Northern Wisconsin advertiser. [volume] (Wabeno, Wis.) 1898-1925, 1918-04-26

will have in pushing the projectile
from its 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
left in order that the projectile will
curve toward its goal At last we have
our gun controlled SO that it will hit
the target.
larry just 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
the weight of powder charges or In the
weight of the projectiles, which will
give slight variations in the flight of
the prOiectiles. 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, well known to students of prob
abilities, gives the mean probable err
ror. Multiplying by two, the result in
wards is what is known as the 80 per
cent zone, within which so per cent of
his projectiles will fall. This cOmpu-
tation is done lOngitudinally and lati-
tudinally, giving a 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
O. time
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
our 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
certain number of hits on a given
target.
And what about Camouf1age? The
enemy airplanes are on the alert and
all gun positions must be disguised.
The battery commander must be
master of camoufiage, able TO erect
shelters and under their cover to build
his emplacements, while by the exer-
else of discipline he restraints his men
from making tracks about the posi-
tons which will give away to the all
seeing eye 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 camouf1ages 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.
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