EFFECTS OF RADIANT ENERGY ON THE EYE. 727 



effects. Silex337, Vossius^°^ Rivers ^76, Dunbar Roy302 and Le 

 Roux et Renaud ^^^ have all noted superficial injuries of the cornea 

 and the last named, as also Oliver 2®° have noted symptoms of chorio 

 retinitis, which seem to indicate lesions due to thermic effects, in the 

 latter case invoking the metamorphopsia frequently associated with 

 eclipse blindness. The case of Le Roux et Renaud was a specially 

 notable one in which the patient, on guard duty at night, was exposed 

 to a very powerful flash. It was immediately followed by violent 

 erythropsia which lasted for some two hours. The Gendarme re- 

 mained at his post and went home and to bed about three hours later. 

 The next morning he woke with acute headache, with substantial 

 blindness in the left eye followed a few hours later by loss of sight in 

 the right eye. There was double acute conjunctivitis with swelling 

 and reddening of the lids and conjunctiva and marked chemosis. A 

 little later there was diffuse interstitial keratitis, a change in the color 

 of the iris from blue to greenish and a grayish haze on the lens front 

 visible in a bright light. These affections of the anterior eye cleared 

 later and when the ophthalmoscope could be used there was marked 

 haze in the vitreous, which cleared very slowly and not completely 

 even after three years. This was believed by Le Roux et Renaud to 

 be associated with chorio retinitis and was certainly secondary to the 

 original lesions. 



It is very difficult to make anything like an exact computation of 

 the energy which produced these results, since not only is the total 

 amount of energy in a lightning flash extremely variable and known 

 only to a rough approximation, but the duration of the flash is also 

 variable and uncertain. Thus much is clear, however, that the very 

 heavy discharges, in which the length of flash is some hundreds or 

 thousands of meters and the quantity of electricity discharged very 

 large, are also the relatively slow flashes, since the equivalent con- 

 denser capacity is very large. The estimates of frequency rising to 

 millions per second can have no place here, since obviously the velo- 

 city of free waves being only 300,000 km. per second, a flash of one 

 or several km. in length cannot have a very high oscillation frequency 

 even supposing it permits oscillations at all. Attempts to measure 

 the frequency of the discharge have often led to results of less than 

 .001 of a second and it is altogether probable that in these long flashes 

 there is no oscillation at all on account of the resistance effects. Start- 

 ing from the estimate of Sir Oliver Lodge of 10^" ergs per second and 

 assuming an effective time of discharge .0001 of a second, and that of 

 the total flash not over .1 is within the effective range of reaching the 



