29(3 MESSRS. E. H. FOWLER E. G. GALLOP, C. N. H. LOCK AND H. W. RICHMOND : 
Introduction. 
This paper contains the results, theoretical and experimental, of work undertaken, at 
the request of the Ordnance Committee, by the authors as Technical Officers of the 
Munitions Inventions Department. Permission to publish such parts as appear to be 
of general scientific interest has now been granted by the Ordnance Committee and 
the Director of Artillery. The publication of this paper has received their sanction. 
The experiments in question were carried out at the firing ground of H.M.S. 
“Excellent,” Portsmouth; the Experimental Department, H.M.S. “ Excellent,” also 
provided the 3-inch guns used and the material for the construction of the range. 
The authors’ best thanks are due to the officers of this department, especially 
Lieut.-Commander R. F. P. Maton, O.B.E., R.N., without whose cordial co-operation 
these experiments could never have been carried out; also to the other officers of the 
Munitions Inventions Department who assisted in the heavy work of making and 
analysing the observations. The aeronautical measurements at low velocities, 
required for comparison, were made in the wind channels of the National Physical 
Laboratory, by arrangement with the Director and the Superintendent of the Aero¬ 
nautical Department, to whom also we wish to express our thanks. 
The subject of this paper is the motion of a spinning shell through air at velocities 
both greater and less than the velocity of sound. We first attempt to describe the 
motion of the spinning shell, considered as a rigid body, under the effects of gravity 
and the reaction of the air; this latter is supposed to be known in terms of the 
position and velocity co-ordinates of the shell, and the state of the air through 
which it moves. We are thus concerned throughout with the “aerodynamical” 
problem of the motion of the shell alone, and not with the general “ hydrodynamical ” 
problem of the motion of the complete system formed by the shell and air together. 
The motion of the shell thus described is then compared with the results of 
experiments, and the more important components of the force system imposed by the 
air are determined numerically as functions of certain variables such as the velocity 
of the centre of gravity of the shell. The actual experiments consist of observations 
of the initial motion of the shell (more particularly the angular motion of its axis of 
symmetry), over a limited range near the muzzle of the gun. The velocities 
experimented with range from 40 f.s A to 2300 f.s., that is from about 0-04 to 2-1 
times the velocity of sound. Using the values of the components so determined, 
the actual motion of the shell can be calculated with equal certainty in the more 
general cases which are inaccessible to direct and detailed observation. 
As stated above, we make no attempt to attack the hydrodynamical problem. 
Such an attack is probably not yet feasible. By obtaining, however, an accurate 
descriptive knowledge of the force system imposed by the air, and the allied system 
* This velocity was obtained in a wind channel, using a current of air and stationary shell. The lowest 
velocity used in actual firing experiments was 880 f.s. 
