ht, and hence the depth of
flotation of the plunger, the same being filled or emptied by the
pump, P. N is the hold for merchandise, partitioned off from the
boiler room as shown.

[Illustration: Fig. 1.--TOMMASI'S HEMI-PLUNGER]

[Illustration: Fig. 2.--THE HEMI-PLUNGER, THE SUBMERGED PORTION]

From the plunger, A, rise two hollow columns, E, to which metallic
plates, F, are attached to diminish friction through the water. These
support the upper division or platform, B. The second shaft (not
lettered), which rises above the platform in Fig. 1, serves to
ventilate the plunger. The columns, E, serve as shoots down which
merchandise is lowered to the compartments, N; and their upper ends
are received in two immense inverted cups attached to the bottom of
the part, B. Through these cups pass large screws, which confine the
columns so that, by removing the connection, the whole submarine
apparatus may in case of necessity be freed from the upper works. On
each side of the platform, B, which is of elliptical figure, is a
large float, seen in Fig. 3, which, by means of racks and gearing, may
be raised or lowered at will. Usually these floats are carried at a
height of a yard above the water. In calm weather, this distance is
increased, and in storms it is diminished, the object of the floats
being to keep the whole vessel on an even plane, and to prevent too
violent oscillations. In order to facilitate navigation in shallow
water, the columns, E, may be made telescopic, and operated by
hydraulic apparatus, so that they may be shortened at will. Any form
of engine or propeller may be used.

[Illustration: Fig. 3.--THE HEMI-PLUNGER ON A VOYAGE]

Besides the advantage of the vessel being unaffected by waves, since
its submerged portion travels far below them, the inventor claims that
it will meet less resistance from the water than would a vessel of
corresponding volume sailing on the surface. It will make faster
progress, because it has no waves to mount and descend; and hence it
always travels in a nearly right line. The screw being submerged at a
great depth will not tend to turn the vessel from her straight path.
The platform being easily detachable may serve as a raft in case of
injury to the submarine boat. For fast travel, on lakes, rivers, and
shallow water generally, M. Tommasi proposes to support his platform
on two floats which rest on the surface of the water. No weight,
therefore, is thrown on the submarine ve