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CHAPTER XL 







EPOCH OF YOUNG AND FRESNEL. 



Sect. 1. Introduction. 



THE man whose name must occupy the most 

 distinguished place in the history of Physical 

 Optics, in consequence of what he did in reviving 

 and establishing the undulatory theory of light, is 

 Dr. Thomas Young. He was born in 1773, at Mil- 

 verton in Somersetshire, of Quaker parents; and 

 after distinguishing himself during youth, by the 

 variety and accuracy of his attainments, he settled 

 in London as a physician in 1801 ; but continued 

 to give much of his attention to general science. 

 His optical theory, for a long time, made few pro- 

 selytes; and several years afterwards, Auguste 

 Fresnel, an eminent French mathematician and 

 engineer officer, took up similar views, proved their 

 truth, and traced their consequences, by a series 

 of labours almost independent of those of Dr. 

 Young. It was not till the theory was thus re- 

 echoed from another land, that it was able to take 

 any strong hold on the attention of the country- 

 men of its earlier promulgator. 



The theory of undulations, like that of universal 

 gravitation, may be divided into several successive 



