ARMOURED DEFENCES. 
321 
Next in order came a series of trials of plates of steel, and of steel Early trials 
and iron combined; some were of thin layers of steel and iron welded compound 
together, others of sandwiches of steel between rolled iron, others of platea * 
faces of steel welded to iron, and others of steel and iron in reverse 
order to this; but none of these competed successfully with a simple 
soft rolled iron plate in resisting chilled iron shot; some plates made 
entirely of steel were tried about this time, as they had been also years 
before, but none of them stood at all well. The difficulty of treating 
steel in large masses, and especially of welding these masses of steel 
and iron together, had evidently not been mastered up to this time. 
In consequence of the growing powers of battering ordnance it now Evidence of 
became evident that our land works would require walls of considerable Smoked 
thicknesses of armour ; but there were two main reasons why very thick walls bein s 
armour plates should not be used in them. In the first place the manu- nece3sary# 
facture of a very thick plate is not so complete as that of one of 
moderate thickness, or at least to make it as complete would involve an 
enormous increase of cost in plant and manufacture; and, next, the 
thicker the plates the deeper the joints must be, and therefore the 
more points of undue weakness will the armour present. 
It therefore became important to see whether the required protection 
could not be gained without the use of very thick plates. 
Against doing this was the prevailing opinion, based chiefly on 
theoretical considerations, that a single plate of given thickness would 
offer something like twice the combined resistance of two plates each 
of half that thickness, or about three times the resistance of three 
plates making up the same total thickness, and so on. 
This view was entirely disputed by those who had to deal with these 
questions officially, but it became our business to prove its fallacy. 
This was done under the following circumstances:— 
In 1867, a total thickness of 7 ins. of iron disposed in one solid plate, piate-upon- 
in two plates of 34 ins., and in three equal thicknesses, instead of ^troductd? 1 
giving resistances of about 100, 50, and 33, gave effects more nearly as 
100, 95, and 88, respectively. 
Next, a 10-in. plate failed to stop a shot which was stopped by two 
5-in. plates, and another 10-in. plate bore out this result. 
Again, in a comparison between a solid 15-in. plate and a wall made 
up of three 5-in. plates, the result was that, although the solid plate 
gave a somewhat better resistance to a single blow, the three-plate 
structure stood repeated blows better than the other. 
Also, in 1871, two targets representing portions of the walls of ships* 
turrets were tried at Shoeburyness. The one was protected by single 
14-in. plates, the other by two thicknesses of armour, 8-in. and 6-in., 
respectively, with 9 ins. of timber between them. In other respects 
the targets were similar. After receiving the same amount of battering, 
the armour of both was taken off, and the effect upon the inner 
skin of the two-plate target was unmistakably less than that on the 
single-plate structure. 
It may also be mentioned that, more recently still, a structure 
composed of three thicknesses of 6^-ins. of iron proved rather superior 
to a solid 16^-in. plate in stopping the 8181b. shot of the service 
38-ton gun, striking with a velocity of about 1415 f.s. 
