236 CHEMISTRY 



or groups of atoms; and, in short, whichever way we turn in physical 

 science we find ourselves, consciously or unconsciously, thinking in 

 atomic terms. And yet we are sometimes told that the atomic theory 

 is outworn, and that some other conception should replace it. We 

 may well ask, therefore, whether atomism has any basis in reality. 

 Is it the truth or only an illusion a concrete fact, or misinterpret- 

 ation of testimony? 



That the atomic theory has rendered great service to chemistry, 

 and that it correlates our positive data, is clear; but after all it is 

 hypothetical, for no atom has been isolated and seen. The molecule 

 and the atom are inferred from the properties of matter in mass; 

 and if we need a theory at all, there is none other at hand. The 

 attempts to evade it are agnostic in character, and are based upon 

 the tacit assumption that it is unscientific to speculate upon ultimate 

 questions, which, in the nature of things, can never be absolutely 

 solved. We can observe and classify relations, but it is useless to ask 

 what they mean. The phase rule has been suggested as a basis for 

 our classification, and under it the different kinds of matter become 

 different phases of something which we may or may not be able 

 to comprehend. Perhaps I misrepresent the position of the anti- 

 ato mists; but if so it is because their statements are to my mind far 

 from clear. If we object to the atom, we must object to the ether, for 

 that is equally unknowable ; we cannot divorce matter and motion, 

 for they are never observed apart; in short, we must reconstruct all 

 physical science and keep within the limits of things known. But is 

 the agnostic position sound? Is not the imagination as truly an instru- 

 ment of science as is the reason? May we never look forward and 

 anticipate what is to come, shall we always observe and experiment 

 without the help of ideals? To do so we must assume limitations 

 where no limits can be seen, and the human mind refuses to work in 

 that way. Speculation is the guide of science ; an indispensable assist- 

 ant in our exploration of the unknown; a good servant, but the 

 worst of masters. Scientific methods differ from unscientific methods 

 partly by their use of system, and partly in their employment of 

 disciplined as against unrestrained speculation. 



That the atomic theory has been a useful tool no one can deny; 

 but can we, in the light of present knowledge, imagine a universe 

 without it? We see that matter differs in its properties from point 

 to point, and all of our experiments end in records of these differences. 

 But is not difference a proof of discontinuity? How could a plenum 

 vary? Even the ether itself, that mysterious medium which is thought 

 to pervade all space, is now believed to have a granular structure, 

 or, in other words, to be atomic. Several mathematicians have worked 

 upon this phase of the problem with curious results; but their con- 

 clusions lie outside of my theme. The chemical atom alone concerns 



