BITTING THE MARK, ETC. 
7 
steel T-square and fine mark, the cylinder being removed 
from the machine and applied between centres as in the wood- 
cut, the actual times of flight are compared with the instants 
of time measured on the paper, correctly, to the 200th of an 
inch.* Next the velocities for the middle point of each interval 
between the screens are calculated. Data are then obtained for 
Fig. 2. 
-comparing the changes in velocity with those which ought to 
arise from a supposed law of resistance for every ten feet of the 
projectile’s flight. The agreement of the calculated with the 
experimental results is then verified. 
From these researches, which, indeed, may be said to form a 
new era in gunnery, it appears as the result of chronographic 
■experiments with some hundreds of rounds of every kind of 
shot used in the service — 
That the diameter being the same, the shot preserves its 
velocity to a greater distance for hitting the mark, as the 
weight is greater. 
That the resistance is less for the same weight as the shot is 
elongated within certain limits. 
That the resistance also varies inversely as the square of the 
diameter. 
That the resistance of the air for velocities used in practice 
(900-1700 f. s.) cannot be expressed by any simple power, or 
* The steel T-square slides along the plate L and the mark b upon it 
being placed accurately upon the successive records of seconds and screens, is 
read off by the vernier (a) to about the ^th of an inch, or 2,000ths of 
a second. The cylinder k is moved from the chronograph before the paper 
record is disturbed. 
