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POPULAR SCIENCE REVIEW. 
serves its purpose very well. For proof firing the rails were made 
to incline upwards to the rear, so that the recoil of the gun would 
he checked, and the piece easily run up ; or it might he made to 
return immediately into the firing position. When once the gun is 
mounted on this carriage, there is no necessity for dismounting 
it. It can travel to any part of England, and he brought into 
action wherever it may be desired, so long as the ordinary 
narrow gauge line (4 feet 8 J inches) exists, laid on a permanent 
way of sufficient strength to carry the gun and carriage, whose 
total weight will probably be finally about 118 tons. 
The gun was at first only bored out to a calibre of 14^ inches, 
in order to obtain some experience as to the burning of the 
powder and the behaviour of the projectile before the final 
dimensions were given to the bore. It was brought down to 
the proof butts in Woolwich Arsenal, and fired for the first time 
on September 17 last. 
On this occasion six rounds were fired with a projectile of 
1,160 lbs. weight, and charges of pebble powder composed of 
cubes of 1 J-inch edge, the weight of the charge gradually in- 
creasing from 170 lbs. up to 240 lbs. There is no occasion to 
enter into the exact details of each round ; it is preferable to 
keep to the object and general results obtained. As mentioned 
above, the pressure in the bore of the gun was to be kept, if 
possible, nearly about 25 tons per square inch, and the velocity 
was to be brought as high as possible consistently with this con- 
dition. It has been already explained that the velocity is 
obtained by measuring the time occupied by the shot in passing 
over the space between two screens, a current of electricity 
being broken or interrupted momentarily as the shot cuts the 
wires of each screen. The pressure was measured by pressure 
gauges fixed in the base of the projectile and the bottom of the 
bore of the gun. 
The charges were 170, 190, 210, 220, 230, and 240 lbs., 
which gave pressures on the ball of the shot of 19*4, 18*2, 19*8, 
21*4, 21*8, and 27*3 respectively, with 24*2, 23*3, 24*8, 22*2, 
and 29*6 on the bore for the first five rounds. The velocities at 
the muzzle were 1,393, 1,423, 1,475, 1,503, 1,550, and 1,550 
feet per second. These must be considered good, although as 
yet the weight of the projectile was but small. A velocity of 
1,550 feet is a very high one for a rifled shot. Smooth-bore 
guns occasionally fire round shot at higher velocities ; but. the 
projectile is very light compared with the charge, is easily pro- 
jected, and loses its velocity rapidly. Those unused to these 
sort of statistics may form a good idea of the speed of a gun- 
shot, from the circumstance that an enemy’s shot comes to you 
rather before the report of the guns. You see the flash, but 
the shot has whizzed past you and done its work so far before 
