168 
POPULAR SCIENCE REVIEW. 
Moreover, the bulging effect of projectiles striking the front 
will open out the incoherent backing, if it do not actually draw 
the bars and timbering out of their footings. The concrete 
behind the face-plating will be quickly disintegrated by any 
heavy battering, and then the bolts being loosened in their 
hold, the armour will clatter about in certainly a very noisy 
manner, if with no further damaging results ; but how the 
multitude of bars will keep together in position under such 
circumstances must be left to the constructors to explain, or 
probably for Providence hereafter to determine. 
In the Gibraltar shield, after the first failures of the bolts, 
others upon the pattern devised by Major Palliser were intro- 
duced. These had plus screw-threads, and were tapered away 
in the middle of the shank, so that when the strain was brought 
upon the bolt, the weakest part yielded and stretched. The 
objection to these bolts was, that they could not be used in 
ships, as there would be a cavity all round them. They stood, 
however, well enough in the land shield. In the Hughes 
shield there was another class of bolts of a much better cha- 
racter, founded by Mr. Parsons upon a similar basis. These 
were hollow cylinders with plus screw-threads, the cavities at 
the ends being closed by steel plugs. The cylinders or shanks, 
having thus the least substance stretched uniformly through- 
out, and being made of good ductile iron, the stretching limit 
was very considerable, and they were thus capable of withstand- 
ing admirably the strains brought upon them by the shot. 
They were cheap, too, as well as very strong. Subsequently, 
Lieutenant English, E.E., produced and patented a compound 
bolt with a carefully turned ball and socket-head on both ends, 
and a spiral spring-washer for buffing the rear nuts. The plan 
may be ingenious, but cui bono ? If cheaper and less com- 
plicated bolts do the work required of them, why employ the 
costly which can do no more ? None have ever stood severer 
tests than Mr. Parsons’, or served their purpose better. 
What the effect of a concentrated broadside of the heaviest 
guns might be on the new Plymouth fort would be very hard 
to estimate ; and happily the heaviest guns at this moment are 
alone possessed by England. It will be remembered, how- 
ever, that at the Shoeburyness trials a salvo of three guns 
broke an orifice in the 15-inch structure through which a 
General entered the casemate. No salvo was ever fired against 
the 20-inch portion there, and the doubt therefore remains 
whether a lamination of 15 inches of iron plus 6 inches of 
concrete will keep out a concentrated broadside from such 
ships as the Hercules or the Devastation . If so, the credit 
will be due to the improvements made in the mechanical dis- 
tribution of the materials by the force of critical comments. 
