28 Journal of the Mitchell Society [July 



and de Boisbaudran to arrange an entire zero group with ap- 

 proximate atomic weights three years before Ramsay's bril- 

 liant discovery of the other inactive gases. 



There are other anomalies in the system which are diffi- 

 cult to explain with the accepted tabulation. Such, for in- 

 stance, is the existence of the rare earths, now some sixteen 

 in number, so closely alike chemically and so different from 

 other chemical individuals. The more they are studied, the 

 less possible does it seem to fit them in any vacant places in 

 the table. Meyer has recently suggested that they may form 

 a miniature periodic system in themselves reproducing the 

 relations of the main system. But a more serious breakdown 

 in the supposed fundamental principle of the system comes in 

 the relative position of such elements as argon and potassium, 

 cobalt and nickel, tellurium and iodine. After most ex- 

 haustive investigation of their atomic weights it has become 

 evident that these can not be used in deciding the relative 

 order and at the same time have these elements fall into the 

 proper grouping with those elements chemically most nearly 

 related to them. So the order of the atomic weights has been 

 tacitly abandoned and the superior determining power of the 

 chemical characteristics acknowledged. This can only mean 

 that the mass of the atom is not the sole, nor indeed the chief, 

 determining variable, and it would seem that the search for 

 the latter can only be ended by the solution of the problem as 

 to the nature of the atom itself. 



Certain clews to this have undoubtedly been in our hands 

 for a long time, but their leading was not clear and the 

 thought of thorn baffling. Such, for instance, were the facts 

 that by taking an atom of nitrogen and four of hydrogen a 

 grouping of atoms was obtained which behaved in general as 

 an atom and was the analogue of potassium. Or, again, 

 carbon and nitrogen give us an analogue of chlorine — and so 

 with compound radicals in general. But while both build- 

 ing and tearing down again were easy, they seemed to throw 

 no light on how those we could not tear down were once built 

 up. 



