Page:The New International Encyclopædia 1st ed. v. 02.djvu/498

BALLISTICS. ducing therefrom algebraic formulas for the burning in air of grains of different shape — size and density of grain, the density of loading, the amount of heirt given off. the pressure of the gases, the "force' of the powder, and many other circumstances too numerous and technical for this article. Assuming the laws of perfect gases (Mariotte"s and Gay-Lussac's laws), he deduces from a study of all of the above circumstances formulae for the motion of the projectile, both inside and outside of the bore, and for the pres- sure inside the bore at different points. This different method; but the problem has never been accurately solved.

^'hen firing for ballistic purposes, one or more ohlc pressurc-fiauges are placed in the bore be- hind the cartridge. This instrument consists of a piston, moving in a cylindrical channel, and a copper cylinder to be compressed, which is in contact with the piston : the cylinder is central and kept in the axis of the housing by a spring. The change in length of this copper cylinder registers the maximum pressure of the powder, which is read off directly by an instrument specially designed for this purpose, called a calipher.

The velocity of this same shot is measured by the Le Boulenge Chronograph, or some similar in- strument. The Le Boulengi? Chronograph consists of two rods suspended vertically from electro- magnets, each ha^-in2 its own current and its 0' 0" A

PBESSURE CrRVE. OP — Axis of Pressures; OX — .Vsi^ o( Bore of Cannon; OP — Pressure if the charge burned instantaneouslj ; OP'P" a b X — Curve of quick-burning powder: OP'P'"b i — Curve of slow-burning or cocoa powder.

pressure, which may be graphically illustrated by the pressure curve, and which is called the 'maximum pressure.' when the chamber is full of powder was found, by experiment, to be 40 tons per square inch. By using the equation of this cure, Xoble and Abel found that, theoretically, one pound of gunpowder is capable of doing 536.35 foot-tons of work. This work is not all done on the projectile: some of it is used up in the recoil of the gun, some heating the gun and projectile, and some is lost in other ways. The factor of effect.' for instance, for the English S-inch gun is alK>ut 0.S3 : or S3 per cent, of the actual work done by the fired gunpowder is available for put- ting energy into the projectile. M. Emile Sarrau. a noted French engineer of explosives, has de- duced the equation

XOBLE PRESSFRE-OirOE. of mOtioU of tllC P— Piston: H— Housing: S— projectile in the fn^Jnif,' C-Cylinder; J-Clos- ^ore of the gun. Xoble and Aliel have made a very close approximation to the pressure- curve in guns, as has also General Mayevski. by a

LE BOULESGE CHROXOGRAFH. a and b — suspended rods; E and E' — el-eorro-magnets: B and S — stand with leveling-screws; O — marking-knife.

own target, and being independent of the other. The first target being broken, its magnet is demagnetized and its rod falls. The second tar- get being broken, its magnet is demagnetized, and the falling of its rod releases a marking- knife, which makes a mark on the first rod. while it is falling. A simple application of the laws of falling bodies furnishes the scale of time.

The forces acting on the fired projectile are the propelling force of the powder, modified by the ro- tating force caused by the bands and grooves: the action of gravity: and the resistance of the air. The exact resulting motion is very complex, but may be stated in general terms as follows: The proj>elIing force of the powder tends to drive the projectile forvard. in a straight line, in