194 Sir David Brewster on the Changes in the Structure 



being a faint blue of tbe first order. On tbe tbird day the two 

 new structures bad become more prominent. Tbe structure 

 No. 2, now a pale wbite of tbe first order, was completely deve- 

 loped, having encroached upon and almost obliterated tbe third 

 structure. The structure No. 4, which was not in existence on 

 the first day, had now the maximum tint, namely a bright white 

 of the first order. On the fourth day the structures No. 2 and 

 4, which at first were not in existence, are now the structures 

 with the maximum tints, and No. 3, which had the maximum 

 tint, is now almost obliterated, a little faint brown light remain- 

 ing in one of the quadrants. 



On the fifth day the four sectors of the inner structure No. 1 

 have almost disappeared. No. 3 has disappeared entirely, and 

 No. 2, which is almost the only polarizing structure, exhibits a 

 more intense white of the first order than appeared in any part 

 of the lens. The ring No. 2 divides the radius of the lens 

 equally. 



On tbe sixth day the structure No. 2 was still bright and uni- 

 form, but tbe polarized light had disappeared from every other 

 part of the lens. 



On the seventh day the lens, which was always placed in water, 

 burst its capsule, and there was no longer any trace of distinct 

 polarizing structures. 



My next observations were made on the lenses of a cow nearly 

 twenty years old. The following were the dimensions of the 

 eye and the lenses : — 



inch. 



Diameter of eyeball 1*66 



Chord of the cornea (largest) . . 1*30 

 Chord of the cornea (shortest) . 1"02 

 Longest diameter of lens . . . - 827 

 Shortest diameter of lens . . . 0793 

 Thickness of lens 0*50 



Both tbe lenses of the cow exhibited when taken out of the eye 

 four beautiful structures, in which the positive and negative 

 structures alternate. Tbe first and fourth were very faint, being 

 the palest white of tbe first order. The third was also faint, but 

 the second was both bright and large, and its tint was a brilliant 

 yellow of the first order. After lying four days in water the 

 lenses swelled so much that their dimensions were as follows : — 



inch. 

 Diameter of one lens .... 0807 

 Diameter of the other .... 0'793 

 Thickness of the first .... 0-647 

 Thickness of the second . . . - 620 



