View of the Undulatory Theory of Light » 17 



be introduced. The nature of any such distinction cannot be 

 made intelligible without some previous statement or expla- 

 nation of the theory referred to : to supply such a statement 

 will be my object in the ensuing pages. And I am the more 

 desirous to do this, because, I believe, the elaborate researches 

 of M. Cauchy are even yet but little known to British students. 

 He has directed his profound analytical skill to the construc- 

 tion of a theory of undulations built on such an hypothesis of 

 the arrangement and mutual action of a system of molecules as 

 leads to results including the general theoretical explanation 

 of the unequal refrangibility. 



The slowness with which a knowledge of the labours of 

 Continental philosophers too commonly finds its way into En- 

 gland, has been singularly evinced in several instances, but 

 more especially in optical science ; and in the present case, 

 partly, perhaps, from the particular form in which these re- 

 searches have been successively given to the world, and partly 

 from an appearance of abstruseness and difficulty in the sub- 

 ject, they do not seem to have become known among us as 

 from their high interest, importance, and elegance they de- 

 serve to be. The first notice of them which appeared in this 

 country was, I believe, that contained in Sir David Brewster^s 

 Report on Optics, read at the meeting of the British Associa- 

 tion at Oxford, 1832; and even this was two years after the 

 publication of the last part of these researches in France. 



In the following short abstract I shall endeavour to put the 

 leading points of M. Cauchy's investigations in as connected 

 and simplified a point of view as the nature of the case will 

 admit. This may, I trust, render the subject more generally 

 accessible, and tend to remove some of its apparent abstruse- 

 ness and difficulty. The abstract mathematical part of the 

 inquiry is of considerable extent; but as the object of the pre- 

 sent paper is confined to tracing it so far as to include the 

 theory of dispersion, it will be found susceptible of abridge- 

 ment. 



I shall abstain at present from all remarks on the physical 

 application of the theory, which it will form an important ob- 

 ject to refer to in the sequel ; and before entering upon the 

 principles of the theory, I will briefly state the original sources, 

 to which those inquirers who wish to examine the subject in 

 all its detail will of course refer. 



The particular researches which we are about to examine 

 are closely connected with various others, of the same author. 



M. Cauchy, in the third volume of his Exercices de Mathe- 

 matiqiies (1828), liv. xxx. xxxi. p. 188, has given an elaborate 

 memoir, entitled " Sur Tequilibre et le mouvement d'un systeme 



Third Series. Vol. 6. No. 31 . Jan. 1835. D 



