54 ON THE CONSTRUCTION OP HOOPED CANNON. 



In all the preceding computations of the force which the cannon is required 

 to resist (both in this paper and in that to which this is intended as a sequel), 

 I have considered the powder, when fired, as acting by a pressure generated with 

 inconceivable rapidity, and with an intensity sufficient to produce the required 

 velocity in the missile; — this velocity being produced by the pressure alone. 

 I am fully aware, however, that the force thus produced, almost instantane- 

 ously, from a single point within the gun, does, and must, throw a shock upon, 

 and a "vibration through, the whole mass, the destructive effect of which must 

 be provided against in addition to that of the mere pressure of the fired powder, 

 if that pressure be supposed to act as the pressure acts in the hydrostatic 



press, for example 



ed and communicated slowly and gently 



object, thus producing its motion without violence or shock. Although we are 

 without the knowledge requisite to subject to a rigorous computation the de- 

 structive effect of this shock and vibration from the discharge, yet it is necessary 

 that a sufficient strength should be provided in the gun to resist it. Nor 

 are we without the light of experience to direct us to this end; for, although 

 it has not yet been determined, by direct experiment, what strength is required 

 in a gun of *ay 14-inch caliber, in addition to that thrown upon it by the 

 pressure of the charge, in order to withstand the sudden shock and vibration before 

 mentioned, yet we have direct experiments which have determined this element 

 in guns of smaller caliber. Thus the cast-iron 32-pound er, 6 J inch caliber, if 

 made of good iron, and in the usual proportions, that is, with walls of one caliber 

 in thickness, has been proved, by the experience of ages, to be quite reliable 

 for long continued use with service charges. 



Now, it was shown, in my former Memoir, that a maximum pressure, from 

 the fired powder, of 920 atmospheres, will give a velocity of 1,600 feet a 

 second to a 32-pound shot ; and, further, that, computing the strength of the 

 gun from the tenacity of the iron, taken at 30,000 pounds per inch, it is 

 capable of resisting a force of 1,333 atmospheres ; or, the strength of _ 

 is to the maxuuum pressure of the powder as 144:100. Hence, we h_ - 

 excess of 44 per cent., which has proved sufficient to sustain all the extra 



the g 



violence from the shock and 



vibr 



occasioned by the suddenness of the 



discharge, from the heat, and from all other adventitious causes. It is furtl... 

 more shown, ,„ the same Memoir, that a spherical shot of 14 inches' diameter 



velocity of 1,600 feet a second, if fl red from 



the bor 



nf ,A; rt k : lio • i - ' **x^u HKJUl U CU11I1UI1, Lilt; *w^ 



*?* " m mChe ? l0D * fr0m *" -at of the ball to the muzzle under a 



maximum pressure of 2,133 atmospheres. But 



that a 14-inch gun 



