176 The Naturalist in La Plata. 
for their protection actually serve to attract the 
beasts of prey, but the confusion and fear caused by 
the bright glare makes it safe for the traveller to 
lie down and sleep in the hght. Mammals do not 
lose their heads altogether, because they are walking 
on firm ground where muscular exertion and an 
exercise of judgment are necessary at every step ; 
whereas birds floating buoyantly and with little 
effort through the air are quickly bewildered. 
Incredible numbers of migratory birds kill them- 
selves by dashing against the windows of lght- 
houses; on bright moonlight nights the voyagers 
are comparatively safe; but during dark cloudy - 
weather the slaughter is very great; over six 
hundred birds were killed by striking a lighthouse 
in Central America in a single night. On insects 
the effect is the same as on the higher animals: on 
the ground they are attracted by the light, but 
keep, like wolves and tigers, at a safe distance 
from it; when rushing through the air and unable 
to keep their eyes from it they fly into it, or else 
revolve about it, until, coming too close, their 
wings are singed. 
I find that when I am on horseback, going at a 
swinging gallop, a bright light affects me far more 
powerfully than when I am trudging along on foot. 
A person mounted on a bicycle and speeding over 
a level plain on a dark night, with nothing to guide 
him except the idea of the direction in his mind, 
would be to some extent in the position of the 
migratory bird. An exceptionally brilliant ignis 
fatuus flymg before him would affect him as the 
gleam of a lamp placed high above the surface 
