The last thing which remains is to close the mouth of the rocket with a strong covering of paper, and to fast en on the stick. This must be made of very straight deal, and planed smooth. For the rocket, whose dimen sions were given above, its length is to be eight feet or more, but not less. At the upper extremity its breadth should be about three quarters of an inch, and at the lower one about a third. It may be wider than it is thick above; but the extremity must be square, that the air may act alike on it in all directions. In fixing it to the stick, it is better if it extends all the way to the rocket head ; and it is to be fastened round the case by two dis tinct windings of twine, which are to be sunk in notches within it, that all unnecessary resistance to the air, or chance of friction in going off the support, may be avoided. The equilibrium should be such, that, in this rocket, whose dimensions have here been taken as a standard, the whole should be poised on the finger at two inches from the mouth of the rocket. This will serve as a general rule for all. But as it is convenient, in the larger rockets, to dispense with length of stick as far as possible, on account of its expense and inconve nience, and, as in the small ones, it is of little conse quence how long they are, provided the proper weight and equilibrium are maintained, we shall subjoin a table of measurement on this subject. We need only add, that if on trial of the equipoise, the tail is too heavy, it may We may add to these numbers, that a general length may be considered as 60 diameters for the smaller rock ets, and 50 for the larger; that half a diameter is a good general rule for the top of the stick, and a quarter for the extremity; but that provided the equilibrium be cor rect, they cannot exceed in length, however long; al though they will not admit of being shortened, as the steerage depends on the distance of the extremity from the centre of gravity of the whole.
There are many projects for varying the effects of rockets, which are described in the books of pyrotechny, and we shall enumerate them for the satisfaction of our readers. We shall, however, take the liberty of no ticing their nature as we go along, as it will be found that some of them are difficult of .execution and others impracticable ; or rather, that they do not produce the anticipated effects. It is useful to know what to avoid, to save both expense and disappointment; and it will be found that, in practice, modern pyrotechnists have aban doned most of these schemes, although they still stand re corded in their works.
The Caduceus rocket, Plate CCCCLXII. Fig. 6. as it is called, consists of two rockets fixed to one stick. For this purpose the rockets must have no heads, as they are unable, from the great resistance which they offer to the air, to carry any unnecessary weight. To enable them to ascend, it is prudent not to place them at a greater angle to each other than 40 or 45 degrees; and, indeed, the less the angle is, so much the more certain and steady will their flight be. At the upper extremity, they must be fastened, the one before, and the other behind the stick. At the lower, they are to be attached to a transverse bar, which is also fastened upon the stick, so as to form an equilateral triangle. But it is to be observed that they must not lie in one plane; and this object is effected by passing the lower extremities on the alternate sides of the transverse bar, in directions the reverse of that which they have at the upper extre mity. Thus, the tendency of each rocket becomes such
as to compel them to turn in a spiral round the line of flight, forming that particular appearance whence the name is derived. The stick is required to be considerably longer than for simple rockets, and the centre of equi librium of the whole should be at least one length of a rocket from the vents. In firing them, it is necessary to be careful that they light together, and great care is required in the suspension. With all these precautions, the performance of this compound rocket is awkward and uncertain.
It has been attempted to fire one rocket from the head of another, after that is expended, and this in vention is called a towering rocket. To put this scheme into effect, a pound rocket will be required to carry a four ounce, in the following manner. The upper end of the large rocket is left unfinished, with a sufficient projection of the case beyond the charge to receive the mouth of the small one. This latter is then fixed loose ly into it, by means of a little tow, with some paper, lightly pasted round ; so that when the principal rocket is expended, the secondary one may have no difficulty in disengaging itself. The stick of the small rocket is brought down parallel to that of the large one, and slightly secured in a -.imilar manner. Thus, when the practice happens to succeed, the small rocket will take fire and continue its ascent when the principal one is done. We must, however, remark, that this is some what of a theoretical rocket; a thing not unusual with pyrotechnists. The check which this additional weight gives to the principal one is very apt to derange its flight; while the slightest irregularity in the disengagement of the secondary one will ruin the expected effect, and cause it to overturn and fall down, with the burnt stick and case of the first. The effect gained by it is at the same time so trivial, even when it does by chance suc ceed, that it is not worth the trial and risk of failure.— Should any one think fit to try this experiment, it must be recollected that a stick considerably longer than for a simple rocket will be required.
There is a project called an honourary rocket, Plate CCCCLXIL Fig. 7, equally hazardous in the perform ance, but which we must also describe. In this con struction, the case or rocket has no head, for the same reasons. Supposing it to be a two pound rocket, as a smaller one will scarcely answer the purpose, a notch must be made in the case, just where the charge and the clay terminate, fitted to receive a transverse case or subsi diary firework. For the size now mentioned, it may be what is called a four ounce case, not exceeding six inches in length. This is driven solid with the same composi tion as the rocket itself, or with that used for tourbillons, since it is in fact a tourbillon, and is closed at both ends. It is then bored with two deep gimblet holes, close to the extremities, on opposite sides, and so that the direction of these is at right angles to the rocket or horizontal. The case thus finished is fixed to the top of the rocket, and a leader of quick match is brought from each of its open ings to the hole which communicates with the end of the composition; after which the rocket head is covered, as usual, with a paper cone.