196 GREAT MEN OF SCIENCE 



disadvantage of the latter. It may actually be regarded as 

 the beginning of our present knowledge of the internal 

 characteristics of atoms. 



THOMAS YOUNG (1773-1829) 

 JOSEF FRAUNHOFER {1787-1826) 

 AUGUSTIN FRESNEL {1788-1827) 



The time had now arrived for a great advance in the know- 

 ledge of light. Fraunhofer in Munich, and Fresnel in Paris, 

 were responsible for this in different ways, while Thomas 

 Young in England had to a certain extent paved the way for 

 their discoveries. Fraunhofer was the first to construct 

 optical appliances of the highest refinement, and he also 

 pointed out new methods in the art of manufacturing them, 

 so that this art could thenceforth develop and spread on a 

 sure basis. His new optical apparatus belonged, however, 

 not only to types already known, such as his astronomical 

 telescopes of hitherto unattained power, but also to those of 

 an entirely new description, such as his optical grating, 

 which enabled him to attack the problem of the nature of 

 light in an entirely new manner. 



It was Fresnel who rendered the wave nature of light, 

 imagined by Huygens and later by Thomas Young, a cer- 

 tainty, and he is therefore to be regarded as the founder of the 

 wave theory of light. He was a fine observer of recondite 

 phenomena of light, in the same way as Newton had already 

 observed quantitatively the colours of thin plates. He 

 however did not merely investigate such phenomena as had 

 hitherto been the subjects of explanation by the wave theory 

 with further regard to this possibility, but actually experi- 

 mented with the light waves themselves, in such a way 



