340 
ARMOURED DEFENCES. 
7 ft. 6 ins. ; made of f-in. plate, very strongly put together, and filled 
with concrete. Into the upper parts of these piers are set the ends of 
solid bars, which have to carry a part of the load of the floor above. 
Next above these lower piers is a ring of 3-in. plate going all round 
the fort. It is slotted with holes, and the upright bar supports, 
already mentioned, are threaded through them. 
On this 3-in. plate the front ends of the radial girders of the upper 
gun floor rest. Their rear ends are carried by box girders bearing on 
the masonry piers of the fort. Between the radial girders are the arch 
plates, which complete the floor. 
The front ends of these floor girders are 'secured to a continuous 
curved plate standing on edge. 
It is to be particularly observed that no part of this floor structure is 
fastened to the 3-in. plate of which I have been speaking. It merely 
rests on it, and the surfaces are free to slide if necessary. The object 
of this provision is that if the front armoured wall should be heavily 
battered, the risk of the racers of the upper guns being thrown out of 
position thereby should be reduced to a minimum. 
The construction of the parts of the skeleton which intervene between 
the lower and upper piers demanded especial care, as these partake of 
necessity of the character of a joint, and it was of the utmost importance 
that this joint should not be a rickety one. 
The construction of the piers and framework of the upper tier is, 
generally speaking, a repetition of that of the lower casemates, except 
as regards a few particulars which I need not mention here. 
The armour bar supports are in one length from the lower floor to the 
roof, where they pass through another continuous ring 1 \ ins. thick. 
The pier casings are filled from top to bottom with Portland cement 
concrete. 
The safe load of the upper gun floor, and of the roof, is equal to a 
mass of concrete 10 ft. thick laid all over it, which is equal to half a 
ton on every square foot. 
Next, with regard to the armoured wall. This, it will be seen, is in 
three thicknesses. The inner ring is all 5 ins. thick, and there is 1 in. 
of wood and Portland cement between it and the skeleton structure. 
It consists of two tiers of plates and two rings of armour bars, and is 
bolted to the inner structure and to the piers. The frames round the 
ports are 2J- ins. thick, and are exactly like those at the Portland Fort. 
The plates of the next or middle thickness all stand on their ends, 
and are 22 ft. ,6 ins. long, reaching from the granite base to the level 
of the roof. The plates in which the ports are formed are 7 ins. thick 
(each weighs 18 tons) the rest are 5 ins. thick. This thickness is 
bolted to the inner plates. The plates in the outer thickness are all 
5 ins. thick, and are in two tiers of about 11 ft. each. They are bolted 
to the middle plates. The intervals between the armour plates are 
filled with concrete except at the port frames, where there is wood. 
At the level of the top of the lower front plates there is a gallery all 
round the outside of the fort. 
The weight of iron work in each of these forts is as follows 
Tons. Tons. Total. 
Skeleton. per gun 50 = 2450 ) r91 . 
Armoured wall. t> 75 — 3764 J 0 
