Suppose that such a bullet describes the trajectory M, and A.B. be the position of its axis, it will be seen that the lower part of the bullet re-establishes the air compressed, whilst the upper part finds itself in the rarified air. That, consequently the lower parts of the cannelures are submitted to the direct action of the air’s resistance, whilst their upper parts totally escape this action. (Plate 21, fig. 2). The resultant of the air’s resistance evidently tends to bring back the point of the moving body, according to the trajectory; but as this action is produced by the pressure of an elastic fluid, it results that the point B, after having been an instant upon the trajectory, will fall below, in virtue of the velocity acquired; but then the upper grooves finding themselves acted on by the action of the air’s resistance, this action, joined to its weight, will force the point of the projectile upwards, which will descend to come up again, so that the projectile will have throughout its flight a vertical swing, which is seen distinctly enough in arrows. ~Union of Robins and Tamisier.~ Let us connect the suggestion of Robins, with the experiments of Captain Tamisier, to cause the posterior end to act as a rudder to guide the projectile in its true path, as undoubtedly during the descent of a bullet there is a tendency for the centre of gravity to fall first, as the ball of the shuttlecock. In the first Prussian balls, and in those used in the Tige, the centre of gravity being nearer the base, the rear end of these balls have a tendency to fall before the foremost, but this is most undoubtedly counteracted by grooves, while it would be impossible to fire an elongated projectile with its centre of gravity backwards, with any accuracy out of a smooth-bored gun. ~Cannelures improved shooting.~ ~Why none in English bullet.~ Captain Jervis says that these grooves have the effect of improving the accuracy of firing when the bullets are not perfectly homogeneous, is certain, but the British Committee on small arms justly considered that owing to the careful way in which the bullets are made in England by compression, these grooves might be dispensed with. ~Variety of forms.~ ~Auxiliaries to expansion, various.~ Almost every conceivable form of projectile, internal and external, have been made and experimented upon. Auxiliaries to expansion have been used, made of metal, horn, wood, and leather, with plugs, screws, or cups of divers shapes. Cannelures are used, of varying forms, depth and number. ~Rotation from smooth bores.~ It has even been attempted to construct bullets upon the screw principle, so that the projectile should receive spirality from the action of the air upon its outer or inner surface, when fired out of a smooth bore musket. ~General characteristics of modern rifles.~