IV/LLIAM 



403 



Dr. Siemens knew from experiments of his own that a shrinkage 

 of 1 in 1,000 meant a strain of 12 tons per square inch. If the 

 shrinkage was 1 in 1,000 upon the inner diameter, there would l>e 

 a strain of 12 tons upon the inner surface of the coil. That in 

 itself presented a very good strain for a material such as iron. If, 

 however, round a tube of 8 inches inside, 28 inches of iron were 

 shrunk in such a way as to put the whole into tensions varying 

 in elastic strain inversely as the diameter, what would be the 

 result ? That the strain on 28 inches would be opposed by the 

 8 inches ; that the area of the outer metal would be resisted by the 

 lesser area forming the side of the lining. The author, in all his 

 calculations, spoke only of what would take place when the 

 powder pressure of 24 tons to the inch was applied ; he did not 

 say what would be the case when the shrinkage pressure was 

 applied in the first instance. That shrinkage pressure would 

 undoubtedly have the effect of crushing or deforming the tube 

 permanently. The tube would be no more able to resist such an 

 amount of shrinking pressure than if it did not exist at all ; and 

 therefore such shrinkage as was contemplated by Mr. Longridge 

 could not practically be applied. The author had criticised rather 

 severely some remarks in the Woolwich reports. Referring to the 

 statement that in " guns of present construction the heavy breech 

 coil compresses the steel barrel to such an extent that the latter 

 becomes in some instances as much as -j-J-oth of an inch smaller in 

 diameter during the process of shrinking," the author had remarked, 

 "It is difficult to imagine a more complete confusion of ideas than 

 that which pervades this sentence." 



Dr. Siemens believed the statements in the official report' were 

 perfectly consistent, not with mathematical, but with engineering 

 or physical facts. It would, he maintained, be impossible to give 

 such shrinkage to the mass of iron surrounding the inner tube as 

 would leave that mass of metal under a sufficient tension to take 

 its full proportion of work when an inner pressure was applied 

 equal to 24 tons to the square inch. But suppose that the inner 

 tube could be made strong enough to resist such a pressure, the 

 use of the gun had then to be considered, and the result of the 

 first few rounds. Shrinkage would then again take place, but 

 upon the wrong side of the gun ; that was to say, expansion by 

 heat would occur inside the gun, which would still farther increase 



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