Essex County herald. [volume] (Guildhall, Vt.) 1873-1964, 1918-04-26

above the level of the gun there is a
ten-mile wind blowing straight across
the line gun target, the thermometer
is up to 81 and the barometer has
dropped to %. Will the projectile 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 going to
do It?
First, you must find the force with
which your proiectIle cleaves the air.
This is called the balliStic co-efficient,
and is reduced by simple formula to
figure. Knowing the weight of the
projectile, its form and its diameter
the ballistic coefficient 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 heavy,
muggy day the atmosphere Is dense,
and you will be surprised the check
ing effect it will have on your proiec-
tile. BY means of elaborate tables one
can find just what this effect is, and
we apply it to the original formula
Also in the atmospheric factor is in
cluded the temperature, for in hot
weather our powder charge when ig-
nited eXorts 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? If
it blows against the projectile II
| checks It; if with it, it helps it along
| So we have two varying factors
which the ballistician iuggleS by utilz
| ing trigOnOmetry until he gets them in
terms where he can once more change
| his ballistic co-efficient, making II
| larger or smaller as the wind i'm
| pedeS or accelerates the prOjectile.
Not quite so easy as you thought, Is
1t? But we are not through yet
We know that under range table
conditions our propelling charge has
n force that gives the prOiectle ar
initial velocity Of so many foot sec
onds, say $3.50. But our powder ha,
| been stored in dugOut whose tenn
| perature is not normal, so by more fig
uring we find out just what this rea
velocity for the day is. Now we car
| begin to figure what elevation the
gun must have to travel that 10000
yard path to the target.
| BY dividing our old friend c, as the
| ballistic co-efficient is termed, by The
distance in feet that the projeCtil,
must travel, we get q. reference mum
! Der. This number we take with II,
! and bury our noses in more tables un
! i'll we find opposite this number in {
| column headed by the muZzle velocity
another number. This number, multi
| piled by c again, gives us the sine Of
| twice the angle of departure. A
quick glance into a table of logarith
mic sines gives this to us, and dividing
| by two we have Il figure in degrees ant
minutes that represents the angle
which the gun must be elevated from
| the horizontal to send its projectilt
! 10000 yards today. Wait a minute
Our target is 200 feet above the Ieve
| Of the gun. Also because Of the curry
allure Of the earth this 200 feet height
| has been reduced somewhat. So once
| more we dclve into mathematics to cor
rect the curvature Of the earth an(
height Of site of the target The re
| suit we subtract from the angle found
and this time our gun is ready foi
business. Is it? No; it is not so easy
The Influence OF the RifIinq.
Every rifled piece of ordnance i'm
parts twist to its projectile, ant
this twist causes the projectile to devi
ate from its course. In our service this
deviation, called drift, Is to the right
and is in ratio with the range II IS
constant, therefore, for each range, an(
we find it very easily, either by math
ematic computation or from drift Ia
| bles. \ Also we 20 back to our vino
problem and find what effect the vino