The morning news. [volume] (Savannah, Ga.) 1887-1900, 1891-09-21
TIMING ACANNoN BALL.
Bow This Nice Work Is Conducted at
the sandy Hook Proving Grounds.
El-o,, Jho Na,. Vol. o.,

bOW AnlS NiCs Work 1S ConQQcteo al
the sandy Hook Proving Grounds.
From the Nelo York sun.
Capt Heath has been burning a lot OF
powder this summer in the big guns at the
United States proving ground at Sandy
Hook, and to people who don't know a big
gun from mortar the most interesting part
of these tests has been the methods by
which the initial velocity OF the projectiles
hes been determined. The difficulty of
such calculation is indicated by the fact
that with our modern high-power guns the
shot is often expelled at an initial velocity
of 1000 feet per second, which is at the rate
of a mile IN less than three seconds. Acou-
rate knowledge Of the velocity Of a projec-
tile is of the greatest Importance to the
ordnance officer, who has to predict the
range of the shot aud its penetration, and
to determine the accuracy and efficiency Of
the gun, or the powder and OF the projectile
itself.
Capt. Heath finds fault with powder that
gives an initial velocity Of 1865 feet per
second to the l,000-pound projectile Of the
new 12-inch rifle at Sandy Hook, when its
velocity should be ,975 feet per second.
This 10 difference of only 10 feet, and the
instrument that records it must be capable
OF measuring the time interval TO within
the five-thousandth part of second. A
difference of 200 or 300 feet in velocity
means IN the big guns an important diff
ference in the powder used in the tests. At
Sandy Hook delicate electrical appliance,
called the Boulanger chronograph, meas
ures this velocity accurately, and records its
own measurements. This Is the way it
does 1t:
In testing the large guns at these proving
grounds two open frames are setup In front
OF the gun at distance OF $50 feet from
each other. Wires are stretched back and
forth across each of these frames, making q
screen through which the projectile must
pass. The wires in each of these screens
form complete electric circuit, which in
cludes also an electric battery and an
electromagnetic. When the gun is fred the
projectile breaks the wire in the first screen,
interrupts the circuit, and at the saane time
the armatuTe OF the magnet is released. In
a very small fraction of a second the
projectile has covered the distance to the
second screen and interrupted its circuit, re-
leasing another arrnature. The interval of
time between the drop of these two armat-
nres represents the time taken by the
projectile to travel $50 feet
This period is so short that it is hardly
conceivable. The chronograph, however,
registers it accurately. Wires run from
each Of these screens to the laboratory near
them, where are placed the ohronographs,
batteries, switchboard and other apparatus,
The two electro magnets in circuit with the
screens are embodied in the chronograph,
The first magnet hes as an armature an
iron rod about three feet long, which is sus-
pended in vertical position from its core
When the wires of the first screen are
broken this iron rod falls. When the shot
ruptures the wire OF the second screen the
armature of he second electro-magnet,
which is placed a short distance be-
low the first, is also released. 1t operates
as knife, and striking the side Of the fall
ing rod makes slight mark. The distance
through which the rod drops while the shot
is passing from one screen to the other Is
indicated by the distance Of the out from
the end of the rod. From this the corre-
spending interval of time is easily COM
puted, and this forms the unit for the cal
culation Of the projectilefs velocity in feet
per second. When it is necessary to obtain
very accurate records several chronographs
may be used for testing the same shot.
OF course, the rate Of projectiles veloc-
ity diminishes rapidly during its flight
from the gun, and the calculations of the
initial velocity must be confined to short
portion of its path imme diatsly after it leaves
the gun. instantaneous photographs are
obtained Of the projectile as it strikes the
target. From these experiments in velocity
the ordinance officer is able to determi ne
the relative strength of different powders