210 Captain Noble on the Pressure required to 



pressure on the studs for parabolic rifling, with the equations 

 subsisting where a uniform twist is used. 



For a uniform twist we have, as I formerly showed, 



Vf+F" + V^A« + (sin S)" 2 



where h is the pitch of the rifling, k the tangent of the angle 

 which the groove makes with the plane of xy, the other con- 

 stants bearing the meaning I have already assigned to them in 

 this investigation. 



20. In the Woolwich guns, where 8=90°, (16) becomes 



R _ 27rp 2 Vl+/: 2 p n7 , 



21. I proceed to apply these formulse, and propose to examine 

 what are the pressures actually required to give rotation to a 

 400-lb. projectile, fl red from a 10-inch gun with battering charges, 

 under the following conditions : — 1st. If the gun be rifled with 

 an increasing twist as at present. 2nd. If it be rifled with a 

 uniform pitch, the projectile in both cases being supposed to 

 have the same angular velocity on quitting the gun. As the 

 calculations for the uniform pitch are the simpler, I shall take 

 this case first. 



22. I have before remarked that with a uniform twist the 

 pressure on the studs of the projectile is a constant fraction of 

 that on the base of the shot, and represents, so to speak, on a 

 reduced scale, the pressure existing at any point in the bore of 

 the gun. Calling the fraction in equation (17) C, we have 



R=C.G, (18) 



where 



c _ 27rp 2 Vl + F - -04426 (19} 



the values of the constants in (19) being in the case of the 

 10-inch gun as follow : — 



p = -312ft., £=12-732, A=.83-888'ft.j r =-41 7 ft., ^ = -167. 

 Hence 



R= 04126. G. ...... (20) 



23. But the values of G are known with very considerable 

 exactness from the investigations of the Explosive Committee 

 under the presidency of Colonel Younghusband. The following 

 Table gives the value of (G that is, the total pressure in tons 

 acting on the base of the projectile) for a charge of 85 lbs. of 



