242 



Pyrotech. published and practised by Lieutenant Bell, of the 

 r -y- Royal Artillery. It was, however, neglected by those 

 """V"* who ought to have taken an interest in it, but was af- 

 terwards revived by Mr. Manby, who obtained from 

 Parliament the splendid reward which, if any where, 

 was due to the inventor. This consisted in throwing a 

 line out of a piece of ordnance, attached to a shot. ^ If, 

 from the shore to the vessel, the elevation was so given 

 as to cause the shot to range beyond it, so as that the 

 line might fall on board across the ship. If, from the 

 vessel, this precaution was unnecessary ; and in case of 

 any vessels being acquainted with this expedient, and 

 having the requisite implements on board, the chances 

 of success were, perhaps, somewhat greater. It must 

 be recollected, however, that very few coasting or 

 trading vessels are provided with a piece of ordnance ; 

 and that, even if they were, it must generally be im- 

 possible to use it, under the circumstances in which a 

 vessel is aground on a lee shore. 



Lately, as an improvement on this method, the same 

 Mr. Manby and a Mr. Trengrouse have proposed the 

 use of a rocket. A small line is attached to it below, 

 which is carefully coiled up like a whale line, so as to 

 deliver freely. Being thrown on board the vessel in 

 such a state, it may be made use of to attach a stronger 

 line to, and so on in succession, till a hawser can be 

 carried on shore. It is evident that this project is 

 more applicable than a piece of ordnance, if it is to be 

 carried by the ship itself; as, if fire can be at all pro- 

 duced, a rocket may be discharged under any circum- 

 stances. 



Causes of 

 the flight 



ets ' 



Causes of the Flight of Rockets. 



There needed not to have been much dispute oh this 

 t at any time, as the causes of the ascent or flight 

 of a rocket ought to have been sufficiently evident. 

 Yet, when such philosophers as Lemery, Wolf, Pa- 

 pin, and many others, considered that the explosive, 

 or expansive force of gunpowder, depended on the ra- 

 refaction of air contained in the interstices of the grains ; 

 when John Bernouilli imagined that it contributed part 

 of the force ; when Muschenbroek, Stahl, Beaume, and 

 Macquer, considered that this effect arose from the con- 

 version of the water of the nitre into steam, whereas 

 nitre contains no water ; when Count Rumford fol- 

 lowed in the same track ; when Lombard added to this 

 the conversion of the nitric acid into vapoui ; and when, 

 lastly, others attributed the elastic force of gunpowder 

 to the radiation of disengaged caloric, it is not very 

 surprising that the cause of the flight of a rocket should 

 have been as much misunderstood. 



Since the true cause of the explosive force of powder 

 has been known, some unaccountable errors have been 

 committed in attempting to solve this question. Some 

 philosophers, forgetting themselves, have imagined 

 that the effect arose from the generated fire or flame, 

 as they considered it, acting on the vent or choke; an 

 action which, it is very evident, would tend only to 

 burst the rocket, not to make it fly. But we may pass 

 by these errors, since there is no difficulty whatever in 

 the question. As the powder or the composition, which 

 does not differ very materially from that, is condensed 

 to''one-half the space which it occupies when in a gun, 

 the production of air, proportioned to the bulk of this 

 composition, is nearly double what it is from gunpow- 

 der in a charge. If taken according to the relative 

 weight, it approaches nearer to that ; but is still in- 

 ferior, on account of the greater disproportion of the 

 6 



nitre necessary to insure a fire sufficiently slow, whence Pyrotech. 

 the whole of the charcoal is not converted into gas, "? 

 But as it is not necessary to be very accurate for the "*~~Y*** 

 present purpose, we may consider that the rocket com- 

 position produces 500 times its bulk of gas at the mean 

 temperature of the air, while its elastic force is increa- 

 sed by the heat to not less than 2000. Thus the rock- 

 et of three inches diameter and two feet long, ( to as- 

 sume a case,) will furnish 96,000 cubic inches of gas of 

 the same density as the atmospheric air, at the same 

 temperature, or at the elevated one at which it is actu* 

 ally generated, 384,000. 



In the rocket, now, of the assumed dimension, the 

 whole of this fluid must be discharged within the 

 space of 20 seconds from an aperture of l| inch in 

 diameter ; and this, therefore, requires an issuing ve- 

 locity for the stream of air, (or flame as it is called,) 

 equal to that which would result from 19.200 cubic 

 inches flowing in a stream of that diameter through 

 every second of time. Here, then, is the source of the 

 moving power, which becomes a case of recoil precise- 

 ly analogous to that which takes place when a piece of 

 ordnance is fired. The resisting body in this case, as 

 in that of a piece of ordnance fired without a wad or 

 a shot, as is clone in Dr. Hutton's pendulum, is the 

 air ; and the flight of the rocket thus depends on a 

 comparison between the weight to be moved, (adding 

 to it the effect of gravity and the anterior resistance of 

 the atmosphere,) and that of the resistance which the 

 air opposes to the issuing current. 



We have here assumed grounds of computation which 

 are not exact, but quite sufficient to explain the gene- 

 ral principle. But it is plain, that, with accurate data, 

 such as the exact quantity of composition contained 

 in the rocket, the exact quantity of gas which a given 

 weight of it would produce, and a true measure of the 

 temperature, the problem that relates to the velocity 

 of a rocket at any one point of time, and so on for the 

 whole flight, might be calculated. Dr. Hutton's ele- 

 ments of calculation for the initial force of gunpowder 

 might, with the necessary addition, be applied to the 

 solution ; if not with accurate results, when the intri- 

 cacy of all the circumstances are considered, yet with 

 not much less than in the case of the firing of ord- 

 nance, and the quantity, whether of the recoil or the 

 propelling power. But our readers would not thank 

 us to enter into these calculations with the requisite 

 accuracy, even if our limits permitted us to enlarge on 

 this part of our subject. 



We shall, therefore, draw in on this question, and 

 only further say, that in considering the nature and 

 action of this force, it might probably be made use 

 of to advantage in obtaining that end of which we 

 spoke before, namely, overcoming the inertia of rock- 

 ets. To effect this purpose, a solid obstacle or plate 

 affixed to the frame might be opposed to the issuing 

 current of air, which, by offering a steady and firm re- 

 sistance to it, would produce a far greater initial effect 

 than can be obtained from that of the atmosphere merely. 

 From this explanation of the action by which a 

 rocket is caused to fly, the reason for its very peculiar 

 construction becomes evident. If there were no bore, 

 no part of it could at any time be inflamed greater 

 than an area of the cylinder ; and the air produced 

 from so small a surface would be insufficient to com- 

 municate the requisite velocity. In consequence of 

 the size or length of the bore, nearly the whole length 

 of the composition is inflamed at the same time, and 

 hence a rapid issue of air is the consequence. Hence 



