194 I(^l<i Days in Patas;onia. 



some time, as tliey will when an owl is confronted 

 with strong sunlight ; and this gave me the im- 

 pression that the fieiy, flashing appearance was 

 accompanied with, or followed by, a burning or 

 smarting sensation. I will here quote a very 

 suggestive passage from a letter on this subject 

 written to me by a gentleman of great attainments 

 in science : " Eyes certainly do shine in the dark — 

 some eyes, c;/. those of cats and owls ; and the 

 scintillation you speak of is probably another form 

 of the phenomenon. It probably depends upon 

 some extra-sensibility of the retina analogous to 

 what exists in the molecular constitution of sulphide 

 of calcium and other phosphorescent substances. 

 The difficulty is in the ■scintilJatioii. We know that 

 light of this character has its source in the heat 

 vibrations of molecules at the temperature of in- 

 candescence, and the electric light is no exception 

 to the rule. A possible explanation is that supra- 

 sensitive retinas in times of excitement become 

 increasedly phosphorescent, and the same excite- 

 ment causes a change in the curvature of the lens, 

 so that the light is focussed, and j^ro tmito 

 brightened into sparks. Seeing how little Ave know 

 of natural forces, it may be that what we call light 

 in such a case is eye speaking to eye — an emanation 

 from the window of one brain into the window of 

 another." 



Probably all those cases one hears and reads 

 about — soiue historical — of human eyes flashing fire 

 and blazing with wrath, are mere poetic exaggera- 



