Big Guns. 129 



tiplying the square of the velocity by one-half the mass of the pro- 

 jectile, since the mass is equal to the weight divided by the force 

 of gravity. 



"The expression of the work stored in the projectile, and which 



must be expended in bringing it to resti^z where W.=weight 



of the projectile, V.=velocity of the projectile in feet, and g= the 

 force of gravity in feet, or the velocity a body will acquire by its- 

 own weight in one second of time. " 



The machines for ascertaining pressure are : The ballistic pendu- 

 lum, Navez's Chronoscope, Benton's thread velocimeter, Bou- 

 lenges' Chronograph, Schultz's Chronoscope, Rodman's pressure 

 guage, Noble's Chronoscope and Vignotti, Cashing and others. 

 Through the kindness of Capt. A. H. Russell, U. S. ordinance corps, 

 we have the opportunity of examining the chronoscopes which were 

 displayed at the War Dep.irtment Exhibit at the Cincinnati Expo- 

 sition. Capt. Russell will demonstrate the practical working of 

 these machines. 



Tne purpose of these michines is to measure the velocity of a 

 bullet or a caniion ball, while passing over the space between two 

 targets. 



Whether we use pendulums, or heavy rods, as in the Boulange 

 machines, the general principles are the same. I have made a draw- 

 ing on the blackboard of the Boulange machine, as it seemed to me 

 to be the simplest to understand. 



This instrument consists of a central standard or supi)orting rod 

 which carries two electro-magnets. The magnet highest upon the 

 Standard is connected by electric wires to target No. i, and it sup- 

 ports a heavy rod of 20 inches in length, which rod drops the 

 instant that target No. i is attained by the projectile. When target 

 No. 2 is ruptured the magnetic current to the second magnet 

 is cut, and instantly the second rod falls. In falling it strikes the 

 disk at the end of a lever, which sets free a circular knife. This 

 knife makes a cut on the first rod, which thus records how far 

 the first rod had fallen before the second rod was set free. 



Before beginning to experiment, you set free the short rod only,, 

 and the cut or nick made by the knife when the long or chronome- 

 ter rod is at rest, will give the "origin" or zero point from which 

 you measure the height fallen by the chronometer rod, while the 

 projectile is traversing the distance between the targets. 



