RAPIDITY OF FLIGHT. 
89 
Again, suppose some Starlings are seen feeding 
in a field at a, at no great distance from a cliurcli 
tower, b c, in wliich 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 he obtained by the usual mode of measuring 
triangles. Thus, let bc he 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 ac, we have to calculate ab, which 
is easily learned, since by the well-known problem 
of Euclid, ab 2 - ac 2 + 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 
