BOMB, in artillery, a shell or hollow ball of cast iron, having a large vent, by which it is filled with gunpowder, and which is fitted with a fuze or hollow plug, to give fire by when thrown out of a mor tar, &c.: about the time when the shell arives at the intended place, the compo sition in the pipe of the fuze sets fire to the powder in the shell, which blows it all in pieces, to the great annoyance of the enemy, by killing the people or firing the houses, &c. They are now common ly called shells simply in the English ar tillery.
These shells or bombs are of various sizes, from that of 17 or 18 inches dia meter downwards. The very large ones are not used by the English, that of 13 inches diameter being the highest size now employed by them : the weight, di mensions, and other circumstances of them, and the others downwards, are as in the following table.
Mr. Muller gives the following propor-' tint for all shells. Dividing the diameter of the mortar into 30 equal parts, then the other dimensions in 30ths of that di ameter, will be thus : Diameter of the bore or mortar 30 Diameter of the shell . . 291 Diameter of the hollow sphere 21 Thickness of metal at the fuze hole Thickness at the opposite part 5 Diameter of the fuze hole . 4
Weight of shell empty . . Weight of powder to fill it . Where d denotes the cube of the di ameter of the bore in inches. But shells have also lately been made with the me tal all of the same thickness quite around. In general, the windage or difference between the diameter of the shell and mortar is one sixtieth of the latter ; also the diameter of the hollow part of the shell is seven-tenths of the same.
Bombs are thrown out of mortars or howitzers ; but they may also be thrown out of cannon ; and a very small sort are thrown by the hand, which are called granadoes.
B011113 chest, a kind of chest filled usual ly with bombs, sometimes only with gun powder, placed under ground, to tear and blow it tip into the air, with those who stand upon it. It was formerly set on fire by means of a saucisse fastened at one end, hut is now much disused.
Boma ketch, a small vessel built and strengthened with large beams for the use of mortars at sea.