222 FACULTIES OP BIRDS. 



bles. Systematic writers afford little information 

 on the subject ; but we have abundant proof of this 

 intensity of vision from other sources. We may, 

 however, reasonably doubt the fact of its fixing its 

 gaze upon the sun, the " naked sun," as Petrarch 

 gives it, even though the authority of Scaliger tells 

 us that having " repeatedly placed an eagle in the 

 sun, it gazed on its rays for a long time intensely 

 and pertinaciously." It does not appear what mo- 

 tive can induce the bird to gaze on the sun, even if 

 it have the power. Larks, indeed, and some other 

 small birds, are attracted by bright objects, as is 

 proved by what birdcatchers call daring, that is, fix- 

 ing a piece of looking-glass on a moveable pivot 

 and whirling it round ; but in this case it is probable 

 the larks are allured by the principle of curiosity so 

 very lively in birds. On the general physiological 

 principle, also, that the more stimulus an organ can 

 bear the less sensible it must be, we may conclude 

 that the two circumstances of piercing sight and ca- 

 pability to gaze on the sun are incompatible. Ac- 

 cordingly, we find that animals which prey in the 

 night, and white animals with red eyes (albinos), 

 while they can see with a faint glimmer of light 

 on account of their extreme sensibility of vision, 

 are so overpowered by the glare of the sun's light 

 that they can scarcely see at all. 



There is, indeed, a peculiarity in the eyes not only 

 of the eagle, but of all birds, tending to defend them 

 from too strong light, to which it may be interest- 

 ing to advert. In the eye of man and many other 

 animals, including birds, a beautiful provision is 

 made for supplying it with the moisture which is 

 indispensable to render its restless motions easy. 

 For this purpose a fountain or gland, situated in man 

 within the upper and outer part of the bony socket, 

 affords a constant supply of tears, about three or 

 four ounces of which it has been computed are 

 discharged upon the human eyeball every twenty- 



