2 
THE SMALL-ARMS OE EUROPE. 
vacuo, the parabolic arc AB'C'B' (Fig. 1), of which the horizontal 
projection is x p3 is given by the formula 
t z= p 
V cos (f) 
During the same time t, the bullet will, in air, have described a 
trajectory ABCD , the projection of which, x 3 will be less than x v . We 
then have 
x / x a \ m 
V cos (j> \a? a — x) 
( 1 ) 
That is to say, in order to retain the same value for t, x must be 
multiplied by a factor which is greater than unity : which re¬ 
presents the action of the air, and must consequently become equal to 
( x \ m 
—= 1, either when 
x a — xj 
Fig. l. oo 
