324 
ARMOURED DEFENCES. 
cupped washer; with these improvements, and that of the enlargement 
of the holes through which the bolt has to pass (all of which have for 
their object the relief of the bolt from cross strains, and the insertion 
of a due proportion of elastic material to be squeezed when the bolt 
is put under tension), all difficulties with bolts have disappeared, and, 
instead of their being sources of weakness, they really, in most cases, 
give assistance to the armour. 
We have had 3-in. armour bolts of our present pattern, and of 
moderate length, which only broke at the 7th blow from a ton monkey 
falling 30 ft., the diameter of the fractured part showing a reduction of 
50 per cent., and the greatest extension of any part being from 1 in. to 
2 ins.; while the bolts made for our early trials would not stand one of 
these blows, and broke off quite short, notwithstanding that the iron, 
in a test machine, had proved ductile and strong. I may say that, 
with these excellent results, we have been contented with wrought- 
iron bolts, and have not run the risk of failure with steel bolts. 
The special washers are of the following make :— 
Coil washer First, a circular washer is made by coiling and welding a bar l^irn 
described, and this is cupped to suit the spherical nut of the bolt. To 
strengthen this part, an outer coil of unwelded bar of about the same 
section is screwed round it: as this outer coil has to expand after the 
inner coil may have given way, and, as in doing so, it would naturally 
unwind itself and open out, this tendency to separation has been met 
by making the thread, by which this outer coil is screwed on to the 
inner, of quicker pitch than that of its own coils, and thus, as it unwinds, 
it actually becomes more and more tightly squeezed together. 
A diagram (No. II.) of a bolt, completely equipped, is given. 
Hammered I must just mention here that, in 1868, a thick wrought-iron plate 
plates given ma q e forging under the hammer, proved much inferior to a plate 
made by rolling, and as there were other disadvantages in the former 
method of manufacture, it has been entirely-superseded by rolling. 
Casemate All other trials of this period may now be passed over until we come 
i 87 o. dof to that casemate shield, set up at Shoeburyness in. 1870, which 
embodied all the experience that we had gained from the previous 12 
years of experiment. 
The guns used were the 12-in. of 25 tons, the 10-in. of 18 tons, the 
9-in. Whitworth gun of 14J tons, and the 15-in. Rodman of 19 tons, 
at 200 yds.; some rounds were fired obliquely, but most of them were 
fired direct at the face of the shield. 
The shield, which presented a front of 12 ft. by 8 ft., received 17 
blows, equivalent to 90,000 ft. tons, and, except in one or two matters 
of detail, which were susceptible of easy improvement, it stood the 
trial remarkably well, and proved that it possessed a great margin of 
strength for these, and even more powerful, guns. 
35-ton gun In 1872, a plate-upon-plate target, representing 17 ins. of armour 
upompfate altogether, stopped a Palliser shot fired direct at it from the 35-ton 
target. 12-in. gun with 110 lbs. of P. powder; and a similar target with 13-ins. 
of armour stopped a shot from the same gun, striking it at an angle of 
60° with its face. 
Turret trials. As the turret is now an important feature in all projects for coast 
