409 
ON THE ABSORPTION OE HEAT-RAYS BY THE HUMOURS 
OE THE EYE. 
Under this title a very interesting paper has recently been 
presented to the Academy of Sciences, Paris, by Monsieur 
J. Janssen, an abstract of which we have now the satisfaction 
of laying before our readers. 
The author states that, from a consideration of the facts 
reported in his memoir, he was led to the belief that the 
humours of the eye would be found to possess the power of 
absorbing the obscure rays of heat w T hich accompany in such 
abundance the luminous rays proceeding from our ordinary 
sources of artificial illumination. He endeavoured, therefore, 
to establish the existence of this property, and to measure its 
amount by very accurately conducted experiments. 
The memoir comprehends— 
1st. The determination of the amount of heat which im¬ 
pinges upon the retina in the eyes of several animals, and from 
various sources of illumination. 
2d. The investigation of the part played by each of the 
several humours in producing the general effect. 
3d. The diathermancy of the humours, and the study of 
their mode of action upon the heat. 
The apparatus of Nobili and Melloni, as constructed by 
M. Ruhmkorff, w 7 as employed in these researches, and with 
all the precautions necessary to ensure trustworthy results. 
It was placed exactly north, and protected from the influence 
of accidental heat-rays both before and at the time of making 
the experiments. The pile wos guarded with a double system 
of metallic screens; one forming a dark cover around the 
whole apparatus; the other smaller, covering the pile merely, 
and capable of being lifted off only at the moment of 
exposure. 
The eye entire .—In order to measure the transmission 
through the entire organ, a portion of the vitreous humour 
was laid bare at the posterior part of the eyeball, which w 7 as 
then placed in a receptacle formed of two perforated rings of 
cork, one of which was provided with a very thin glass for 
the purpose of retaining the vitreous humour. The eye thus 
prepared was rested on a plate of metal which carried the 
screen intended to define the incident calorific pencil. This 
plate w 7 as moveable and allowed of placing the optic axis of 
the eye in the line of direction of the heat-rays, and of re¬ 
moving it to a distance at which the intensity of this heat 
could be conveniently measured. 
