THE ROYAL ARTILLERY INSTITUTION. 
81 
have in this manner been enabled to proceed with our sea defences 
without increasing the total estimates for fortifications included in the 
Schedule of the Fortification Act. Independently, moreover, of the 
necessity of deferring the provision of iron shields until funds are avail¬ 
able for the purpose, it has been desirable to do so, pending the 
settlement of Artillery questions by which the amount of strength 
necessary to be given to the shields, could be more positively defined, 
and the dimensions and precise position of the embrasures in the shields, 
could be finally decided with reference to muzzle-pivoting carriages. 
Besides increasing the thickness of the exposed masonry and substituting 
iron for granite in the space immediately about the guns, the arches of the 
casemates have been constructed so as to make the whole roof afford support 
to that part of the masonry above the shields and piers. (See Figs. 3 and 4, 
Plate IV.). 
Figs. 1—3, Plate III. show the mode of construction thus described, as 
compared with the recent American casemated sea defences;, and which, as 
before stated, are the most approved of the previous construction. 
Experimental casemates , and objects of experiment . 
10. With a view of ascertaining the quantity and weight of fire from 
heavy rifled artillery which must actually take effect upon any one portion 
of a casemated battery of the late English construction to render that 
portion no longer tenable by its defenders, two casemates were erected at 
Shoeburyness in 1864-5. 
There were also other objects attained by the experiment, viz. 
(1) Some improvements in the detail of construction, in order to afford 
greater resisting power at trifling additional cost, were suggested by the 
experiment. 
(2) The trial showed, contrary to expectation, that a brick arch, 
representing the intermediate floor of a casemate, of 20 feet span and 
only 18 inches thick, with a layer of concrete over it only 6 inches 
thick at the crown, was amply strong enough as a platform from which 
to fire shot or shell with full charges from a 600-pr. gun. 
(3) The experiment further showed that the casemates were admirably 
adapted for the working of 12-ton guns, or even larger guns if thought 
desirable, and valuable information was obtained as to the appliances 
necessary for working great rifled guns in casemates. 
(4) Two different kinds of iron embrasure shields were tried, one 
12 feet long by about 8 feet high, arranged so that it could be put 
into its place at any'time after the completion of the masonry, on the 
plan adopted in our sea defences; the other 6 feet by 6 feet, and built 
into the work. 
(5) The amount of battering which each of these shields would resist, 
and the relative advantages of each were ascertained. 
