THE PLYMOUTH BREAKWATER FORT. 
165 
it. In form it is an oval, measuring upon its major axis at 
the base 143 feet 6 inches, and upon the minor axis 113 feet 
6 inches ; the curves being struck from two radii, one of 90 
feet 3 inches, the other 50 feet 9 inches. The batter of the 
wall is 1 in 11. In structure the iron wall consists of 15 
inches of iron in three thicknesses, in the following order : —a 
front armour of three tiers of 5-inch plates, 21 feet 9 inches 
long, and respectively 4 feet 9 j inches, 4 feet 1 J inches, and 
3 feet 5j inches wide (giving a total external height of 12 feet 
5 inches) ; a backing of 6 inches of common concrete ; next 
a layer of 5-inch bars 16 J inches wide; these being crossed 
behind by another layer of similar bars laid horizontally ; the 
whole supported internally by vertical iron bars, 5 inches thick 
and 12 inches deep, placed upright and edgewise and let into 
the floor through a footplate, as also into the roof at short 
intervals. The entire circumference is pierced, at distances of 
21 feet 9 inches from centre to centre, by eighteen ports for 
10-inch 400-pounder rifled guns, which when in position 
will point variously — some seaward, some across each of the 
two shipways, and others up the Sound ; but in no case does 
it appear that a converging fire of more than four guns can be 
obtained. 
This brief view of the situation will show that the passage 
of any hostile fleet would have to be made along the contiguous 
VOL. X. — NO. XXXIX. N 
