Fig. 130. A five-pointed star. This has been already described.
It is desirable, sometimes, to convey the fire from a movable or rotating piece, to a fixed, or second rotating piece, which is effected thus. A leader, a, fig. 131, comes from the tail of the last case of the first rotating piece. This leader is tied, in one or more places, to one of the spokes of the wheel, and to the nave; and is left protruding at b. A tin box, or a bit of a mine case, d e f g, is attached to the fixed, or second movable piece in such a manner, as to surround, but stand clear of, the end of the match, b, as it revolves, with the wheel. A hole is made at c, and the end of a leader, from the second piece, brought through it. The inside surface of the box, d e f g, is smeared with meal-paste. When the leader catches at a, it blows through to b; this lights the smeared surface of the box; the flash communicates the fire to c, and this carries it where desired.
Sometimes a piece is made to drop, which is thus effected. Suppose a cylindrical piece of iron, 6 inches long, 3 inches diameter, standing upright; on this a second cylinder, 12 inches long, 2 inches diameter; and, on this, a third cylinder, 2 inches long, and 1 inch diameter. If now a brass ring 11⁄4 or 11⁄2 inches diameter be put on the top, it will slip down, and rest on the 2-inch cylinder; if a ring 21⁄2 inches diameter be slipped over the top, it will fall, and rest on the bottom 3-inch cylinder. It is obvious that, if a horizontal wheel, having a hole in the nave, 21⁄2 inches diameter, be slipped on, it will drop, and rest on the bottom cylinder; and that a second wheel, with a 11⁄2 inch hole in the nave, will rest on the second cylinder. The two wheels, then, may be placed on, and held together with a piece of thickly leadered match; the top wheel plays for a while, and carries the second wheel with it; the tail of the first, or other case, lights the bottom wheel, and at the same time blows the match to pieces, and the wheel drops. Of course three or more wheels may drop, one after another. See the design, fig. 166.
Sometimes a horizontal motion is changed to a vertical, thus. Suppose an upright wooden post, 3 inches square. Saw off the top 18 inches, and fix it on again, with a hinge; drive a staple, on the other side, into the top piece; also one into the bottom piece; and connect the staples with a piece of string, to prevent the top piece falling. In the top drive a spindle, as usual, to receive a horizontal wheel. On the side of the fixed post, against the hinge, fasten an iron bracket, to stand forward, so that the top part, when the string is cut, can fall down, and rest on the bracket. Now slip over the spindle a brass tube, 3 inches long, and almost a fit; then put on it a horizontal wheel, carrying a smeared box, as above described, to convey the fire to a fixed piece; on the top of the spindle screw a nut. To the bottom post, tie a piece of shell fuse, and let the string, that prevents the top piece from falling, be drawn over the mouth of this, and secured. It is obvious that if, after the wheel has played awhile horizontally, the shell fuse is lit by a leader, the string will be burnt in two; the top part will fall on to the bracket; and the horizontal motion will be changed to a vertical one.
Roman candles are best fired in bouquets of three or more; connect them with leaders about 3 inches long; and set them in a block of wood, containing three or more holes, diverging right and left; or tie them to struts of wood, nailed together, like the supports for garden flowers.
Two vertical wheels may be made to run round the outside of a table, to imitate the motion of the machine for grinding drugs, crushing clay, &c., like two parallel grindstones going round in a circular trough. Conceive a circular table, 20 inches diameter. With a gimlet bore a hole in the centre, large enough to admit a screw-eye, with liberty to turn easily round; slip through it a stair-rod, 2 feet long; it will overhang 2 inches at each end, and may be swung round. At the distance of about 4 inches from each end of the rod, imagine a cotton reel, or a pulley; when the rod is moved round, the reels or pulleys will roll round in a circle, like the cylinder-crushers, above mentioned. Now, if a vertical wheel were fixed at each end of the rod, so as to hang outside the table, it is obvious that, upon firing it, the wheels would run round. Of course it must not be a screw-eye and a stair-rod; but anyone will understand, from this description, how to effect it.
These contrivances have fallen somewhat into disuse, since the introduction and variety of colours, but it is well to understand them.
To Fire a Girandole of 100 Rockets at once.
Suppose a cubical tea-chest. In the top, bore ten rows of holes, ten in a row, with a centre-bit; the same in the bottom, in such a way that the bottom holes fall perpendicularly under the top holes. Fasten the box upon four legs, one at each corner. Sift from a pepper-box a layer of meal powder over the top; put in the rockets, with their primed mouths, naked, to rest on the sifted meal. It is evident that, upon conveying fire to the meal, by a leader, the flash will ignite the whole of the rockets, at once. Of course it ought not to be a tea-chest, but a box constructed on purpose, with a penthouse lid, to fall over, and protect the rockets, till desired to be fired. It may be furnished with four legs, as in fig. 173. The shelf, fig. 172, fits in at a b c, fig. 173.