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WHEN the Council of Military Education directed my attention to the science of ballistics in 1864, I came to the conclusion that a thoroughly good chronograph would solve all practical difficulties. The newly-invented instrument was first tried in 1865 with ten screens 120 feet apart, by the ue of a 12-pr. Armstrong B.L. gun, when eleven satisfactory rounds were obtained. (Report (84/B/1941), and (Proc. of the R.A. Inst., 1866.) Afterwards Government decided to have systematic experiments made to determine the resistance of the air to ogival headed projectiles (1.5d) fired from 3, 5, 7 and 9-inch M. L. guns, which were carried out in 1867–68 for velocities 900 to 1700 f.s. The results then obtained are still in use.

In a previous communication to the Royal Society, the author exhibited a curve which may be described as the characteristic curve of any gun, charge and projectile, in which the abscissæ are ranges, and ordinates are tangents of the angles of elevation, or simply these angles when they are small. That communication contained (1) a geometrical construction for deducing a new characteristic curve when the air density or the gun’s calibre is changed; (2) the analytical proof of that law; (3) the law for deducing a new characteristic curve when the muzzle velocity is changed; (4) a comparison of range-tables showing how, by help of these laws, from the characteristic curve for a gun of any calibre and muzzle velocity, to deduce the curve for a gun of any other calibre and muzzle velocity; and (5) empirical formulæ enabling a practical gunsight to be so constructed that when set for true range, it is also set for the true elevation, whatever the calibre of the gun, the muzzle velocity, the air density, and the rate of change of range may be.