d repeats the operation. I know personally of
some fifty bombs thus dropped, not one of which struck anywhere near
the target. The effect of the bombs is of small consequence and damage
is seldom done except to the people who happen to be standing in the
immediate neighborhood.

The crater of the bombs thrown by German aeroplanes, when striking
macadam or similar surfaces, is about fifteen inches in diameter and
four inches deep. I have seen three such craters. The shrapnel bullets
from the exploding bombs fly with a killing force to a distance of
about fifty yards, and at the latter range the lowest bullets fly at a
height of about twelve or fifteen feet. These bombs weigh about
fourteen pounds.

Aeroplanes have proved to be almost invulnerable in war. They are
extremely difficult to hit, because one must calculate for three
dimensions and for the speed of the aeroplane; when hit they seldom
suffer serious damage. I know of a case where first and last nearly
200 bullets passed through a machine without its ever being put out of
action. Indeed, it seems impossible to bring down an aeroplane except
by a freak shot. The gasoline tank is high and narrow and is protected
by a thin metal plate underneath, while struts and steering wires are
usually double. Wounding the aviator does not usually bring down a
machine, because he is sitting and is strapped in, and on calm days
needs to employ only a slight muscular effort to steer. Moreover,
there are usually two officers in an aeroplane and the systems of
double control enable the aeroplane to return to its base even if one
of them is killed outright.

Anti-aircraft guns are not greatly feared by aviators, and they
consider it merely an extraordinary piece of bad luck to be hit by
one. The aviators fear most of all the fire of large bodies of
infantry, and in flying over a regiment at an altitude of 1000 yards
they realize that they run serious risk of being brought down.

Rifle bullets are effective against aeroplanes up to a height of
about 5000 feet. Observers fly just above this altitude, at about 5500
feet, since they wish to fly as low as possible and yet be reasonably
safe. Aviators have told me that this height is so well recognized
that they nearly always encounter other observers in the same plane.

Aeroplanes, flying at a height of 5500 feet, can observe the movement
or presence of large bodies of troops and the flashes of artillery.
They cannot observe very mu