Royal Microscopical Socieiy. 249 



exhibit complementary colours — the film being that producing a 

 green, the successive colours will be, on one side, G, B, P, V, E, 0, Y, 

 and on the other, in the reverse order. 



If the selenite film be placed between the polarizer and the 

 silvered prism it will be found, as explained in the paper previously 

 mentioned, that on rotating the analyzing prism we shall have all 

 the phenomena of successive or circular polarization, but, with the 

 selenite between the analyzing plate or prism, when the polarizer is 

 at the polarized ray is reflected unaltered by the silver plate, 

 " but when the polarizer is turned to 45°, 135°, 225°, or 315^, the 

 plane of polarization of the ray falls 45° on one side of the plane 

 of reflexion of the silver plate, and the ray is resolved into two others, 

 polarized respectively in the plane of reflexion and the perpendi- 

 cular plane, one of which is retarded on the other by a quarter of 

 an undulation, and consequently gives rise to a circular ray ;" when 

 the polarizer is turned, " so as to place the plane of polarization in 

 any intermediate position between those producing rectilinear and 

 circular light, elliptical light is obtained." 



To say more on the subject would be to detail the various expe- 

 riments described in the ' Proceedings of the Koyal Society,' in which 

 Sir Charles Wheatstone's paper appears, and from which I have 

 already quoted ; but I may add that by this trifling addition to our 

 instrumental means we are enabled to determine which is the thicker 

 of two films of the same crystalline substance, to examine the 

 coloured rings of crystals by light circularly or elliptically polarized, 

 to produce the succession of colours with selenite or other plates 

 as previously mentioned, as well as other phenomena which are 

 " numerous and varied." 



