138 POPULAR LECTURES AND ADDRESSES. 



structure possess the helicoidal rotational property 

 in reference to the plane of polarisation of light 

 is one of the notable points of meeting between 

 Natural History and Natural Philosophy. His 

 observations on " cpipolic dispersion" gave Stokes 

 the clue by which he was led to his great discovery 

 of the change of periodic time experienced by 

 light in falling on certain substances and being 

 dispersively reflected from them. In respect to 

 pure mathematics Sir John Herschel did more, I 

 believe, than any other man to introduce into 

 Britain the powerful methods and the valuable 

 notation of modern analysis. A remarkable mode 

 of symbolism had freshly appeared, I believe, in 

 the works of Laplace, and possibly of other French 

 mathematicians ; it certainly appeared in Fourier 

 but whether before or after H arsenal's work I 

 cannot say. With the French writers, however, 

 this was rather a short method of writing formula- 

 than the analytical engine which it became in the 

 hands of Herschel and British followers, especially 

 Sylvester and Gregory (competitors with Green in 

 the Cambridge Mathematical Tripos struggle of 



