26 THE SCIENTIFIC PAPERS OF 



MR. SIEMENS explained the action of the two instruments, 

 and showed their process in operation. 



Mr. Crampton inquired whether the charcoal in the casing of 

 the instrument would not get heated by the tube of high-pressure 

 steam passing through it during the experiment, and so super- 

 heat the steam in the internal cylinder ? 



Mr. Siemens explained, that it was not possible for such an 

 effect to take place, as the end of the steam-pipe was exceedingly 

 small, and was protected by a thick non-conducting casing. He 

 had also observed several times during the experiments, that 

 whenever any priming took place in the boiler, and a drop of 

 water came out with the steam, and fell on the bulb of the 

 internal thermometer, the mercury fell immediately to 212, or the 

 boiling point of water, and remained steadily there for four or 

 five minutes, until the whole of the priming water was converted 

 into steam, when the mercury again gradually rose to its former 

 temperature. This showed that the increased temperature above 

 212 in the internal cylinder was entirely due to the extra heat 

 in the expanded high-pressure steam, and not to any heat derived 

 from the charcoal casing. As a check on the accuracy of the 

 observations, he had tried them successively in an ascending and 

 descending series, when an error from the source alluded to would 

 have been apparent, and^ been doubled in effect, but he could not 

 detect more than one degree difference in the observations. 



In the discussion of the Paper 



"ON THE USE OF HEATED AIR AS A MOTIVE 

 POWER," by Mr. B. CHEVEKTON, 



ME. C. W. SIEMENS,* after sketching a diagram explanatory of 

 the action of Ericsson's engine, stated that he had not seen the 

 machine, but he believed the description which had been given of 



* Excerpt Minutes of Proceedings of the Institution of Civil Engineers 

 Vol. XII. Session 1852-1853, p. 345 etscq. 



