THE ROYAL ARTILLERY INSTITUTION. 
71 
The quantity of granite actually knocked off, or so splintered as to be 
easily picked out, amounted to about 4060 lbs, to which an addition of 
about 5 per cent, or another 120 lbs., may perhaps be made for dust and 
small splinters so dispersed that they could not be collected. 
Eeport No. 3991 (12/12/65). 
The Committee have the honour to report their further experiments upon 
the granite casemate and iron shields erected at Shoeburyness in 1864, and 
which have been framed with a view— 
(1) To ascertain the quantity and weight of fire from heavy rifled guns 
required to render such a structure indefensible, and (2) To enable a 
judgment to be formed on the relative value of granite and iron as applicable 
to the construction of works of defence. 
2. The work subjected to attack represented two adjacent casemates on 
the ground tier of a fort, with their embrasures protected by iron shields. 
It was built of granite, in blocks of considerable size, which were disposed in 
seven courses. The largest block in the structure contained 104 cubic feet, 
the smallest 29 cubic feet. They would weigh about 7*7 and 2*2 tons 
respectively. 
The whole was surmounted by a parapet wall of brickwork 3 feet 2 inches 
thick, and 3 feet 9 inches high. 
The total frontage of granite was 43 feet to 46 feet (being different on 
different courses of stone). 
ft. in. 
Height of do. 16 8 
Height, including brickwork. 20 5 
Greatest thickness of granite in the piers ... 12 0 
Least thickness. 8 0 
Total thickness including brickwork. 14 0 
The vault over the right or east casemate, which represented an inter* 
mediate floor, was turned in four rings of bricks, total thickness 1 foot 7 inches> 
and was surmounted with a platform of concrete whose greatest thickness 
was 3 feet 6 inches. There was altogether 5 feet 6 inches of granite and 
1 foot of concrete immediately over the shield; the total thickness over the 
vault was 2 feet 8 inches. 
The vault over the left or west casemate was intended to be bomb-proof, 
and was turned in 6 rings of bricks; total depth 2 feet 4 inches, and sur¬ 
mounted by a platform of concrete 6 feet deep behind the granite, and 
3 feet 9 inches deep over the crown of the vault. 
The greatest height of the arch of the right or east embrasure was 8 feet 
2 inches, length 12 feet. It was closed by an iron shield having an opening 
or port hole 28 x 36 inches in the centre. 
The shield was composed of 3 slabs of rolled iron 4 inches thick, behind 
which were 8 inches in depth of f ths inch iron plates placed vertically on 
their edges, then a 2-inch solid plate, next 6 inches of teak, and finally, a 
1-inch iron platen the whole being bolted together from front to rear and 
