pulley, K, and reaches the sounding lead, S, after traversing a guide,
g, where there is a small sheave upon which it can bear, whatever be the
inclination of the boat. The wheel, B, carries upon its axle an endless
screw that sets in motion two toothed wheels that indicate the number
of revolutions that it is making. One of these marks the units and the
other the hundredths (Fig. 5). This last is graduated up to 10,000
meters. As every revolution of the wheel, B, corresponds to one meter,
the number indicated by the counter represents the depth. Upon the axle
of the winding pulley there is a break pulley, p. The brake, f, is
maneuvered by a lever, L, at whose extremity there is a cord, C, which
is made fast to the carriage, A. When, during the motions due to
rolling, the tension of the steel wire that supports the lead diminishes
or increases, the carriage slightly rises or falls, and, during these
motions, acts more or less upon the brake and consequently regulates the
velocity with which the wire unwinds. When the lead touches bottom, the
wire, being suddenly relieved from all weight (which is sometimes as
much as 70 kilos), instantly stops.

[Illustration: FIG. 4.--GENERAL VIEW OF THE SOUNDING APPARATUS IN THE
"TALISMAN:"]

The maneuver of this apparatus may be readily understood. The apparatus
and its weights are arranged in the interior of the vessel. A man bears
upon the lever, L (Fig. 3), and the counter is set at zero. All being
thus arranged, the man lets go of the break, and the unwinding then
proceeds until the lead has touched bottom. During the operation of
sounding, the boat is kept immovable by means of its engine, so that the
wire shall remain as vertical as possible. The bottom being reached, the
unwinding suddenly ceases, and there is nothing further to do but read
the indication given by the differential counter, this giving the depth.