38 Dr. Brewster's experiments on the 
on each side of the common image, like those which I have 
described in my paper on mother of pearl.* 
37. Whalebone depolarises light, and has neutral axes pa- 
rallel and perpendicular to the direction of the fibres. 
38. Horn. This substance also depolarises light in every 
position, and exhibits the coloured rings by polarised light. 
39. Mother of pearl depolarises light in every position when 
the polarised pencil has a small angle of incidence ; but when 
the angle of incidence is about 60®, and the plate about the 
thirtieth of an inch thick, it acts exactly like a bundle of glass 
plates, shifting merely the vanishing place of the image, f 
40. Bladder of a cow depolarises light in every position. 
41. Human cornea depolarises light in every position, and 
exhibits coloured rings by polarised light. The tunica retina 
and the crystalline lens exercise no peculiar action on light. 
42. Cornea of a cow depolarises light in every position, and 
exhibits colours by polarised light. When it is pressed hard 
between the lenses, so as to induce a milky opacity, it still 
retains the power of depolarisation. The crystalline lens does 
not possess any of these properties. 
43. Cornea of a fish depolarises light in every position, but 
most powerfully near its junction with the sclerotic coat, and 
exhibits coloured rings by polarised light. The crystalline 
lens, the sclerotic coat, and the capsule of the crystalline lens, 
exercise no action upon polarised light. When two capsules 
* Phil. Trans. 1814. Part II. p. 397. 
f We have here omitted the consideration of the nebulous image formed by mother 
of pearl at an oblique incidence. An account of the remarkable optical properties of 
this substance has been given in another paper. 
