~Effects of Fouling.~ Fouling occasions loss of power from the increased friction, and causes inaccuracy in direction and elevation, by filling the grooves, and thus preventing the proper spiral motion being imparted to the projectile. EFFECTS OF GUNPOWDER ON METALS. ~Difference of effect on brass and iron guns.~ The effect produced by Gunpowder on metals, in long continued and rapid firing, is very extraordinary. Several of the guns employed at the siege of San Sebastian were cut open, and the interior of some of the vent holes, which were originally cylindrical, and only two-tenths of an inch in diameter, were enlarged in a curious and irregular manner, from three to five inches in one direction, and from two to three inches in another, but the brass guns were much more affected than the iron. In December, 1855, there were lying in the arsenal at Woolwich several of the heaviest sea mortars, which had recently been used at the bombardment of Sweaborg, and the continuous firing on that occasion had split them into two nearly equal portions from muzzle to breech, a trunnion being with each half. Heavy guns for garrisons, sieges, &c., are made of cast iron; guns for field purposes, where lightness is required, are made of gun metal. ~Difference of effect of brass and iron guns~ These guns are generally denominated brass guns. They can be loaded, properly pointed at an object, and fired about four times in three minutes, but they will not stand long continued rapid firing, or more than 120 rounds a day, as the metal, when heated, softens, and the shot then injures the bore. Heavy iron guns may be loaded, fired, &c., once in two minutes. They suffer more from the total number of rounds that have been fired from them, without reference to the intervals between each round, than from the rapidity of the firing. Four hundred and five hundred rounds per day have not rendered an iron gun unserviceable. MISCELLANEOUS EXPERIMENTS. The following experiments, extracted from Mr. Wilkinson’s “Engines of War,” serve to illustrate the capability of metals to resist the force of gunpowder, and may be of some practical utility, as well as prove interesting merely as matter of curiosity.