II. CHEMICAL ESSAYS 



HOW DISCOVERIES ARE MADE 



THERE is a difference between discovery and invention. 

 A discovery brings to light what existed before, but what 

 was not known ; an invention is the contrivance of some- 

 thing that did not exist before. I suppose, however, that 

 inventions and discoveries are made in much the same 

 manner ; though I have no claim to speak as an inventor, 

 except in a very small way. 



Many people, probably most people, think that when a 

 discovery is made, it comes all in a flash, as it were that 

 a new idea suddenly crops up, and its conception is a dis- 

 covery. That may sometimes be the case. 



We have all heard of the puzzle given to Archimedes ; 

 how he was asked to find out, without injuring it in the 

 least, whether a certain crown consisted of silver or of 

 gold ; and by weighing it in air and in water, he invented 

 the method of taking specific gravity; for the crown when 

 weighed in water lost weight equal to that of the water 

 which it displaced. And he ran through the streets of 

 Alexandria, crying, ' Heureka ! I have found it ! ' 



His finding that the crown was of gold was a discovery ; 

 but he invented the method of determining the density of 

 solids. Indeed, discoverers must generally be inventors ; 

 though inventors are not necessarily discoverers. 



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