THE DALTONIAN ELEMENT 125 



the chemical element. So was taken the first step 

 which ultimately was to make the term chemical 

 element, as it is at present understood, denote a 

 definite but highly complex chemical conception, 

 incapable of being- defined or even understood with- 

 out long years of training in the science, and totally 

 different in every single respect from what a plain 

 man or a beginner in the subject might reasonably 

 suppose the term element ought to connote. The 

 elementary and even the homogeneous character 

 has departed from the conception of the chemical 

 element, but the conception remains, and, whatever 

 we choose to call it, will remain. The criterion of 

 the chemical element soon came to be, in fact, the 

 possession of a unique chemical character, distin- 

 guishing it and sufficing for its separation from all 

 other elements. To this Dalton added a new 

 criterion, the magnitude of the weight of the atom 

 of the element, and each element unique in chemical 

 character (as it happened) proved also to possess a 

 unique atomic weight. 



The discovery of the periodic law introduced the 

 idea of families of chemically analogous elements, 

 the members of which recurred after regular intervals 

 when the elements were arranged in order of atomic 

 weight. With the exception of hydrogen, every 

 element became one of a group all totally distinct, 

 but with obvious similarities. Boyle's practical 

 definition of the element as that which could not be 

 further resolved, more and more, as the century 

 advanced, fell into desuetude. It became replaced 

 by a theoretical conception, to which subsequently I 

 propose to apply the term "heterotope," meaning the 

 occupant of a separate place in the periodic table of 

 elements. With this place came to be associated 

 the unique chemical character, unique atomic weight, 

 and later unique spectrum. On the claims of a 



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