726 VERHOEFF AND BELL. 



was, from the description, in the neighborhood of 1 sq. mm. Assum- 

 ing a pupillary diameter of 5 mm. likely to be found in working in a 

 moderate degree of light when surprised by the short circuit, the 

 energy entering the pupil would be at least 6 X 10® ergs per second 

 concentrated in the image, that is an energy density amounting to in 

 the neighborhood of 6 X 10^ ergs per second per square centimeter 

 reckoned without regard for absorption. Allowing one third of the 

 energy absorbed in the eye the energy density in the image should be 

 4 X 10^ ergs per second per square cm. two or three times, at least, 

 greater than the corresponding energy density for a direct ol)servation 

 of the sun, very possibly, owing to the intensity of the short circuit, 

 even several times greater than this. It is little wonder then that 

 although the exposure time is stated to be less than 1 second the results 

 were serious. In true eclipse blindness the length of fixation is the 

 chief factor in the damage. 



Thermic Effects on the Retina from Lightning Flashes. 



A consideration of these miscellaneous energy effects on the eye 

 would be incomplete without referring to the injuries to the eye 

 received from lightning. In such cases a sharp distinction must be 

 drawn between cases in which the patient is actually struck by light- 

 ning, with more or less serious effects, and those in which the patient 

 is clearly not struck, but subject to direct radiation from a nearby 

 flash of lightning. In the former class of injuries electrolytic action 

 and exceedingly severe nervous shock generally occur and the final 

 results may include various grave ocular symptoms sometimes ending 

 in complete blindness due to cataract or atrophy of the optic nerve. 

 In the second r class of cases the effects are usually limited to severe 

 scotomata which may impair vision for some hours or days but as a 

 rule there are no lesions visible either superficially or with the ophthal- 

 moscope, and no permanent damage is done. This immunity is 

 chiefly due to the usually considerable distance between the actual 

 lightning bolt and the observer, since the amount of energy actually 

 involved in a lightning discharge of the first order of magnitude may 

 be enormously great. Sir Oliver Lodge estimates it as high as 10'-° 

 ergs. There are a few instances, however, in which the energy re- 

 ceived at the eye has been great enough to produce typical lesions 

 both from abiotic action and probably also from purely thermal 



