110 HISTORY OF OPTICS. 



ment," but that " they have not thought it right to delay any 

 making known a work of which the difficulty is attested by the fruit- 

 less 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 meantime, however, a controversy between the theory of 

 undulations and the theory of moveable polarization which M. Biot 

 had proposed with a view of accounting for the colors produced by 

 ii, 'polarizing crystals, had occurred among the French men of science. 

 It is clear that in some main features the two theories coincide ; the 

 intervals of interference in the one theory being represented by the 

 intervals of the oscillations in the other. But these intervals in M. 

 Biotas explanations were arbitrary hypotheses, suggested by these very 

 facts themselves ; in Fresnel's theory, they were essential parts of the 

 ral scheme. M. Biot, indeed, does not appear to have been 

 averse from a coalition; for he- allowed* 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 1 ' 1 ' 1 

 the oscillations of moveable polarization. But Fresnel, whose hypo- 

 thesis was all of one piece, could give up no part of it, although he 

 allowed the usefulness of M. Blot's formula). Yet M. Biot's specula- 

 tions fell in better with the views of the leading mathematicians of 



O 



Paris. TVe may consider as evidence of the favor with which they 

 were looked upon, the large space they occupy in the volumes of the 

 . Vudemy for 1811, 1812, 1817, and 1818. In 1812, the entire vo- 

 lume is filled with a memoir of M. Biot's on the subject of moveable 

 \ olarization. This doctrine also had some advantage in coining early 

 before the world in a didactic form, in his Tmite de Physique, which 

 was published in 1816, and was the most complete treatise on general 

 physics which had appeared up to that time. In this and others of 

 this author's writings, he expresses facts so entirely in the terms of his 

 own hypothesis, that it is difficult to separate the two. In the sequel 

 M. Arago was the most prominent of M. Biot's opponents ; and in his 

 report upon Fresnel's memoir on the colors of crystalline plates, he 

 exposed the weaknesses of the theory of moveable polarization with 

 s->mc severity. The details of this controversy need not occupv us ; 

 but we may observe that this may be considered as the last struggle 



Ann. Chim. 1 )in. xvii. p. 2.31. 10 " Xoimit " 



