminated, 

 is it not most inaccurate in substance to 

 say that a knowledge of nature 's laws is all 

 we seek when investigating nature? The 



physicist looks for something more than 

 what, by any stretch of language, can be 

 described as 'co-existences' and 'sequences' 

 between so-called 'phenomena.' He seeks 

 for something deeper than the laws con- 

 necting possible objects of experience. His 

 object is physical reality: a reality which 

 may or may not be capable of direct per- 

 ception; a reality which is in any case in- 

 dependent of it ; a reality which constitutes 

 the permanent mechanism of that physical 

 universe with which our immediate em- 

 pirical connection is so slight and so de- 

 ceptive. That such a reality exists, though 

 philosophers have doubted, is the unalter- 

 able faith of science; and were that faith 

 per impossible to perish under the assaults 

 of critical speculation, science, as men of 

 science usually conceive it, would perish 

 likewise. 



If this be so, if one of the tasks of sci- 

 ence, and more particularly of physics, is 

 to frame a conception of the physical uni- 

 verse in its inner reality, then any attempt 

 to compare the different modes in which, 

 at different epochs of scientific develop- 

 ment, this intellectual picture has been 

 drawn, can not fail to suggest questions of 

 the deepest interest. True, I am precluded 

 from dealing with such of these questions 

 as are purely philosophical by the character 

 of this occasion ; and with such of them as 

 are purely scientific by my own incom- 

 petence. But some there may be suffi- 

 ciently near the dividing line to induce the 

 specialists who rule by right on either side 

 of it to view with forgiving eyes any tres- 

 passes into their legitimate domain which I 

 may be tempted, during the next few min- 

 utes, to commit. 



Let me, then, endeavor to compare the 

 outlines of two such pictures, of which the 

 first may be taken to represent the views 

 prevalent towards the end of the eighteenth 

 century ; a little more than a hundred years 

 from the publication of Newton's 'Prin- 



