P Y R O T E C H N Y 



239 



Kxpcri- 

 inents of 



In a subsequent et of experiment* made by Mr. 

 Canton and Mr. Robins together, rockets of two inches 

 and a half in diameter were adopted. Some of these rose 

 to 500, some to 600, and one to 6[)0 yard*; and here, 

 Ctatodand contrarv t() ^ r - Robins'* former opinion, it was inva- 

 riably found that the largest rose the highest. SMUT.' 

 larger rockets were afterwards made by Mr. Da ( 

 of about three inches and a half in diameter ; and in 

 these, the vertical ascents were 833 and 915 yards. 

 Another trial made with one of four inches in diame- 

 ter, gave a perpendicular flight of 11 90 yards. The 

 last of these experiments was made in April 1750; 

 and on that occasion there were twenty-eight rockets 

 fired, made by different persons and of different sizes, 

 varying from the diameter of an inch and a half to 

 one of four inches. The n^ost remarkable flights of 

 these are here tabulated, for the convenience of in- 

 spection. 





Diameter. 

 Inch 14 

 Do. 2 

 Do. *i 

 Do. 3" 

 Do. 3 



Ascent in Yard*. 

 743 

 659 

 880 to 1071 



I ,V> t 

 1109 



In these experiments, the four inch rockets failed, 

 having overset in their ascent ; probably from negli- 

 gence in the stick, or too great a length of charge. 



At the same time, trials were made on the largest 

 sizes of rocliets which, as far as we know, were ever 

 constructed. These were twenty-four inches in dia- 

 meter ; one of them rose to 784-, and another to 833 

 yards. It is evident that these are both failures ; and 

 we have no doubt they are to be attributed to defects 

 in the construction. It is not possible to use exactly 

 the same proportions, either in the length of the case, 

 the proportional length of the bore, or the nature of the 

 composition, in large as in small sizes. If Mr. Banks's 

 and Mr. Da Costa's largest rockets were formed on 

 the scale of the one pounders, it was impossible that 

 they should have succeeded. In such cases also, the 

 stick, the cap, and all the minuter parts of the rocket 

 require a degree of care to obtain the best results, 

 which are of little comparative moment in the smaller 

 calibers. Nor is it possible that rockets of such enor- 

 mous diameters could have been driven properly by 

 hand, as it is probable these were ; the pile-engine not 

 having been generally introduced till it was applied by 

 Sir William Congreve to his military rockets. Thus, 

 then, the failure of these large machines may easily be 

 accounted for, without assuming, as these experiment, 

 ers or their reporters have done, that the sizes of rock- 

 ets could not be augmented with advantage. 



But we imagine that a very serious additional defect 

 arose from the use of paper cases. If these be adopted, 

 the diameter of the whole rocket becomes so rapidly 

 enlarged in proportion to that of the composition, that 

 the resistance of the air increases in a great ratio, and 

 thus the flight becomes materially retarded, and the 

 range consequently diminished. Such increase of re- 

 sistance is often opposed to the ascent of the smaller 

 signal rockets, by making the diameter of the head 

 larger than that of the case, a practice very properly- 

 exploded in the one pound signal ones made for the 

 service of government- I c is not improbable that this 

 cause was superadded to all the rest in the case of 

 these very largo ones ; as the value of the air's resist- 

 ance was not at that time thoroughly estimated. Mr. 

 Robins's experiments on this subject, as applied to the 

 purpose of calculating the fall of a shot had not long 



been mad*-, and were not sufficiently before the public 

 to have attracted the attention which they merited. 



We cannot therefore agree in all the conclusion* of 

 Mr. Ellicott on this subject. In his report, read be- 

 fore the Royal Society, he says, that " not only is the 

 making of large rockets very expensive, but much 

 more uncertain than those of a lesser size." " It is 

 also evident from the experiment*, (those, namely, 

 iihr.ve mentioned,) that rockets from two inches and a 

 half to three inches and a half in diameter, are suffi- 

 cient to answer all the purposes they are intended 

 for," &c. &c. They are unquestionably much more 

 expensive and difficult to make when of a large size; 

 nor, a> Mgnal rockets, is it necessary that they should 

 be so large, as it is very seldrm that it can be requir- 

 ed to make or receive signals from distances of 

 fifty miles. But it is far from true, that the greater 

 ranges may be obtained from the smaller sizes if the 

 rockets are well made ; and though these ranges are 

 not required, either for signals or for purposes of 

 amusement, *hey are of great importance in using 

 rockets for military service. 



This matter has been proved, and the question set Sir U*. 

 at rest by Sir William Congreve's experiments; he Conjre**'* 

 having, by the adoption of iron cases, materially re- '""P"**- 

 duced the resistance, while he has also made various ment * 

 improvements in the proportions, in the composition, 

 in the sticks, and in all the minor details, the neglect 

 of which before his time had been the common causes 

 of failure. The amplitude of his ranges, and of 

 course the vertical elevation, (were that wanted,^ have 

 been thus materially augmented : but we shall have 

 occasion to notice the nature and construction of the 

 iron rockets, in that part of our article which relates 

 to military fireworks. 



When Mr. Ellicott's report was presented to the Ellicott'* 

 Royal Society, the heights given for the flight of these expen- 

 rockets was received with incredulity, and were sup- menu. 

 posed to have arisen from the imperfect method of 

 measuring the elevations by means of one quadrant 

 only. There is no doubt, however, that if they were 

 not absolutely correct, the general results are suffi- 

 ciently true. They have, indeed, been amply> con- 

 firmed by computing the vertical elevations of the Cor.- 

 greve rockets from the lengths of the ranges; a task 

 not difficult; as from the continued action of the 

 rocket during the time of flight, the path forms a 

 much more regular and manageable curve than that of 

 a shot through the air, where the action of gravity in 

 causing what would be only such a regular deflection 

 as would produce the parabola, is exceedingly modi- 

 fied by the retardation produced by the air," which 

 commences from the first moment tha't it quits the gun, 

 and acts unequally till the very moment of its descent. 



But that no doubts on this subject might remain, Experi- 

 we repeated the experiments on the ascents, with sig- menu by 

 nal rockets; using, two quadrants at once, that the l - e aulbor 

 errors of observation might be diminished, and reject- ' 

 ing all the flights which, materially deviating from u 

 the perpendicular, would have given false results and 

 disturbed the general averages. The mean ascents of 

 pound rockets were thus found to be 480 yards, the 

 greatest being about 520 and 5SO, and the least at 450 

 and 460. We shall conclude this part of the subject 

 by adding, that the vertical power of ascent, in the 

 Congreve rockets, as in others fired at an elevation of 

 45, may be computed from the theory of the parabola. 

 The fl'jht of a rocket is not indeed exactly in this 

 curve ; but the difference of its path from that line is 



