dial is set, so that when the torpedo is steering direct for the object to
be struck, or other desired point, one end of the needle of the compass,
P, is between the steeds, _p_, but contact with neither, the needle of
course pointing to the magnetic north. Should the torpedo however deviate
from this course, the needle makes contact with one or other of the studs
according to the direction in which the deviation takes place, and
completes the circuit through the corresponding electromagnet, which
attracts the armature and causes the disk to move, so as to diminish the
supply of water to one motor and increase it to the other, and so cause
the torpedo to again assume the required direction. Supposing the object
which it is intended that the torpedo should strike be a large mass of
iron, such as an ironclad, the needle will be attracted, and, making the
corresponding contact, will cause the torpedo to be steered directly away
from the object. In order to prevent this, a second compass, Q, is mounted
in the front of the torpedo, and when attracted by a mass of iron, it
short-circuits the battery, D, and thus prevents the armature being
attracted, and consequently the torpedo from deviating. This needle is
also capable of slight movement in a vertical plane, so that when passing
over or under a mass of iron it is attracted downward or upward, and
completes a circuit by means of the stops, which operate so as to explode
the charge. The charge can also be exploded in the ordinary manner, viz.,
by means of the firing pin, X, when the torpedo runs into any solid
object.

The depth at which the torpedo travels below the surface of the water is
regulated by means of a flexible diaphragm, M, secured in the outer casing
and connected to a rod sliding freely in fixed bearings. A spiral or other
spring, O, is compressed between a color on the rod and an adjustable
fixed nut, by which the tension of the spring is regulated so that the
pressure of water on the diaphragm, A, when the torpedo is at the desired
depth just counterbalances the pressure of the spring, the diaphragm being
then flush with the outer casing. The rod is connected by suitable levers
to two horizontal fins, S, pivoted one on either side of the torpedo, so
that they shall be in equilibrium. Should the torpedo sink too deep or
rise too high, the diaphragm will be depressed or extended, and will
operate on the lines so as to cause the torpedo to ascend or descend as
t