These wheels may also be made without pasting the turns together ; securing them only at particular points with a bit of glue or sealing-wax. Thus, in burning, the spiral unfoads after each fastening of this nature, so as to inet ease the diameter of the circle of fire.
In firing such wheels, two may be applied on one axis, so as to revolve in opposite directions, which pro duces a very pleasing effect ; but in this case the pin must be somewhat thicker, and must also be provided with an intermediate button, so as to keep them separate. They may also be variously combined ; but as these combinations are applicable to all wheels alike, we shall dull, and requires to be varied by other additions. But that effect may be improved by causing two opposed cases, one above and one below, to act at the same time, or else by making two act above, alternately with two below. The means of effecting this by a proper disposition of the leaders is too obvious to require de scription.
The horizontal wheel, Plate CCCCLXXII. Fig. 19-24. may also be constructed in another manner, and that, such as to discharge its fire at an angle either upwards or downwards. For either of these purposes the rockets are all to be laid obliquely as to the wheel, as in the former case; but in a parallel consecutive manner. Thus all the vents will look either upwards or downwards, as the artist may choose, and each head and tail are then to be alternately connected by means of an attached leader of the requisite length. It is evident that the effect of these will be a succession of streams of fire in a direction oblique to the revolution of the wheel, but always either upwards or downwards. These wheels may also be made both very forcible and far more durable than a common wheel in one plane. To give them force it is only necessary to make the angle which they form with the plane of the wheel very small, such as 10 or 15 degrees instead of 45, by which means the recoil of the rocket is caused to coincide more nearly with the plane of revolution.
Thus also they may be made of almost any degree of durability, because the cases may, in this way, lie close to each other, so as to form a solid ring round the wheel. As the weight in this case, however, becomes
considerable, it will not be amiss to give these wheels an impulse at the commencement. Or, as there is abundance of materials, they may be lighted on both sides at once.
The stone plan is applicable to vertical wheels, and with the same effect of producing a far longer duration than in the common constructions already described. At the same time the effect is somewhat varied from the pee uliar direction of the issuing stream of fire.
All these horizontal wheels, when fixed, are com monly provided with a central white light, or with a gerbe, or with a succession of these. This is a peculiar convenience in the horizontal wheel ; as the pressure being downwards on the shoulder of the axis, which must be properly adapted for this purpose, there is no danger of disturbing the equilibrium. It may also carry a Roman candle in the centre, or a number of these or of other fires upon the spokes, and that either upwards or downwards. Thus also these may be fixed, in any order of succession as to the fire of the wheel which the artist pleases ; merely by selecting some par ticular case for the leaders to each of them. Thus this wheel becomes a complicated firework. But as it is not necessary to treat of it again under that head, par ticularly considering the endless variety of which it admits, we shall barely suggest here, that it may be varied with good effect even in ten different ways or more, because there is no limit to the number or cases of different kinds, which the spokes will carry, if the centres are made very fine and free, nor to the number of leaders that may be used to fire them in different ways. To put one instance of many, after it has re volved simply for a time, it may light a circle of white light's looking downwards. These may he followed by a few sparkling fires upwards, to be succeeded by Ro man candles, then again by cases of serpents, and, lastly, by a central gerbe, ending by a bounce, or by a general explosion of serpents or stars. To say more on this subject would be merely to describe what the ingenuity of the operator will easily suggest.