396 THE SCIENTIFIC PAPERS OF 



as steel. Now as the outer shell of a boiler with internal flues had 

 only to resist internal pressure, and was apt to corrode more than 

 the fire-tube of the boiler, the shell, when constructed of the steel 

 he proposed to use, would have all the advantage, that there would 

 be undoubtedly less corrosion in steel of that temper than there 

 would be in steel of a very mild temper. 



A defect in the construction described in the paper had been 

 pointed out by Mr. Paget, which must be patent at first sight, 

 namely, that the metal of the rings did not aid in any way to give 

 longitudinal strength to the boiler as a whole. That no doubt was 

 the case, and it involved the necessity of providing for that longi- 

 tudinal strength, which was done by the separate bolts ; but a little 

 calculation would show that the amount of metal necessary to 

 provide against longitudinal rupture in a cylindrical boiler under 

 any given pressure was very much less than the amount of metal 

 necessary to provide against the lateral bursting strain. Although 

 he could not answer the question absolutely, whether the bursting 

 strain upon the metal would or would not incapacitate it for 

 bearing its full quota of longitudinal strain as he did not think 

 there were any experiments to show this exactly, and it was always 

 very hazardous to theorise upon a question of that sort yet, 

 supposing the metal was not in any way incapacitated for bearing 

 its full amount of longitudinal strain, he could show that a vessel 

 constructed on this very principle, notwithstanding the weight 

 necessarily put into the bolts, was a very much lighter vessel for 

 the same strength than if the plates were riveted together at the 

 circular joints in the ordinary \vay. In the case of a hydraulic 

 cylinder made in lengths, the bolts holding the successive lengths 

 together had no strain to bear ; only the lateral bursting pressure 

 had to be dealt with, and the bolts had only to be strong enough 

 to make the joints good. 



Mr. A. Paget inquired whether Dr. Siemens had intended to say 

 that in a hydraulic cylinder there was no tendency to burst the 

 cylinder endways. He could understand that to be the case so long 

 as the ram was free to move ; but as soon as the ram was stopped 

 by the resistance, how then ? 



DK. SIEMENS said that whether the ram was free to move or was 

 held from moving, there was no tendency to strain the cylinder 

 endways, i.e., provided the end away from the ram was supported 



