468. When ranges are desired to be obtained by reduced charges, the measuring and filling of the cartridges must always be done in the magazine, no matter how inconvenient it may be; and the utmost exactness is to be observed in filling the powder-measures and levelling off the top, as an ounce of powder makes an important variation in the range of the bomb.
469. Extra cotton bags are to be provided to receive the reduced charges, which are to be stowed in half barrels.
470. Every precaution that suggests itself to the officers in command to prevent accidents, should immediately be put in force, and a memorandum of the matter transmitted to the Ordnance Officer of the squadron.
GENERAL RULES AND OBSERVATIONS.
471. To estimate the distance by the bursting of a bomb, where the flash can be seen, multiply the number of seconds which elapse between it and the sound of the report by 1,100, and the product will be nearly the distance in feet.
472. The officer in charge of a mortar must always note the time of flight and distance, by the above rule, for every bomb that is fired, and likewise note when the report is not heard from the bursting charge.
473. When going into action for a bombardment, the fore-rigging must be come up on the side where the mortar is to be used, the fore-topmast sent down, foresail unbent, boom and gaff laid on deck, rigging lashed in close to the mast, head-sails to be thoroughly wetted, spring on the cable, boats lowered from the side davits, and all the hatches covered with tarpaulins.
474. The broadside-guns must be kept ready for action, and muskets loaded and at hand, in case the squadron should be attacked by the enemy's gunboats.
475. Besides bombs, various other projectiles are fired from mortars, such as carcasses, which are shells having three holes of similar dimensions to the fuze-hole, pierced at equal distances apart in the upper hemisphere, with their exterior openings touching the great circle which is perpendicular to the axis of the bore.
476. These carcasses are placed in the mortar in the same manner as the bomb, and are filled with inflammable mixtures, and should be transported in a vessel by themselves, as they are dangerous companions. Thirteen-inch carcasses weigh 194 pounds each.