496 POPULAR SCIENCE MONTHLY. 



closing years of the old century and the opening years of the new as 

 notable as the greatest which have preceded them. 



Now what is the task which these men, and their illustrious fellow- 

 laborers out of all lands, have set themselves to accomplish ? 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 con- 

 necting phenomena.' But this is certainly a misleading, and in my 

 opinion a very inadequate account of the subject. To begin with, it 

 is not only inconvenient, but confusing, to describe as ' phenomena ' 

 things which do not appear, which never have appeared, 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 lin- 

 guistic 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 some- 

 thing more than what by any stretch of language can be described as 

 * coexistences ' and ' sequences ' between so-called ' phenomena.' He 

 seeks for something deeper than the laws connecting possible objects 

 of experience. His object is physical reality; a reality which may or 

 may not be capable of direct perception ; a reality which is in any case 

 independent of it; a reality which constitutes the permanent mechan- 

 ism of that physical universe with which our immediate empirical con- 

 nection is so slight and so deceptive. That such a reality exists, though 

 philosophers have doubted, is the unalterable faith of science ; and were 

 that faith per impossible to perish under the assaults of critical specu- 

 lation, science, as men of science usually conceive it, would perish 

 likewise. 



If this be so, if one of the tasks of science, and more particularly 

 of physics, is to frame a conception of the physical universe in its inner 

 reality, then any attempt to compare the different modes in which, at 

 different epochs of scientific development, 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 incompetence. But some 

 there may be sufficiently near the dividing line to induce the specialists 

 who rule by right on either side of it, to view with forgiving eyes any 

 trespasses into their legitimate domain which I may be tempted, dur- 

 ing the next few minutes, 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 ' Principia,' and, roughly speaking, 

 •about midway between that epoch-making dale and the present mo- 



