Horizontal wheels are often fired two at a time, and made to keep time, like vertical wheels, only they are made without any slow or dead fire; ten or twelve inches will be enough for the diameter of wheels, with six spokes. [Fig. 40.] represents a wheel on fire, with the first case burning.
Of Spirali Wheels.
Spirali wheels are nothing more than double horizontal wheels, and are thus made: The nave must be about six inches long, and somewhat thicker than the single sort; instead of the pintle at top, there must be a hole for the case to be fixed in; there must also be two sets of spokes, one set near the top of the nave, and the other near the bottom. At the end of each spoke cut a groove, wherein you tie the cases, there being no fell; the spokes should not be more than three inches and a half in length each from the nave, so that the wheel may not be more than eight or nine inches diameter; the cases are placed in such a manner, that those at top play down, and those at bottom to play up, but let the third or fourth case play horizontally. The case in the middle may begin with any of the others, you please; six spokes will be enough for each set, so that the wheel may consist of twelve cases, besides that on the top: the cases for these sort of wheels need not be more than six inches in length each.
Of Plural Wheels.
Plural wheels are made to turn horizontally, and to consist of three sets of spokes, placed in the following manner, six at top, six at bottom, and four in the middle, which must be a little shorter than the rest; let the diameter of the wheel be ten inches; the cases must be tied on the ends of the spokes, in grooves cut on purpose, or in pieces of wood, nailed on the ends of the spokes, with grooves cut in them as usual; in cloathing these wheels, make the upper set of cases play obliquely downwards, and them at bottom obliquely upwards, and them in the middle horizontally. In placing the leaders, you must order it so that the cases may burn thus: viz. first up, then down, then horizontal, and so on with the rest, but another change may be made, by driving in the end of the eighth case, two, or three ladles full of slow fire, to burn till the wheel has stopped its course; then let the other cases be fixed the contrary way, which will make the wheel run back again: for the case at top, you may put a small gerbe; and let the cases on the spokes be short, and filled with a strong brilliant charge.
Of the Illuminated Spiral Wheel.
First have a circular horizontal wheel made two feet diameter, with a hole quite through the nave; then take three thin pieces of deal, three feet in length each, and three quarters of an inch in breadth each; one end of each of these pieces, nail to the fell of the wheel, at an equal distance from one another, and the other ends nail to a block with a hole in its bottom, which must be perpendicular, with that in the block of the wheel, but not so large. The wheel being thus made, have a hoop planed down very thin and flat, then nail one end of it to the fell of the wheel, and wind it round the three sticks in a spiral line, from the wheel to the block at top; on the top of this block fix a case of Chinese fire; on the wheel you may place any number of cases, which must incline downwards and burn two at a time. If the wheel should consist of ten cases, you may let the illuminations and Chinese fire begin with the second cases; the spindle for this wheel must be a little longer than the cone, and made very smooth at top, on which the upper block is to turn, and the whole weight of the wheel to rest, see [fig. 41.]
Of the Double Spiral Wheel.
For this wheel, the block, or nave, must be as long as the height of the worms, or spiral lines, but must be made very thin, and as light as possible. In this block must be fixed several spokes, which must diminish in length, from the wheel to the top, so as not to exceed the surface of a cone of the same height. To the ends of these spokes nail the worms, which must cross each other several times; these worms cloath with illuminations, the same as those on the single wheels, but the horizontal wheel, you may cloath as you like. At top of the worm, place a case of spur-fire, or an amber light, see [fig. 42.] This figure is shewn without leaders, to prevent a confusion of lines.
Of Ballóón Wheels.