The velocity of this same shot is measured by the Le Chronograph, or some similar in strument. The Le Boulengi; Chronograph consists of two rods suspended vertically from electro magnets, each having its own current and its pre-sure. which may be graphically illustrated by the pressure curve. and which i- 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 curve. Noble and Abel found that. theoretically. o n e 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 in-lance. for t he S-inch gun is about 0.S3: or 53 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 ciliation of motion of the projectile in the bore of the gun. Noble and Abel have made a very close approximation to the pressure curve in guns. as has also General iayevski. by a 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 ma!_met is demagnetized. and the falling of its rod relea-es a marking knife, which makes a mark on the first rod. while it is falling. A -imple 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 re-i-tanee of the air. The exact resulting motion is very complex. but may be stated in general terms as follows: The propelling force of the powder tend- to drive the projectile forrard. in a straight line, in continuation of the axis of the bore; the action of gravity tends to pull the projectile down ward, in a straight line. toward the centre of the earth; the resistance of the air, combined with the action of gravity and the rotation of the projectile, causes the axis of the projectile to describe a cone about the tangent to the trajectory, and forces the projectile to the right out of the plane of lire. From this Wl• see that the trajectory is a curve of double curvature; the trajectory which we ordinarily consider, being the projection of the actual curve on the plane of fire. The resistance which the projec tile meets from the air depends upon the form and cross-section on the projectile, the density of the air, and the velocity of the projectile. It has been found from experiment that the ogival head of two to three calibres' radius offers less resistance than any other. The resistanee of the air varies directly with the area of •ross section of the projectile. The inherent resistance which the air offers to the motion of the pro jectile depends upon the density and movements of the air—the density depends upon the tem perature, the amount of moisture, and the baro metric pressure; the effects of the movement of the air depend upon the direction and velocity of the wind. To make a proper study of the resistance of the air,. we use a therminneter to measure the temperature; a barometer to measure time weight or pressure of the air; an anemoseope (wind-vane) to find out the direc tion of the wind; an anemometer to determine the velocity of the wind; and a psychrometer to determine the humidity.
The relation between the velocity of the pro jectile and the resistance of the air is a very complicated one. and must be studied in text books on the subject. The Rev. Francis Bash
forth made a series of very valuable experiments upon this subject between 1863 and 1880, using a very accurate instrument and comparatively modern projectiles, from which he concluded that the resistance varies with sonic power of the velocity, and that this power varies with the velocity, being generally as follows: velocities b.-tweet, Sq0 sad 11011 feet per WWI /Rd .N'* Velocities between I WO and 135n feet per second Velocities above MO feet per second Theme results have not been materially changed by subsequent experiments. The most recent and now generally used experiments are those made at K•upp's in 1881, and, discussed by Oeneral Nayevski, who deduced valuable. but complicated, formulas for resistance and retarda tion as a function of the velocity.
BALLisTics or PENETRATioN. hi ballistics of penetration, Are determine the effect on the tar get, knowing the energy and inclination NV th which the projectile strikes, the resisting pow ers of the matetial of the target, etc. Be cause it lies been longer in the service, and niore experimented upon than any other, most of the formulas for penetration are deduced for wrought-iron armor, on sue of two supposi tions: First, that the projectile• acting as a punch, separates a disk of octal from the plate; and second, that the projectile, acting as a wedge, forces the particle I if nuelal The Fairburn. English .Admiralty, and the Aluggiano formulas are based on the first supposition, and the de tlarre, Alaitland, Krupp, and Oavre on the second. For steel armor the unsatisfactory method was formerly used of caleulating the penetration by the wrought-iron formulas. and adding a Pertain percentage 14 increase of re sistan•e, varying from 10 to 30 per cent. In modern llarveyized plates penetration seldom occurs, owing to the hard face of the plate, unless the gun greatly overniat•lies the plate. To give an idea of what the penetration really is, Captain O•de-Browne's rule may be quoted: "The penetration of a projectile in wrought-iron armor is one calibre for i•very 1000 feet of striking velocity." For example. a 12-in•h pro jectile striking with a velocity of 2000 feet per serunil, should penetrate inches of wrought iron. See ARMOR PLATE.
Ballistic Tables consist of the tabulated value of the .space, altitude. inelinat ion. and time func tions of the velocity.
These functions. together with various auxili ary data. are calculated and tabulated for all practicable ranges and velocities. and for all the guns in service.
Those desiring further information on the sub ject of ballistics, are referred particularly to the works of Colonel Ingalls, of the U. S. Artil lery Corps, who is one of the greatest living au thorities on ballistics: these may be found in the Artillery Circulars published by the United states War Department. The bibliography available includes: Ingalls. Infrrior Ballistics (New York, 1886) : 3IeKinley. Tc.rt-Book of Gunnery ( England, 1887) ; Noble and Abel, E• perintent.s on Eircd Gnopoi•der I England, 1880) ; Aleigs and Ingersoll, l ntcrior Ballistics (I'. S. Naval Academy, 1887 ) Bruff. Ordnance and Gunnery (New York. IS06) ; Mayevski, Trait/ le balist Wine inWrieurc (Saint l'etersburg, 1870) ; Longridge. Internal Ballistics (New York, 1887) ; Olennon, interior Ballistics (Baltimore. 1894). Other authorities on the subject aw: Siact-i, Otto, Bashforth, Nivens. Sladem Sarreau. Ilojel, Hutton, Robins. Piohert. :Morin. and Didion.
For the practical questions involved in the actual construction of ..runs and carriages, the reader should consult the article ORDNANCE, where the process of manufacture and assembly is described. See also GUNNERY: ARMOR PLATE; ARTILLERY: EXPLOSIVES, and similar articles.