20 



[March 13, 



variations are much less than those of an ordinary shell not made 

 purposely eccentric. 



He states that, concentricity * being unattainable in shells, it is 

 needless to inquire whether that or eccentricity is to be preferred, 

 the real question being how best to deal with the eccentricity of all 

 shells. 



Of solid shot, Sir Howard Douglas remarks that not more than 

 one out of a hundred, when floated in mercury, remained indifferent 

 to the position in which they were placed in the mercury ; while it 

 was made manifest, by the experiment with eccentricity, that that 

 quality was of all others by far the most fertile cause of deviation. 



I now proceed to my own experiments'!*. My first idea (in 1854) 

 was to employ, with the least amount of eccentricity sufficient to 



Fig. 3. 



Actual size of bore and trans- 

 verse section of spherical shot 

 (allowing for windage). 



Fig. 4. 

 Side-view of spheroid. 



a, Plug of wood. 

 6 6, Plane surfaces. 



effect cycloidal rotation, a form of projectile and section of bore of 

 gun of very little oblateness. I procured two model mortars ; one 



* Dahlgren, p. 92. 



t While endeavouring to rifle a small model mortar, and holding it obliquely, 

 I was struck by the elliptical form of the muzzle presented by thus inclining the 

 circular bore to one side ; and happening at the time to be thinking of some of the 

 details of the experiments with eccentrical spherical projectiles in the ' Naval 

 Gunnery,' it occurred to me that if a gun was elliptically bored, but the bore 

 straight and not helical, the long' axis being in a plane perpendicular to the 

 common axis of the trunnions, and' the shot an oblate spherical eccentric (as 

 already described), and properly placed in the bore, such would be an advanta- 

 geous application of the eccentric principle, as the shot would rotate ad inilio 

 about its natural or shortest diameter, and the direction of such axis and of 

 the plane of rotation could not alter within the gun, or be likely to alter through 

 the air. 



