The Kansas City sun. (Kansas City, Mo.) 1908-1924, 1918-04-27

above the level of the gun there is a
ten-mile wind blowing straight across
the line gun target, the thermometer
Is up to So and the barometer has
dropped to 20. Will the ~projectlle hit
the target now2 Not unless you cor
rect the elevation of the gun for some
Of these conditions and its laying for
the others. How are you golug to
do It?
First, you must find the force with
which your %projectile cleaves the air.
This is called the ballistic co-efficient,
and is reduced by a simple formula to
a figure. Knowing the weight of the
projectile, its form and its diameter
the ballistic co-efficient is easily cal
culated.
The Air as a Check.
You have now taken the first step.
You have the force of projectile to
penetrate the atmosphere under stand
ard conditions. But this force varies
with the atmosphere. On a heavy,
muggy day the atmosphere is dense,
and you will be surprised the check
ing effect 1t will have on your projec-
tile. BY means of elaborate tables one
car find just what this effect is, and
we apply it to the original formula.
Also in the atmospheric factor is In
Guided the temperature, for In hot
weather Il powder charge when ig-
nited exerts more strength in decom-
posing into gases than it does on a
cold day.
So far so good. What about this
troublesome wind that is blowing? II
1t blows against the p~rojectile II
checks It; If with 1t, 1t helps II along
So we have two varying factors
which the ballistician juggles by utiliz
Ing trigonometry until he gets them in
terms where he can once more change
his balllstic co-efficient, making II
larger or smaller as the wind i'm.
pedes Or a~ccelerates the proiectlle.
Not quite so easy as you thought, is
1t? But we r not through yet.
We know that under range table
conditions our propelling charge has
a force that gives the proiectile an
initial velocity of so many foot sec.
onds, say $3.50. But our powder has
been stored in a dugout whose TEN.
perature is not normal. sc by more fig.
uring we find out just what this real
velocity for the day is. Now we can
begin to figure what elevation the
gun must have to travel that 10000
yard path to the target.
By dividing our old friend c, ms the
ballistic co-efficlent is termed, by the
distance In feet that the projectilt
Der. This number we take with us
and bury our noses in more tables un
til we find opposite this number In 6
column headed by the muZZle velocity
another number. This number, multi
piled by G again, gives us the sine o.
twice the angle of departure. A
quick glance into a table of logarith
mic sines gives this to us, and dlvidinl
by two we have a figure in degrees ant
minutes that represents the angle
which the gun must be elevated from
the horizontal to send its projectil,
lOgOOO gulho NONog 4 u nlluulG
Our target is 200 feet above the leve
of the gun. Also because of the curry
AZURE Of the earth this 200 feet helgh
has been reduced somewhat. So one,
more we delve into mathematics to cor
rect the curvature of the earth AM
height Of site of the target. The re
suit we subtract from the angle found
and this time our gun Is ready TO
business. Is 1t? No; 1t is not so easy
The Influence Of the Rifiinp.
Every rifed piece of ordnance i'm
parts a twist to Its projectile, ant
this twist causes the p~rojectile to dew
ate from its course. In u service thi
deviation, called drift, is to the right
and is In ratio with the range. Il 1
constant, therefore, for each range, an,
we find it very easily, either by math
ematic computation or from drift ia
bles. Also we go back to our win,
problem and find what effect the win,