U-i HISTOEY OF OPTICS. 



thirty years later. Dr. Wollaston was a person whose character led 

 him to look long at the laws of phenomena, before he attempted to 

 determine their causes ; and it does not appear that he had decided 

 the claims of the rival theories in his own mind. Herschel (I now 

 speak of the son) had at first the general mathematical prejudice in 

 favor of the emission doctrine. Even when he had himself studied 

 and extended the laws of dipolarized phenomena, he translated them 

 into the language of the theory of moveable polarization. In 1819, 

 he refers to, and corrects, this theory; and says, it is now "relieved 

 from every difficulty, and entitled to rank with the fits of easy trans- 

 mission and reflection as a general and simple physical law ;" a just 

 judgment, but one which now conveys less of praise than he then in- 

 tended. At a later period, he remarked that we cannot be certain that 

 if the theory of emission had been as much cultivated as that of undu- 

 lation, it might not have been as successful ; an opinion which was 

 certainly untenable after the fair trial of the two theories in the case 

 of diffraction, and extravagant after Fresnel's beautiful explanation of 

 double refraction and polarization. Even in 1827, in a Treatise on Light, 

 published in the Encyclopaedia Metropolitana, he gives a section to the 

 calculations of the Newtonian theory ; and appears to consider the 

 rivalry of the theories as still subsisting. But yet he there speaks with 

 a proper appreciation of the advantages of the new doctrine. After 

 tracing the prelude to it, he says, " But the unpursued speculations of 

 Newton, and the opinions of Hooke, however distinct, must not be put 

 in competition, and, indeed, ought scarcely to be mentioned, with the 

 elegant, simple, and comprehensive theory of Young, a theory which, 

 if not founded in nature, is certainly one of the happiest fictions that 

 the genius of man ever invented to grasp together natural phenomena, 

 which, at their first discovery, seemed in irreconcileable opposition to 

 it. It is, in fact, in all its applications and details, one succession of 

 felicities ; insomuch, that we may almost be induced to say, if it be 

 not true, it deserves to be so." 



In France, Young's theory was little noticed or known, except per- 

 haps by M. Arago, till it was revived by Fresnel. And though Fresnel's 

 assertion of the undulatory theory was not so rudely received as Young's 

 had been, it met with no small opposition from the older mathemati- 

 cians, and made its way slowly to the notice and comprehension of men 

 of science. M. Arago would perhaps have at once adopted the concep- 

 tion of transverse vibrations, when it was suggested by his fellow- 

 laborer, Fresnel, if it had not been that he was a member of the Insti- 



