386 Prof. Thomson on a remarkable property of Steam 



The mean monthly values of the several subjects of investi- 

 gation are published in the Quarterly Report of the Registrar- 

 General. Their quarterly values are shown in the preceding 

 table. 



The mean of the numbers in the first column is 29*605 

 inches, and it represents that portion of the reading of the ba- 

 rometer due to the pressure of the air ; the remaining portion, 

 or that due to the pressure of water, is 0*397 inch ; the sum of 

 those two numbers is 30 002 inches, and it represents the mean 

 reading of the barometer at the mean level of the sea for the 

 quarter ending September 30, 1850. 



The mean of the numbers in the second column for Guern- 

 sey and Jersey is 60 o, l ; for those places in the counties of 

 Cornwall and Devonshire, is 59°*2 ; south of latitude of 52° 

 is 58°*4; between latitudes 52° and 53° is57°*3; between 

 the latitudes of 53° and 54° is 55°*7 ; at Liverpool and White- 

 haven is 57°*3; for Durham, Newcastle and North Shields, is 

 54?°-6 ; and for Glasgow and Dunino is 56°*1. 



The highest reading of the thermometer in air was about 88°, 

 and the lowest was 32°. The extreme range of temperature 

 during the quarter in England was therefore about 66°. The 

 least daily ranges of temperature took place at Guernsey and 

 Liverpool, and the greatest occurred at Uckfield and in the 

 Vale of Aylesbury. 



Rain fell on the least number of days at Jersey and Torquay, 

 and on the greatest number of days at Wakefield, Stony- 

 hurst and North Shields, The places where the least falls 

 took place are London and Truro ; and the mean amount at 

 these places was 5*3 inches. The largest falls occurred at 

 Whitehaven and Falmouth, and their average was 12*4 inches. 



L. On a remarkable property of Steam connected with the The- 

 ory of the Steam-Engine, By William Thomson, Esq., 

 F.R.S.E., Professor of Natural Philosophy in the University 

 of Glasgow. Communicated by J. P. Joule, Esq., F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



I AM permitted by my friend Professor Thomson to com- 

 municate the following letter to the Philosophical Maga- 

 zine, containing an explanation of the true cause of the non- 

 scalding property of steam issuing from a high-pressure boiler. 

 The proposition announced by Mr. Rankine is certainly one 

 of very great importance; as it would appear from it that 

 when saturated steam is allowed to expand so as to evolve 



