were fired from the six-inch quick-firing gun, with a muzzle velocity of nearly nineteen hundred feet per second, which completely perforated three inches of steel and burst behind the plate. Encouraged by these results, this system was adopted by our army officials, but, on trial in larger calibers at Sandy Hook, it gave rise to premature explosions, and the tale of disaster reached its climax on April 29, 1899, when Captain Stuart, of the Ordnance Corps, was superintending the loading of a twelve-inch torpedo shell with wet gun cotton by compressing it into the shell, for an explosion resulted which killed four men instantly and fatally wounded two others, Captain Stuart being one of them. [Illustration: SIMS-DUDLEY PNEUMATIC GUN, LIMBERED UP. (Courtesy of the Scientific American.)] [Illustration: SIMS-DUDLEY PNEUMATIC GUN, IN BATTERY. (Courtesy of the Scientific American.)] [Illustration: TYNDALL’S BRONZE BELL-MOUTHED GUN.] The history of the attempts made to use nitroglycerin, dynamite, explosive gelatin, and explosives of this class as bursting charges for shell fired from service guns is even less satisfactory than that given for gun cotton. It is not surprising, therefore, that inventors should have proposed catapults, slings, rotary wheels, and other means for projecting these powerful agents into the enemy’s midst, but the Mefford air gun, as mounted on the United States steamship Vesuvius, and the Sims-Dudley gun, in which a reduced charge of powder is fired in a chamber exterior to the gun proper, were deemed to possess sufficient merit to warrant their trial in the field. These devices were employed in the recent war with Spain, the pneumatic guns on the Vesuvius being used to throw shells containing three hundred pounds of gun cotton, while the Sims-Dudley guns were used on land to throw small charges of dynamite or explosive gelatin; but, beyond frightening the enemy by the startling character of their reports, these superficial charges produced no serious effect. [Illustration: MIRROR OR REFLECTOR IN WHICH TO FIRE GUN COTTON.]