1862.] 23 



bore 1^ inch, and of disk nearly the same, and transverse diameter 

 f inch (see figs. 1,2). Thus the disk was virtually a slice from a 

 sphere, and across a zone of about 48 or 49. Its long diameter 

 was about 2 times the short diameter. 



The gun was first bored to a cylinder, and the bore was then 

 reduced to the proper shape by the insertion of two cheek pieces. 

 I had difficulty in securing the cheeks of the gun, and found, after 

 two failures with side-bolt Fig. 8. Perspective view of cheeks, 



fastenings, that it was re- 

 quisite to secure the cheeks 

 in the line of their length 

 by attaching them to the The crosses show places for side-bolts to keep 

 head of a bolt (like the cheeks close to sides of cylindrical bore. 



prongs of a tuning-fork to its handle), which passed through the 

 breech end of the gun in the line of its axis, and was secured on the 

 outside on its projecting screw end by a nut (see fig. 8). 



The gun was made so that the longer axis of the bore was, 

 throughout the gun, perpendicular to the common axis of the trun- 

 nions. The gun weighed about 130 Ibs. It was simply a cylin- 

 drical block with trunnions ; I had, in it t to learn how to effectually 

 secure the cheeks, and therefore had the gun made of a thickness 

 otherwise unnecessary. 



The first disks made were cast with the mould in a horizontal posi- 

 tion ; and several such disks were fired ; but scarcely one of them had 

 the centre of gravity in the equatorial plane ; and I found that a disk 

 that would not roll tolerably straight (as on a level table), had cor- 

 responding lateral deviation in the air when fired. Other disks were 

 then cast with the mould in a vertical position, and these were much 

 more symmetrical in respect of the sides. 



The eccentricity was given at first by a hole through the disk, 

 plugged with gutta percha, or with an alloy of lead and tin ; expe- 

 rience, however, showed that plugs of any kind, though riveted, 

 were often blown out, and could only be secured by being screwed 

 in ; and eventually I found no way better than to employ symme- 

 trical shallow cavities * wrafilled, on each side of the disk, at about 

 half the radius from the centre. The least amount of metal 



* I am indebted to Mr. Braid, late R.A., of the Dep. Military Prison, Devon- 

 port, for his kindness in making these cavities in the disks by a lathe. 



