Page:The New International Encyclopædia 1st ed. v. 02.djvu/499

continuation of the axis of the bore; the action of gravity tends to pull the projectile downward, 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 fire. From this we 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 projectile 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 resistance of the air varies directly with the area of cross-section of the projectile. The inherent resistance which the air offers to the motion of the projectile depends upon the density and movements of the air — the density depends upon the temperature, the amount of moisture, and the barometric 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 thermometer to measure the temperature; a barometer to measure the weight or pressure of the air; an anemoscope (wind-vane) to find out the direction of the wind; an anemometer to determine the velocity of the wind; and a psychrometer to determine the humidity.

MARKER OF THE BUOLENGÉ CHRONOGRAPH. t — trigger; s — spring; m — marking-knife; b — pan for catching short rod; s' — spring.

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 1865 and 1880, using a very accurate instrument and comparatively modern projectiles, from which he concluded that the resistance varies with some power of the

velocity, and that this power varies with the velocity, being generally as follows:

Velocities between 900 and 1100 feet per second V Velocities between 1100 and 1350 feet per second V Velocities above 1350 feet per second V

These results have not been materially changed by subsequent experiments. The most recent and now generally used experiments are those made at Krupp's in 1881, and, discussed by General Mayevski, who deduced valuable, but complicated, formulas for resistance and retardation as a function of the velocity.

Ballistics of Penetration. In ballistics of penetration, we determine the effect on the tar- get, knowing the energy and inclination with which the projectile strikes, the resisting pow- ers of the material of the target, etc. He- cause it has been longer in the service, and more experimented upon than any other, most of the formulas for penetration are deduced for wrought-iron armor, on one of two supposi- tions: First, that the projectile, acting as a punch, separates a disk of metal from the plate; and second, that the projectile, acting as a wedge, forces the particles of metal apart. The Fairburn, English Admiralty, and the Muggiano formulas are based on the first supposition, and the de Marre, Mailland, Krupp, and Gavre on the second. For steel armor the unsatisfactory method was formerly used of calculating the penetration by the wrought-iron formulas, and adding a certain percentage of increase of re- sistance, varving from 10 to 30 per cent. In modern Harveyized plates penetration seldom occurs, owing to the hard face of the plate, unless the gun greatly overmatches the plate. To give an idea of what the penetration really is, Captain Orde-Browne's rule may be quoted: "The penetration of a projectile in wrought-iron armor is one calibre for every 1000 feet of striking velocity." For example, a 12-inch pro- jectile striking with a velocity of 2000 feet per second, should penetrate 24 inches of wrought iron. See Armor Plate.

Ballistic Tables consist of the tabulated value of the space, altitude, inclination, and lime functions of the velocity.

These functions, together with various auxiliarv data, are calculated and tabulated for all practicable ranges and velocities, and for all the guns in service.

Those desiring further information on the subject of ballistics, are referred particularly to the works of Colonel Ingalls, of the U. S. Artillery Corps, who is one of the greatest living authorities on ballistics; these may be found in the Artillery Circulars published by the United States War Department. The bibliography available includes: Ingalls, Interior Ballistics (New York, 1886); McKinley, Text-Book of Gunnery (England, 1887); Noble and Abel, Experiments on Fired Gunpowder (England, 1880); Meigs and Ingersoll, Interior Ballistics (U. S. Naval Academy, 1887); Bruff, Ordnance and Gunnery (New York, 1896); Mayevski, Traité de balistique intérieure (Saint Petersburg, 1870); Longridge, Internal Ballistics (New York, 1887); Glennon, Interior Ballistics (Baltimore, 1894). Other authorities on the subject are: Siacci, Otto, Bashforth, Nivens, Sladen, Sarreau, Hojel, Hutton, Robins, Piobert, Morin, and Didion.

For the practical questions involved in the actual construction of guns and carriages, the