194 Idle Days in Patagonia. 
some time, as they will when an owl is confronted 
with strong sunlight; and this gave me the im- 
pression that the fiery, 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: “* Kyes certainly do shine in the dark— 
some eyes, e.g. 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 scintillation. 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 retinz 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 pro tanto 
brightened into sparks. Seeing how little we 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—some historical—of human eyes flashing fire 
and blazing with wrath, are mere poetic exaggera- 
