On the Forces of Translation and Rotation in Rifled Guns. 195 



determination, with plane-parallel glasses slightly inclined to 

 each other, whether the ray reflected at the limit of glass and air 

 was retarded towards the other. It was seen, at least with the 

 angles of incidence used by the author, that the ray reflected 

 from metal must always be retarded, in order to bring the inter- 

 ference-bars, glass- metal, into the same position as the inter- 

 ference-bars, glass-glass. 



It would thus follow from these experiments, that the luminous 

 rays polarized in the plane of reflexion undergo the greatest 

 alterations of phase, that vibration takes place in the plane of 

 polarization, in accordance with Prof. Neumann, and that the 

 elasticity of the sether differs in different media. 



XXVIII. Note on the Ratio between the Forces tending to produce 

 Translation and Rotation in the Bores of Rifled Guns. By 

 Captain Noble {late Royal Artillery) * 



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 formula?, which I 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 my knowledge, been published, and partly because, as 

 several erroneous statements on the subject have appeared, the 

 formula? themselves may possibly be of use to some artillerists. 



The case we shall first examine will be that in which the rota- 

 tion 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, the line drawn from the centre of the bore to the groove 



is coincident with the section of the 

 driving-surface. A section of such 

 a form of rifling is shown in fig. 1 . 

 The reader is supposed to be looking S^ 



from the muzzle towards the breech of / 

 the gun, and the direction of rotation / 

 is shown by the arrow A B. It will be 

 seen that the radius C D is coinci- \ 

 dent with the section of the driving V 

 surface DP. . \v 



In entering upon this investiga- *■ 



* Communicated by the Author. 



02 



Fig. 1. 



