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XXVI. On the Pressure required to give Rotation to Rifled Pro- 

 jectiles. By Captain Noble, F.R.S. fyc, (late Royal Artillery)*. 

 [With a Plate.] 



1. TN a paper published in the Philosophical Magazine for 1863 

 jL (vol. xxvi.), and subsequently in the Revue de Technologie 

 Militaire, I gave some investigations on the ratio between the 

 forces tending to produce translation and rotation in the bores 

 of rifled guns. 



2. My object in these investigations was to show, 1st, that in 

 the rifled guns with which experiments were then being made 

 the force required to give rotation was generally only a small 

 fraction of that required to give translation ; 2ndly, that in all 

 cases (and this was a point about which much discussion had 

 taken place) the increment of gaseous pressure (that is, the in- 

 crease of bursting force) due to rifling was quite insignificant. 



3. In the paper referred to, although the formulae were suffici- 

 ently general to embrace the various systems of rifling then under 

 consideration in England, they did not include the case of an 

 increasing twist, which has since been adopted for the 8-inch and 

 all larger guns of the British service; neither was our knowledge 

 of the pressure of fired gunpowder sufficient to enable me to 

 place absolute values on either of the forces I was considering. 



4. Since the date at which I wrote, an extensive series of expe- 

 riments has been made in this country; and the results of these 

 experiments enable me to give with very considerable accuracy 

 both the pressure acting on the base of the projectile and the 

 velocity at any point of the bore. I am therefore now able not 

 only to assign absolute values where in my former paper I 

 only gave ratios, but also to show the amount by which the 

 studs of the projectiles of heavy guns have been relieved by the 

 introduction of the accelerating twist known as the parabolic 

 system of rifling. 



5. Very little consideration will satisfy any one conversant 

 with the subject, that in the ordinary uniform spiral or twist the 

 pressure on the studs or other driving-surface is a maximum 

 when the pressure on the base of the shot is a maximum, and 

 becomes greatly reduced during the passage of the shot from its 

 seat to the muzzle of the gun. In my former paper I showed, in 

 fact, that in a uniform twist the pressure on the studs was a con- 

 stant fraction of the pressure on the base of the shot, the value of 

 the fraction of course depending on the angle of the rifling ; and 

 as it is evident that the tension of the powder-gases at the muzzle 

 is very small when compared with the tension of the same gases 



* Communicated by the Author. 



