90 



RAPIDITY OF FLIGHT. 



Again, suppose some Starlings are seen feeding 

 in a field at A, at no great distance from a church 

 tower, B c, in which they are building; or a Crow 

 flies from a certain spot to the top of a tree; we 

 may proceed in the same manner: for the height of 

 the tower or tree will, in most cases, he too incon- 

 siderable to make any material alteration in the 

 result, though, if greater accuracy is required, it 

 may be obtained by the usual mode of measuring 

 triangles. Thus, let BC be the height of the tower, 

 and A the point from whence the Starling rose, flying 

 to the point B. Knowing the height of the tower and 

 the distance A c, we have to calculate AB, which 

 is easily learned, since by the well-known problem 

 of Euclid, AB 2 r= AC 2 -f BC 2 ; by extracting the 

 square root, we therefore find the exact length 

 of AB. 



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 



