130 BIOGRAPHIES OF SCIENTIFIC MEN 



work of savants was done in discovering as exactly as 

 possible the weights of these atoms. This done, many 

 laborious attempts were made, with only partial success, 

 to link the atomic weights with the properties, etc., of 

 the chemical elements. Newlands, De Chancourtois, 

 Odling, Gmelin, and others made attempts to formulate 

 the law, but success was left to the genius of Mendeleeff. 

 He arranged the elements then known in series, standing 

 in a sort of arithmetical progression according to their 

 atomic weights, and chemical and physical properties. 

 He says in his great work (loc. cit.) that " even the 

 physical properties of selenium and its compounds, not 

 to speak of their composition, determined by the group 

 in which it occurs, may be foreseen with a close approach 

 to reality from the properties of sulphur, tellurium, arsenic, 

 and bromine. In this manner it is possible to foretell the 

 properties of still unknown elements." 



In the series some gaps presented themselves, and so 

 great was Mendele'eff's confidence in the periodic law, 

 that he at once predicted the discovery of new elements 

 to fill these gaps. This was one of the most daring pro- 

 phecies ever made in science and in an exact science 

 too, the science of weighing and measuring but events 

 have justified the seeming audacity. 



In 1871 the prediction was made that three elements 

 would be discovered having certain properties to fit into 

 the gaps of Mendeleeff's table, and to these undiscovered 



