THE WAVE THEOKY. 273 



surfaces and of thin, thick, and mixed plates. Here 

 the young officer of engineers to whom I have already 

 referred — Fresnel — entered the field. He presented iu 

 1815, to the French Institute, a memoir on Diffraction 

 which marks an epoch in the history of the wave theory. 

 It is usual, when such a paper is presented, to refer it 

 to a ' Commission,' who consider it and report upon its 

 merits. The Gommissionnaires in this instance were 

 Arago and Prony. 



Arago had read the memoirs of Young in the 

 'Philosophical Transactions,' but had not understood 

 their full significance. The study of Fresnel's memoir 

 caused the full truth to flash upon him that his young 

 countryman had been anticipated thirteen years pre- 

 viously by Dr. Young. Fresnel had re-discovered the 

 principle of interference independently, and, with pro- 

 found insight and unrivalled experimental skill, had ap- 

 plied it to the phenomena of diffraction. It was no light 

 thing for Fresnel to find himself as regards the principle 

 of interference suddenly shorn of his glory. He, how- 

 ever, bore the shock with resignation. He might have 

 readily made claims which would have found favour 

 with his countrymen and with the world at large. But 

 he did nothing of the kind. The history of science 

 indeed furnishes no brighter example of honourable 

 fairness than that exhibited throughout his too short 

 life by the illustrious young Frenchman. Once assured 

 that he had been anticipated — whatever might have 

 been the extent of his own labours, however indepen- 

 dently he might have arrived at his results — he unre- 

 servedly withdrew all claim to the discovery. There 

 is, I repeat, no finer example of scientific honour than 

 that manifested by Augustin Fresnel. 



Fresnel was a powerful mathematician, and well 

 versed in the best mathematical methods of his day. 



