8 ON RIFLED GUNS. 



the torsion strain, all expressed in pounds, and the lever arm of the latter being the radius of 

 the bore. The strength of the gun material will readily suggest the figure and dimensions 

 necessary to resist these strains. The strength of the material should be ascertained by care- 

 ful experiments, so conducted as to subject cylinders of the metal simultaneously to the three 

 kinds of strain, the intensities of the strains bearing to one another the proportions suggested 

 by the formulas. 



(10)— To apply these formulas, it will only be necessary to find, experimentally, the value 

 of jOj, and that of V, for different values of y, and to compute from the known figure and 

 dimensions of the projectile the value of Jc v The values of p v corresponding to given values 

 of y, may be found by a modification of Rodman's process of plugs. To find V, for the same 

 value of y, let a gun of each of the calibres employed in service, be successively reduced in 

 length, and the initial velocity at each reduction determined by the electro-ballistic pendu- 

 lum, observing to keep the charges of powder, as well as the projectiles, as nearly alike as 

 possible in the several trials. 



(11) — Let us illustrate the mode of computation by applying the formulas to a probable 

 case. 



In Major Rodman's work, entitled "Experiments on Metals and Gunpowder," page 200, it 

 appears that in a 42-pounder, 8 pounds of powder behind a solid shot and sabot gave a pressure 

 of the gas on a square inch, at 14 inches from the bottom of the bore, equal to 46,100 pounds; 

 at 28 inches 12,200; at 42 inches 5,500; at 5G inches 5,350; at 70 inches 4,970, and at 84 inches 

 5,700; showing a pretty rapid decrease after the projectile begins to move, and from which it 

 may be assumed that the missile acquires half its initial or maximum velocity at about one 

 third the distance from the starting point to the mouth of the piece. 



In a little pamphlet by Mr. Tarrott, entitled "Ranges of Parrott Guns and Notes for 

 Practice, 1 ' we find, at page 9, that with 10 pounds of powder, a shell, of which the weight 

 was 101 pounds, was projected from his 100-pounder witli an initial velocity of 1,250 feet; 

 and at page 10, that the same charge of powder, in same gun, gave, with an 80 pound missile, 

 a pressure, according to the plug process, of 81,000 pounds to the square inch. It is assumed 

 that the pressure behind the 101-pound shell was not less than this, and that this pressure 

 occurred soon after the projectile began to move. Then, assuming, according to the sugges- 

 tions of Rodman's experiments, that this pressure was reduced to one-third at one-third the 

 distance from the point of the projectile's departure to the mouth of the gun, and taking the 

 dimensions of the 100-pounder from the pamphlet, page 19, the data for computation will 

 stand : 



/ 

 P = 0.2C6 pi = J X 81000 X 144 = 3SSS00O. 



7=10.833 .J -. y -. = 90° X J — 30° 



n = 3.5 V = 625 



Af = 0.035378 c=\ 



(320) 



