SIR WILLIAM SIEMENS, F.R.S. 399 



metal is separated from the slag in subjecting it to the melting 

 jinn-ess, when we get the maximum strength of which the metal is 

 r;i|i:il)l''in all directions, and we have, in fact, metal of the greatest 

 rth for moderate strains that can be obtained, as we have 

 sivn, that even the hardest steel elongates as much as the mildest 

 metal when subjected to moderate strains. 



At another Institution Mr. Longridge has severely criticised the 

 coil system of construction, which is still followed at Woolwich, 

 upon the ground that the stresses are not properly distributed ; 

 but whilst not agreeing with him, chiefly as regards the limits to 

 which shrinkage can be advantageously resorted to, I cannot, on 

 the other hand, but think it is wrong in principle to use the 

 harder and more resisting material in the inside, and the weaker 

 material outside the gun, as is still practised at Woolwich. 



Mr. Longridge says that the inner tube of the gun should be 

 under compression, and therefore one or several layers of rings 

 should be shrunk on with such increasing force as to bring the 

 metal into considerable tension, in order that when the powder 

 gas acts expansively upon the inside of the gun, the compression 

 of the inner ring may be such as to resist the first part of the 

 impact of the powder, and then after having come to its condition 

 of neutrality take up its proper portion of the tensile strain. But, 

 practically, I believe the shrinkage is not carried to any such 

 extent, and it appears to me reasonable that it should not be, not- 

 withstanding Mr. Longridge's argument, because if the large mass 

 of iron he suggests to use is put under compression to the extent 

 indicated by theory, it would inevitably crush or permanently 

 deform the inner tube. But if the inner tube is of steel and the 

 outer portion of iron, a metal of less elastic range than steel, it 

 follows that by repeated expansive actions, the external metal will 

 be strained beyond the limit of elasticity before the metal of 

 greater elastic range in the interior. 



Again in firing the gun the inner metal will be expanded by the 

 heat, which will increase the pressure exerted by the inner ring 

 against the outer rings. This action will result in excessive strain 

 on the outer rings tending to enlarge and loosen them, or in com- 

 pressive action upon the inner tube, tending to produce the same 

 result through crushing. 



It appeara, therefore, to me to be evident that, in constructing a 



