A good method of Conductors for magazines built of masonry, would be such as already described, regard being had to the position of the building, its extent, and most prominent points, also to the nature, state, and condition of the soil, whether it be moist or dry, alluvial calcareous, or of hard rock; we must also consider the extent, disposition, and peculiar position of the metallic bodies entering into the general structure of the building, whether the roof be flat, pointed, or angular in various parts. The pointed projecting extremities of the two Conductors, one or more as the case may be, will be commonly sufficient; but, in buildings having tall chimneys or other elevated prominent points, at a distance from the Main Conductor, it will be requisite to guard such chimneys or other parts, by a pointed rod, led along them to the metals of the roof, or directly connected with the Main Conductors, by metallic connections. 12.--Pointed terminations of the Conductors in the air, are so far important that they tend to break the force of a discharge of Lightning when it falls on them. In fact, before the great shock actually takes place, under the form of a dense explosion, a very large amount of the discharge, which otherwise would be concentrated, runs off, as it were, through the pointed Conductor; but they have no other influence. With respect to these pointed terminations, no great care need be taken about them, except that they should consist of solid copper rod, of about three-quarters of an inch in diameter, and about a foot in length, and be united by brazing to the conducting tube, elevated at such convenient height above the walls of the building as the case may suggest. As a support to the Conductor, when raised above the wall, we may employ a small staff or spar of wood fixed to the masonry. 13.--Copper linings to the doors and window shutters of magazines are not objectionable, if requisite, as a precaution against fire; but they are useless as a means of keeping out Lightning; on the other hand, it is not easy to conceive a case in which the explosion of the gunpowder is to be apprehended from the action of Lightning on the doors or windows. Supposing, however, such metallic linings desirable as a precaution against common cases of fire, then the masses of metal should, according to the principles already laid down, have metallic communication with the general system of conduction in the building and the Main Conductor. ON THE EXPLOSIVE FORCE OF GUNPOWDER. ~Advantages of Gunpowder~