248 FACULTIES OF BIRDS. 
soaring to an altitude. In this situation, their prey 
on the ground is seen by them, however minute it 
may be, and their appearance is merely their de- 
scent from high regions of the atmosphere to within 
the scope of our optics.” 
With respect to the smell of vultures, Willoughby 
says, ‘they have an excellent sagacity of smelling 
above all other birds, so that they can perceive the 
savour of dead carcasses from far,” to which Ray 
adds, ‘‘ many miles off they say.”* Somé of the old 
authors, indeed, such as Thomas Aquinas, specify 
the distance at which a vulture can scent out a 
dead body to be five hundred miles, and Isidore al- 
leges it is no matter even if the sea itself intervene. 
It may well be disputed, however, that the smell 
of the vulture or any other bird extends to the dis- 
tances alleged by these writers, for, as was long 
ago remarked by Celius Rhodiginus, odorous efflu- 
via cannot be distinguished at any considerable dis- 
tance, as they are not only diluted by being diffused 
in the air, but may even be thereby wholly changed 
in their qualities. The observations of Avicenna 
are still more to the point. “I have,” he says, 
“ observed vultures wheeling about in the air, and, 
of course, their vision must be extensive, to enable 
them to see from a higher elevation than the highest 
mountains, since they can in such circumstances 
discern a piece of carrion in the plains below them. 
But if it is denied that colours can be perceived at 
such distances, much more ought the same to be 
affirmed of odours, whose power is weaker than 
that of colours.” 
From all these various facts, we think Dr. John- 
son’s remarks are decidedly the most plausible; 
and even those authors who speak in the most un- 
hesitating manner of the powers of smell, furnish 
from their own accounts circumstances to prove 
* Ornith., by Ray, p. 66. 
