322 
ARMOURED DEFENCES. 
Surfaces of 
plates 
should 
not be in 
contact. 
Best spacing 
between 
plates. 
Void spaces 
between 
armour 
plates. 
Perforation 
of a plate- 
upon-plate 
structure 
compared 
with that of 
a solid plate. 
In thus dealing with this subject it must not be supposed that the 
formation of iron walls made up of a number of very thin plates was 
ever advocated by us. The trial of the boiler-plate targets, already 
mentioned, for ever disposed of that kind of construction. 
Also, it should be mentioned that the above trials of the plate-upon- 
plate system showed plainly that the most satisfactory results were not 
obtained when the surfaces of the armour were in contact, but 
that, on the contrary, some thickness of a softer and more elastic 
material between the plates was necessary to prevent their breaking 
under heavy blows. 
To settle the best proportions, quantity, and best nature, of material 
to be interposed between armour plates, a series of careful experiments 
was set on foot, and the result was that a uniform spacing of about 5 ins. 
(to be slightly modified under certain circumstances) between the 
different plates in all structures was decided upon; and also, although 
an iron concrete made by working up together cast-iron borings, 
asphalte, bitumen, and pitch, gave the best result, mainly on account 
of its great weight, yet brickwork in asphalte, Portland cement 
concrete, and hard wood, proved so satisfactory that these materials 
have been adopted, as circumstances required, in all our armoured 
walls. 
It may be well to mention here a very remarkable result that was 
obtained in the course of the early trials with plate-upon-plate structures. 
When void spaces were left between the plates of these structures, 
it was found that the heads of the Palliser shells collapsed completely 
under the work they had to do in penetrating them, and, naturally, the 
effect produced upon the target was thereby very much reduced. 
In one case a chilled shot from the 38-ton gun which was capable of 
piercing 19^ ins. of armour, was found sticking in a finely divided state 
against a 10-in. plate, after having passed through only a 4-in. plate a 
few feet in front of it; and on another occasion, a 4-|-in. plate, set up 
18 ins. in front of a masonry wall, with a void space between them, so 
far reduced the effect of a chilled cast-iron projectile from the 38-ton 
gun, at 50 yds., that it broke up on first striking the granite, and was 
afterwards dug out in pieces at a depth of only about 3 ft. 6 ins. from 
the original front of the masonry. 
Eepeated and well-pronounced instances of this utter destruction of 
chilled projectiles from this cause have been gained and carefully 
investigated, with a view to turning the principle to some account 
in defence works ; but partly on account of certain difficulties of detail, 
and mainly on account of the action not being produced on steel 
projectiles, the idea of using void spacing in practice has been nearly 
given up. 
To explain, to some extent, the way in which a well-constructed 
plate-upon-plate wall offers resistance to a shot, I have had a diagram 
(No. I.) prepared, from which it will be seen that each plate does not act 
independently of the other, but that by the back moulds of each one being 
forced against that next behind it a continuous resistance is offered to 
the shot during the whole of its passage through the mass. Of course 
to get the full effect, the several plates must be well held together. To 
