RECEPTION OF THE UNDULATORY THEORY. 475 



have not thought it right to delay any longer 

 making known a work of which the difficulty is 

 attested by the fruitless efforts of the most skilful 

 philosophers, and in which are exhibited, in the 

 same brilliant degree, the talent for experiment 

 and the spirit of invention." 



In the mean time, however, a controversy be- 

 tween the theory of undulations and the theory of 

 moveable polarization which M. Biot had proposed 

 with a view of accounting for the colours produced 

 by dipolarizing crystals, had occurred among the 

 French men of science. It is clear that in some 

 main features the two theories coincide ; the inter- 

 vals of interference in the one theory being repre- 

 sented by x the intervals of the oscillations in the 

 other. But these intervals in M. Biot's explana- 

 tion were arbitrary hypotheses, suggested by these 

 very facts themselves; in Fresnel's theory, they 

 were essential parts of the general scheme. M. 

 Biot, indeed, does not appear to have been averse 

 from a coalition; for he allowed 9 to Fresnel that 

 " the theory of undulations took the phenomena at 

 a higher point and carried them further." And M. 

 Biot could hardly have dissented from M. Arago's 

 account of the matter, that Fresnel's views " linked 

 together" the oscillations of moveable polarization. 

 But Fresnel, whose hypothesis was all of one piece, 

 could give up no part of it, although he allowed 

 the usefulness of M. Biot's formulae. Yet M. Biot's 



9 Ann. Chim. torn. xvii. p. 251. 10 " Noiiait." 



