The novel form of vessel, to which the above odd name has been given by its inventor, M. Donato Tommasi, of Paris, France, is a combination of a boat wholly submerged with a raft: a connecting link, to borrow the naturalist's expression, between the submerged torpedo boat and the monitor. The advantages which are expected to be realized from this hybrid craft, the inventor describes as follows: "It is evident that a vessel, plunged several yards below the surface of the sea, is no longer influenced by wind or wave. Let the sea be agitated, let there be the most violent tempest, yet the boat which navigates under water will never be wrecked, for the same reason that a fish cannot be drowned. * * * What a beautiful vision, that of traversing the ocean, as a balloon floats through the air, with the same tranquillity, without shocks, without the insupportable rolling and pitching!" etc. The construction of the invention introduced in this glowing manner will be understood from Figs. 1 and 2. A is the plunger cylinder, shown with its side broken away in Fig. 2. In Fig. 1, G is the rudder, H the propeller, and I the tube through which sea water passes to the pump. In Fig. 2, C is the smokestack, M M are compartments in which water may be admitted to increase the weight, 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]