In time of war the boat would destroy the keels of the enemy’s ships. At the port-holes were placed big cannon. An arrangement of packing with a plug valve prevented the introduction of water. At the moment of firing the guns were brought close to the openings and the plug-valve was raised; after the shot had been discharged the plug fell automatically back to its place. In order to replenish the air pneumatic machines and ventilators would be used; for steering, the compass would act as well beneath the waves as on the surface; for lighting, phosphorescent bodies would be used. The boat was to have wheels and was to be moved by means of oars. Mersenne was the first to affirm that even the most violent tempests could not be a source of danger to the submarine vessel as the disturbance was felt but a little distance below the surface. [Illustration: RACING THE “CAMPANIA.” Apostoloff’s Proposed Submarine. ] Another monk of the same order, Father Fournier, about the year 1640 gave to the world his ideas on the problem of navigating beneath the water. In the year 1653 a Frenchman, whose name we have been unable to discover, is said to have built and operated a submarine boat at Rotterdam. It was 72 feet long, 12 feet high, and 8 feet broad. It was traversed down its entire length by a system of very solid girders whose extremities projecting beneath the bottom were covered with iron. Ordinarily the boat was not meant to be submerged lower than the “awash” condition, but the part above the water was made to slope with the idea of turning aside the projectiles aimed at it. In the centre of the boat was a kind of paddle wheel, but the inventor was careful to keep many details secret regarding its propulsion and its method of attack. For some little time he showed his invention for a small pecuniary remuneration, but it failed to attract the notice of those in authority. In the _Annual Register_ of the year, 1774, at page 245, there appears an authentic account of a late unfortunate transaction with respect to a diving machine at Plymouth. This relates to the death of a Mr. Day who lost his life in a boat of his own construction in Plymouth Sound. [Sidenote: Day.]