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 
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