1871.] 



On the Successive Polarization of Light. 



381 



zontal position. The curling round of the scapula-rod is described, and 

 the outgrowth from the rod of plates of bone bounded by the acromial, 

 glenoid, and coracoid borders. The relations of the sterno-mastoid, trape- 

 zius, and levator anguli scapulae muscles are referred to. The growth of the 

 glenoid cavity outwards from the acromion and coracoid is noticed at about 

 the eleventh week, at which period the scapula has acquired its chief per- 

 manent characters. 



March 23, 1871. 

 General Sir EDWARD SABINE, K.C.B., President, in the Chair. 

 The following communications were read : — 

 I. "Experiments on the Successive Polarization of Light, with the 

 description of a new Polarizing Apparatus." By Sir Charles 

 Wheatstone, E.R.S. Received Eeb. 2, 1871. 



I. 



The term successive polarization was applied by Biot to denote the 

 effects produced when a ray of polarized light is transmitted through a 

 plate of rock-crystal cut perpendicularly to the axis, or through limited 

 depths of certain liquids. In these cases the plane of polarization is found 

 to be changed on emergence, and differently for each homogeneous ray ; so 

 that, when white light is employed, on turning the analyzer round con- 

 tinuously in one direction different colours successively appear, rising or 

 falling in the scale according to the nature of the substance. 



If, while the analyzer is turned from left to right, the tints ascend 

 (i. e. follow the order B, O, Y, G, B, P, Y), the substance is said to ex- 

 hibit right-handed successive polarization, but if the tints descend, the 

 successive polarization is said to be left-handed. 



These phenomena were satisfactorily explained by Fresnel in the following 

 way. The incident polarized ray, instead of resolving itself into two plane- 

 polarized rays at right angles to each other, as in the ordinary cases of di- 

 polarization, resolves itself in these instances into two circularly polarized 

 rays, one right-handed the other left-handed, which are transmitted with 

 different velocities ; each homogeneous ray, thus resolved into two opposite 

 circularly polarized pencils, on emergence composes a ray polarized in a 

 single plane, the deviation of which from the primitive plane of polariza- 

 tion depends on the difference of phase of the two circularly polarized 

 rays on emergence. 



The rotation of the planes of polarization is from left to right, or from 

 right to left, according to whether the right-handed or left-handed circular 

 rays are transmitted with the greater velocity. 



II. 



The term dipolarization, proposed by Dr. Whewell to express the 



VOL. XIX. 2 G 



