L1S J11STOKY OF OPTICS. 



Fresncl to Young,^ in November, 1824 : " For a long time that sen 

 sibility, or that vanity, which people call love of glory, is much Wanted 

 in me. I labor much less to catch the suffrages of the public, than to 

 obtain an inward approval which has always been the sweetest reward 

 of my efforts. Without doubt I have often wanted the spur of vanity 

 to excite me to pursue my researches in moments of disgust and dis- 

 courao-ement. But all the compliments which I have received from 

 MM. Arago, De Laplace, or Biot, never gave me so much pleasure as 

 the discovery of a theoretical truth, or the confirmation of a calcula- 

 tion by experiment." 



Though Young and Fresnel were in years the contemporaries of 

 many who are now alive, we must consider ourselves as standing to- 

 wards them in the relation of posterity. The Epoch of Induction 

 in Optics is past ; we have now to trace the Verification and Applica- 

 tion of the true theory. 



CHAPTER XIII. 



CONFIRMATION AND EXTENSION OF THE UNDULATCEY THEOKI. 



A FTER the undulatory theory had .been developed in all its main 

 -*- features, by its great authors, Young and Fresnel, although it 

 bore marks of truth that could hardly be fallacious, there was still 

 here, as in the case of other great theories, a period in which difficul- 

 ties were to be removed, objections answered, men's minds familiarized 

 to the new conceptions thus presented to them ; and in which, also, it 

 might reasonably be expected that the theory would be extended to 

 facts not at first included in its domain. This period is, indeed, that 

 in which we are living ; and we might, perhaps with propriety, avoid 

 the task of speaking of our living contemporaries. But ifwould bo 

 unjust to the theory not to notice some of the remarkable events, 

 characteristic of such a period, which have already occurred ; and this 

 may be done very simply. 



I \vas able to give tin's, and some other extracts, from tlie then unedited 

 correspondence of Young and Fresnel, by the kindness of (the Dean of Ely) 

 Professor Peacock, of Trinity College, Cambridge, -whose Life of Dr. Young line 

 since been published. 



