PROCEEDINGS 



ROYAL SOCIETY OF EDINBURGH. 



VOL. III. 1850-51. No. 41. 



Sixty-Eighth Session. 

 Monday^ 3^ March 1851. 



Sir DAVID BREWSTER, K.H., Vice-President, in the 



Chair. 



The following Communications were read : — 



1. On Iron and its Alloys. Part I. By J. D. Morries 



Stirling, Esq. 



2. On the Weight of Aqueous Vapour, condensed on a 



Cold Surface, under given conditions. By James 

 Dalmahoy, Esq. 



The paper was accompanied by two tables, containing the results 

 of sixty-three experiments respecting the rate at which vapour con- 

 denses on a cold surface. 



In planning the experiments, it was assumed that C= m (/" — /''' ), 

 where C is the weight of moisture condensed on a surface of given 

 area in a given time ; /" the tension of vapour at the dew-point ; 

 /'" the tension at the temperature of the condensing surface ; m a 

 co-efficient varying with the velocity of the current of air. 



But, in the course of experiments, it was found that the co-efficient 

 m was not constant, even when there was no sensible current ; and 

 that under this state of the air, it was necessary to change m into 



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