Safe to be opened by Detonation of Nitroglycerin. Before the charge was fired. long-used form of fuse, no provision has yet been made to supply the service with charges for its costly armor-piercing projectiles.
Happily, the force resident in explosives may be applied to the saving as well as to the destruction of human life, advantage having long since been taken of the penetrating power of the report from the discharge of a gun to employ them as signals of distress at sea or as warnings in foggy weather. The English Lighthouse Board, under Professor Tyndall's guidance, some years ago sought to find the form of gun best suited to this purpose, and their experiments led them at first to a bronze gun with a bell-shaped mouth. Subsequently, their attention being called to the sharpness and carrying power of the report from detonating gun cotton, an apparatus was devised in which the gun cotton was detonated in the focus of a parabolic mirror. The best results, however, 
After firing Charge. were attained with rockets carrying gun-cotton charges arranged to be exploded in mid air.
Guns have also been arranged for projecting life-lines between stranded ships and the adjacent shore, and are now employed on a smaller scale for conveying lines to the upper stories of our monumental buildings when they are on fire.
By means of guns or rockets, projectiles filled with oil may be cast
