The Benson signal., 1918-04-27


will have in pushing the projectile
from it's course, either to the right or
left. These two corrections are
brought together and determine the
amount in degrees and minutes that
the muzzle Of the gun must be shift
ed from the target to the right or
left in order that the projectile will
curve toward it's goal. At last we have
our gun controlled so that it will hit
the target.
Tarry just a moment. A gun, the
text books tell US, is the simplest form
of gas engine. Did you ever know
two gas engines of the same model
that acted alike? Neither will two
guns of the same model.
The Fifty Per Cent Zone.
If you have an automobile you know
that the piston rings wear out, allow
ing gases to escape, and thus reducing
the force with which the piston Is
forced down. Also the cylinder be-
comes scored with the same result.
Now, If you fire your gun many times
the same thing happens. The prOjec-
tile is the piston and the retaining
band of copper the piston ring that
seals the bore. If the bore Is erOded
or if the rotating bands are not per-
feet a certain escape Of gases occurs
and the flight of the projectile is con-
sequently affected.
Again, there may be a difference in
49, IrA% 0Fv oh nr n
weight of the projectiles, which will
give slight variations in the flight Of
the projectiles. SO that the battery
commander must know the dispersion
Of each piece. This he finds out from
observation Of his shots, and 1t
changes as the gun grows older. By
figuring the deviation Of a certain
group Of projectiles from the target,
and which are known as trial shots or
fire for adjustment, he finds out what
is known as the mean error OF the
gun. This, multiplied by the factor
.S45. we'll known to students Of prob
abilities, gives the mean probable er-
ror. Multiplying by two, the result In
yards is what is known as the 90 per
cent zone, within which 80 per cent or
his Droiectiles will fall. This compu-
tation is done longitudinally and lati-
tudinally, giving certain oblong strip.
IF the center Of this strip can be
placed on the target by observation OF
fire the battery commander has done
all that he can, and may now open
fire for effect. Four times the 80
per cent zone gives the 100 per cent
zone, within which practically all his
shots will fall.
knowledge Of these zones is all I'M
portant. BY this means he can figure
out how near he can come to our own
first line trenches without numbering
orr infantry, and, what is almost as
important, when it is necessary to save
ammunition he can easily compute how
many shots will be necessary to make
q certain number of hits on given
| target.
And what about camouflage? The
enemy airplanes are on the alert and
all gun positions must be disguised.
The battery commander must be a
master Of camoufage, able to erect
shelters and under their cover to build
his emplacements, while by the exer-
else of discipline he restrains his men
from making tracks about the posi-
tions which will give away to the all
seeing eve Of the camera In the air
the fact that guns are mounted there.
So that is why the student officers
at Fort Monroe blistered their
hands and strained their backs erect
ing camoufages and digging dugouts
and bombproofs that is why they dove
and crawled under motortrucks and
delved into differentials and gear
cases. emerging dirty and grimy, but
happy: that is why they toiled for
hours at night, working out lengthy
problems in trigonometry until angles
danced before their eyes when they
tried to sleep and endless chains OF
logarithms curved themselves through
their brain cells.