24 , [March 13, 



abstracted, which I found would effect rotation, was y^ only of the 

 disk's weight, and was removed from the sharp edge at the sides of 

 the zone by filing at four points. Rotation was effected also in a 

 homogeneous disk, and without any cavity, by making it slightly 

 oval in periphery in fact, as if it were a middle slice from a very 

 slightly ovoid or egg-shaped body, instead of from a spherical one, 

 the larger enc[ or heaviest part being put uppermost in the bore. 

 Excepting one other form, better described presently, these were all 

 the forms I experimented with. 



The gun being too small to effectually destroy a sabot, I com- 

 monly used a horse-shoe electro-magnet sliding in one end of a flat 

 wooden rod of similar section to the bore of gun, with which to place 

 the shot in any desired position. Having previously marked, by a 

 spot of chalk, the face of the shot to be seen in front when in its 

 place, I placed the shot as desired in the bore, and then by throw- 

 ing in light with a mirror, I saw that the position was that wanted. 

 Sometimes, if the shot turned in entering, it could not be again with- 

 drawn but by firing; and thus such cases conveyed no meaning, 

 unless the spot of chalk was not altogether out of sight, in which 

 case the position and result were recorded. 



In September 1859, by the kind permission of Captain Jerning- 

 ham, R.N., in command, the gun was placed on board the ' Cam- 

 bridge,' the gunnery ship at Devonport. 



The first experiment was to ascertain the ranges due to centre of 

 gravity above and below ; and this would also show whether rotation 

 occurred in one or the other position, or in both. Four disks were 

 selected of within a few grains' weight of one another, average weight 

 7J ounces ; three of the disks were to illustrate respectively concen- 

 tricity, and the two opposite positions of centre of gravity " above " 

 and "below." The charge was 1^ ounce, and the elevation 5 in 

 each case ; the powder was that known as " Lawrence's No. 4, large- 

 grain," and is a powder of great strength. 



The concentric disk dropped at 550 yards; the eccentric with 

 centre of gravity "below," at 500 yards; the eccentric with centre 

 of gravity " above," at 1000 yards. The two first-named disks made 

 much noise in passing through the air ; the long-ranging disk, fired 

 with centre of gravity above, made but little such noise. 



The other eccentric disk was then fired with 2 ounces instead of the 



