BOMB, a term formerly used for an explosive shell (see AM MUNITION) fired by artillery. The word is derived from the Gr. (36µ(3os, a hammering, buzzing noise, cf. ".bombard" (q.v.) . At the present day it is most frequently used of a shattering or in cendiary grenade (q.v.), or an explosive vessel actuated by clock work or trip mechanism, employed to destroy life or property. In naval warfare, before the introduction of the shell gun, explosive projectiles were carried principally by special vessels known as bomb-vessels, bombards or, colloquially, bombs.
In geology, the name "bomb" is given to certain masses of lava which have been hurled forth from a volcanic vent by explosive action. In shape they are spheroidal, ellipsoidal or discoidal; in structure they may be solid, hollow or more or less cavernous; whilst in size they vary from that of a walnut to masses weighing several tons. It is generally held that the form is partly due to rotation of the mass during its aerial flight, and in some cases the bomb becomes twisted by a gyratory movement. According, how ever, to Dr. H. J. Johnston-Lavis, many of the so-called bombs of Vesuvius are not projectiles, but merely globular masses formed in a stream of lava; and in like manner Prof. J. D. Duna showed that what were regarded as bombs in Hawaii are in many cases merely lava-balls that have not been hurled through the air.