22 [March 13, 



I also made the mortars of the same length, namely small. They 

 were fired from a moveable wooden platform, but each from the 

 same bed or block of wood, which slid in a groove in the platform ; 

 the bed admitted of their being fired at the horizontal and at low 

 elevations. 



Recoil could be marked ; the usual charge was 3 drachms of fine 

 canister powder ; the disk caused more recoil than the spherical shot, 

 as in the former windage could be more effectually suppressed. 

 Centre of gravity below in both gave more recoil than centre of 

 gravity above. The eccentric disks and spheres were usually fired 

 with centre of gravity below. The disk ranged to first graze about 

 i, and at the extreme range about f further than the range of the ec- 

 centric spheres ; that is, as 4 to 3 to first graze, and at the extreme 

 range (after grazing) as about 8 to 5. But there can be little doubt, 

 from the light thrown on this point by my later experiments, that no 

 sufficient rotation of a cycloidal kind could have been imparted to 

 the disks from the mortar, the centre of gravity being below, but only 

 from their striking the sand, as if the disk were bowled from the 

 hand; the disks ricochetted to between 600 and 700 yards up to 3 

 elevation, above which angle there was no good ricochet. The mor- 

 tars were about 10 or 12 inches above the level of the sand. 



When a disk touched a rough place, though much oscillation was 

 set up (as known by the noise it produced), this lasted only to the 

 next one or two grazes ; for at the end of the range, where the disk 

 rolled before stopping, and the sand happened to be soft and dry, 

 the track was continuous like that of a wheel, and in a line that was 

 very straight. 



Some experiments with these mortars and disks were shown by 

 me at Shoeburyness in 1855 ; but the ground there consists of mud 

 with pools, and is not level enough for so small an apparatus. After 

 a few comparative trials of the two mortars, the cheeks blew out from 

 the disk mortar. 



In 1859 I was afforded an opportunity of resuming the subject; 

 but still, necessarily, with a model only ; instead, however, of a length 

 of 3 calibres only, as in the mortars, I had a disk-gun made of 

 between 1 and 1 1 calibres, or about howitzer proportion ; and instead 

 of, as previously, a weight of disk of 5 ounces, the weight was 

 about 8 ounces. Length of bore of gun 20 inches, long diameter of 



