41 



February 21, 1856. 

 The LORD WROTTESLEY, President, in the Chair. 



The following communications were read : 



I. " On the Thermal Effects of Fluids in Motion." By Pro- 

 fessor WILLIAM THOMSON, F.R.S., and J. P. JOULE, 

 Esq., F.R.S. Received February 11, 1856. 



A very great depression of temperature has been remarked by 

 some observers when steam of high pressure issues from a small 

 orifice into the open air. After the experiments we have made on 

 the rush of air in similar circumstances, it could not be doubted that 

 a great elevation of temperature of the issuing steam might be 

 observed as well as the great depression usually supposed to be the 

 only result. The method to obtain the entire thermal effect is 

 obviously that which we have already employed in our experiments 

 on permanently elastic fluids, viz. to transmit the steam through a 

 porous material and to ascertain its temperature as it enters into and 

 issues from the resisting medium. We have made a preliminary 

 experiment of this kind which may be sufficiently interesting to 

 place on record before proceeding to obtain more exact numerical 

 results. 



A short pipe an inch and a half diameter was screwed into an 

 elbow pipe inserted into the top of a high pressure steam-boiler. A 

 cotton plug placed in the short pipe had a fine wire of platina passed 

 through it, the ends of which were connected with iron wires passing 

 away to a sensitive galvanometer. The deflection due to a given 

 difference of temperature of the same metallic junctions having been 

 previously ascertained, we were able to estimate the difference of 

 temperature of the steam at the opposite ends of the plug. The 

 result of several experiments showed that for each Ib. of pressure by 

 which the steam on the pressure side exceeded that of the atmo- 



