PRINCIPLES OP GUNNERY. 
457 
ship.* The bolts which passed through the backing to hold on the 
armour did not perforate the plate entirely; they were only screwed 
in about as far as the centre of the thickness of the steel. The first or 
horizontal layer of wood backing was further strengthened by angle-iron. 
Another target of similar dimensions, so far as thickness of plate 
and backing are concerned, was made, having a front plate of 22 ins. 
of wrought-iron instead of steel, and the whole structure arranged in 
a similar manner to the steel target. 
These two targets were subjected to the fire of 10-in. and 11-in. 
guns. The effect of these comparatively light guns on the Schneider 
steel target was to crack it. These cracks gradually extended, and 
the destructive effect of repeated shocks from these guns proved con¬ 
clusively that the steel armour was quite unsuited for resistance to 
continued firing from these guns. 
The wrought-iron target resisted the fire more successfully. Slight 
cracks occurred in the immediate proximity of the part struck; but 
these cracks did not spread, and there were no signs of cracks in other 
parts. The extreme penetration was 18 ins.; so that the wrought-iron 
target was quite strong enough to withstand the fire of 10 and 11-in. 
guns. Yet this target was completely perforated by the 100-ton gun, 
while the steel target was more successful in resisting the blow; so 
that the Committee of Italian officers at Spezia unanimously considered 
that a solid plate of Schneider steel is more advantageous than wrought- 
iron of similar thickness as armour-plating for ships* sides.f 
Experiments have since been made at Portsmouth with the view of Compound 
combining the greater resistance to perforation offered by steel with plates * 
the greater tenacity of wrought-iron. The advantage of wrought-iron 
as a material for armour-plates is that the effect of the blow is localised, 
and consequently answers better under the fire of ordinary heavy guns 
than steel. Plates thus made up of different metals are called compound 
plates. The object sought after is to have a hard steel surface welded 
on to soft wrought-iron, to prevent the steel from splitting. J 
A Wilson compound plate, consisting of a 5-in. hard-steel plate 
welded on to a 4-in. wrought-iron plate, was tested at Shoeburyness. 
The steel front was struck by a 7-in. Palliser shell, which broke up on 
impact, and penetrated to a depth of 3*2 ins., cracking the steel 
armour, but it did. not extend to the iron. The penetration is much 
less than would have occurred in an ordinary wrought-iron plate of 
good quality; showing that on account of the breaking up of the pro¬ 
jectile on the hard-steel plate, there was a considerable loss of work on 
the plate. The wrought-iron plate prevented the steel plate cracking 
so much as it would have done if the plate had wholly consisted of steel. 
Other experiments have not been so satisfactory for the compound 
armour-plate; but it is probable that some combination of wrought- 
iron and steel will be employed as armour for ships* sides. 
* Vide letter from Special Correspondent of the “ Times/’ dated Spezia, October 25, 1876. 
f Vide p. 474, “ Mittheilungen fiber Artillerie und G-enie Wesen,” 1877. 
X Vide a paper in the “Proceedings of the Institution of Mechanical Engineers,” “On the 
Construction of Armour to resist Shot and Shell,” by Captain C. O. Browne, late It.A. 
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