In the meantime M. Paixhans had made further progress toward perfecting the details of his shell gun system. A _canon-obusier_ of 80 pounds was made to his design, a chambered howitzer of the same weight (about 72 hundredweight) as the French 36-pounder truck gun and of 22 centimetres calibre. This was designed to project a hollow shell of the same size as the French 80-pound solid shot, but weighing, when its cavity was filled with a charge of 4 pounds of powder, 56 pounds French (62½ pounds English). The shell gun itself was of a distinctive shape. The characteristics of short chase, large bore, a chamber, a small propelling charge, and a scientific elimination of all useless metal, resulted in a form of ordnance quite different from that of the long-accepted smooth-bore cannon. It was easily recognizable by its straight muzzle, smooth lines and the absence of the usual ornaments and reinforcing rings. When, eventually, the New Arm was adopted by other powers, their shell guns too, though independently evolved, were found to exhibit the same external features: the features of what came to be known universally as a “Paixhans gun.” The terrific effect of charged shell, fired from this form of gun with sufficient velocity to find a lodgment in a ship’s timbers, was demonstrated at Brest in 1821 and 1824; in the latter trials the target being a frigate, the _Pacificateur_, moored in the roadstead. High range and accurate shooting were obtained. The incendiary effect of the shell was prodigious: so impressive, indeed, that in spite of a strong opinion in the French navy against further carriage of bombs in ships-of-the-line, the Commission recommended “that _canons-à-bombe_ be adopted, even in ships-of-the-line, but in small numbers.” But though the principle of the shell gun was accepted by experts, public opinion was not yet ready for the change. The Commission had shown a sage circumspection in regard to the extent of the change proposed; but public opinion was not yet satisfied that the new arm was sufficiently safe. The scheme suffered a long postponement. In the meantime several further trials were held. The design of the piece was again modified; a larger chamber was arranged and a support was cast, at the commencement of the chase, for carrying a sight. Tests _à outrance_ were made to find what maximum charge such a shell gun would safely stand; and at last, in 1837, the principle of shell fire was accepted by the government, the Paixhans gun being assigned a place in the prescribed armament of the fleets of France. To the impairment of the unity-of-calibre principle, lately achieved, shell guns of 22 centimetres were admitted as part-armament of ships the greater number of whose pieces were 30-pounders firing solid shot. [Illustration: A PAIXHANS GUN] §