thsobt of the motion of rockets* iqg 



Scholium. 



In this solution, the resistance of the air to the rocket's Schotiura. 

 motion ^s supposed to vary directly as the square of the ve- 

 locity ; an hypothesis which experiments disprove when ap- 

 plied to military projectiles with cannon balls: but it is to 

 be apprehended, that in the motion of rockets the deviation 

 from this law is scarcely to be regarded, since, what lakes 

 place in the flight of shot and shf;!ls to violate it, is in a 

 great Pleasure obviate J i:. the rockets, by the extreme heat 

 of the flame that rushes iVom them; this rarifying the am* 

 bient air promotes the motion of the particles striking 

 the head of the rocket towards its hinder parts; and 

 since it is only the immediate motions of such particles 

 backwards that can cause the law to obtain (for it would 

 obtain correctly, if, after the impact of the particles they 

 had no power to impel others lying before them, but either 

 glided off from the surface struck, or had their force anni- 

 hilated by it at the moment of striking) it is to be expected 

 that the conclusions here brought out which are grounded 

 on this law of resistance, will be found to agree pretty cor- 

 rectly with the results determined from experiment. 



But if they should not, let then the law of resistance be 

 as the nth power 6f the velocity ; and the method of solu- 

 tion will remain precisely the same as before. For it is 

 only the fourth equation in the preceding process, namely* 

 k d" t' — &c, that will vary or become aftected by any devi- 

 ation from the law we have assumed ; and therefore when 

 this shall have been settled by experiment {the only way 

 in which it ever can be settled), and the absolute resistance 

 determined in any one case of velocity, and the real strength 

 ©f the rocket composition ascertained ; then, and not till 

 then, shall we be able to off*er any unerring rules to the mili- 

 tary practitioner. 



lU 



