II. REPORT OX THE PROGRESS AND PRESENT STATE OF 

 PHYSICAL OPTICS. 



Report of the British Association for the Advancement of Science for 1834. 



Ix the Report which I have the honour to submit to the Associa- 

 tion, I have attempted to consider in some detail the present state 

 of our knowledge with regard to the physical theory of light, and 

 the successive advances which have, in late years, been made 

 towards its establishment. The method which I have thought 

 it expedient to adopt in this review has been to take, in the first 

 instance, a rapid survey of the several leading classes of optical 

 phenomena, which the labours of experimental philosophers have 

 wrought out in such rich profusion, and afterwards to examine 

 how far they are reducible to one or other of the two rival 

 theories which have alone advanced any claim to our considera- 

 tion. This is, in fact, the only way in which the truth of a 

 physical theory can be established ; and the argument in its favour 

 is essentially cumulative. 



But in making this comparison it is not enough to rest in 

 vague explanations which may be moulded to suit any theory. 

 Whatever be the apparent simplicity of an hypothesis whatever 

 its analogy to known laws it is only when it admits of mathe- 

 matical expression, and when its mathematical consequences 

 can be numerically compared with established facts, that its 

 truth can be fully and finally ascertained.* Considered in this 

 point of view, the wave-theory of light seems now to have reached 



* C'est en tirant des formules les consequences les plus subtiles et les plus eloigne'es 

 des principes, puis allant les verifier par 1' experience, que 1'on peut r6ellement s' assurer 

 si une theorie est vraie ou fausse, et si Ton doit s'y confier comme & un guide fidele, 

 ou la rejeter comme un systeme trompeur. Biot, Traite de Physique, torn, i., p. xiv. 



c2 



