16 SIXTH REPORT. — 1836. 



any theory of liglit, though I have no doubt that the undulatory 

 theory will ultimately accommodate itself to this as well as to other 

 classes of phenomena which it does not at present embrace. The 

 difficulty, however, is increased by another result of my experiments 

 which it is important to notice. On the faces of the spar which are 

 inclined 0°, 45°, and 90° to the axis of double refraction, the action 

 of the new force is symmetrical upon the two pencils of polarized 

 light, whose planes are inclined + 45°, and — 45° to the plane of in- 

 cidence, whereas in all intermediate faces whose inclination to the 

 axis is 2'2i° and G7^", the plane of one of the polarized rays remains 

 stationary, while that of the other is turned round 15°. 



This effect is undoubtedly a very extraordinary one, and indicates 

 some singular structure in calcareous spar, the nature of which it is 

 not easy to conjecture. 



1 have examined these phenomena by using in place of oil of cassia 

 various fluids whose refractive powers descend gradually to that of 

 water ; but it would be a waste of time to give any detailed account 

 of them at present. I shall only state that the action of the new 

 force becomes weaker and weaker as the force of ordinary reflexion 

 is increased by diminishing the refractive power of the oil which is 

 placed in contact with the spar. With an oil of the highest refractive 

 index the action of the new force predominates over the feeble power 

 of the ordinary force of reflexion. With an oil of a lower index the 

 two forces exactly balance each other, while with oils of still lower 

 indices of refraction the ordinary force overcomes and conceals the 

 action of the new one. 



Although I have obtained pretty accurate measures of the amount 

 of the deviations produced by the new force on eight surfaces diff^er- 

 ently inclined to the axis, and in various azimuths on these surfaces, 

 yet many experiments are still necessary before we can hope to dis- 

 cover the physical law of the phenomena ; and if this should be done 

 I have no doubt that Mr. MaccuUagh will be equally successful in 

 the higher attempt of accounting for them by some modification of 

 the undulatory theory. 



On a singular Development of Polarizing Structure in the Crystalline 

 Lens after Death. By Sir David Brewster, K.G.H., V.P.R.S.Ed. 



In exatnining the changes which are produced by age in the 

 polarizing structure of the crystalline lenses of animals, I was in- 

 duced to compare these changes with those which I conceived might 

 take place, after death, when the lens was allowed to indurate in the 

 air, or was preserved in a fluid medium. After many fruitless ex- 

 periments I found that distilled water was the only fluid which did 

 not aflfect the transparency of the capsule, and my observations were 

 therefore made with lenses immersed in that fluid. The general 

 polarizing structure of the crystalline in the sheep, horse, and cow, 

 consists of three rings, each composed of four sectors of polarized 



