410 ABSORPTION OP HEAT-RAYS BY THE EYE. 
By this method of examination the following numbers were 
obtained as the mean of general experiments: 
Hays which pass through to the retina for 100 rays from a 
moderator lamp, incident upon the cornea. 
Eye of an ox. Eye of a sheep. Eye of a pig. 
77 8*4 9-1 
With lamps of inferior illuminating power the results 
were even lower, and so also with an incandescent coil of 
platinum wire; thus the proportion of rays which pass to the 
retina decreases rapidly with the illuminating power of the 
source. 
Absorbing power of the several humours .—The author gives in 
the table appended the results he has been led to adopt:— 
Absorption by tlie several parts of the eye for 
the heat-rays of a 
moderator lamp. 
Ox. 
Sheep. 
Pig. 
Rays reflected at the surface of the cornea 
4-0 
40 
4-0 
Rays absorbed by the cornea 
59-8 
569 
57*5 
Rays absorbed by the aqueous humour 
19-2' 
20-6 
Raj's absorbed by the crystalline lens . 
6-8 
£ 307 
7‘2 
Rays absorbed by the vitreous humour 
2-5. 
) 
1*6 
Rays which penetrate to the retina . 
77 
8*4 
91 
Rays incident .... 100-0 
100-0 
100-0 
From certain theoretical considerations treated in the 
papers, the author draws the conclusion that the radiations 
which are suffered to impinge upon the retina have almost 
entirely been deprived of their obscure rays; hence it follows 
that the parts composing the structure of the eye must pos¬ 
sess the power of effecting a complete separation between the 
two kinds of radiations—“The heat which penetrates to the 
retina appears to be the expression of calorific power for the 
luminous rays/” 
Diathermancy .—The examination of the humours of the 
eye, from this point of view, has shown their mode of action 
upon the radiant heat to be identical with that of water. 
The conclusions which the author deduces from the re¬ 
sults of his experiments are stated in the following propo¬ 
sitions : 
1st. That among the superior animals, the eye, although 
so perfectly transparent for light, possesses, on the contrary, 
the property of absorbing most completely the obscure heat- 
rays, effecting thus a perfect separation between the two 
kinds of radiations. 
2d. From a physiological point of view this property of 
