As in all such simple wheels the power is sufficient to carry a considerable weight round, if the centres be carefully made, it is easy to attach to different parts of them burning fireworks of different kinds, which have not in themselves any moving force ; notwithstanding which, they can be made to produce circles as if they had a power of their own. Thus also, either the cases of the wheels themselves, or others connected with the movement, may be caused to project stars ; and in this way also varieties are produced.
As we need not, however, enter now into any more of these general details respecting the attainable variety in simple combinations, we must proceed to notice the general principles on which the more complicated fire works of these kinds are made. In these, different kinds of the simpler forms, or of the first order of com binations, are caused to act in succession, or together ; and thus the further we proceed in combining, the more numerous do the varieties become. Thus moveable and fixed works of all kinds may be united to an ex tent which is only limited by the size, and weight, and bulk of the machinery, and by the expense. A very few hints on the most general parts of this subject may be useful.
If a complicated succession consists of fixed pieces only, they may be so managed as to fire each other, without any further intervention of the operator than the first lighting. This is done by a proper disposi tion of the leaders, on which the operator must calcu late according to his views The communicating lea der, of course, extends from the end of that which has been burnt out, to the commencement of the one that is intended to follow. If Many and distant ones, as in the case of extensive groups of illuminating lights, are to be fired so as to burn together, it may become requi site to have more leaders than one from the same point to different ones, otherwise such works may light in a slow succession instead of simultaneously ; in conse quence of which, not only the first effect will be un pleasant, but the terminations will be more so, as they will die out in succession, instead of expiring altogether. Such leaders must be so firmly fixed, as to insure them against being displaced by any explosion from the works that have burnt out ; and in cases of large and expensive complications, it is prudent to have a spare conductor, known to the operator, so that he may be able to light it by means of his port-fire, should the ex pected communication fail. In very complicated ma chines, such as architectural fireworks of great extent, it becomes impossible to produce, or unsafe to trust, the communications to a continous set of ieaders ; and proper ones must therefore be provided in different paces, that the artist may himself light them when the proper time is arrived.
Now as fire can be conducted from one fixed piece to another, so it may from fixed to moveable ones through any mode of succession that may be requisite. The leader from the last fixed piece may, for example, be attached to the first case in a wheel. To this it must be fixed in such a manner, that the first lighting of the wheel may burn and separate the connection by which the wheel was kept steady in its place. This is easily managed by means of cotton quick-match, which is sufficiently strong to support any thing very firmly, but which is burnt and detached in an instant. But it is not possible to communicate from moving to fixed pieces, as is easily understood. A separate leader is, therefore, required for all these communications, which is carried away out of the risk of casual fire, and brought under the command of the artist who directs the work.
Of Machinery, Frames, and Transparencies.
Although many of the motions of fireworks can be produced by their own powers of recoil, there are many cases where it is convenient, or even necessary, to have recourse to mechanical powers ; sometimes to accelerate these, and thus produce more perfect effects, and some times tor the purpose of causing movements that could not be made by the fireworks themselves. The &out ings and supports for fireworks also require some atten tion to render them as little cumbrous as possible, and, at the same time, as firm as is necessary to bear the shocks to which they are subjected from recoils and explosions ; while it is also requisite that every thing should be done in the most economical manner.
For single rockets, vertical frames or poles are re quisite; but we have described these more particularly in our directions for firing this class of fireworks. But when flights are to be discharged together, it is neces sary to have a different apparatus. This is usually constructed of successive shelves, in which they arc placed in alternate order, so that the sticks may stand clear of each other; the whole forming a pyramid. A cheaper and more convenient apparatus, however, for this purpose, is formed by making two wide shelves, each perforated with holes, exactly corresponding to each other, sufficient to admit the sticks, and to support the mouth of the rockets. These should be separated to a distance of about two feet from each other, and framed in that position by uprights at the angles, pro longed to the ground ; in which they are fastened firmly, so as to form a kind of double perforated table. The matches from the whole being collected together, they are easily fired ; and their flight is directed by the guide which the position of the two holes for each presents.