No step of importance seems to have been made in gunnery till the year 1742, when Dr Jurin proposed some questions, which the Royal Society appointed a commit tee to investigate. The first of these questions was, Another series of experiments was made at La Fere, with different pieces, elevated to different angles, and charged ivith different quantities of powder. The follow ing were the results.
In the year 1740,a series of experiments were made at Metz with great care and attention. In the experiments of La Fere, the medium ranges only were given, but at Metz the result of each trial was set clown. 'I he piece which was used was a 24 pounder, 10 long. It was charged with different quantities of powder, 8 to 20 lb. It had always an elevation of ; but as it was placed about 78 feet above the plain where the bullets fell, the elevation should be considered as s°. The following ate the results.
Hitherto no general principle had been established by the numerous experiments of which we have given a short account ; but the subject of gunnery was now destined to receive the most important improvements from the labours of Mr Benjamin Robins, who published an account of them in 1742, in his IVCIU Principles of Gunnery, containing the determination of the force of Gunpowder, and the investiga tion of the dyferenccs in the resisting power of the air to swift and slow motions. In this valuable work, he begins by determining the explosive force of gunpowder, (see our article GUNFOWDER, p. 187.) and he found that this force was owing to an elastic fluid like air, which existed in a highly condensed state in the powder, and being suddenly separated from it by combustion, expanded, and impelled the bullet with prodigious force.
Mr Robins then proceeds to determine the velocity with which gunpowder will impel a shot of a given weight from a cannon of given dimensions ; and in order to compare the velocities thus computed with the real velocities, he in vented an instrument called the Ballistic Pendulum, by which he was enabled to measure the real velocities of bul lets of all kinds with such accuracy, that in the case of a bullet moving with a velocity of 1700 feet per second, the error will never amount to part of the whole.
With this machine he made a great number of experi ments, with musket barrels of different lengths, charged with different quantities of powder, and carrying balls of different weights ; and the agreement between the calcu lated and observed velocities is so surprising as to establish his theory on the firmest foundation.
Mr Robins proceeds to point out the changes which take place in the force of gunpowder, from variations in the heat and moisture of the atniospherc : Ile determines the velocity which the flame of gunpowder acquires by expand ing itself, to be 7000 feet per second : lie ascertains the manner in which the flame of the powder impels a ball, placed at a considerable distance from the charge ; and he enumerates the various kinds of powder, and describes the best methods of examining its goodness. • Mr Robins then treats of the resistance of the air, and of the track described by the flight of shot and shells. He chews, from experiments made with the ballistic pendu lum, that at different velocities there was a gradual in crease of the resistance over the law of the square of the velocity, as the body moved quicker. He then proves, that a 24 pound ball fired with a full charge of powder, expe riences, when it first issues from the piece, a resistance more than 20 times its weight ; that the paths of projec tiles, when the velocity of projection is considerable, is not nearly a parabola ; and that, in their flight; bullets are not only depressed beneath their original direction by the ac tion of gravity, but are frequently deflected to the right or left of that direction by the action of some other force. Ro bins' Principles of Gunnery was translated into German by Euler, who honoured it with learned and valuable commen taries.
About eight or ten years after the publication of Robins' Works, the Chevalier D'Arcy published, in the Memoirs of the Academy for 1751, a Treatise on the Theory of Ar tillery, in which he gives an account of a series of experi ments made with great care. He employed two pendu lums, against one of which he fired the ball, while the other, from which the small cannon was suspended, served to measure the recoil. These experiments were afterwards extended, and published in his Essais d'une Theorie de r?irtillerie, which appeared in 1760.