EFFECTS OF RADIANT ENERGY ON THE EYE. G49 



path of the rays is shown by the dotted hnes in the figure. The effect 

 of the arrangement was to pass through the cornea a strongly diverg- 

 ing pencil producing a circle of intense light on the retina. The axial 

 length of the ordinary rabbit's eye is about 16.5 mm. and the ordinary 

 diameter of the area of intense illumination produced by our appara- 

 tus was about 11 mm. at the retina as was determined by actual 

 experiment upon a freshly removed eye. With this apparatus a large 

 amount of energy could be concentrated on any required area at or 

 within the surface of the cornea or lens, and by aid of these lens sys- 

 tems we were able to obtain exposures enormously more severe than 

 could possibly be obtained from artificial light sources in ordinary use 

 or than have ever been obtained by previous experimenters in this 

 field. The image was kept fixed during the exposure by slight 

 shifting of the source or lens, since the arc itself tends to wander. 



By the use of photo paper the following data were obtained con- 

 cerning the relative intensities of radiation at the focus and on the 

 retina with the double lens system. The size of the area of most 



Figure 4. Quartz condensing system. Screens omitted for simplicity. 



intense illumination at the focus was 2 X 4j mm. The diameter 

 of eft'ective illumination at a distance of 16 mm. from the focus, 

 corresponding to the position of the retina, was 11 mm. Through 

 a euphos glass screen an exposure of 5 seconds at the focus closely 

 corresponded in intensity to an exposure of 75 seconds at the position 

 of the retina, so that neglecting absorption by the media of the eye the 

 intensity of the illumination of the retina with this lens system was 

 about fifteen times less than that of the cornea. This ratio was con- 

 firmed by photographs taken with a model schematic eye without 

 screen and with a picric acid screen, so that it may be assumed to hold 

 over a very wide range of wave lengths. 



' The results of these experiments are given l)elow. For purposes of 

 comparison other experiments with the magnetite are also given here, 

 although they have no direct bearing on the determination of the 

 critical wave length of abiotic action. For the same reason experi- 

 ments are given showing the length of exposure to the quartz mercury 



