223 FACULTIES OF 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 mah 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- 
