142 Geological Society : — 



which at the freezing of water act as forces of crystallization, 

 is not expressed in our equation employed for the determina- 

 tion of w, because in constructing that equation forces of this 

 kind are not taken into consideration. Hence arises for the 

 determination of a an uncertainty, since different values of a 

 are obtained, according to the temperature to which the water- 

 volume employed for the determination refers. If the observed 

 volume at 20° is employed, there comes 



« = 0-000754; 



and when this number is subtracted from that above given for 

 y, we get 



/3=0'001815. 



Upon the calculated values of the vapour-volume s the un- 

 certainty existing in relation to the constant a has only a very 

 slight influence, since the total quantity of «, in comparison 

 with the vapour-volume at all temperatures which are not too 

 near the critical temperature, is very small. The calculated 

 values of s for the above-considered series of temperatures are, 

 as already mentioned, annexed to the last Table; they exhibit 

 the volume, in cubic metres, of a kilogram of vapour. 



If, lastly, to the equation determining the pressure p be 

 given the form adduced under (11), 



_p__ _1 AT~"-B 



ET~ v-x (v + py ' 



the constants A and B herein occurring have for water the 

 following values: — 



A = 45-17; B = 0-00737. 



XVI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 71.] 



December 7, 1881. — Robert Etheridge, Esq., F.R.S., President, 

 in the Chair. 

 rPHE following communications were read : — 

 -*■ 1. " The Zones of the Blackdown Beds and their Correlation with 

 those at Haldon, with a List of the Fossils." By the Rev W 

 Downes, B.A., F.G.K. 



The author, after some remarks on the inexact way in which 



