The record-union., 1898-08-15
MODERN PROJECulES.
SOME TRAVEL A MILE IN THREE
SECONDS OR LESS.
How Their Speed IL Accurately
Measured-The Trajectory
Of q Projectile.

| Mention is often made during these
warlike days of the great speed OF pro-
| jectiles fired from modern guns. The
velocity ranges from 1,5OO to 1900 feet
per second. 1t is computed that the
average velocity of the larger guns on
the cruiser New York is 2,1OO feet per
second. To the uninitiated the way in
which this is found out should be of in
| terest
| In the first place, it may be stated
! that one cannot time proJectile as one
would a race horse. Some OF them can
| be seen as they rush through the air.
| 1t is a favorite amusement during the
| battery drill with the old seacoast guns
at West Point to stand behind and
slightly above the gun, and watch the
projectile from the moment 1t leaves
| the muzzle until it strikes the target
painted on old Gro Nest Mountain,
about a mile away. Spectators with
good eyesight can also see the she'll fired
| from the large mortar rise to the high
est point of it's course, and then de-
scend with rush upon the. mountain
| top, a mile and a half away, where it
bursts into many pieces
| 1t is reported that during the recent
| bonn bardment Of Santiago the shells of
| the cruiser New Orleans could be fol-
| lowed by the eye. This was largely
due to the use of smokeless powder,
which permitted clear vision.
| But in the case of smaller projectiles,
| with greater velocity, it is impossible
to see them during flight But whether
| they can be seen or not, 1t is quite out
of the question to time them as one
| would a race, by simply using the eye
and a stop watch. The least hesitation
| in pushing the spring would make a
difference Of hundreds Of feet in the
distance Travelled. Errors such as these
would make the results of no practical
value
Our small arm shoots bullet only
one-third Of an inch in diameter, which
travels two thousand feet in a second,
or mile in three 1t goes SO fast that
| it becomes hot to the touch, due to the
resistance of the air which it pushes
aside. Strange to say, the heated bull
| let will cauteriZe the wound of its own
| making, and few of the wounded in
our war with Spain will bleed to death
| unless struck in vital spot.
A ROTATIONAL VELOCITY.
| The projectile has, besides the for
| ward velocity rotational velocity,
| which is given to it by the rifiing Of the
gun. Otherwise, since its length is much
greater than its diameter, it would soon
begin to turn end on. The rifling pre-
vents this by causing the bullet to bore
| a path through the air, and the higher
| the forward velocity the higher, too,
must be the rotational. This turning
over and over would destroy the range
and the accuracy Of the gun.
The determination of the forward We
locity is now made with extreme ac-
curacy. The knowledge pf is Of the
utmost Importance to military science.
Various methods have been adopted for
| its determination within the gun, as
we'll as at various points of the traject-
ory.
| The following method is the one
| adopted by all nations for finding the
| velocity of a projectile at any point Of
| its path after leaving the muzzle Of the
gun. 1t is so simple that a brief expla-
nation of it will make it Ineligible to
all.
Two screens, so closely strung with
copper wire that a projectile in passing
! through must break one or more of the
strands, are placed fifty yards apart
| The wire on each screen is connected
with a battery which sends a current
| through it, and two instruments, one
called a disjunctor the other the chron-
| ograph. Although both circuits pass
though these instruments, yet they are
! kept distinct and separate.
The chronograph answers the purpose
Of a stop watch Of greatest accuracy.
| Two bars are held up by electric mag
nets; the currents flowing in one mag
net also flow through its respective
screen, while the current Of the other
passes through the second screen. The
disjunctor is an instrument which is
used to break both circuits at the same
| instant. AS soon as this is done the
| bars fall. since the electro magnets
| cease to act when there is no current
| flowing through them. The bar con-
nected with the first screen falls upon
| small platform, which releases a
wedge shaped piece of metal This
| strikes the bar connected with the sec
ond screen, leaving wedge shaped slit
| in 1t as line of reference during the
| experiments. af
l DETERMINING THE VELOCITY.
This being done, the currents are es-
| tablished again and the rods placed
| once more under the influence of the
electro-magnets. Let a 3.2-inch rife
! whose muzzle velocity is to be found be
| placed in front of the first screen. The
| gun is aimed, fired, and it's projectile
passes quicker than the roar Of the dis
| charge through the first screen, break
| ing some Of its wires; in another in
| slant it is through the second screen,
destroying it's electric current, and at
| last finds a resting place in some dis
| tant sand pile.
The break In each circuit is commu-
nicated to all parts of the line Instant
/ w. If the times at which both occur
| can be determined the problem is solved
For instance, let the time it took to pass
! over the fifty yards be .O75 of a second.
| Then dividing the one by the other
j gives 1900 feet per second as the veloc-
ity of the projectile.
The time is found by accurately
measuring the distance between the
| first dent, the origin, and the second
dent, caused by the projectile breaking
| the circuits at different times. To IL
| lustrate the principle involved: If the
projectile be Of low velocity the dis
tance will be greater than if it Travelled
i at high rate. of speed, since the first
| rod would have a longer time to fall
before the second starts. If the dis