190 
MINUTES OF PROCEEDINGS OF 
the gun. When the gun recoiled it drew back a tracing point which marked 
a straight line on the surface of the cylinder at rest. If, whilst the gun was 
stationary, the cylinder was made to rotate, the tracing point described a 
circle on the surface of the cylinder. If now the cylinder be made to rotate 
rapidly, and left to itself, and if the gun be fired, the point will trace out 
a curve on the surface of the cylinder, the ordinate of which will represent 
the time occupied by the gun in recoiling through a space equal to the 
abscissa. The law of the work done to produce the recoil thus becomes 
known. By measuring the initial velocity of the shot, the total amount of 
the work done by the powder is found. The law of the pressure of the gas 
would be found with greater exactness if the tracing point was connected 
with the projectile. This method of experimenting seems to be the only 
one likely to give a satisfactory result, for if the rotation of the cylinder be 
uniform for the very short time the explosion is in progress, there can be 
no doubt that the co-ordinates of the diagram would give us a connexion 
between the time and space, and knowing the weight and velocity of the 
moving body at any one point, we can tell the amount of pressure that was 
acting upon it at any instant, or for any position. From what has been said, 
it is evidently of great importance in the proof of gunpowder, that besides 
the trial for initial velocity, there should be some test of the stress thrown on 
the gun. 
The law of penetration of iron plates by hardened steel shot is another 
purely mathematical question. When a particular form of head of shot has 
been decided upon, and when a satisfactory method of hardening the shot 
has been discovered, it will be an easy matter to determine the laws which 
govern the perforation of iron plates. The quantities to be connected are 
the velocity, the weight, and the diameter of the shot, and the thickness of 
the iron plates. It is probable that a series of experiments conducted with, 
plates of tolerably good iron of a uniform quality would be sufficient to 
afford all necessary information. A few comparative experiments might be 
made with plates of different qualities of iron but of equal thicknesses. 
When opportunity offers, it is intended to repeat and extend the experi¬ 
ments of Bobins and Hutton with the whirling machine. It is evident that 
this chronograph would give the exact time of each revolution of the machine 
from rest up to the attainment of uniform motion. Each experiment would 
thus afford a determination of the law of resistance of the air to the motion 
of the particular form of body. If a sufficient fall could be obtained it 
would be easy to make some very exact experiments on the force of gravity 
and the resistance of the air at low velocities. Comparative experiments 
on the velocity of shot and the velocity of the sound of the explosion of the 
gun may be made, provided the concussion of the air can be caused to break 
for a moment a galvanic current. If this can be done, the time occupied by 
the sound in passing over every successive 100 feet can be measured; and 
when the law r s of resistance of the air have been determined, it is probable 
that the simplest instrument that can be used to find mere initial velocities 
will be one which measures the comparative velocities of the shot and the 
sound of the explosion. 
The chronograph here described was contrived solely with a view to the 
satisfactory measurement of the velocities of bodies, and the determination of 
the resistance of the air to their motion, and without the slightest concern about 
