Small gerbes may be made of four, eight ounces, or one pound cases, pasted and made very strong, of what length you please; but, before you fill them, drive in dry clay one diameter of their orifice high, and when you have filled a case, bore a vent through the center of the clay to the composition; the common proportion will do for the vent, which must be primed with a slow charge. These sort of cases without the clay, may be filled with Chinese fire. To make Paste-board and Paper Mortars. Fig. 26, a former, and 27, an elm foot for the mortar; 28, a mortar compleat; these mortars are best when made with paste-board; your paste-board must be well pasted before you begin; or, instead of paste, you may use glue. For a coehorn mortar, which is four inches two fifths diameter, roll the paste-board on the former one sixth of its diameter thick; and, when dry, cut one end smooth and even, then nail and glue it on the upper part of the foot; when done, cut off the paste-board at top, allowing for the length of the mortar two diameters and a half from the mouth of the powder chamber; then bind the mortar round with a strong cord wetted with glue. U, the bottom part of the foot, is one diameter two thirds broad, and one diameter high; and that part which goes into the mortar is two thirds of it’s diameter high. W, is a copper chamber for powder, made in a conical form, and is one third of the diameter wide, and one and a half of its own diameter long; in the center of the bottom of this chamber, make a small hole a little way down the foot; this hole must be met by another of the same size made in the side of the foot, as is shewn in Fig. 28. If these holes are made true, and a copper pipe fitted into both, the mortar when loaded will prime itself, for the powder will naturally fall to the bottom of the first hole; then, by putting a bit of quick-match in the side hole, your mortar will be ready to be fired. Mortars of five and a half, eight, and ten inches diameter, may be made of paper, or paste-board, by the above method, and in the same proportion; but if larger, it will be best to have them made of brass. N. B. The copper chamber, must have a small rim round its edge with holes in it, for screws to make it fast in the foot. SECT. IV. The Manner of loading Air Ballóóns, with the Number of Stars, Serpents, Snakes, Rain-falls, &c. contained in Shells of each Nature. As ballóóns are held in great esteem, by most admirers of fire works, I shall here give a full description of them in every particular, in so clear a manner, that a young practitioner may, by taking a little pains, be pretty certain of succeeding the first trial.