The modern contest began with the introduction of horizontal shell fire in the third decade of the century. This term must be explained. It has been said that all ships’ guns up to 1815 threw non-explosive projectiles. In practice this is true; although Nelson alludes to certain shell supplied to him for trial, which he was unwilling to use because he wished not to burn his prizes, but to take them alive. A shell is a hollow projectile filled with powder, the idea of which is that upon reaching the enemy it will burst into several pieces, each capable of killing a man, and the flame not impossibly setting woodwork on fire. It was necessary that the powder within should not explode from the combustion of the cartridge of the gun, for if it did its force, combined with the latter, might burst the gun; yet the process that should result in bursting must begin at that moment or else it would not take place at all. This difficulty was met by a short column of hard, compressed powder called the fuse, which extended from the outside to the inside of the shell. The outer end was inflamed by the charge of the gun, but from its density it burned slowly, so that the charge of the shell was not enkindled for five, ten, or more seconds. This expedient was in use over a century ago; but owing to imperfections of manufacture, no certainty was attained that the fuse might not be driven in or broken by the force of the discharge, or the shell itself be cracked and so explode prematurely. Shell, therefore, were fired with very light charges; and, to obtain sufficient range—go far enough—they were used in very short, very thick guns, called bombs or mortars, to which great elevation was given. Such firing, because the shell flew high in the air, was called vertical firing, in contradistinction to the fire of the long gun or carronade, called horizontal fire because their projectiles rose little above the level.