Evening star. [volume] (Washington, D.C.) 1854-1972, 1914-09-12

I serving officer between the aiming point
i and the target. The gun has been given
direction.
Suppose. as is usually the case. the
officer had taken as his observing station
place some distance away from the
battery or line of guns. The angle
measured there would have to be trans
formed for use at the guns. There is a
mate results. When this scheme was in
! troduced the method was called the par
allax method. The parallax Of the aim.
ing point or the parallax Of the target
subtended by the width between gun
muzzles. Ordinarily that interval Is
/, twenty yards.
| ITO obtain the parallax Of the target
I 1t Is only necessary to divide the dis.
lance between guns by the number Of
thousands of the yards in the range
| Thus the parallax Of the target at i,V
yards is 20, 1900 yards 10. 1900 yards q
| 1000 yards 5. 5000 yards 4.
ITO obtain the parallax OF the aiming
point correction must be made for ooilqu-
| ity. Normal to the battery front the
parallax is at its maximum. 1t dimih-
ishes until at 1.600 mills. on the right OF
the battery. it is zero. then 1t increases
again until it reaches its maximum at
5000 mills, in rear of the battery. then II
dimfnishes again until at 800 mills. on
the left of the battery. 1t is zero: ana
then 1t increases and is at its maximum
at 64O0. or in front Of the battery.
1.-THE allowance for obliquity may De
read on a table of parallaxes on the bat
terry commanders ruler, but the usual
way Is to subtract one-tenth from the
maximum parallax for the first 40 NILS
obliquity, two-tenths for the second 4oV.
three-tenths for the third 400 ana tour-
tenths for the fourth 400. Or ready
way is to knock of fourth of the maxi
mum parallax at the first 400 mills obliau-
ity, half Of it at 800 and three-quarters OF
1t at 1,20O.
X II
1T the angle is measured at the right
piece and the guns are in line. the angle
at the next gun on the left will be the
first angle diminished by the parallax OF
the aiming point minus the paraliax OF
the target, plus sign being attached to
the target parallax and minus sign to
the aiming point parallax If the point is
behind the guns and plus sign II In
front. The same difference in the angle
between the first and second guns may
be applied in arithmetical progression 70
all other guns in the same line and the
same distance apart. That formula Will
converge the fire Of the guns. II parallel
fire Is wanted. to have the shots strike
the same distance apart that the guns
are the angular difference will be the
angle of the first gun diminished by the
parallax of the aiming point applied IN
arithmetical progression to the guns on
the left.
"To produce a wider distribution Of fire
than parallel fire the detection difference
or the angular difference between guns.
will equal the parallax of the aiming
point, minus the .parallax Of the target
plus the width of the target in mills d.
vided by the number of guns. Modifica-
lions of this distribution of fire may be
made by opening or closing the sheaf.
and this is done by increasing or dimin-
ishing the detection difference. and the
whole sheaf of fire may be shifted to the
left by adding to the original DETECTION
or to the right by subtracting from it
II tell you this to show you how the
thing Is worked. A skillful man may do
all this by estimation very much quicker
than it can be told. I want to impress
on you that q good officer will work out
these data and the battery begin shoot
ing in less time than any reader can read
one paragraph Of this interview.
Recently the parallax method has
been generally superseded by a shortcut
plan called the graphic method. but that
is another story. I have told you only
Of a simple case where the angle is
measured at the right piece. And l am
explaining to you only how the gun in
indirect fire. is given the proper 'direc-
ton"