THE ROYAL ARTILLERY INSTITUTION. 
409 
NOTE ON THE RATIO 
BETWEEN 
THE FORCES TENDING TO PRODUCE TRANSLATION AND ROTATION IN THE 
BORES OE RIFLED GUNS. 
Br CAPTAIN NOBLE, late E.A. 
[Reprinted from the Philosophical Magazine, with permission of the Proprietors, to whom 
thanks are due for the use of the blocks for the wood cuts.] 
The magnitude which the rifled ordnance of the present day have 
attained, and the large charges which are consumed in their bores, render it 
an object of great interest that we should be able to assign the pressures on 
the grooves (or other driving-surfaces intended to give rotation) due to 
different modes of rifling, as well as to determine the increment in the 
gaseous pressure arising from the nature of rifling adopted. 
The formulse, which we shall hereafter give, have, with slight modifications, 
been used at Elswick for nearly three years, and are now given, partly, 
because no investigation of the question has, to our knowledge, been 
published, and partly because, as several erroneous statements on the subject 
have appeared, the formulse themselves may possibly be of use to some 
artillerists. 
The case we shall first examine will be that in which the rotation is given 
by means of grooves, the driving-surfaces of which are such that if a section 
of the gun, perpendicular to the axis, be made, 1# 
the line drawn from the centre of the bore to the 
groove is coincident with the section of the driving- B 
surface. A section of such a form of rifling is 
shown in fig. 1. The reader is supposed to be 
looking from the muzzle towards the breech of the 
gun, and the direction of rotation is shown by the 
arrow AB. It will be seen that the radius CD is 
coincident with the section of the driving surface 
DP. 
In entering upon this investigation, it will be 
more convenient to consider the projectile in its motion along the bore of the 
gun as moving on a fixed axis, and, further, to suppose that the motion of 
rotation is communicated to the projectile by a single groove. These 
suppositions will not interfere with the accuracy of our results, and will 
enable us very much to simplify the equations of motion. 
