_Explosives._--The desire to make the most effective explosives for gunnery led to their invention not only for that purpose but for the more peaceful pursuit of blasting. _Gun Cotton_, that mixture of nitric acid and cotton, made by Schönbein in 1846, and experimented with for a long time as a substitute for gunpowder in cannon and small arms and finally discarded for that purpose, is now being again revived, but used chiefly for blasting. This was followed by the discovery of nitro-glycerine, a still more powerful explosive agent--too powerful and uncontrollable for guns as originally made. They did not supersede gunpowder, but smokeless powders have come, containing nitro-cellulose, or nitro-glycerine rendered plastic, coherent and homogeneous, and converted into rods or grains of free running powder, to aid the breech-loaders and magazine guns, while the high explosives, gun-cotton, nitro-glycerine, dynamite, dualine, etc., have become the favorite agencies for those fearful offensive and defensive weapons, the _Torpedoes_. From about the time of the discovery of gunpowder, stationary and floating chambers and mines of powder, to be discharged in early times by fuses (later by percussion or electricity), have existed, but modern inventions have rendered them of more fearful importance than was ever dreamed of before this century. The latest invention in this class is the _submarine torpedo boat_, which, moving rapidly towards an enemy’s vessel, suddenly disappears from sight beneath the water, and strikes the vessel at its lowest or most vulnerable point.