ON RIFLED GUNS. 10 



laws were accurately known, it would be easy to find the maximum of gas pressure, by tbo 

 Rodman process, from the known depth of ping penetration and the resistance due to the unit 

 of penetration. In the absence of these laws, it would be better to modify the experiments 

 bv inserting a number of plugs around the circumference of the same cross section of the gun, 

 made at different distances from the mouth, and keep the plugs in their places by suitable 

 dynamometers strained to different degrees; and after firing, find that plug which has made but 

 a faint indentation on the copper. The indication of the dynamometer on this plug would be 

 the measure of the maximum elastic force of the gas. 



(21) — These objections to Major Rodman's results are made in no spirit of criticism; they 

 are unavoidable, and belong to the discussion which was proposed at the outset. The labors 

 of that distinguished officer have been beset with difficulties, and, considering the range and 

 nature of his experimental researches, it would be matter of surprise if he had made no 

 mistakes. The spirit of professional improvement which seems to have animated him from his 

 entrance into the ordnance corps, has given the country much valuable information, and to 

 find fault with it because it is not all that could be desired, would be unreasonable and unjust. 

 (22) — Let us next find the number of turns the projectile makes in a second of time, on 

 leaving the piece. For this end, take Eq. (7). 



tc 0.4971509 



V 3.09G9100 



2 a c 9.6939700 



u a c 9.4559320 



/ a c 8.965:2513 



u = 51.S 1.7142142 



(23) — The ladius, denoted by p u of the interior surface of the shell, is 0,266—0,094, equal 



to 0,172 of a foot; and the actual rotary velocity, denoted by Vi, of this surface around its 



axis, is given by 



V 1 = 2tt. /0 i.x. 



2 0.3010300 



■k 0.4971509 



p 1 9.2355284 



v 1.7142142 



Vx = 55 f .9 1.7479235 



That is, on leaving the piece, the velocity of rotation of the interior surface of the shell is 



nearly fifty-six feet; half of which would be sufficient to ignite a wooden or heat to redness an 



iron axle, if rubbed under moderate pressure by the turning shell without a lubricant; and it 



is not necessary to attribute the frequent explosions of rifle shells within the gun to any other 



cause. The powder thrown by centrifugal action against the inner rough surface of the shell 



before it has taken the rotary motion of the latter, would be subjected to friction enough to 



explode it. Here is a real source of failure with rifled guns. 



(331) 



