The length and form of the torrent of fire in all the sparkling compositions, render the possible combina tions of these still more numerous and various. Effects may be produced by this intersection in this case, which could not in the former ; as there also may by the mere quantity of the fire. To put a few of the most obvious instances: If a number of these arc disposed in a circle, they may form a blazing star or sun; and by again combining two such circles, the one of which is of larger dimensions than the other on the same centre, an effect still more splendid may be obtained. Three such fires properly dispersed may be made to represent a plume of feathers; four may be caused to produce a cross of fire. Such fires may also radiate inwards as well as outwards, ur they may be disposed so as to produce a pyramid, or a cascade ; or they may cross or intersect each other from the angles of tri angles, or squares, or hexagons, or any other geo metrical figures; and in these ways the fires may be directed outwards or inwards, or in both modes at once. Different sizes may also be combined together in various figures ; but it would be endless to desei ibe all these possibilities, which may be safely trusted in general to the taste and resources of the artist. NV e subjoin a few figures in the plates by which a gene ral notion of their construction and effects may be formed.
In the next place, the flaming and the sparkling lights may be combined in an endless variety of ways. The very same case may alternately throw out both the kinds of fire. Or the angles of a sparkling trian gle, or of a square, or else the centres of these figures, may be occupied by coloured stars, or their sides may be clotted with such lights ; or alternations of figures of lights with figures of sparkling fire may be adopted. Thus, for example, the centre of a sun may be filled with a blaze of lights, while its margin radiates with sparks; or else it may commence with one spe cies, and terminate with another. But, for the same reasons, we need not attempt to describe varieties which only become more numerous as they become more complicated. We must refer to the plates, and to our future examples, for a few such specimens as may serve to illustrate this part of the subject, trusting to the artist's ingenuity for conceiving farther what we may not find room to describe.
The varieties of moving fireworks is much greater than that of fixed, abstractedly considered; yet these are not susceptible of so many distinct and complicat ed combinations. As the most simple ease we may mention that of burning bodies projected into the air by explosions, such as stars, serpents, Ste. whether out of rockets, or shells, or from Roman candles. The sky-rocket is the chief of those which act by their own force of recoil, and the varieties of which it is susceptible will be described when we come to treat of that firework. On a similar principle, line rockets and water rockets produce their particular effects : the principle of recoil being modified by the particular kind of restraint to which they are subjected. In the
tourbillon, the recoil of a wheel, or that of revolution, is combined with that of motion in a straight line, and thus the very striking effects of this simple firework are produced.
But the most various effects of recoil in fireworks are produced by restraining that force within circles, and hence arises the great varieties of wheel movements. The spiral, or pin wheel, is a familiar, but not the most simple case of circular recoil. By suspending a simple cylinder on a pin passing transversely through its own centre, and using lateral instead of direct apertures, a revolving recoil is caused, and hence arises a circle of fire or a wheel. But in works of this nature, which are required to burn longer, it becomes necessary to form larger circles than can be produced from one case. Thus many of these are disposed round the margin of a wheel, or, what is the same thing, on radii proceeding from a centre, suspended on an axle in the same man ner as a carriage wheel. This is the common Cathe rine wheel as it is called ; and according to the desired length of time in burning, the cases may consist of any number from two upwards, the effects being altered in appearance by placing these at greater or less distances from the centre. At very small distances, and with greater velocity, a continuous circle of fire may be pro duced ; at much larger ones, the form described by this is of a very different nature.
The simple circular recoil may be modified as to its effects, by disposing the fireworks in an angle not coin ciding with the plane of the wheel, or radii, on which they are to revolve. Thus the effort is much diminish ed according to the resolution of forces, but the figure of the fire becomes entirely different Such wheels as this are commonly disposed on verticle instead of ho rizontal axes ; and they are susceptible of still further changes of appearance, by alternately reversing the mouths of the fireworks, so that the stream of fire may be directed in an alternating manner obliquely upwards and downwards.
Combinations of circular recoil motions are also ma naged so as to produce very entertaining effects. Thus if the radii of the larger wheel are caused to carry small er ones, it is plain that a very compound path of light will be produced by the latter, resembling exactly that path which the moon performs round the earth ; the principal circle including smaller ones, which move forwards along an orbit concentric to the first. Other simple combinations of single wheels are also easy ; but we shall only here further mention, that in which two, either of different sizes or the same, are caused to re volve in opposite directions in a common centre. The effects of mese movements are very lively and bril liant.