24 Clarke, TJie Atomic Theory. 



the atomic theory the same tendency is at work, and the 

 very nature of the atom itself, that thing which we can 

 neither see nor handle, has become a legitimate subject 

 for our questionings. Shall we, having gone so far, 

 assume that we can go no further? 



" All roads lead to Rome." If we accept the atomic 

 theory, we sooner or later find ourselves speculating about 

 the reality of the atom, and at last we come face to face 

 with the old, old problem of the unity or diversity of 

 matter. We can, if we choose, employ the theory as a 

 working tool only, and shut our ears to these profounder 

 questions ; but it is not easy to do so. What is the 

 chemical atom? Is all matter ultimately one substance? 

 We may be unable to solve either problem, and yet we 

 can examine the evidence and see which way it points. 



I think that all philosophical chemists are now of the 

 belief that the elements are not absolutely distinct and 

 separate entities. In favour of their elementary nature we 

 have only negative evidence, the mere fact that with our 

 present resources we are unable to decompose them into 

 simpler forms. On that side of the argument there is 

 nothing more. On the other hand we see that the 

 elements are bound together by the most intimate relations, 

 so much so that unknown elements can be accurately 

 described in advance of their discovery, and facts like 

 these call for an explanation. Something belonging to the 

 elements in common seems to underlie them all. If, 

 however, we study the atomic weights, we are forced to 

 observe that the elements do not shade into one another 

 continuously, but that they vary by leaps which are some- 

 times relatively large, and sometimes quite small. To 

 Mendeleeff this irregular discontinuity is an argument 

 against the unity of matter, or, rather, an indication that 

 the periodic law lends no support to the belief; but such 



