448 HISTORY OF OPTICS. 



Among the remarkable earlier applications of 

 the undulatory doctrine to diffraction, we may 

 notice those of Joseph Fraunhofer, a mathematical 

 optician of Munich. He made a great number of 

 experiments on the shadows produced by small 

 holes, and groups of small holes, very near each 

 other. These were published 7 in his New Modifica- 

 tions of Light, in 1823. The greater part of this 

 Memoir is employed in tracing the laws of pheno- 

 mena of the extremely complex and splendid ap- 

 pearances which he obtained ; but at the conclusion 

 he observes, " It is remarkable that the laws of the 

 reciprocal influence and of the diffraction of the 

 rays, can be deduced from the principles of the 

 undulatory theory : knowing the conditions, we 

 may, by means of an extremely simple equation, 

 determine the extent of a luminous wave for each 

 of the different colours ; and in every case, the cal- 

 culation corresponds with observation." This men- 

 tion of " an extremely simple equation," appears to 

 imply that he employed only Young's and Fresnel's 

 earlier mode of calculating interferences, by con- 

 sidering two portions of light, and not the method 

 of integration. Both from the late period at which 

 they were published, and from the absence of ma- 

 thematical details, Fraunhofer's labours had not 

 any strong influence on the establishment of the 

 undulatory theory; although they are excellent 



7 In Schumacher's Astronomiche Abhandlungen, in French ; 

 earlier, in German. 



