It only remains to prime the wheel, which is done by carrying a single leader from one orifice to the other, and securing it with pasted paper at each. To the middle, an additional leader is attached in the same manner, which is reserved of an incIefinite length, to be after wards adapted to any place that may be required.
It is possible to prolong the action of these wheels by burning only one hole at a time, and causing the com mon leader to commence near the axis on one side, and be inserted into the second orifice. In this case the first priming leader is inserted into one orifice. A wheel so constructed burns and revolves very regularly at first, but is apt to become irregular as the equilibrium is de stroyed. To prevent this, the communicating leader may be inserted half way between the axis and the first orifice ; and thus the burning of the wheel is prolonged for one half more the time that it would be if lighted at both ends together.
Such wheels may also be varied, so as to give two circles of fire instead of one ; and this has a good effect, particularly if they are of large size. Even three circles may be introduced ; but in this case it is necessary that the firework should be of extraordinary length, as it would otherwise burn out too quickly. In boring for the former purpose, one of the holes should be made towards the axis, and the other at the extremity, still however, on opposite sides ; and if three circles arc wanted, it is easy to understand that two or more opposed holes are to be made at a convenient intermediate dis tance. The arrangement of the leaders for this purpose is easily comprehended; and the operator may also understand how the effect of such a wheel will be im proved, by forming the external circle of brilliant fire, and the internal one of a white or blue light.
This kind of firework, from its great simplicity, ad mits of being easily compounded, so as to produce very pleasina. effects. To describe one mode, will suggest to the artist many other ways of producing variety from this expedient Two or more cases differing in length may be fixed on an axis ; each being secured in its place by an intermediate button, so that they may not inter fere in their revolutions. If two, for example, are used,
the one should be made to revoke in a direction the reverse of the other, which is easily managed by a pro per position of the cut holes. Thus also many concen trate circles of fire can be produced, either in the saute or opposite directions, by placing many cases of differ ent lengths on the same axis.
But in doing this, the larger cases should have quicker compositions than the inner ones, so that they may not last much longer. Or, what is still better, each wheel leader should be separate, and all of them provided with bits of slow-match of different lengths. Thus the outer wheel may be caused to burn first, when, after a few revolutions, the second will take fire, and so on in suc cession till all the circles are inflamed. It is plain that all these thinge are very easy to execute, but that they require attention to be well done.
The single case wheel may also be compounded, by placing and fixing two on a common wooden centre, at right angles to each other, as in the table rocket ; and they admit of the same variations already mentioned.
Of Spiral or Fire Wheels.
reserve any description of these till we corhe to treat of combinations of wheels.
These may be made of any number of cases in the manner already described, disposed round the circum ference of a circle. Thus they may reach from two up to twelve, as there is no rule but the particular view of the artist If two only are required, they may be fastened on the opposite sides of a single arm provided with a proper centre and axis, and the leader must then be crossed from the end of one to the commencement of the other. Four may be used in the same manner; and in this case the circle of fire may be impro%ed, with the same dura tion, by causing the two on opposite sides to burn to gether. If six, or twelve, or any equal number of cases, enter into the wheel, the artist has it equally in his power to improve the circle, by managing the leaders so as always to burn two on opposite sides at the same time. Nothing more need be added respecting the mode of making these, as that was already explained in the ge neral directions for making wheels at the head of this division of the subject.