.sVA' WILLIAM SIEMENS, F.R.S. 453 



great as to render the assistance of hooping comparatively small ; 

 hut. if that was the case, surely a lighter hoop of steel would have 

 ansuvivd the purpose of the larger hoop of iron. It might have 

 1 .! n u !_;< <!, " Oh, but we wanted the material for recoil purposes," 

 hail not the author said the objects were to make the gun light, 

 j>o \\vrful, and safe. He thought that to realise these three 

 qualities, steel must, undoubtedly, have been better than iron. 

 Nor could he admit that large powder was not known twenty years 

 ago, because he held in his hand a very interesting paper that was 

 read before the Institution of Civil Engineers, in that very room, 

 in I860, entitled " Our National Defences," in which Rodman's 

 perforated cake powder was described and very fully discussed by 

 the meeting. They had, therefore, during the last twenty-one 

 years, been in possession, not only of large powder but of a state- 

 ment of the advantages obtained by its use in the United States. 

 Perhaps Colonel Maitland would favour them with further ex- 

 planation on this point. 



Another and a purely scientific point connected with the state- 

 ment made by Colonel Maitland had reference to the temperature 

 to which the hoops were heated before they were shrunk on. The 

 author said that that temperature was of little importance provided 

 it was sufficiently high. He begged to differ from him ; he 

 believed that it was of the utmost importance that the tempera- 

 ture to which the hoops were raised should be adjusted with the 

 greatest nicety, and if they would allow him he would make his 

 meaning plain. (Dr. Siemens drew upon the blackboard a hoop 

 surrounding a tube.) He asked them to suppose that to be a 

 hoop which was bored so as to be a little smaller than the tube 

 upon which it had to be shrunk. Supposing they heated the hoop 

 considerably beyond the point that would allow it just to slip on, 

 what would be the result ? When the inner surface of the hot 

 ring came into contact, or nearly into contact, with the cold tube, 

 it would chill all round, and form in itself an abutment against 

 the further shrinkage of the heated ring ; and the metal behind, 

 being still hot, would readily yield by stretching tangentially 

 instead of contracting radially. It would be fallacious to suppose 

 that a ring cooled internally would shrink back to its original 

 diameter. A ring so cooled would, under no circumstances, shrink 

 back entirely to its original diameter, although not resisted by nn 



