2 Seconds 39⅛ Inches. ½ Seconds 9.8 ¼ Seconds 2.45 _Length of Pendulums to vibrate 2 Seconds at every Fifth Degree of Latitude._ +----------+---------+ |Degrees of|Length of| |Latitude. |Pendulum.| | |Inches. | +----------+---------+ | 0 | 39.027 | | 5 | 39.029 | | 10 | 39.032 | | 15 | 39.036 | | 20 | 39.044 | | 25 | 39.057 | | 30 | 39.070 | | 35 | 39.084 | | 40 | 39.097 | | 45 | 39.111 | | 50 | 39.126 | | 55 | 39.142 | | 60 | 39.158 | | 65 | 39.168 | | 70 | 39.177 | | 75 | 39.185 | | 80 | 39.191 | | 85 | 39.195 | | 90 | 39.197 | +----------+---------+ =Rule.=—_To find the Length of a Pendulum to make any Number of Vibrations, and_ vice versa. Call the pendulum, making 60 vibrations the standard length; then say, as the square of the given number of vibrations is to the square of 60; so is the length of the standard to the length sought. If the length of the pendulum be given, and the number of vibrations it makes in a minute be required; say, as the given length is to the standard length, so is the square of 60, its vibrations in a minute, to the square of the number required. The square root of which will be the number of vibrations made in a minute. _PETARDS_—are of four different sizes:—First, contain 12 lbs. 13 oz.—Second, 10 lbs. 11 oz.—Third, 1 lb. 10.—Fourth, one lb. Blind fuze composition { mealed powder 7 lbs. for Petards. { wood ashes 3 oz. _Stores for One Petard._ Hooks to hang the petard 2 Gimblets 2 Brass fuze 1 Wrench to screw the fuze 1 Blue paper portfires 6 Slow match yards 4 Props or forks 2 Copper funnels 1 Tallow ounces 8 Cartridges 1 _PLATFORMS._—The common platforms for gun batteries require the following materials for each:—5 sleepers or joists, 6 inches square, 14 feet long.—1 hunter, 8 or 10 inches square, 8 feet long, 14 planks, 1 foot wide, 11 feet long, 2½ inches thick.—20 pickets. The usual slope of platforms for guns is one inch to every yard. The platforms for mortar batteries are made with 3 sleepers 8 inches square, and covered with about 11 timbers of the same thickness. They are laid perfectly horizontal, about 15 feet asunder, and 12 feet from the epaulment. This is the distance commonly practised for firing only at 45 degrees elevation; but if the platforms be placed at the undermentioned distances from the epaulment, the mortars may be fired at the angles corresponding.