important of the mortar's defects and makes the fire accurate from
long ranges down to within a few yards of the gun. It is obvious that
the pressure can be usefully controlled in two ways: (1) by keeping
the elevation of the gun fixed and using a valve that can be set to
cut off any quantity of air, according to the range desired; (2) by
keeping the pressure in the reservoir constant, and using a valve
which will cut off the same quantity of air every time, changing the
elevation of the gun according to the distance. Another important
discovery consists in the application of subcalibered projectiles for
obtaining increased range.

The gun is smooth-bored and a full-sized projectile is a cylinder with
hemispherical ends, to the rear of which is attached a shaft having
metal vanes placed at an angle, which causes the projectile to revolve
round its longer axis during flight. A subcalibered projectile,
however, being of less diameter than the bore of the gun, has the
vanes on its exterior, and is held in the axis of the gun by means of
gas checks which drop off as the projectile leaves the muzzle. The
shock to the explosive is, of course, greater than in the full-sized
projectile, but the increase can be calculated, and so far a dangerous
limit has not been reached. From the fifteen-inch gun with a pressure
of 1,000 pounds per square inch and a velocity of about 800 f.s., a
range of 4,000 yards has been obtained at an elevation of 30° 20, with
a ten-inch subcalibered projectile, about eight calibers long and
weighing 500 pounds. This projectile will contain 220 pounds of
blasting gelatine. With improved full-sized projectiles weighing 1,000
pounds, a range of 2,500 yards will doubtless be obtained.

At elevations below 15° these long projectiles are liable to ricochet,
and what is now wanted is a projectile which will stay under water at