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Pyrotech- others of less brilliancy. All of them depend upon the 

 principle of recoil, until they become much complicated 

 and intermixed with other works, so as to be required 

 to carry additional weight ; when the assistance of re- 

 volving machinery becomes necessary, as we formerly 

 suggested. In their next simple state they admit of 

 considerable variety, depending on their dimensions, 

 their velocity, and the quality of their fires. But they 

 also admit of so many modifications, by which they 

 pass gradually into the second class of complicated fire- 

 works, that we must treat of each variety under sepa- 

 rate heads. 



It will be necessary here to repeat some of the gene- 

 ral remarks formerly made, with the addition of others, 

 for the artist's government. Where they are to move 

 by their own force, the cases require to be choked and 

 driven just as for rockets. But it is not often neces- 

 sary to bore them, unless a very great velocity or force 

 is wanted ; in which case they must be driven on the 

 spindle in the usual manner. Supposing that a wheel, 

 formed of cases, an inch or more in diameter is wanted, 

 as there is a considerable weight to be brought into 

 motion from a state of rest, it may be necessary to make 

 the case, which is first intended for lighting, with a 

 long bore, or to make it, in fact, a sky rocket. Thus, 

 there will be gained so great a velocity at the begin- 

 ning, that a very small additional force in the succes- 

 sive cases will be sufficient to maintain the motion to 

 the end. The second and third cases may, therefore, 

 pass without boring, or even the whole ; or else a short 

 bore, varying from one diameter to two or more in 

 length, may be used ; or, lastly, the cases may alter- 

 nately be bored or left solid; but on all these points it 

 is only necessary to give the general principles, as the 

 artist must after all be guided by his own discretion, 

 and by the nature of his particular views. 



The cases for wheels must be as strong as those for 

 sky rockets, as they have to bear a considerable force, 

 in consequence of the strength of their charges. Nor 

 is the weight any objection : on the contrary, when 

 once it is in motion, a heavy wheel acts better than a 

 light one, because it does not easily lose the velocity 

 which it has acquired ; but, acting like a fly wheel, 

 maintains during the burning of any slow part of the 

 composition which may be introduced, that motion 

 which it had acquired from a stronger one. These ca- 

 ses need not, however, be limited in length as those of 

 rockets are, but may be made of twelve diameters, or 

 even more. But a foot of length will be found a very 

 good general rule tor a case whose interior diameter is 

 an inch. 



When driven, a little clay may be laid on the mouth, 

 .if the artist thinks proper, to preserve the choke from 

 being burnt ; and if this is done, and the cases are 

 sufficiently strong, they will admit of being used a se- 

 cond time. The ends are to be left open, and no boun- 

 ces are to be admitted, as they would be apt to derange 

 the wheel, and throw it off the spindle. If a bounce 

 is wanted at the end, which may be desirable, it can 

 be attached loosely like a maroon to the last case by 

 means of a leader, and laid upon one of the spikes, so 

 as to disengage itself when it takes fire, without in- 

 juring the machinery. The same may indeed be done 

 more extensively, as we shall hereafter notice in treat- 

 ing of hexagonal wheels. 



In filling wheel cases, three or more compositions 

 may be used, and for the nature of these we may refer 

 to the tab.le. But we will here suppose that three 

 have been selected, namely, an iron sparkling fire, a 



common charcoal one, and a blue or white flame. A Pyrotecli- 

 diameter of the case or more, near the mouth, must be 

 laid with a strong charcoal composition, and that is to 

 be followed by the same quantity or more of a brilliant 

 one, which may again be succeeded by a blue or white 

 flame, and so on alternately, as the taste of the opera- 

 tor may direct. It must be remembered, however, 

 that the flaming compositions should never be placed 

 far away from the mouth in the cases, as these flames 

 will not reach very far, and might be suffocated or 

 burnt out within the rocket, instead of showing as they 

 ought to do. The artist must also recollect that half a 

 diameter of any of these will be sufficient, as they bum 

 comparatively slow ; and as their force is very small, 

 they might, if they lasted too long, retard the motion 

 of the wheel inconveniently. Whenever there is any 

 fear of this event happening, a strong one must be 

 made to succeed, for the purpose of recovering the ve- 

 locity. 



The artist must now, however, recollect, that if a 

 case is to be bored, no such changes of the composition 

 are admissible ; as the bore would render all this 

 useless, by causing the different kinds to burn together. 

 In such a case, any one composition must reach at 

 least to half a diameter beyond the bore, after which a 

 change is admissible. 



The last general direction applicable to all wheels 

 alike, is the fixing and priming. Supposing the case 

 of an hexagonal wheel, as applicable to all, the rockets 

 must be tied on the circumference with strong twine, 

 which is afterwards to be covered with a turn or two 

 of pasted paper. Great care must be taken that they 

 are placed in the plane of the wheel, so that no force 

 may be lost, and that they are placed in succession so 

 that the choke of one is next to the end of the preced- 

 ing. A whole diameter of the case must also be left 

 between each pair, that the fire may flow freely with- 

 out meeting any obstruction from the end of that last 

 burnt. This being done, a thick strand of quick-match 

 must be introduced between each head and tail, and 

 fixed in both ; when the joint must be secured with 

 pasted paper. This should not, however, be made too 

 strong, to prevent the wheel from being shaken by the 

 explosion which takes place at the lighting of the cases. 

 Lastly, a long leader is to be fixed to the first, and 

 being reserved closed, it may afterwards be cut to the 

 proper length, and affixed to any firework which it is 

 intended that the wheel should follow. 



Of Single Case Wheels. 



These are extremely convenient for attaching to other or single 

 fireworks, where there is little room to spare, or where case 

 much weight cannot be carried ; and, from their acting wheels, 

 at two orifices at once, the effect is very good. They 

 are, however, of very short duration, so that they are 

 not fit to be used alone. In the Chinese drum they 

 are indispensible ; as the necessity of packing close 

 renders any other kind of wheel scarcely admissible. 

 They may also be attached to line rockets, and to many 

 other classes of fixed and moving fireworks; but we 

 need not give particular directions for these uses, as a 

 dexterous artist will easily learn to avail himself of the 

 advantages which they offer. 



Wheels of this construction may be made of all sizes, 

 from two ounces upwards to a pound or two ; and the 

 cases must be as strong as those intended for tourbil- 

 lons, as they have a considerable force to bear. This 

 wheel indeed bears a resemblance to the tourbillon in 

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