232 3Ir. F. J. Bramwell [June 13, 



pressure per inch as the bore of the gun is receiving at the part 

 where the gauge is inserted, and in this way the piston is subjected to 

 an outward pressure equal to the maximum pressure per square inch 

 prevailing in that jDart of the gun multij^lied by the area of the end 

 of the piston. You will see that the only thing which prevents the 

 piston from being driven outwards under tliis pressure is the copper 

 cylinder ; but this cylinder is designedly made too small in area to 

 suj^port the pressure without being shortened and thickened out. By 

 trial in a proper machine, where the pressures are known, the beha- 

 viour of similar copper cylinders under varying loads is ascertained, 

 and in this manner an examination of the extent to which the cylinder 

 has been shortened by the pressure in the gun gives at once the infor- 

 mation needed, namely, what that pressure had been. 



Reverting to Diagram 6a, I will now state that this shows by the 

 full lines the maximum and varying pressures which have been 

 ascertained by experiment to prevail in such a gun as that which 

 burst on board the ' Thunderer ' when using 85 lbs. of pebble powder, 

 occupying 30 cubic inches to the pound. You will remember that 

 the maximum is 24 tons on the square inch, that this pressure prevails 

 over the length of the powder chamber, and for a short distance 

 beyond, and that then the pressure drops in the manner indicated by 

 the curved line, until at the muzzle it is only 2J tons per inch, as 

 shown by the vertical line B E. With such a curve of pressures it is 

 easy to ascertain what is the strain tending to burst the gun at any 

 part of the bore ; for example, at the point h the pressure would be 

 represented by the vertical line h i, and would be found to be 10 tons, 

 while at the point m it would be represented by the line m n, and 

 would be found to be 5 tons. 



I will now ask your attention to the projectiles used in these guns. 

 Two kinds are employed. One is known as a common shell ; it is 

 a hollow cylinder of ordinary cast iron, terminating in a conoidal 

 point, and containing within it a very considerable bursting charge. 

 This shell weighs, when fitted with its gas check, but empty, 590 lbs., 

 and to propel it that which is known as the full charge, namely 

 85 lbs. of pebble powder, is employed. Such a shell would be unfit 

 to penetrate armour plating, as the point of the shell would fail on 

 striking the plate ; but if proper iron (that which is known as mottled 

 pig-iron) be employed, and if when fluid it be poured, not into a sand 

 or loam mould, but into a mould made of cast iron, the exterior of the 

 casting will be rapidly cooled (chilled) by contact with the iron sides 

 of the mould, and the result will be the production of a material ex- 

 ceeding in hardness the very highest tempered steel. Such a projectile 

 is competent to penetrate armour plate ; and if time admitted I should 

 very much like to go into the reasons why, but I must 0;bstain from 

 so doing. These shells contain only a small bursting charge. They 

 weigh when empty, but with their gas check, as much as 700 lbs., 

 and they are propelled by the battering charge of 110 lbs, of pebble 

 powder. Samples of the actual shells, cut open, are before you. 



