The boat which the other day twice crossed the Channel between Dover and Calais affords an example of the rapid progress which has lately been made in the science of electricity. This little craft, which is only thirty-seven feet in length, glided over the water with no visible means of propulsion. The voyage was an experimental one, and was designed to show that this plan of electrical propulsion was as practicable on the sea as before it had been proved to be on inland waters. Such a boat could, say her promoters, be carried hanging to the davits of a ship, and be ready for immediate use. The required electrical current is derived from accumulators, or secondary batteries, stored and acting as ballast beneath the deck floor of the little vessel. These require to be charged by a dynamo machine at intervals, and such a charge this Channel trip amply proves will suffice for a run of between forty and fifty miles. Supposing that the system were adopted for torpedo vessels, it is obvious that this amount of storage capacity would be far more than sufficient for ordinary needs. Another vessel which obtains its motive-power from a very different source, but which must also be looked upon as an experimental boat, has been invented and built by Messrs Secor of Brooklyn. Unlike the electric boat, it possesses no screw propeller or other moving parts. But it is furnished on each side with open ports below the water-level, which are in communication with an ‘exploding chamber.’ This chamber is constructed of steel, and is capable of sustaining an enormous internal pressure. It is filled with charges of petroleum vapour and air under pressure, and this explosive mixture is ignited by electricity. It will therefore be seen that the propelling apparatus of this boat may be compared to a gas-engine; but the explosions, which occur several times in a minute, instead of forcing forward a piston to act upon a fly-wheel, impinge upon the water at the stern of the vessel, and so push the boat forward. Should this method of driving a vessel through the water prove efficient, it will certainly be economical, for little more than half a barrel of petroleum will suffice for a twenty-four hours’ run.