The early methods adopted in the construction of cannon to impart to the projectile the desired rotary motion are as interesting as the early methods adopted in the construction of the projectile. Heavy rifled artillery was introduced in 1856 against Cronstadt. The English artillery at Sebastopol used the Lancaster Gun, illustrated in Fig. 19. The form of the bore section of this gun was that of an ellipse of 8" and 8-5/8" diameters, the bore being generated by the section of such an elipse making a revolution of about one-quarter turn in the length of the bore, the center of the section always co-incident with the longitudinal axis of the gun, forming thereby a continuous elliptical cylinder, the greater axis at the muzzle lying in the vertical plane and gradually becoming horizontal at the breech section, or in other words, the whole length and section of the bore was a rifle twist of one quarter of a turn in its length. The projectile was a wrought iron shell of the form and size indicated in Fig. 20, as ascertained by measurement of one found in the trenches at Sebastopol. [Illustration: Fig. 20] The use of these guns in the siege was by no means satisfactory, giving neither precision of fire nor extraordinary range, while the gun more often failed by bursting than other types. The principle, however, met with favor and was studied and improved upon. Another method of applying the rifle principle to heavy guns consisted in casting a segment of a sphere (nearly) on the side of the cylinder part of the shot with corresponding grooves in the bore of the gun, making about one turn in twenty feet. It is somewhat like the principle of the solid musket ball, Fig. 7 with a difference in the shape of the projections, as shown in the annexed Fig. 21, giving the form and size (nearly) of the shot. Guns of this pattern were adopted for many of the gunboats fitted out by France for operations in the Baltic in 1856, some with four and others with two guns each. [Illustration: Fig. 21] [Illustration: Fig. 22] The bore of the gun had a circular section of 6-1/2" diameter with two grooves cut in it, as shown in Fig. 22, which in the length of the bore had a twist equal to one turn in six meters. Figures 23 and 24 represent cast iron shot "of very peculiar shape, intended apparently, as a substitute for the rifle groove. They were cylinders of about four inches diameter, with a flattened spherical head from which three spiral openings communicate with the open interior of the cylinder. The cylindrical part was formed with grooves...." [Illustration: Fig. 23] [Illustration: Fig. 24] The Modern Type of Gun