THE ROYAL ARTILLERY INSTITUTION. 
251 
system of muzzle-pivoting; as it is quite clear that the height of the 
embrasure cannot be materially reduced, so long as the trunnion remains 
the centre of oscillation for elevation or depression; in fact, on the present 
system of elevation, the height of the embrasure depends on the length of 
the gun from the trunnions to the muzzle, representing the radius of the 
arc described by the muzzle when elevated or depressed. 
An embrasure for a 12-ton gun elevated on the old principle, would have 
to be 4 ft. 6 in. high by 2 ft. 4 in. wide, so as to allow for a reasonable 
amount of elevation and depression ; and supposing the shield for protecting 
the casemate to be 6 ft. by 8 ft., the embrasure old pattern would nearly cut 
it in half, and would only leave a strip of 9 in. of plating above and below 
which would detract enormously from the strength of the shield (vide 
Diagram, Plate I. Pig. 1), besides the embrasure would offer llj feet 
open area for the admission of shot, shell, and rifle bullets, whereby the 
gunners might be picked off, and the gun and carriage disabled; and' as 
modern guns and carriages are very expensive articles, it behoves us to 
protect them by every means in our power. Por a 12-ton gun, elevated 
on my principle I should not require an embrasure to be more than on 
opening 2 ft. 4 in. in height, and the same in width (vide Diagram, Pig. 2), 
thereby affording complete protection to the gunners, gun, and carriage, and 
adding immensely to the strength of the shield. 
In cupola ships on Captain Cowper Coles* plan, the want of a system of 
muzzle-pivoting is felt still more than in land fortifications, as in them, from 
their limited height above the deck, it is impossible, having due regard to 
the strength of the cupola, to have a port more than 2 ft. 9 in. in height; 
and to enable the gun, mounted on the ordinary carriage, to fire through 
this port, at different angles of elevation and depression, the platform on 
which the carriage is mounted has to be raised and lowered bodily by a very 
expensive arrangement of screws and wedges; the operation also is very 
tedious, whereas by adopting my principle the whole of this costly apparatus 
can be dispensed with, and the port can be considerably reduced. I am now 
making a 12-ton muzzle-pivoting wrought-iron carriage for the turret ship 
“ Prince Albert/* the size of the port will be 2 ft. 1 in., and the platform 
will be a fixture. In my opinion, this system is peculiarly adapted to this 
admirable class of ships; the turret itself being sighted, the man who lays 
the gun does not require to look through the port to get his object on, 
consequently it may be reduced to the exact size of the muzzle of the gun, 
thereby adding materially to the strength of the turret, and affording 
complete shelter to the gun*s crew. 
You will naturally ask, then why not make the ports in the “ Prince 
Albert ** the exact size of the muzzle of the gun ? The reason is this, the 
turret is only 16 ft. 6 in. in interior diameter, and the gun itself is 11 ft. 
long, so that in order to allow room for recoil, I have to pivot the gun 1 ft. 
in from the muzzle, thereby slightly increasing the size of the port. 
It is doubtful whether this system can be applied at present with advant® 
age to broadside ports in iron-clad ships, as owing to the centre of motion 
being at the muzzle, the breech has to go through a much larger arc than 
when the motion is given from the trunnions; for instance, in a ship of the 
“ Bellerophon ** class, a 300-pr. mounted upon my principle would, when 
