74 
RAPIDITY OF FLIGHT. 
be obtained by 
the usual mode 
of measuring tri- 
angles. Thus, 
let b c be the 
height of the 
tower, and a 
— * A the point from 
whence the Star- 
ling rose, flying to the point B. Knowing the height of the 
tower and the distance A c, we have to calculate a b, which 
is easily learned, since by the well-known problem of Euclid, 
a B 3 = a c 2 4- b c 2 ; by extracting the square root, we there- 
fore find the exact length of a b. 
It was by an application of this simple rule that the flight 
of an eagle was ascertained to be little short of one hundred 
and forty miles an hour. The bird was seen hastening on 
its way over a valley in the Pyrenees, and the number of 
seconds was observed which elapsed between its passing from 
the summit of one high point till it reached the brow of a 
mountain on the other side, the space between which was 
known by reference to a good map, in which the distances 
were well laid down. Such a rapid progress, we are aware, 
will scarcely be credited; but a celebrated naturalist, in 
speaking of the large white Pishing Eagle of North America, 
gives reasons for suspecting that its speed is still greater : he 
says, that, from an immense height, on perceiving their prey, 
they glide downwards with such rapidity as to cause a 
mighty rushing sound, not unlike that produced by a violent 
gust of wind passing among the branches of trees ; and that 
the fall of this bird, enormous as it is, Ban on such occasions 
be scarcely followed by the eye.* Those who ride over com- 
mons of fine turf may often have witnessed a quickness of 
flight, probably not much inferior to these Eagles ; for they 
will, even at their fullest speed on the fleetest horse, have 
seen Swallows skimming in all directions, pursuing the small 
* Audubon. 
