I 



Mr. W. J. M. Raakine on Pressures of Saturated Vapours, 255 

 Analyses of Soapstones. 



These analyses furnish ns with the following : — 

 Number of Atoms. 



From this table we deduce the formula 6Si 0^ AFO^, lOMgO, 

 14H0j which gives as rational formula probably the following : — 

 5 {2MgO, Si 03} + { AP 03, Si 03} + 14.H0. 



XXXIII. On Pressures of Saturated Vapours. 

 By W. J. Macquorn Rankine, C.E., F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen^ 



THE perusal, this day, of a recent paper by Sir John Lub- 

 bock on Astronomical Refractions, has made me aware of 

 the fact, that in 1840 that author published a general formula 

 for the pressui'cs of saturated vapours of the following form : — 



logP=A(logE+log(l+^)); 



(1) 



P being the pressure, t the absolute temperature, and /3, E, F 

 constants. 



Sir John Lubbock points out the resemblance between the 

 above formula and that which was published by me in the Edin- 

 burgh Philosophical Journal for July 1849, viz. 



logP = A-^-^- (2) 



That rcHcmblancc I freely admit ; inasmuch as the develop- 



