27 



tion independently of each other. A ray of common light has the 

 condensation symmetrically arranged about the axis. 



May 25, 1846. 



A Theory of the Polarization of Light on the Hypothesis of Un- 

 dulations. By the same Author. 



This paper is a continuation of the foregoing. A ray in which 

 the condensation is not arranged symmetrically about the axis is 

 considered to be polarized. Polarization in this theory corresponds 

 to difference of condensation in different directions transverse to the 

 axis of the ray. The sensation of light is due to the transverse vi- 

 brations. By assuming that the bifurcation of a ray takes place so 

 that the transverse velocity at each point is resolved into two velocities 

 at right angles to each other, and that these are respectively the 

 velocities at the corresponding points of the two parts into which the 

 ray is divided, Professor Challis finds, — 1, that if the original ray be 

 one of common light, the two parts are symmetrical about planes at 

 right angles to each other passing through the axis, and are each of 

 half the intensity of the original ray ; 2, that if the original ray has 

 been once polarized, the ratio of the two parts is equal to the square 

 of the tangent of the angle which the plane of the second polariza- 

 tion makes with that of the first ; 3, that whether the original ray 

 be one of common light or a polarized ray, the two parts, on pursuing 

 , the same path, form a compound ray the intensity of which is in- 

 dependent of the difference of phase. According to this theory, 

 elliptically or circularly polarized light is produced whenever a ray 

 of first polarization is divided into two parts which subsequently 

 pursue the same path in different phases. If the parts be made to 

 meet in the same phase, they constitute the original polarized ray. 

 Hence is explained the necessity of the analysing plate for the pro- 

 duction of colours by polarized rays transmitted through thin pieces 

 of uniaxal or biaxal crystals. The compound rays, if received directly 

 by the eye on leaving the crystal, would be of the same intensity 

 whatever be the difference of phase. But when they fall on the 

 plate, those incident in the same phase, being equivalent to rays of 

 first polarization, are incapable of reflexion, while the remainder, 

 which are incident in the form of elliptically or circularly polarized 

 light, are reflected in different degrees of intensity according to the 

 difference of phase. The author states that he has extended this 

 theory to the phsenomena of double refraction. 



On a Change in the State of Vision of an Eye affected with a 

 mal-formation. By G. B. Airy, Esq[., Astronomer Royal. 



Twenty years ago, the author communicated to the Society a state- 

 ment of the effects of a mal-formation in his left eye. The rays of 

 light coming from a luminous point, and falling on the whole surface 



