ARMOURED DEFENCES. 
341 
Strengthening plates will probably be provided for the lower batteries 
of these forts so soon as any number of ships of foreign powers shall 
be armed with guns equal in power, say, to our 80-ton and 100-ton 
guns. The masonry on which these batteries stand will then require a 
corresponding addition of strength, for which provision was made 
originally by leaving an offset on which armour plates can rest, and 
boles have been formed in the masonry for armour bolts. 
Each of these sea forts at Spithead, Spitbank, and Plymouth is pre- Turrets on 
pared for the addition hereafter of turrets on their roofs to carry two sea forta ' 
of the heaviest ordnance in each. The Spithead forts to have five 
turrets each, the others two each. 
Every gun mounted behind iron protection is to have a suitable Mantlets 
mantlet made of rope-work for the three-fold object of deadening the 
effect of vibration caused by shot blows on the exterior, of stopping 
splinters driven off from the iron itself and bullets and fragments that 
may enter the port, and of keeping out smoke. 
As hemp rope is liable to catch fire on the discharge of the gun, it is 
washed with a solution of chloride of calcium, which renders it com¬ 
pletely uninflammable. Professor Abel helped us with his valuable 
advice on this point. 
I have now come to the last of the works to be described—namely, Turret on 
the turret, for two 80-ton guns, now on the point of completion, at the Dover Pler ‘ 
extremity of the Admiralty Pier at Dover. (Diagram XIII.) 
The work to carry this turret consists of an enlargement of the outer 
end of the pier, as at present completed. The foundations are laid at 
a depth of about 7 fathoms below low water mark, and the guns will 
be at a level of about 33 ft. above high water. The structure, there¬ 
fore, from the bed of the sea to the guns is about 95 ft. high. 
Speaking in general terms, the turret consists first of a live ring, and 
rollers of steel running on a path of steel laid on a massive cylinder of 
masonry. On this live ring runs a structure of iron framework of the 
form shown in the diagram, weighing about 240 tons. This framework 
contains the gun chamber, which is protected by three thicknesses of 
7-in. armour, with two intermediate thicknesses of 2-in. plates, making 
together a weight of about 460 tons. If to these weights be added 
that of the guns, carriages, and the slides on which they will stand, the 
total running weight will be about 895 tons. This will throw upon 
each of the 32 rollers of the live ring a pressure due to about 28 tons. 
The outside diameter of the turret is 37 ft., its internal diameter is 
32 ft., the interior height of the gun chamber is 8 ft. 8 ins., the height 
of the turret armour is 9 ft. 
It will be seen that a massive central casting is first held firmly 
down to the masonry, and that inside this there is a thick cylinder of 
hammered Bessemer steel surrounding the built-up wrought-iron 
cylinder, which forms the centre of the turret framework. I draw 
attention to this part, because, of course, the shock of blows on the 
turret walls, or more strictly speaking the unabsorbed part of it, 
ultimately comes to this part, and it has received especial consideration 
on that account. The framework is generally of wrought-iron. 
The roof of the turret is of strong splinter-proof construction. Over 
42 
