720 VERHOEFF AND BELL. 



destructive effects such as have been often clinically noted and which 

 we have observed in our experiments. From the relatively small 

 absorption by the eye media in the case of solar radiation it is clear, 

 however, that it is far more dangerous, in proportion to its intensity, 

 than any artificial source of radiation. 



Passing from the general absorption of the eye for radiant energy 

 here considered to the specific absorption of the several media, the 

 facts have been pretty thoroughly established by the researches of 

 Hallauer^^^, Schans and Stockhausen^^^ and Martin ^^^. As regards 

 the general volume of radiant energy received by the eye there is no 

 specific absorption except that already noted due to the aqueous 

 content. Aside from this the numerical proportion of the energy from 

 most soiu'ces specifically absorbed in the eye is very small and is con- 

 fined to the ultra violet region. The human cornea cuts off practi- 

 cally all the energy of w^ave length less than 295 mi. The lens wipes 

 out the remaining ultra violet up to a point between 380 /x/x and 400 ^c/i. 

 The vitreous absorbs strongly in the general region between 250 /jl/j 

 and 300 h/jl in the thickness in which it exists in the human eye. Only 

 a very minute proportion of energy within this range gets through so 

 that the general effect of the absorption in the vitreous in the case of 

 an aphakic eye is to re-enforce that of the cornea, as is well shown by 

 the immunity from abiotic action of the retina in our experiment No. 

 89. In his experiment on the eye of a young rabbit, Martin found the 

 limits of transmission to be about those here noted, except that the 

 lens transmitted freely radiations longer than 350 (x/jl. As the human 

 lens yellows with age its absorption reaches down into the violet, 

 extending even to 420 fifx. 



Eclipse Blindness and Allied Phenomena. 



Every recent eclipse of the sun has given rise to numerous cases 

 of so-called eclipse blindness, due to careless observation of the phe- 

 nomenon in its partial stages, either with the naked eye or with 

 altogether insufficient protection. We should not here consider the 

 matter worthy of attention were it not for the fact that it has been 

 loosely ascribed, like many other imperfectly investigated ocular 

 injuries, to the malign effects of ultra violet light. Eclipse blindness 

 appears in literature as far back as Plato's Phaedo, and is repeatedly 

 mentioned through classical and post classical times as an appar- 

 ently not vmexpected phenomenon. The eclipse of April 17, 1912, in 



