A HISTORY OF SCIENCE 



Dmitri Mendeleeff in Russia, and Lothar Meyer in 

 Germany. Mendeleeff gave the discovery fullest ex- 

 pression, explicating it in 1869, under the title of " the 

 periodic law." 



Though this early exposition of what has since been 

 admitted to be a most important discovery was very 

 fully outlined, the generality of chemists gave it little 

 heed till a decade or so later, when three new elements, 

 gallium, scandium, and germanium, were discovered, 

 which, on being analyzed, were quite unexpectedly 

 found to fit into three gaps which Mendeleeff had left in 

 his periodic scale. In effect the periodic law had en- 

 abled Mendeleeff to predicate the existence of the new 

 elements years before they were discovered. Surely a 

 system that leads to such results is no mere vagary. So 

 very soon the periodic law took its place as one of the 

 most important generalizations of chemical science. 



This law of periodicity was put forward as an expres- 

 sion of observed relations independent of hypothesis; 

 but of course the theoretical bearings of these facts 

 could not be overlooked. As Professor J. H. Glad- 

 stone has said, it forces upon us " the conviction that 

 the elements are not separate bodies created without 

 reference to one another, but that they have been orig- 

 inally fashioned, or have been built up, from one an- 

 other, according to some general plan." It is but a 

 short step from that proposition to the Proutian hy- 

 pothesis. 



NEW WEAPONS SPECTROSCOPE AND CAMERA 



But the atomic weights are not alone in suggesting 

 the compound nature of the alleged elements. Evi- 



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