WILL/AM S/KMKNS, I'.K.S. 



397 



by an abutment of some kind, as was usually the case, to take the 

 thrust, as shown in Fig. 5, Plate 84. 



With regard to the inquiry about any tendency of the separate 

 i-inus or cylinders composing the boiler described in the paper to 

 slip transversely upon one another, or to become depressed vertically 

 when the boiler was arranged horizontally, he had made no special 

 provision against this, and there was really, as far as he could see, no 

 need to do so. The copper packing-ring of about * inch thickness, 

 forming the joint, was wedged in between the four faces of the 

 grooves in which it was laid, and would, he thought, be capable of 

 resisting any amount of accidental side straining that might come 

 upon the separate lengths of the vessel. The pressure of the steam 

 would of course have no tendency to slide one length past another. 

 If it was thought necessary, a hoop round the joint could easily 

 be provided on the outside to prevent slipping ; but he would 

 prefer not to do so, but to let each cylinder be perfectly at liberty 

 to take its own position and to expand as it liked. The utmost 

 lateral pressure that could be brought to bear upon the vessel to 

 displace any cylinder in that way would be amply borne by the 

 mere friction, even if there were nothing else. 



In the discussion of the Paper 



"ON THE DESIGN GENERALLY OF IRON BRIDGES 

 OF VERY LARGE SPAN FOR RAILWAY TRAFFIC," 



By THOMAS CURTIS CLARKE, M. Inst. C.E., 



DR. SIEMENS * remarked that it was stated in the paper that 

 the strength at which the iron, was to be tested was equal to 

 60,000 Ibs. (nearly 30 tons) to the square inch, and that it was to 

 be subjected only to 10,000 Ibs. of strain in tension. Surely then.' 

 must be some error in that statement, as he knew of no iron that 



* Excerpt Minutes of Proceedings of the Institution of Civil Engineers, Vol. 

 LIV. Session 1877-78, pp. 234-235. 



