120 Mr GREEN's SUPPLEMENT TO A MEMOIR, &c. 



to the corresponding term in the second equation of system (29)*. 

 If, therefore, we reject these second terms, and conceive the common 

 interval r- so small that the result due to the first terms may not 

 differ very sensibly from that which would be produced by a single 

 refraction, we should have to replace the system (29) by (30), and the 

 intensity of the reflected wave would then agree with the law assigned 

 by Fresnel. In virtue of this law, however highly refracting any 

 substance may be, homogeneous light will always be completely po- 

 larized at a certain angle of incidence ; and Sir David Brewster states 

 that this is the case with diamond at the proper angle. But the phe- 

 nomena observed by Professor Airy appear to him entirely inconsistent 

 with this result (Vide Camb. Phil. Trans., Vol. iv. p. 423.) ; what im- 

 mediately precedes seems to render it probable that considerable dif- 

 ferences in this respect may be due to slight changes in the reflecting 

 surface. 



* In fact, in the system (33) each of the last terms will, in consequence of the factors 

 (/*,* - 1'*)*' &c be quantities of the order -5 compared with the last term of (29')» and 



as their number is only n, their joint effect will be a quantity of the order - compared 

 with that of the term just mentioned. 



