Plural Wheels.
9. Plural Wheels.
So called from there being several of them fixed on the same axis; they are generally horizontal, and in number three. The diameter of the middle wheel may be a little less than the other two.
The cases must be fixed to the ends of the spokes in notches cut on purpose, or there may be half cylinders of tin nailed to the ends of the spokes, and the cases tied in them. The bottom cases should play obliquely upwards; the middle set horizontally; and the upper cases obliquely downwards. The leaders must be arranged so that the cases may burn first up, then down, then horizontal, through the whole sets. By driving in the end of the last case two or three ladles full of slow-fire, it will cause it to burn till the wheel has stopped its course; and if the other cases are fixed in the contrary way, the wheel will then revolve in a contrary direction, and have a pleasing appearance. For the case at top of the axis, a gerbe may be well employed; the case on the spokes should be filled with a strong brilliant charge.
Spiral Wheels.
10. Spiral Wheels.
These in their principal construction differ but little from the foregoing: the following are the principal differences. The nave should be about seven inches long; instead of a spindle at top, make a hole for the case to be fixed in; in the nave must be fixed two sets of spokes near the top and bottom; the spokes should not be more than about three inches long; the cases must be placed in such a manner, that those at top play downwards, and those at bottom play upwards, but the third or fourth case must play horizontally. The case in the middle may begin with any of the others; six spokes will be sufficient for each set, by which the wheel may contain twelve cases, besides the top one: the cases should be about seven inches in length.
Illuminated Spiral Wheels.
11. Illuminated Spiral Wheels.