514 Notices respecting Neio Books. 



we have 



s„-s A -f B ^=o. 



J A l 



Thus, if the system can pass from the position A to the po- 



C*da 

 sition B by several irreversible equilibrium paths, then 1 — - 



has the same value for all the paths. *^ A 



Again, when the temperature is constant throughout the 



modification, the heat absorbed will be 



*(Sb-S a ). 



An example of this will be found in equation (4), page 408 

 (May 1888). 



In particular, consider the formation of unit weight of a 

 liquid cryohydrate under a pressure equal to the pressure of 

 the saturated vapour of ice. The cycle may be completed by 

 the following operations, performed at constant temperature 

 and pressure : — 



(1) Let the cryohydrate be dissociated by evaporation into 

 the saturated vapour of ice and the anhydrous salt or a hy- 

 drate. In the latter case, the cryohydrate is supposed to have 

 been formed from the hydrate and ice. 



(2) Let the aqueous vapour be separated from the salt, and 

 then condensed into the solid state. 



Since the pressure is constant throughout the cycle, the 

 total work done and heat absorbed are both zero. 



But if S be the entropy of the cryohydrate, and S x the sum 

 of the entropies of the salt and ice of which it is composed, the 

 heat absorbed in the reversible parts of the cycle will be 



i.(Si-S). 



Hence the heat absorbed in the formation of the cryohydrate 

 — an irreversible process — will be 



Q=^.(S-S 1 ). 



LXIV. Notices respecting New Boohs. 



Transactions of the Edinburgh Oeoloqical Society, Vol. V., Part III. 

 (Pp. 335-483.) Edinburgh, 1887. 

 \ N interesting inaugural address by Mr. Ralph Richardson, 

 -^*- treating of the discoveries of Fos.sil Mammalia in Scotland, 

 with a map and lists of the places at which the individual species 

 have been found, commences this number of the 'Transactions.' 

 Following this, Mr. John Henderson treats of the Sands and 

 Gravels of Musselburgh and Stockbridge, containing remains of 



