Evening star. [volume] (Washington, D.C.) 1854-1972, 1891-09-16
TIMING A CANNON BALL.
How This Nice Work 10 Conducted at the
sandy Hook Proving Grounds.

How This Nice Work 10 Conducted at the
sandy Hook Proving Grounds.
Capt Heath has been burning lot of powder
this summer in the big guns at the United
States proving ground at Sandy Hook, says the
New York San, and to people who don't know a
big gun from a mortar the most interesting
part Of these tests has been the method by
which the initial velocity of the projectiles has
been determined. The difficulty of such q
calculation is indicated by the fact that
with our modern high-power guns the shot is
often expelled Mt an initial velocity O. 1000
feet per second, which is at the ratio of a mile
in less than three second5 Accurate knowl-
edge OF the velocity of = projectile is Of the
greatest importance - the ordnance officer.
who has to predict the range Of the shot ard
its penetration and to determine the accuracy
and efficiency Of the gun, Of the powder and Of
the projectile itself.
Capt. Heath finds fault with powder that
gives initial velocity of / 1855 feet per Sec
ond to the 1,00O-pound projectile of the new
Pinch rifle dt Sandy Hook. when its velocity
should be 1918 feet per second. This is a diff
ference of only ITO feet, and the instrument
that records il must be capable Of measuring
the time interval to within the dve-thousaudth
part of a second. difference of two or three
hundred feet in velocity means in the big guns
an important difference in the powder used in
the tests At SANDY Hook q delicate electrical
appliance called the Boulanger chronograph
measures this velocity accurately and records
| its own measurements. This is the way it
does it:
In testing the large guns at these proving
grounds two open frames are set up in front OF
the guns ut distance Of -150 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 u complete
electric circuit, which includes also electric
battery and an electro-magnet. When the gun
is fired the projectile breaks the wire in the
first SCREEN interrupts the circuit and at the
same time the armature Of the magnet is re-
leased. In Il very small fraction Of u second
the proiectile has covered the distance to the
second screen and interrupted its circuit. re-
leasing another armature. The interval of
| time between the drop of these two armatures
represents the time taken by the projectile to
travel $50 feet.
This period is so short that it is hardly con-
ceivable. The chronograph, however, registers
| II accurately. Wires run from each o. these
screens to the laboratory near them, where are
| placed the chronographs. batteries, switchboard
and other apparatus. The two electro-magnets
III circuit with the screens are embodied in the
chronograph The fret magnet has an arm
allure an iron rod about three feet long, which
IL suspended III 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 the
| second electro-Inagnet, which is placed short
distance below the first, is also released. 1t OPP
crates as IA knife, and. striking the side OF the
falling rod, makes a slight mark. The distance
through which the rod drops while the shot is
passing from one screen to the other is iEdi-
| Gated by the distance of the cut from the end
| OF the rod. From this the corresponding in
terval of time is easily computed and this forms
she unit for the calculation OF the projectile S
velocity In feet per second. When it is neces-
| sary to obtain very accurate records several
/ chronographs may be used for testing the same
| shot.
Ot course the rate Of . projectiles velocity
! diminishes rapidly during its flight from the
gun, and the calculations Of the initial velocity
must be confined to short portion of its path
! Immediately after it leaves the gun. In
Simultaneous photographs arc obtained Of the
projectlle as II strikes the target From these
| experiments in velocity the ordnance officer il
able 10 determine the relative strength Of diff.
| ferent powders