184 FRESNEL. 



that an author knows all that he might be supposed to 

 know ; and the right with which it is invested, to treat 

 with implacable severity those who knowingly borrow 

 from the labours of their predecessors, is the origin of 

 more than one act of injustice. Thus, Lagrange has 

 recounted that in his youth he experienced just such a 

 profound mortification, on finding, by accident, in the 

 works of Leibnitz, an analytical formula which he had 

 completely forgotten, and of which he had spoken to the 

 Academy of Turin as a discovery of his own. From 

 that day he had nearly renounced altogether the study 

 of mathematics. The demonstration of aberration was 

 a matter of too little importance to inspire Fresnel with 

 a similar discouragement ; and besides, he had not print- 

 ed it ; but this circumstance rendered him extremely 

 timid ; and subsequently he never published any memoir 

 without assuring himself by the testimony of some of his 

 friends, to whom the academical collections were more 

 familiar, that he had not, according to a popular proverb 

 which he habitually adopted, " broken through open 

 doors." * 



* It is much to be regretted that this early production of Fresnel 

 should not have been preserved more especially when we recollect 

 that the theoretical explanation of the aberration of light, though ap- 

 parently well given by Clairault and others, was for a long time by 

 no means clearly apprehended, and far from being exempt from all 

 necessity for further elucidation. In proof of this it may suffice to 

 allude to the fact that, on the occasion of the transit of Venus in 

 1769, two eminent astronomers, Bliss and Hornsby, calculated the 

 effect of aberration as accelerating the phases of the transit, while 

 Professor Winthrop, of Cambridge, U. S., argued that it ought to be 

 that of retarding them. Other discrepancies of opinion in past times 

 might also be cited; but the most striking fact has been the contro- 

 versy in which the whole subject has been involved in our times, 

 arising out of the somewhat startling ideas proposed by Professor 

 Challis. and so largely discussed by that eminent mathematician and 



