326 
ARMOURED DEFENCES. 
with safety be increased to the extent which, I believe, has been pro¬ 
posed for them—as, for instance, 90 lbs. P 2 for the 10-in. 18-ton gun, 
110 lbs. P 2 for the 11-in. 25-ton gun, and 160 lbs. P 2 for the 12^-in. 38-ton 
gun—then these guns will be nearly, if not quite, able to pierce, at 
short range, a thickness of solid iron equal to 1J times their calibre. 
While upon this subject, I may say that no great advance has been 
made in late years towards determining a law for the resistance of 
armour, nor do I think that, for practical purposes—whatever may be 
the case from a scientific point of view—much good will come of enquiry 
in this direction. The conditions and effects are altogether too 
variable and uncertain for the construction of mathematical formulas. 
For instance, in recent practice, under apparently similar conditions of 
projectiles and plates, there has been an unaccounted-for variation of 
effect of something like 5 per cent, plus or minus. 
But we can, by building upon results obtained with one gun, say within 
a little what another gun will do, and so construct tables of penetrations 
for all velocities, or, in other words, for all ranges. I will not, however, 
go further into this matter now than to mention one or two approximate 
rules which may be easily borne in the memory. Thus, with the average 
service conditions of weight and length of battering projectiles, a shell of 
good quality, with a velocity between 1050 to 1150 f.s., will pierce solid 
iron equal in thickness to its own calibre; with a velocity between 1500 
and 1650 it will pierce iron of a thickness equal to one and a half times its 
calibre; and with a velocity between 2000 and 2200 it will pierce solid 
iron equal in thickness to double its calibre. To obtain the latter degree 
of perforation at the muzzles of the latest guns, the powder charges 
must, I believe, be equal to, at least, one-half the weight of the shot. 
I have already had occasion to mention that a target composed of 
three thicknesses of 6^-in. rolled iron plates, with layers of 5 ins. of 
teak between them, ■was used against the 38-ton gun. 
This gun just perforated this target when firing its service Palliser 
shot with 130 lbs. of P 2 powder, at 70 yds. range, striking velocity of 
shot 1420 f.s., ft. tons = 11,400; but when a fourth 6^-in. plate was 
added to the target, it was a good deal more than a match for the same 
gun after it had been chambered, when it fired 200 lbs. P 2 powder, 
striking velocity of shot 1525 f.s., ft. tons — 13,000. 
A solid 164-in. iron plate resisted the 38-ton gun nearly as well as 
the three 64-in. plates did, and it was also nearly pierced by a shot 
from the long 8-in. gun (Armstrong) already spoken of, firing an 
exceptional charge of 111 lbs. P. powder, at short range. 
A Palliser shot, fired from this (38-ton) gun with 130 lbs. P. powder, 
went through a wall composed of 5 ft. 6 ins. of granite and 6 ft. of 
brickwork, but the wall had been shaken by previous practice. 
At Gtavre, in 1876, a Whitworth 35-ton gun of 12-in. (maximum) 
calibre, fired with 120 lbs. P. powder, is reported to have sent a 
flat-headed steel shell of 808 lbs. through two 8-in. plates; but our 
experience with flat-heads would not lead us to expect so much effect 
upon a well-constructed two-plate target of this thickness. 
I may say at once, that neither with direct nor oblique fire have 
flat-headed shot proved themselves, in our trials, at all equal to pointed 
shot in piercing armour. 
