378 PROFESSOR CHALLIS, ON A THEORY OF THE POLARIZATION OF LIGHT, ETC. 



be composed, does in fact produce coloured rings, but the two sets being exactly complementary, 

 the colours disappear. 



Circularly and elliptically polarized light is capable of reflexion at the analyzing plate (in the 

 experiment above alluded to) because it consists of two rays polarized in opposite planes, which 

 cannot therefore both coincide at the same time with the plane of incidence. The analyzing plate 

 is necessary for the production of the colours, because the rays come out of the crystal in opposite 

 polarizations, and therefore not interfering Those that fall on the plate in the same phase consti- 

 tute a sino-le ray polarized in the plane of original polarization, and are therefore incapable of 

 reflexion when the plane of incidence on the plate is perpendicular to the plane of original 

 polarization. The rest of the rays fall on the plate in the form of circularly or elliptically 

 polarized light, and consequently from what we have already seen, are capable of reflexion. 

 This explanation does not require the supposition of the loss of half an undulation. 



The Theory might be compared with experiment in many other instances ; but perhaps those 

 I have adduced may suffice to gain for it the favourable consideration of mathematicians. I will 

 only add, that having applied it in some degree to the pha;nomena of Double Refraction, 1 find 

 that it leaves the mathematical Theory of Fresnel unaltered, while it off'ers in several respects a 

 iliff'erent physical explanation of the facts. Before I conclude it may also be proper to remark, that 

 I have argued on the supposition that the quantity k which enters into this Theory is a constant. 

 The reasoning would remain the same if k were a function of X, provided it did not vary witli the 

 intensity of tlie ray. 



Cambridge Observatory, 

 May 25, 1846. 



