372 



arrests the chemical radiations which accompany the more refran- 

 gible rays." He founded this conclusion on experiments made 

 with guaiac resin ; but as this substance is by no means very sensi- 

 tive to actinic influence, it seemed desirable to test the question 

 whether the eye can transmit the chemical rays of light, by an 

 appeal to those highly impressible actinolytes (as they may be 

 called) which the recent progress of photography has revealed 

 to us. 



The necessary trials were kindly made for me by Messrs Dick and 

 Spiller of London, and their results, which are opposed to those of 

 Wartmann, were published last autumn in the Appendix (p. 166) 

 to my Researches on Colour-Blindness. 



I now lay upon the Society's table photographs of small objects, 

 on glass and paper, produced by rays which, before reaching the 

 sensitive surfaces, had traversed the transparent humours of an ox's 

 eye. These photographs were obtained by the gentlemen I have 

 named in the following way : — 



'' An ox-eye was prepared by cutting away the sclerotic until the 

 choroid came into view ; a circular aperture of one-eighth of an inch 

 in diameter was then made through this membrane and the retina, 

 which laid bare the vitreous humour at a point opposite to that 

 where the light enters. The eye was then supported in the brass 

 mounting of a photographic lens {i.e., a brass tube adapted to the 

 front of a camera), resting at the posterior end on a ring of cork 

 which fitted tightly into the tube, and retained in front by a dia- 

 phragm, so as to permit the cornea to protrude. From the arrange- 

 ment of the fittings, we are quite satisfied that no light excepting 

 that which passed through the eye could enter the camera. 



" Within the dark box, a strip of black paper, with a diamond- 

 shaped or rhombic aperture occupying the greater part of its breadth, 

 was extended across in front of the prepared collodion glass plate, so 

 as to throw its image on the latter, in the event of any chemical rays 

 finding their way to it. The camera was then pointed to the sky 

 (the morning being bright and the sun shining), and the plate ex- 

 posed for fifteen seconds. On developing with solution of sul- 

 phate of iron, a very decided picture appeared. The glass plate 

 which accompanies this paper was the result of twenty seconds' 

 exposure. 



*' The conclusion. derived from this experiment, although perfectly 



