WILLIAM SIEMENS, F.R.S. 69 



at erne-third the Btroke ; and there did not appear to be a 

 steam-jacket to the cylinders. He had found a great advantage 

 in employing a jacket not only round the sides of the cylinders, 

 but also at the ends, and it was more important to have a jacket 

 at the ends than round the sides ; for on the steam first entering 

 the cylinder, a much larger extent of surface was offered to it by 

 tin, 1 end than by the small portion of the sides then exposed. 

 "When the cylinder was not protected by a jacket, the end of the 

 cylinder being cooler than the steam on first entering, caused a 

 portion to be condensed, which was partly evaporated again in 

 the latter part of the stroke, when the pressure and consequent 

 temperature of the steam was lowered by expansion. The effect of 

 this generation of steam in the cylinder was to increase the pressure 

 at the end of the stroke beyond that due to the expansion ; and the 

 line of the indicator diagram was thus raised in the latter part of the 

 figure above the regular curve of expansion. But this did not appear 

 to be the case in the indicator diagram from the Crystal Palace 

 engines, which showed the steam entering the cylinder at a total 

 pressure of about 34 Ibs. per square inch, cut off at one-third of 

 the stroke, and expanded down to a final pressure of 11 Ibs. due to 

 the expansion. 



In the discussion of the Paper 



"ON THE PERFORMANCES OF THE SCREW STEAM 

 SHIP ' SAHEL,' fitted with Du Trembley 1 s combined-vapour 

 engine, AND OF THE SISTER SHIP ' OASIS,' fitted with 

 steam-engines worked expansively, and provided with partial 

 surface condensation" by JAMES WAEDROP JAMESON, 



MR. SIEMENS * said, when treating of air-engines, in a paper 

 which had been read at the Institution in the Session 1852-53, | he 



* Excerpt Minutea of Proceedings of the Institution of Civil Engineers, 

 Vol. XVIII. Session 1858-59. pp. 256-259. 



t Vide Minutes of Proceedings of the Institution of Civil Engineers, Vol. XII. 

 p. 571, and p. 29, ante. 



