Blasting gelatine.......................... 1.45
Forcite " .......................... 1.51
Dynamite No. 1............................. 1.6
Wet gun-cotton............................. 1.32
Dry " ............................. 1.06
Gunpowder.................................. 0.9

Their relative efficiency under water per cubic foot, according to
Bucknill, is as follows:

Blasting gelatine.......................... 1.38
Forcite " .......................... 1.27
Dynamite No. 1............................. 1.00
Dry gun-cotton............................. 0.66
Wet " ............................. 0.66
Gunpowder.................................. 0.14

The wet gun-cotton has twenty-five per cent. of added water.

Mines for harbor defense are of two kinds--buoyant and ground. The
buoyant are usually spherical, and contain from 400 to 500 pounds of
explosive. They bring the charge near to the ship's bottom, but are
difficult to manage in a tideway, and can be easily found by dragging.
The ground mines can be made of any size and are not easily found by
dragging, but are of little value in very deep water. They are either
cylindrical or hemispherical in shape, and contain from 500 to 1,500
pounds of explosive in from thirty to eighty feet of water. Mines of
any kind are exceedingly difficult to render efficient when the water
is over 100 feet deep. On account of the tendency of all high
explosives to detonate by influence or sympathy, and the liability of
the cases to collapse by great exterior pressure, harbor mines are
separated a certain distance, according as they are buoyant or ground,
and according to the nature of the explosive.

Five hundred pounds buoyant gun-cotton mines require 320 feet spacing.

Five hundred pounds buoyant blasting gelatine mines require 450 feet
spacing.

Six hundred pounds ground gun-cotton mines require 180 feet spacing.

Six hundred pounds ground blasting gelatine mines require 230 feet
spacing.

Of torpedoes, other than those described, we have several modern
varieties; submarine projectiles, submarine rockets, automobile and
controllable locomotive torpedoes. The first two varieties, though
feasible, are not developed and have not yet advanced beyond the
experimental stage. Of the automobile, we have the Whitehead,
Swartzkopf and Howell. The first two are propelled by means of
compressed air and an engine; the last by the stored-u