A wheel of this kind may be made of any diameter. The nave may be of moderate size, and to it fix four spokes at right angles to each other, and united to the fell or circumference; round the latter you are to fix any number of port-fires: on the front of the spokes form, with some strong iron wire, a scroll or volute, in dimensions proportionate to the wheel, beginning at the centre; on this scroll tie cases of brilliant fire, which should not be too large, and placed head to tail, as in other similar arrangements. The case nearest the circumference must be fired first, which being farthest from the centre has most power to set the wheel in motion. The port-fires may be before, at the same time, or after the scroll.
This wheel may be wrought into one far more ornamented and complex. A double scroll might be formed on the spokes, as well as a double set of port-fires on the circumference; a pot of some kind at the centre would readily suggest itself.
Remarks on Wheels.
REMARKS ON WHEELS.
In all articles of the wheel kind, the Tyro must observe to increase the strength of his composition for cases, as his wheels increase in diameter; for a rocket proper for a twenty-four inch wheel will not do well for one that is much larger.
The following rule as to this particular may serve in many cases: divide the diameter of your wheels, taken in inches, into three parts, and it will give the length of your cases, and generally within one, the number it will require to go round it. Thus suppose your wheel is twenty-four inches diameter, divide by 3; 24/3 equals 8, which is about the length of your cases: and 7 : 22 :: 24 : 528 which divided 528/7 = 75,3 and 75/8 = 10 equal 10, the number of eight-inch cases it will take to go round the circumference.
This is not given as a particular, but as a general rule; or one that will assist a little in the arrangement of these articles.
To represent the Fir Tree.
16. To Represent the Fir Tree.
Provide a post six or seven feet long, and three inches square; then on the far side at nine inches from the top, fix in four short pegs to fit the inside of the cases; nine inches from these fix similar pegs; nine inches lower fix others similar to the last; and from these, the same distance, fix other pegs; all these four sets must incline upwards; below them, at the same distance, must be fixed another set inclining downwards, the angles of inclination in all may be about forty-five degrees from the upright post. At the top of the post place a four-inch mortar loaded with stars, rains, crackers, &c. In the middle of this mortar place a case with any sort of charge fired with the others, which should be filled with a brilliant charge. The tree may be made of any size, and other ornaments made use of, as suits the operator.