the Media of the Eye. 181 



The aqueous humour during the investigation was placed in a 

 brass vessel blackened on the inside, and with two parallel glass 

 sides. The relatively better transmission of the yellow rays, 

 which was so decided in the case of the cornea, was not seen in 

 this case. The luminous rays traversed the aqueous humour in 

 proportions equal to those obtained in the case of water. For 

 the dark zone there was obtained as the mean of two observa- 

 tions, 



Red zone 1O0 



First dark zone .... 9*1 

 Second dark zone . . . 4*4 

 Third dark zone ... 1*2 



The crystalline lens was pressed between two glass plates, so 

 that, changing its form, it consisted of a parallel layer 2 

 millims. thick, enclosed between both glass plates. The lens 

 soon becomes clouded, even if only a few hours have elapsed 

 since the death of the animal. Hence the crystalline lenses 

 from recently-killed animals were subjected to investigation 

 with the utmost rapidity. With the lens, as with the cornea, 

 although not to the same extent, the transmissibility of the 

 heat contained in the yellow zone was comparatively better 

 than had been observed with water. This phenomenon is not, 

 however, to be understood in the sense that the yellow thermal 

 pencil can traverse the crystalline easier than the aqueous 

 humour, but more of the red rays are absorbed, and hence the 

 proportion of the yellow zone increases. If, therefore, for the 

 red zone the number 10 is to be retained as that which expresses 

 the quantity of the heat from this zone which penetrates the 

 lens, the numbers which indicate the quantity of heat which 

 penetrates the other zones must be proportionally larger than 

 we have noticed in the case of water. The mean of three series 

 of experiments was, 



Green zone 5*1 



Yellow zone 

 Red zone . 

 First obscure zone 

 Second obscure zone 

 Third obscure zone 



9-9 

 10-0 

 8-9 

 7-3 

 32 



In the fourth dark zone, in one series, a trace of heat was per- 

 ceptible. 



the case ; but the loss in flint glass cannot be said to be equal to that ob- 

 served by Melloni for terrestrial sources of heat. Melloni gives for the 

 ratio of the heat radiated through rock salt and flint glass the numbers 100 

 and 6964. (Pogg. Ann. vol. xxxv. p. 291.) 



