132 BIOGRAPHIES OF SCIENTIFIC MEN 



magnetic properties, hydrocarbon radicles, etc. ; in fact, 

 a full list is to be found in the index of the Principles of 

 Chemistry a book which gives the views of Mendele"eff 

 on most subjects. The work has been translated into 

 nearly all the languages of Europe. 



Concerning the element argon discovered by Lord 

 Rayleigh and Sir William Ramsay, Mendeleff wrote to 

 the author on 18/30 March 1895, as follows : 



A mon avis 1'argon (molecules) est au N 3 , form^e de 1'azote N 2 avec 

 dedagement de chaleur, au A 6 , si A = 6'6 de l re se'rie'. La premiere 

 hypothese est, pour moi, la plus probable, comme j'avais deja com- 

 munique" dans la Societ4 Chimique Russe. 



When Mendeleeff delivered the Faraday Lecture at the 

 Royal Institution in 1889, he said : " The law of periodicity 

 enables us to perceive undiscovered elements at a distance, 

 which formerly were inaccessible to chemical vision; 

 and long ere they were discovered new elements appeared 

 before our eyes possessed of a number of well-defined 

 properties. ..." Since then argon, helium, neon, xenon, 

 metargon, krypton, radium, and possibly other forms of 

 matter have been, and may be, discovered, throwing 

 wondrous light on the structure of material things, but 

 by no means invalidating Mendel^effs famous periodic 

 law that is, as far as we know at the present time. It 

 is possible that the law may be modified as time rolls 

 on. The evolution or mutability of the elements may 

 throw new light on the nature of the chemical element 

 the law of combination in simple proportions, and 



