Horizontal wheels are best when their fells are made circular; in the middle of the top of the nave, must be a pintle, turned out of the same piece as the nave, two inches long, and equal in diameter to the bore of one of the cases of the wheel; there must be a hole bored up the center of the nave, within half an inch of the top of the pintle; the wheel being made, nail at the end of each spoke (of which there should be six or eight) a piece of wood, with a groove cut in it to receive the case. These pieces fix in such a manner, that half the cases may incline upwards, and half downwards, and that when they are tied on, their heads and tails may come very near together; from the tail of one case, to the mouth of the other carry a leader, which secure with pasted paper. Besides these pipes, it will be necessary, to put a little meal powder inside the pasted paper, in order to blow off the pipe, that there may be no obstruction to the fire, from the cases. By means of these pipes, the cases, will successively take, burning one upwards, and the other downwards. On the pintle, fix a case of the same sort as those on the wheel; this case must be fired by a leader, from the mouth of the last case on the wheel, which case must play downwards: instead of a common case in the middle, you may put a case of Chinese fire, long enough, to burn as long as two or three of the cases on the wheel. [Illustration: PLATE. 3] 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.