er the fire of
our guns, so that they cannot be removed by the enemy. These torpedoes
are generally exploded by electricity from batteries located in
casements on shore, these casements being connected with the torpedoes
by submarine cables. It is easy to see how the torpedo may be so
arranged that when struck by a ship the electric current will be
closed, and, if the battery on shore is connected at the same instant,
an explosion will take place; on the other hand, if the battery on
shore is disconnected a friendly ship may pass in safety over the
torpedoes. Many ingenious contrivances have also been devised by which
the torpedo may be made to signal back to the shore station either
that it has been struck or that it is in good order for service, in
case the enemy should undertake to run over it. One simple plan for
this is to have a small telephone in the torpedo with some loose
buckshot on the diaphragm, which is placed in a horizontal position,
and will be slightly tilted as the torpedo is moved about by the
waves. By connecting the shore end of the cable with a telephone
receiver, the rolling of the shot may be distinctly heard if the
torpedo is floating properly, but if sunk at its moorings, or if the
cable is broken, no sound will be heard.

The use of torpedoes involves the use of both electricity and high
explosives, and a careful study based upon actual experiments has been
carried on for many years, by the engineers and naval officers in all
civilized countries. Some of these experiments have supplied
interesting and useful data, for the use of the agents in question,
for various industrial purposes.

Another form of torpedo is that known as the locomotive torpedo, of
which there are several kinds; some are propelled by liquid carbonic
acid, which is carried in a strong tank and acts through a compact
engine in driving the propeller. One of these is steered by
electricity from the shore, and is known as the Lay-Haight torpedo,
and can run twenty-five miles per hour. The Whitehead torpedo is also
propelled by liquid carbonic acid, but is not steered from shore. Its
depth is regulated by an automatic device actuated by the pressure of
the water. The Howell torpedo is driven by a heavy fly wheel which is
set in rapid rotation just before the torpedo is launched. It has but
a short range and is intended for launching from ships. Another
torpedo is propelled and steered from shore by rapidly pulling out of
it t