BURSTING OF HEAVY GUNS. 
189 
charge between them became considerable; and this is when the 
pressure becomes greatest, and its register becomes most important. 
Sir W. Palliser suggests another standard of comparison of pressures 
—namely, the permanent enlargement of the bore of the gun—which 
he considers applicable to cases of very great strains. To this is to be 
objected that there is no standard of this kind established at present; 
moreover, that such a method of register depends much on the 
material employed, and is open to the greatest objection when different 
materials are used. For example, supposing we find a large per¬ 
manent expansion registered in Sir W. Palliser’s gun with coiled iron 
linings, the advocates of such guns may argue from it that the pressure 
was enormous, and the gun to be accordingly praised; opponents, 
on the other hand, may urge that it showed the material yielded, and 
was therefore bad, rather than that the pressure was great. I am not 
now speaking of other proofs that may exist of the high pressure, but of 
the value of the systematic measurement of permanent expansions for 
this purpose, which I think, under present conditions, open to grave 
question. To come briefly, however, to what might be looked for in these 
trials, we have a gun that has already suffered the most severe usage 
subjected to what any candid person must admit are very exceptionally 
severe tests. We have the means of forming an idea of the amount of 
strain due to the powder pressure, if fired under ordinary conditions, if 
we ascertain what pressures are obtained in the Royal Arsenal from 
the service 7-in. gun with the same powder. We have no means of 
directly ascertaining the pressure actually developed, which may be 
exceptional, the front charge being fired under the impact of the 
hinder projectile, and, whether by flash or blow, under abnormal 
conditions. It may be questioned, however, whether the pressure- 
gauge at Woolwich in the base of the front shot told us very 
much more than we may safely assume to be the case. We have 
Sir W. Palliser'’s system of measuring the bore in various places, 
which, if not comparable with any known standard, at all events has a 
special value of its own in telling the exact place where the maximum 
pressure was exerted. This I hope will be made clear by Fig. 1, 
which shows the gun in section, double loaded with the maximum 
weights of charges and shot, as laid down for round No. 5. Under¬ 
neath this will be seen five spaces running parallel to the bore, like 
five narrowed longitudinal sections of the bore, with the lengths 
measured from the muzzle in feet and inches, and the positions of 
projectiles and charges marked for the five rounds. The diameters of 
the bore in the various places where it was measured at the conclusion 
of each round will be found entered on the space so numbered; that 
is to say, between the upper parallel lines marked “No. 1 round 33 
are entered the measurements of the bore after the first round. 
The object of this is to enable us to see at once where the enlargement 
took place, and how far the gun permanently expanded opposite each 
cartridge or each projectile. 
Hound 1 .—The gun was loaded as laid down in the programme, 
first with a charge of 13 lbs. 12 ozs., then with an 88-lb. cast-iron shot 
