Morning journal and courier., 1891-10-02
TIMING A CANNON BALL.
How This Nice Work Is Conducted d at the Sandy Hook Proving

Grounds.
 From the New York sunl
 Captain Heath has been burning 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 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 a calculation is indicated by the fact that with our modern high-power guns the shot is often expelled at an initial velocity of two thousand feet per second, which is at the rate of mile in less than three sec- onds. Accurate knowledge of the veloei- ty of projectile is of the greatest impor- tance to the ordnance officer, who has to predict the range of the shot and its pen and efficiency of the gun, of the powder | and of the projectile itself.
 Captain Heath finds fault with powder 1 that gives an initial velocity of 1, 1865 feet per second to the one thousand pound pro- | iectile of the new twelve inch rife at San | dy Hook, when its velocity should be r. 1 975 feet per second. This is difference of only one hundred and ten feet, and the instrument that record it must be capable | of measuring the time interval to within the five-thousandth part of a second. A | difference of two or three hundred feet in velocity means in the big guns an impor tant difference in the powder used in the tests At Sandy Hook delicate electrical appliance called the Boulanger chrono graph measures this velocity accurately | and records it's own measurements This is the way it does it:
 In testing the large guns at these prov ing grounds two open frames are set up 1T front of the gun at distance of one hun dred and fifty feet from each other Wires are stretched back and forth across each of these frames, making 8 scree1 through which the projectiles must pass The wires in each of these screens form complete electric circuit, which includes
 also an electric battery and an electro mag
 net. When the gun is fired the projectil
 breaks the wire in the first screen, inter
 rupts the circuit, and at the same time tn
 armature of the magnet is released. In
 very small fraction of second the pro
 jectile has covered the distance to the sec
 ond screen and interrupted its circuit, re
 leasing another armature. The interval 0
 time between the drop of these two arma
 lures represents the time taken by the pro l Jeculle to traSel one nunureo ana uICy Ieet
 This period is so short that it is hardl
 conceivable. The chronograph, however registers it accurately. Wires run fror , each of these screens to the laborator
 near them, where are placed the chrono
 graphs, batteries, switchboard and othe l apparatus. The two electro magnets i circuit with the screens are embodied i the chronograph. The first magnet has a
 an armature an iron rod about three fee long, which is suspended in vertical pc sition from it's core. When the wires C t the first screen are broken this iron TO . falls. When the shot ruptures the wire (
 the second screen the armature of the se' ond electro magnet, which is placed a shol r distance below the first, is also released , It operates as knife, and striking u