74 RAPIDHT OF FLIGHT. 



be obtained by 

 the usual mode 

 of measuring tri- 

 angles. Thus, 

 let B c be the 

 height of the 

 tower, and 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 2 = A c 2 + 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 Fishing 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, can on such occasions 

 be scarcely followed by the eje* 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. 



