For 21⁄2 inches?—21⁄2 x 5 = 121⁄2 drams = 3⁄4 oz.
For 3 inches?—3 x 6 = 18 drams = 11⁄8 oz.
It is by no means necessary to be exact; but the formula will serve as a guide.
Fig. 123. A jack-in-the-box. This is a case formed on a square prism of wood. The paper is to be pasted all over, but as it cannot be rolled, it must be folded over, one side at a time, and rubbed smooth with a tooth-brush handle, or pressed with the fingers. The bottom may be formed by bending in, to a right angle, two opposite sides, and pressing them flat; then, upon them, the two remaining sides, like packets of cocoa, &c. Or a square piece of wood may be glued in for a bottom. The same blowing charge as for mines.
Fig. 124. A devil-among-the-tailors: a mixture of crackers and serpents; a roman candle in the middle, having its bottom stopped with shell fuse, instead of plaster of paris: 3, or 4, or any number of roman candles, at regular distances, round the outside: these are to be tied with string, and a strip of pasted paper fastened round.
Fig. 125. A line-rocket: two rockets tied to a piece of roman candle case, head to tail: that is, one rocket tied in one direction, the other, in the reverse. This simply runs up and down a line.
Fig. 126. A pigeon frame (of which fig. 127 is a cross section) may be made by taking a piece of deal, or alder, say 6 inches long, and 11⁄2 inch square: bore a hole through the length to receive the line upon which it is to run; plane off the corners, lengthwise, and channel them with a gouge, to form 4 semi-cylinders for the rockets to lie in: in the middle glue 4 spokes, each about 4 inches long; and round the spokes nail a wheel. A piece of cane makes good spokes, light and strong. Tie on the frame, lying in the channels, four 6⁄8 rockets, two pointing one way; two, the other: the clay or plaster of paris, in these rockets, is not to have a hole through it, as usual, but to remain perfectly closed. On the wheel, tie four 5⁄8 wheel cases, charged with wheel case fuse, No. 1 or No. 10. Leader it thus: touchpaper the mouth of one wheel case. From the tail of this first wheel case, carry two leaders; one to the next wheel case, and one to the rocket whose mouth is nearest: the tail of the second wheel case lights the third wheel case and second rocket; and so on. A long clothes line must be stretched tight for this to run along; it should start 3 or 4 yards, at least, from the post to which the line is tied: and the rope should be so long that the first rocket could not carry it to the end; otherwise the leaders are apt to snap and spoil the piece. Towards the end, as the piece gets lighter, it will run the whole length of the rope, without injury. It is necessary to indicate the first, or starting rocket, by some means; a piece of red paper may be pasted round the mouth; or, an inch or two of string may be tied to it; or the match may be bent and tied so as to project an inch or two longer than the others. On fixing it on the line, in the dark, you can then feel which is the starting rocket, and place its mouth towards the starting post, without hesitation. Of course the pigeon runs away in the opposite direction.
Fig. 128. A pigeon-house, made with lances; this may be fixed in a central position, and have 4 lines running from it: east, west, north, and south. As soon as the lances are well alight, start the pigeons. This is not necessary for amateurs. One pigeon is sufficient, without any pigeon-house.
The piece, fired at the Crystal Palace, termed a comet, is a combination of the pigeon, fig. 126, and the turning sun, fig. 114. Construct a pigeon frame, with two hoops, one at each end; to these hoops, attach brilliant cases, or gerbes, placed obliquely: point the mouths of all the rockets and gerbes in the same direction. The whole of the cases may be lit at once; or a short case may fire the rockets after the piece has partly descended the line, by its own weight. The line, at the Crystal Palace, is stretched from the top of the northern tower to the ground.
Fig. 129. A double guilloché, or windmill piece. This represents two windmills, turning in opposite directions; and imitates the engine turning, on the backs of watches.