Cases for scrolls, should be made four or five inches in length, and their interior diameter three eighths of an inch; one end of these cases must be pinched quite close, before you begin to fill, and and when filled, close the other end, then in the opposite sides make a small hole at each end, to the composition, in the same manner as in Tourbillons; and prime them with wet meal powder: you may put in the head of a rocket, as many of these cases as it will contain; these cases being fired turn very quick in the air, and form a scroll or spiral line. They are generally filled with a strong charge, as that of serpents, or brilliant fire. Of Swarmers or small Rockets. Rockets which go under the denomination of swarmers, are those from two ounces downards. These small rockets are fired sometimes, in flights, and in large water-works, &c. Swarmers of one and two ounces, are bored, and made in the same manner as large rockets, except when headed, their heads must be put on without a collar; the number of strokes, for driving one ounce rockets, must be eight; and for two ounce rockets, twelve. All rockets under one ounce, are not bored, but must be filled to the usual height, with composition, which is generally composed, of fine meal prowder four ounces, and charcoal or steel dust two drams; the number of strokes for ramming these small swarmers, is not very material, so as they are rammed true, and moderately hard. The necks of unbored rockets, must be in the same proportion, as in common cases. Of the cause of sky Rockets rising. [Illustration] Having promised in the second section, to prove that the effect of sky rockets, and proportion of their charge, depends on the size of the cavity in the composition; I shall here endeavour to give a mathematical demonstration thereof. Let ABC be the hollow cone for the fire, AYCZB, the superficies of that cone, all the lines OZ at right angles with BC, all the lines OY at right angles with AC: now all the angles ZOY being towards R, whether the angles ZOY are obtuse or acute, but the more acute the better. The rays of fire ZO and YO issuing from the sides of the cone BC and AC, and continually acting with the greater force one upon another at O, forcing the whole BCA upward from the point R; and the wider the cone is, (so as not to exceed one third at bottom, and one sixth at top, of the exterior diameter of the rocket,) the greater velocity will the rocket rise with. Of Stands for Sky Rockets.