[ 466 ] 

 LXIII. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



[Continued from p. 397-] 

 February 21, 1856. — The Lord Wrottesley, President, in the Chair. 



THE following communication was read : — 

 " On the Thermal Efifects of Fluids in Motion." By Professor 

 WilUam Thomson, F.R.S., and J. P. Joule, Esq., F.R.S. 



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 metaUic 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 lb. of pressure by 

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

 phere on the exit side there was a cooling effect of 0*2 Cent. The 

 steam, therefore, issued at a temperature above 100° Cent., and, 

 consequently, dry \ showing the correctness of the view which we 

 brought forward some years ago * as to the non-scalding property of 

 steam issuing from a high pressure boiler. 



February 28. — The Lord Wrottesley, President, in the Chair. 



The following communication was read : — 



The following Letter was read, from Professor Hansteen of Chris- 

 tiania. For. Mem. R.S. : — 



To the Royal Society of London. 



As a Corresponding Member of the Royal Society, I have the 

 honour herewith to transmit a Research " On the Secular Changes of 

 the Magnetical System of the Earth, and more specially on the 

 Secular Variation of the Magnetical Inclination in the Northern 



* See letter from Mr. Thomson to Mr. Joule, published in the Philosophical 

 Magazine, Nov. 1850. 



