h to enable the observer to complete his work. A lucky rifle
volley, or the stream of bullets from a machine gun may riddle the
envelope, precipitating a hurried descent, owing to the greater number
of perforations through which the gas is able to escape, but as a rule
the observer will be able to land safely.

Consequently the general practice is to shatter the aerostat, and to
this end either shrapnel, high explosive, or incendiary shells will be
used. The former must explode quite close to the balloon in order to
achieve the desired end, while the incendiary shell must actually
strike it, so as to fire the gas. The high explosive shell may explode
effectually some feet away from the vessel, inasmuch as in this instance
dependence is placed upon the terrific concussion produced by the
explosion which, acting upon the fragile fabric of the balloon, brings
about a complete collapse of the envelope. If a shrapnel is well placed
and explodes immediately above the balloon, the envelope will be torn to
shreds and a violent explosion of the gas will be precipitated. But as
a matter of fact, it is extremely difficult to place a shrapnel shell so
as to consummate this end. The range is not picked up easily, while
the timing of the fuse to bring about the explosion of the shell at the
critical moment is invariably a complex problem.

One favourite method of finding the range of a balloon is shown in the
accompanying diagrams. The artillery battery is at B and the captive
balloon, C, is anchored at A. On either side of B and at a specified
distance, observers O1 and O2 respectively are stationed. First a shell
is fired at "long" range, possibly the maximum range of the gun. It
bursts at D. As it has burst immediately in the line of sight of B, but
with the smoke obscured by the figure of the balloon C, it is obvious
to B that the explosion has occurred behind the objective, but at what
distance he cannot tell. To O1 and O2, however, it is seen to have burst
at a considerable distance behind C though to the former it appears to
have burst to the left and to the second observer to the right of the
target.

Another shell, at "short" range, is now fired, and it bursts at E. The
explosion takes place in the line of sight of B, who knows that he has
fired short of the balloon because the latter is eclipsed by the smoke.
But the two observers see that it is very short, and here again the
explosion appears to O1 to have occurred to th