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These shells are fired upon impact； a detonator exploding the
main charge。 The detonator； comprising fulminate of mercury； is
placed in the head or tail of the missile。 To secure perfect
detonation and to distribute the death…dealing contents evenly in
all directions； it is essential that the bomb should strike the
ground almost at right angles： otherwise the contents are hurled
irregularly and perhaps in one direction only。 One great
objection to the percussion system； as the method of impact
detonation is called； is that the damage may be localised。 A
bomb launched from a height of say 1；000 feet attains terrific
velocity； due to the force of gravity in conjunction with its own
weight； in consonance with the law concerning a falling body； by
the time it reaches the ground。 It buries itself to a certain
depth before bursting so that the forces of the explosion become
somewhat muffled as it were。 A huge deep holea miniature
volcano crateris formed； while all the glass in the immediate
vicinity of the explosion may be shattered by the concussion； and
the walls of adjacent buildings be bespattered with shrapnel。
Although it is stated that an airship is able to drop a single
missile weighing one ton in weight； there has been no attempt to
prove the contention by practice。 In all probability the
heaviest shell launched from a Zeppelin has not exceeded 300
pounds。 There is one cogent reason for such a belief。 A bomb
weighing one ton is equivalent to a similar weight of ballast。
If this were discarded suddenly the equilibrium of the dirigible
would be seriously disturbedit would exert a tendency to fly
upwards at a rapid speed。 It is doubtful whether the planes
controlling movement in the vertical plane would ever be able to
counteract this enormous vertical thrust。 Something would have
to submit to the strain。 Even if the dirigible displaced say 20
tons； and a bomb weighing one ton were discharged； the weight of
the balloon would be decreased suddenly by approximately five
per cent； so that it would shoot upwards at an alarming speed；
and some seconds would elapse before control was regained。
The method of launching bombs from airships varies considerably。
Some are released from a cradle； being tilted into position ready
for firing； while others are discharged from a tube somewhat
reminiscent of that used for firing torpedoes； with the exception
that little or no initial impetus is imparted to the missile； the
velocity it attains is essentially gravitational。
The French favour the tube…launching method since thereby it is
stated to be possible to take more accurate aim。 The objective
is sighted and the bomb launched at the critical moment。 In some
instances the French employ an automatic detonator which
corresponds in a certain measure to the time…fuse of a shrapnel
shell fired from a gun。
The bomb…thrower reads the altitude of his airship as indicated
by his barometer or other recording instrument； and by means of a
table at his command ascertains in a moment the time which will
elapse before the bomb strikes the ground。 The automatic
detonator is set in motion and the bomb released to explode
approximately at the height to which it is set。 When it bursts
the full force of the explosion is distributed downwards and
laterally。 Owing to the difficulty of ensuring the explosion of
the bomb at the exact height desired； it is also made to explode
upon impact so as to make doubly sure of its efficacy。
Firing timed bombs from aloft； however； is not free from
excitement and danger； as the experience of a French airman
demonstrates。 His dirigible had been commanded to make a
night…raid upon a railway station which was a strategical
junction for the movement of the enemy's troops。 Although the
hostile searchlights were active； the airship contrived to slip
between the spokes of light without being observed。 By
descending to a comparatively low altitude the pilot was able to
pick up the objective。
Three projectiles were discharged in rapid succession and then
the searchlights； being concentrated； struck the airship；
revealing its presence to the troops below。 Instantly a spirited
fusillade broke out。 The airmen； by throwing ballast and other
portable articles overboard pell…mell； rose rapidly； pursued by
the hostile shells。
In the upward travel the bomb…thrower decided to have a parting
shot。 The airship was steadied momentarily to enable the range
to be taken； the automatic detonator was set going and the bomb
slipped into the launching tube。 But for some reason or other
the missile jambed。
The situation was desperate。 In a few seconds the bomb would
burst and shatter the airship。 The bomb…thrower grabbed a tool
and climbing into the rigging below hacked away at the bomb…
throwing tube until the whole equipment was cut adrift and fell
clear of the vessel。 Almost instantly there was a terrific
explosion in mid…air。 The blast of air caused the vessel to roll
and pitch in a disconcerting manner； but as the airman permitted
the craft to continue its upward course unchecked； she soon
steadied herself and was brought under control once more。
The bomb carried by aeroplanes differs consider ably from that
used by dirigibles； is smaller and more convenient to handle；
though considering its weight and size it is remarkably
destructive。 In this instance complete reliance is placed upon
detonation by impact。 The latest types of British war…plane
bombs have been made particularly formidable； those employed in
the 〃raids in force〃 ranging up to 95 pounds in weight。
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 a