126 
SHORT NOTES ON PROFESSIONAL SUBJECTS, 
The action of the apparatus is as follows :—■ 
Upon the explosion of the charge, the gas, acting on the area of the piston, 
crushes the copper cylinder against the anvil. The amount of compression which 
the copper thereby sustains becomes an indication of the pressure. The area of 
the copper cylinders found most suitable with the 8-inch gun was ^ of a square 
inch, while the area of the piston was of a square inch. 
A series of experiments having been made by means of a testing machine to 
determine the pressure required to produce a definite amount of compression in 
copper cylinders corresponding to those used in the instrument, the tabulated 
results furnished a means of comparison whereby the amount of compression 
produced in the “ crusher ” becomes a direct indication of the pressure at that part 
of the bore where the plug is inserted. 
The committee found that much greater dependence could be placed upon the 
results furnished by this apparatus than upon those obtained with the “ Hodman 51 
gauge. 
The Gun and Projectiles. —The gun employed in the experiments now under 
discussion was an 8-inch wrought-iron muzzle-loading gun of 6J tons, having a 
length of bore of 126 ins. 
It was tapped at three places in the powder chamber, to receive either “ Rodman ” 
or “ crusher ” gauges. These holes could be closed with solid plugs when not 
required. The cutting plugs belonging to the chronoscope were fourteen in number, 
and were fitted into holes at various intervals along the bore. When not required, 
those holes were closed with solid plugs. With a 20 lbs. charge, and a shot 15 ins. 
in length, the projectile, when rammed home, was flush with the edge of No. 1 
plug. When battering charges were used, the projectile was flush with No. 2, 
which then became the first plug of the series. 
Six cutting plugs were used in each observation, those of the breech and those 
of the muzzle being alternately employed. The projectiles used were cast-iron 
cylinders of 15 ins. in length, 180 lbs. weight, and 7‘975 ins. diameter. 
The loading of the gun was conducted as follows :— 
The cartridge was made up to the full diameter of the bore; it was then inserted 
into the shot chamber, the projectile was next pushed home gently until a stop on 
the rammer came into contact with the face of the muzzle; thus, the head of the 
shot was brought to the same position in each round, and the cartridge always 
touched the base of the projectile. 
The “ Rodmans/’ “crushers,” and cutting plugs were then inserted into their 
respective holes and screwed home. 
Finally, the wires of the cutting plugs were connected with the main wires 
leading to the instrument, and the tube inserted in the vent. 
After the discharge, the first operation was to w r ash out the gun; all the plugs 
were then removed, and the holes dried preparatory to another round. 
The coppers were taken from the “Rodmans” or “crushers,” stamped with 
the number of the round, and the measurements recorded. 
From the various descriptions of powder which have been experimented with, 
up to date, four kinds have been selected for the purpose of this preliminary report, 
as furnishing good illustrations of the different results obtained with battering 
charges of different kinds of powder; these are :— 
(1) R.L.G. service powder, 
(2) Pellet service powder, 
(3) Russian prismatic powder, 
(4) Pebble powder No.. 5, 
