A single lever is now employed, a single turn of which will close or open the breech, and when opened expel the shell by the same movement. Formerly breech-loaders were confined to the heaviest ordnance; now they are a part of the lightest field pieces. As to the operation of those immense guns above referred to, which constitute principally sea-coast defences and the heavy armament for forts, gun carriages have been invented whereby the huge guns are quickly raised from behind immense embrasures by pneumatic or hydraulic cylinders, quickly fired (the range having been before accurately ascertained) and then as quickly lowered out of sight, the latter movement being aided by the recoil action of the gun. It is essential that the full force of the gases of explosion shall be exerted against the base of the projectile, and therefore all escape of such gases be prevented. To this end valuable improvements in _gas checks_ have been made,--one kind consisting of an annular canvas sack containing asbestos and tallow placed between the front face of the breech block and a mushroom-shaped piece, against which the explosion impinges. As among projectiles and shells for cannon those have been invented which are loaded with dynamite or other high explosive, a new class of _Compressed air ordnance_ has been started, in which air or gas is used for the propelling power in place of powder, whereby the chances of exploding such shells in the bore of the gun are greatly lessened. The construction of metals, both for cannon to resist most intense explosives and for plates to resist the penetration of the best projectiles, have received great attention. They are matters pertaining to metallurgy, and are treated of under that head. The strife still continues between impenetrable armour plate and irresistible projectiles. Within the last decade or so shells have been invented with the design simply to shatter or fracture the plate by which the way is broken for subsequent shots. Other shells have been invented carrying a high explosive and capable of penetrating armour plates of great thickness, and exploding after such penetration has taken place. A great accompaniment to artillery is “The Range Finder,” a telescopic apparatus for ascertaining accurately the location and distance of objects to be fired at.