The same method is to be followed for all these, with the requisite variations for the leaders and other connections. We shall suppose the simplest case of one flourish within the principal circle, as the method of arranging this, will serve for the explanation of the whole. If there are six cases in the outer wheel, and the diameter of it is two feet, then the diameters of the smaller wheels will be from four to six inches. Three of these will be required ; and of whatever Shape they are made, each of them must be equal in the time of burning to two cases of the outer wheel. They must then be fastened in opposite spokes, so as to preserve the proper balance of the wheel, by means of spindles in the usual way. For firing, a leader must join the commencement of the principal wheel with one of the small ones ; a second leader must join the begin ning of the third case with the next ; and a third leader is required to join the fifth case with the last. Thus one of the small wheels will burn with each two cases of the large one, and the effect will be continued during the whole time of the revolution, so that the whole will ex pire together.
Balloon Ilrheels.
This is one of the fireworks mentioned in the books on pyrotechny ; but it is scarcely worth describing, after the remarks formerly made on the methods of varying the effects of horizontal wheels. The name is not very appropriate. It is a common horizontal wheel, with horizontal cases revolving in the usual manner. On each spoke near the end of each case is placed a pot of serpents or of stars, or of both alternately. These com municate by means of a leader with the end of each case, so that whenever a new one is lighted, a dis charge of serpents or stars takes place. The same expedient may be applied to a vertical wheel, but in this, stars are not admissible, on account of their dan ger, as they would be thrown forwards among the spectators. Small serpents may safely be used, as they do not fly forwards, and are therefore not likely to oc casion accidents in this way, more than in the horizontal wheel.
Star Wheels.
These may be used either horizontally or vertically; but in the two kinds the stars require to be differently disposed. We shall give a direction for each. If the wheel is to be horizontal, the best method of dispersing the stars is to fix as many Roman candles in the centre of the wheel as there are cases in its circumference. This we formerly alluded to in speaking of horizontal wheels. These must be in a vertical position, so as to throw their stars upwards, and they must be calculated as nearly as possible, so that one may last as long as one of the wheel cases. To prepare this firework
for firing, a leader must be conducted from the com mencement of each case, to the top of each Roman candle in succession ; so that a constant discharge of stars, together with a central fountain of fire, will continue as long as the wheel lasts. The Roman can dles may also be disposed in such a manner as to throw the stars downwards, instead of upwards, or al ternately upwards and downwards, or both ways at the same time, all of which produce fireworks of different appearances.
In using stars with vertical wheels, (Fig. 34, 35,) a dif ferent disposition of the Roman candles is required. They must be fastened on the spokes of the wheel, with their mouths looking outwards ; and the leaders must be placed in the sante manner, so that one Roman candle may fire with each fresh case. The stars will thus be projected sidewise, without any chance of in jury to the spectators, who are always in the front on those occasions ; and as they receive two motions, one from the wheel and the other from their own pro jectile force, they form very pleasing curves in the air, adding much to the beauty of the effect, while they also seem as if they were projected from the mouths of the wheel itself.
If it is wished that a vertical wheel should throw up stars in a vertical direction, a separate firework is required for this purpose. This must consist of as many Roman candles as will last out the time of the wheel, and they must be fixed behind the wheel on the same part which carries the axle. But if it is wished that stars alone should be seen, without any ver tical fire, so that the wheel itself may appear to throw up the stars, they must only have a very slow compo sition, which gives little fire, such as that used for port fires, which will be found in its proper place. The orifices may be also concealed behind a board, so that nothing but the stars will be seen. As many of them must be connected alternately by the head and tail as will last out the time of the wheel, and the same leader will serve to fire both. It is proper that all wheels and fireworks of this kind should end with a report, or with a general explosion of stars.
Of the Alternating Wheels.
The effect of this is entertaining, nor is the construc tion difficult. In burning, a .large and a small wheel are seen alternately, and in concentric order. This firework is required particularly for a spe cies of transparent star, which will be described here after; and to aid the understanding in its construction, a plate of it is given.