diameter, and weighs 4-1/3 tons.  The “300-pounder” smooth-bore has 11 feet length and 10-1/2 inches diameter of bore, 38 inches maximum diameter, and weighs 10-1/2 tons.  The Mersey Iron-Works guns are of wrought-iron, and are forged solid like steamboat-shafts, or hollow by laying up staves into the form of a barrel and welding layers of curved plates upon them until the whole mass is united.  But few of these guns have been fabricated.  The most remarkable of them are, 1st, the Horsfall smooth-bore, of 13 inches bore, 44 inches maximum diameter, and 24 tons weight,—­price, $12,500; 2d, the “Alfred” rifle, in the recent Exhibition, of 10 inches bore,—­price, $5,000; 3d, the 12-inch smooth-bore in the Brooklyn Navy-Yard, which, though very light, has fired a double 224-pound shot with 45 pounds of powder:  if properly hooped, it would make the most formidable gun in America.  Blakely has constructed for Russia two 13-inch smooth-bore guns, 15 feet long and 47 inches maximum diameter, of cast-iron hooped with steel:  price, $10,000 each.  He has also fabricated many others of large calibre, on the principles before mentioned.  The 15-inch Rodman smooth-bore cast-iron gun is of 48 inches maximum diameter, 15 feet 10 inches long, and weighs 25 tons.  The cost of such guns is about $6,000.  The Dahlgren 15-inch guns on the Monitors are about four feet shorter.

Results of Heavy Ordnance.  The 10-1/2-inch Armstrong gun sent a round 150-pound shot, with 50 pounds of powder, through a 5-1/2-inch solid plate and its 9-inch teak backing and 5/8-inch iron lining, at 200 yards, and one out of four shots with the same charge through the Warrior target, namely, a 4-1/2-inch solid plate, 18-inch backing, and 5/8-inch lining.  The Horsfall 13-inch gun sent a round 270-pound shot, with 74 pounds of powder, entirely through the Warrior target at 200 yards, making an irregular hole about 2 feet in diameter.  The same charge at 800 yards did not make a clean breach.  The Whitworth shell burst in the backing of the same target has been referred to.  Experiments on the effect of the 15-inch gun are now in progress.  Its hollow 375-pound shot (3-inch walls) was broken without doing serious damage to 10-1/2-inch laminated armor backed with 18 inches of oak.  The comparative test of solid and laminated armor has already been mentioned.  The best 4-1/2-inch solid plates, well backed, are practically proof against the guns of English iron-clads, namely, 68-pounder smooth-bores and Armstrong 110-pounder rifles, the service charge of each being 16 pounds.

Rifling and Projectiles.  The spherical shot, presenting a larger area to the action of the powder, for a given weight, than the elongated rifle-shot, has a higher initial velocity with a given charge; and all the power applied to it is converted into velocity, while a part of the power applied to the rifle-shot is employed in spinning it on its axis.  But, as compared with the rifle-shot, at long ranges,