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

, Is necessary that I tell you about the
angular measure used in artillery. For
US, the circle has been divided into 800
degrees. each degree into sixty minutes
and each minute into sixty seconds, there
being 21,60O minutes in a circle or
1.aD600O seconds. This fine division is
called for because two lines forming
an angle Of one second may be projected
4 into space SO far that the arc or the
chord Of that arc may be many miles
! Wide. Such refined measure is not re-
CURED In field artillery. With us, the
circle a;,e Is divided into 600 parts. called
OF this circle begins at the top and
progresses toward the right. It divides
conveniently. At 800 mills one has the
very common angle Of forty-fve degrees,
at l,6OO mills right angle, at $500 mills
straight angle and thence onward re-
mex angles to the point of beginning.
This division Is small enough for artil-
lery purposes. in that two lines forming
an ansle OF one mil and projected to the
unit OF hre for the three-inch field piece.
approximately 1900 yards. would be sub
| tended by only seven and a half yards.
width only about one-third the width
covered by the balls Of sharpneI at its
normal height Of burst above the target
IN hre Tor effect, which is laid down
IN the text books as three mills.
TO quote Capt William L. Wester-
Welt who. while in the 9Th Field Ar
ttllery. produced q brochure Of value
on 'Gunnery and Explosives the true
NIL 70 one one-thousandth part Of a
radian. or practically 1-157Oth part Of a
right angle. The mil adopted Is IL, eOOth
part Of right angle and is smaller than
the true mil by approximately four Sec
onds OF arc: Based on the assumption
that 9. 400 mills equal $50 degrees, degrees
may be converted into mills by reducing
the degrees to minutes and multiplying
by three-tenths. The quick way of re-
ducing degrees to mills is to multiply
by eighteen
The mil besides being very nearly
1-6. 40oth part Of circle is thus very
nearly 1-1.OOOth part Of the range-that is,
II two lines forming an angle of one
mill be projected LOCO yards the chord Of
the arc will be one yard. at 2O00 yards
the chord will be two yards and at 5000
yards five yards. This, of course, Is true
whether the circle be measured hori-
zontally OF vertically. So much for
rough description of the unit of artillery
angular measure.
y
''The battery commanders telescope is
an instrument by which angles. horizon
tai and vertical, may be measured in mills.
THE panoramic sight on the gun has
an azimuth scale graduated in mills. Now
suppose the officer having the direction
Of fire takes his observing station direct
ly above the gun. He sees the target,
because he is higher, but 1t cannot be
seen from the gun. There is some OBJ
ject in the rear Of the gun, or on either
flank. or no matter where. It is visible
from the gun. This object is the aiming
point. The observer sets his telescope at
zero, lays the cross hairs on the aiming
point and turns the instrument through
the proper arc till the cross hairs are on
the target. He reads the number of mills
Of one arc which the instrument has
traversed
Let us suppose that the aiming point
is in prolongation Of the right flank of
the battery. The reading will be 1900
The command to the gunner will be,
Aiming point. that steeple. tree or what
not. DETECTION LOCO The gunner turns
the head Of his panoramic sight till the
reading is 1,600. He has thus set Off the
same angle between the Ion eitudinal axis
Of his piece and his line of vision through
the panoramic sight that the observing
officer has measured with his telescope
The gunner then traverses his piece til!
the cross-hairs Of his panoramic sight
are on the aiming point, and thus the
gun will be pointed at the target The
same angle between the gunner's line of
sight and the guns line of fire has been
established as that measured by the OBJ