258 



1'yrotcch- gether. 



PYROTECHNY. 



That no misapprehension about this may provided with oblique cases tending different ways, and Pyrotech- 

 anse, it is plain that such a wheel, when completed, with horizontal ones, or with both ; and it is easy to v 



Reversed 



wheels. 



PLATE 



Of conical 

 horizontal 

 wheels. 



will be double, and that, when looked on, each proxi- 

 mate pair of cases will cross each other in the middle. 

 Each extremity of a case on one side will also be attach- 

 ed to the result of a following one. Thus, on burning-, 

 two circles of fire will be formed, one outside of the 

 other ; but owing to the obliquity in the positions of 

 the cases, these, during the revolution of the wheel, 

 will form two sets of spiral curves, producing a very 

 pleasing effect. It is evident that, if the divergence of 

 the cases was as great as 45 degrees, the force of revo- 

 lution would be equal to that of a single wheel. But 

 as the whole angle need not exceed 10 or 20, the power 

 will be far greater, and the velocity of course more 

 considerable than that of any single wheel, whose cases 

 are tangents to the circle. 



Reversed Wheels. 



It is easier to manage these horizontally than verti- 

 cally, but they may be made in either way. If the ho- 

 rizontal construction is to be adopted, a double or tri- 

 ple wheel, as formerly described, may be taken, either 

 with two rows of oblique cases, or with these two and 

 an intermediate horizontal one. But to take the sim- 

 plest case, and suppose any two of whatever nature. 

 The last case of the wheel must be made so slow, that 

 its motion may nearly cease before it is burnt out. To 

 distract the attention of the spectators, then, from the 

 wheel and its motions, a gerbe, or some other brilliant 

 case, should be lighted in the centre ; and a little while 

 before that is expended, a leader should be conducted 

 from its case to the second wheel, which is to be so 

 constructed as to fire in the reverse order. 



In the vertical wheel the same effect may be pro- 

 duced in the same manner, two sets of cases being 

 applied to the same felly. At the period intended for 

 reversing the motion, a set of lights may be fired upon 

 the spokes. These will continue to revolve in circles 

 for a time, gradually lessening in velocity as the wheel 

 comes to a state of rest. From one of these a leader is 

 then conducted to the commencement of the second 

 wheel, the mouths of which have been placed in an 

 order the reverse of the first, so that the wheel will 

 commence to move back again as it were in a contrary 

 order, when the spectators imagine it expended. This, 

 and all other similar expedients to excite surprise, have 

 a very good effect in this art ; and a thorough-bred 

 pyrotechnist will not despise any kind of quackery that 

 may answer his purpose. 



To reverse the motions of wheels, however, suddenly, 

 it is necessary to have two on an axis, as will be de- 

 scribed hereafter. 



Of conical horizontal Wheels. 



These are described by pyrotechnists, and we must 

 therefore notice them, although their effects are not 

 sufficiently different from others, to render it worth 

 while to adopt them, unless much variety is wanted, 

 as may happen in the case of very extensive exhibi- 

 tions. They may be varied in many ways as to the 

 form of their fires ; but a brief description of the gene- 

 ral principle will be enough for the artist in fireworks. 

 In these, two, three, or four wheels are fixed upon one 

 vertical axis, but differing in their diameters. Thus there 

 may be a succession of three or four, forming a cone, or 

 else the smallest may be in the middle, and the largest 

 above and below, or the reverse. They may also be 



see how the effects may be varied. The different wheels 

 may also be fired together, or in different orders of suc- 

 cession, on which we need not dwell ; and it is easy 

 to see that their chief differences from the compound 

 wheels formerly mentioned, will arise from the different 

 sizes of the circles of fire. 



The Extending and Diminishing Wheel. 



The effect of this is very good, from the variation in The ex- 

 the size of the circle of fire, and it has the advantage that tending 

 it can be made extremely durable. An ordinary framed aiu ' dimi- 

 wheel being formed in the usual manner, a strong wire ni 

 or a hoop must be conducted in a spiral direction from 

 the centre to the circumference; and it is necessary that ' 

 a wheel of this nature should be of considerable dimen- 

 sions. Short cases are required for it, particularly for 

 the inner turns of the spiral, but the centre ones may 

 be of the usual length. The cases are then all attached 

 in regular succession upon the spiral, and connected 

 in the usual manner. When this is fired, it is evident 

 that the circle of fire will gradually increase or diminish 

 as the cases burn in succession from or towards the 

 centre. But as the force of the fire near the axis is 

 not sufficient to put a large wheel into motion, it is 

 better that they should be fired from the outer end, in 

 which case the circle will diminish and still preserve a 

 sufficient velocity. 



This wheel may be varied to advantage by provid- 

 ing a circle independent of the spiral. Thus, the large 

 circle will burn, while the spiral line, being fired from 

 the centre at the same time, is gradually extending its 

 circle till they meet. This operation may farther be 

 reversed in this manner. Let two circles of cases be 

 provided on the outer margin of the wheel, and two 

 spirals within ; care being taken that there is the same 

 length of case in the spiral as there is in the circle. 

 When the first circle of fire is lighted, the outer end 

 of the spiral may also be fired by the communication 

 of their mouths, or by a joint leader. When that circle 

 is expended, the second will be lighted, appearing to 

 the spectators as a continuation of the same, when the 

 corner of the second spiral will then be lighted from 

 the extremity of the first. In this way, during one 

 half of the wheel, there will appear to be an inner 

 circle of fire, gradually diminishing; while, during the 

 remainder, the same inner circle will appear as gra- 

 dually to increase. 



Of Compound Wheels. 



There are various methods of compounding wheels, Of cora- 

 and they are all so easy in the execution, and so bril- P ound 

 liant in the effects, that they well deserve the attention w e 

 of pyrotechnists. They are, however, almost solely 

 limited to vertical movements ; as in the horizontal 

 ones the effects are lost to the eye. We shall describe 

 a few of the most striking, aiding the descriptions by 

 proper figures, which will be found in the plates, as to 

 describe the whole is unnecessary, since they admit of 

 endless variety. 



Concetilric, Direct, and Reverse Wheels. 



There are two modes of performing this, and they Concentric, 

 also admit of some subordinate varieties. Two sets of direct, and 

 cases may be applied on two circles, one within the reverse 

 other on the same spokes. In such a contrivance, both wheels - 



