THE 80-TON GUN. 
347 
breech-piece, which was put on before the interior of the tube was 
“finish-bored. - ” This compression reached its maximum of *02 in. at 
from 240 ins. to 270 ins. from the muzzle. The gun, after firing 
21 rounds, exhibited, as shown by the table, a slight contraction in 
front of 226 ins. from the muzzle, and a slight expansion in rear of this 
point, both being so small that the bore may be said to be practically 
unaltered; and thus the outer coils retain undiminished their power of 
promptly taking up the strain imposed On the tube. 
It may here be remarked that the object of the tube is not so much 
to afford transverse strength as to furnish a good and impenetrable 
surface. In fact, the Woolwich guns are constructed to stand with 
safety, even if the tube should split. 
It will be observed that I have hitherto omitted all reference to the 
relation between the expected strain of the discharge and the thickness 
of the various layers of metal composing the gun. The fact is that 
no really trustworthy data exist for accurate calculations on this point. 
The time during which the maximum pressure is exerted is exceedingly 
small, and the rate at which the strain is taken up by the coils is 
altogether unknown, while experiments on masses of size sufficient to 
give practical results would be enormously expensive. Rough calcu¬ 
lations do exist, but I confess that I do not put much faith in any of 
them; believing that, as a plain matter of fact, the real limit to the 
power that can be got out of a gun of the present construction, when 
suitable powders and shot are employed, lies in the recoil. I mean 
that we can increase the charge and weight of projectile of our guns, 
boring them up if required, till no carriages can be made to stand the 
shock, and that therefore a certain weight is necessary. It is obvious 
that, in anything so risky as a gun, such weight as must be carried 
should be so disposed as to strengthen the piece to the utmost, even 
though some additional expense should be thereby incurred. Ordinary 
prudence demands this,' and hence I do not consider the possession 
of a true theory of the relation between strain and dimensions to be 
at present of very great practical importance, though I fully admit its 
interest from a scientific point of view. 
It was thought desirable, in order to obtain as much information as 
possible, to bore the 80-ton gun to 14Jins, in the first instance, and 
to increase the calibre by half-an-inch at a time till the full size of 
16 ins. should be reached. It is anticipated that, by carrying on experi¬ 
ments at each stage, much valuable knowledge relating to the behaviour 
of powder and the manufacture of heavy projectiles will be acquired. 
The gun was ready, in its 14J-in. calibre, for firing early in Sept. 
1875, having taken just eighteen months to complete. Of this time, 
several months were occupied by the necessity for enlarging various 
parts of the plant in the Royal Gun Factories. The unprecedented 
size of the bars forming the coils entailed much heavy forge work, and 
the rolling mill then in use was not powerful enough to turn out such 
sections of iron ; the coiling furnace required alteration; the roof of 
the tempering house, where the steel tube is toughened in oil, had to 
be raised; the hydraulic crane had to be patched up to take weights 
beyond its safe strength; a lathe and boring machine of immense 
