born during the fifteenth century, four of them at least 

 at so nearly the same time as to be contemporaries. 



Leonardo da Vinci, whose artistic genius has 

 charmed succeeeding generations, was also the first 

 practical engineer of his time, and the first man after 

 Archimedes to make a substantial advance in develop- 

 ing the laws of motion. That the world was not pre- 

 pared to make use of his scientific discoveries does not 

 detract from the significance which must attach to the 

 period of his birth. 



Shortly after him was born the great navigator 

 whose bold spirit was to make known a new world, thus 

 giving to commercial enterprise that impetus which 

 was so powerful an agent in bringing about a revolution 

 in the thoughts of men. 



The birth of Columbus was soon followed by 

 that of Copernicus, the first after Aristarchus to dem- 

 onstrate the true system of the world. In him more 

 than in any of his contemporaries do we see the 

 struggle between the old forms of thought and the 

 new. It seems almost pathetic and is certainly most 

 suggestive of the general view of knowledge taken at 

 that time that, instead of claiming credit for bringing 

 to light great truths before unknown, he made a 

 labored attempt to show that, after all, there was noth- 

 ing really new in his system, which he claimed to date 

 from Pythagoras and Philolaus. In this connection it 

 is curious that he makes no mention of Aristarchus, 

 who I think will be regarded by conservative historians 

 as his only demonstrated predecessor. To the hold of 

 the older ideas upon his mind we must attribute the 

 fact that in constructing his system he took great pains 



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