228 On Polarization of Light by Refraction. 



I was now desirous of ascertaining the influence of refractive pow- 

 er, although I had already determined in 1813, that a greater quan- 

 tity" of light was polarized, at the same angle of incidence, by plates 

 of a high than by plates of a low refractive power. I experienced 

 great difficulty in this part of the inquiry, from the necessity of having 

 plates without any crystalline structure. I tried gold leaf in a varie- 

 ty of ways ; but I found it almost impossible to obtain correct results, 

 on account of the light which was transmitted unchanged through its 

 pores. ^ 



By stretching a film of soapy water across a rectangular frame of 

 copper wire I obtained the following measure. 



WATER. 

 Incidence. Inclination. Rotation. 



85° . . . . 54° 17' . . . .9° 17^ 

 I next tried a thin plate of metalline glass of a very high refractive 

 power. 



METALLINE GLASS. 

 Incidence. Inclination. Rotation. 



0° . . . . 45° 0' . . . . ■ 0° 9' 

 20 .... 45 42 ... . 42 

 30 .... 46 50 ... . 1 50 

 40 .... 48 ... . 30 

 55 .... 51 12 .... 6 12 

 80 .... 62 32 .... 17 32 

 From a comparison of these results it is manifest that the rotation 

 increases with the refractive power. 



In examining the effects produced at different angles of incidence, 

 it becomes obvious that the rotation varies with the deviation of the 

 refracted ray ; that is, with i — i', the difference of the angles of inci- 

 dence and refraction. Hence from a consideration of the circum- 

 stances of the phaenomena I have been led to express the inclination 

 cp of the planes of polarization to the plane of refraction by the for- 

 mula, 



Cot (p = cos {i — i^), 

 the rotation being =9 — 45°. 



This formula obviously gives a minimum at 0°, and a maximum 

 at 90° ; and at intermediate points it represents the experiments so 

 accurately, that when the rhomb of calcareous spar is set to the cal- 

 culated angle of inclination, the extraordinary image is completely in- 

 visible,- — a striking test of the correctness of the principle on which it 

 is founded. 



