The type of bomb which has proved to be the most successful is pear-shaped. The tail spindle is given an arrow-head shape, the vanes being utilised to steady the downward flight of the missile. In falling the bomb spins round, the rotating speed increasing as the projectile gathers velocity. The vanes act as a guide, keeping the projectile in as vertical a plane as possible, and ensuring that the rounded head shall strike the ground. The earlier types of bombs were not fitted with these vanes, the result being that sometimes they turned over and over as they fell through the air, while more often than not they failed to explode upon striking the ground. The method of launching the bomb also varies considerably, experience not having indicated the most efficient method of consummating this end. In some cases the bombs are carried in a cradle placed beneath the aeroplane and launched merely by tilting them in a kind of sling, one by one, to enable them to drop to the ground, this action being controlled by means of a lever. In another instance they are dropped over the side of the car by the pilot, the tail of the bomb being fitted with a swivel and ring to facilitate the operation. Some of the French aviators favour a still simpler method. The bomb is attached to a thread and lowered over the side. At the critical moment it is released simply by severing the thread. Such aeroplane bombs, however, constitute a menace to the machine and to the pilot. Should the bomb be struck by hostile rifle or shell fire while the machine is aloft, an explosion is probable; while should the aero plane make an abrupt descent the missiles are likely to be detonated. A bomb which circumvents this menace and which in fact will explode only when it strikes the ground is that devised by Mr. Marten-Hale. This projectile follows the usual pear-shape, and has a rotating tail to preserve direction when in flight. The detonator is held away from the main charge by a collar and ball-bearing which are held in place by the projecting end of a screw-releasing spindle. When the bomb is dropped the rotating tail causes the spindle to screw upwards until the projection moves away from the steel balls, thereby allowing them to fall inward when the collar and the detonator are released. In order to bring about this action the bomb must have a fall of at least 200 feet. When the bomb strikes the ground the detonator falls down on the charge, fires the latter, and thus brings about the bursting of the bomb. The projectile is of the shrapnel type. It weighs 20 pounds complete, is charged with some four pounds of T.N.T., and carries 340 steel balls, which represent a weight of 5 3/4 pounds.