GUNPOWDER : ITS MANUFACTURE AND CONVEYANCE. 
49 
having been selected for the experiment, six or eight holes are 
drilled in one side of it, penetrating to the bore, at intervals along 
its length from the seat of the shot to the muzzle. Through 
each of these holes an insulated wire enters the gun, its lower 
extremity being in contact with but insulated from a sharp 
cutting edge, so arranged in the bore of the gun that the 
passage of the shot would force it down upon the wire and 
destroy the insulation. Each of the wires is connected with the 
secondary wire of an induction coil. The recording apparatus 
consists of a series of discs of polished silver, coated with lamp- 
black, and made to revolve simultaneously by the action of a 
falling weight and multiplying wheels at a very high velocity. 
One of these discs corresponds to each of the wires, the end of 
which is placed in a small discharger close to its circumference. 
On firing the charge the shot cuts the insulation of wire after 
wire in rapid succession, and as each is cut a current passes and 
a spark darts from the discharger to the edge of the revolving 
disc, striking off a speck of the lamp-black, and leaving the 
bright silver bare. Now, supposing the velocity of the circum- 
ference of the discs to be one thousand inches per second, and 
the mark of the electric spark on the second disc to be one inch 
farther on than that upon the first, this would show that the 
shot took the one-thousandth part of a second to pass from the 
first wire in the gun to the next. Similarly, if the distance 
between the marks on the first and last discs were five inches, 
this would indicate that the time the shot took to traverse the 
whole length of the gun was five-thousandths, or one two- 
hundredth of a second. In reality, the time is even shorter than 
this. In the 10-inch gun, a 300-lb. shot, with a charge of 43 lbs. 
of powder, passes down the bore in something less than the 
one two-hundred-and-twentieth part of a second. So delicate 
is this apparatus that, by dividing each inch of circumference 
of the discs into thousandths with the help of the vernier, the 
one-millionth part of a second would become an appreciable 
quantity. 
It is found, by careful experiment with these appliances and 
the crusher gauge (by which pressure is estimated by the com- 
pression of a copper cylinder placed in the bore of the gun), 
that the denser the powder is the slower it burns, giving a 
lower initial velocity to the shot, and exerting a smaller strain 
on the gun. As an instance of the great differences caused 
by the smallest variations in density, we give the following 
results of an experiment with the 10-inch gun, with a charge of 
Initial Velocity, Maximum Pressure, 
Peet per Second. Tons on Square Inch. 
1474 29 
70 lbs. : — 
Density. 
1-732 
1-732 
1432 
21 
VOL. XIV'.— NO. LIV. E 
