THE ATOMIC THEOEY. 257 



reasoning could have accounted for isomerism, much less for the facts 

 which stereochemistry seeks to explain. 



Just here we tind the prime difficult}^ of all attempts to evade the 

 atomic theory. Up to a certain point we can easily dispense with it, 

 for we can start with the fact that every element has a definite com- 

 bining- mimber, and then, without an}' assumptions as to the ultimate 

 meaning of these constants we can show that other constants are 

 intimately connected with them. So far we can ignore the origin of 

 the so-called atomic weight; but the moment we encounter the facts 

 of isomerism or chemical structure, and of the partial substitution of 

 one element by another, our troul)les begin. The atomic theory con- 

 nects all of these data together and gives the mind a simple reason 

 for the relations which are observed. We can not be satisfied with 

 mere equations; our thought will seek for that which lies behind 

 them; and so the antitheorist fails to accomplish his purpose because 

 he leaves the human mind out of account. The reasoning instrument 

 has its own laws and requirements, and they, as well as the empirical 

 observations of science, must l)e satisfied. Even in astronomv the law 

 of gravitation is not enough; men are continualh' striving to ascertain 

 its cause, and no number of failures can prevent them from trying 

 again and yet again to penetrate into the heart of the mystery. In 

 the atomic theory the same tendencj^ is at work, and the ver}- 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 farther? 



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

 sooner, or later tind ourselves speculating about the realit}' 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 eas}^ to do so. What is the chemical atom? 

 Is all matter ultimately one substance? We ma3M3e unable to solve 

 either pi'ol)lem, 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 favor 

 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 discoverv, and facts like 

 these call for an explanation. Something belonging to the elements 

 in connnon seems to underlie them all. If, however, we study the 

 atomic weights, we are forced to observe that the elements do not 



