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 light. 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 light- 

 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 flying before him would affect him as the 

 gleam of a lamp placed high above the surface 



