395 
Transactions of the Bombay Geographical Society, Vol. XV. 8vo. 
— From the Society. 
The Assurance Magazine and Journal of the Institute of Actuaries. 
January 1861 . — From the Institute. 
Journal of Agriculture and Transactions of the Highland and Agri- 
cultural Society of Scotland, No. 71, New Series . — From the 
Society. 
Monday , 21 st January 186]. 
The Very Rev. DEAN RAMSAY, V.P., in the Chair. 
The following Communications were read : — 
1. On a Method of taking Vapour Densities at Low Tempera- 
tures. By Dr Lyon Playfair, C.B., F.R.S., and J. A. 
Wanklyn, F.R.S.E. 
The authors refer to Regnault’s experiments, which have shown 
that aqueous vapour in the atmosphere has the same vapour density 
at ordinary temperatures as aqueous vapour above 1 00° C. ; and 
they bring forward fresh experiments upon alcohol and ether to show 
that when mixed with hydrogen these vapors preserve their normal 
density at 20° or 30° C. below the boiling points of the liquids, and 
infer generally that vapours, when partially saturating a permanent 
gas, retain their normal densities at low temperatures. 
From their researches the authors deduce the consequence — re- 
markable, but quite in harmony with theory, that permanent gases 
have the property of rendering vapour truly gaseous. Stated in 
more precise terms, the proposition maintained by the authors is, 
“ The presence of a permanent gas affects a vapour, so that its expan- 
sion-coefficient at temperatures near its point of liquefaction tends 
to approximate to its expansion-coefficient at the highest tempera- 
tures. ’’ 
The authors anticipate that admixture with a permanent gas 
may serve as a kind of re-agent to distinguish between cases of 
unusually high expansion-coefficient in a vapour, and cases where 
chemical alteration takes place. It will also be possible, by the 
employment of a permanent gas, to obtain vapour-densities of com- 
pounds which will not bear boiling without undergoing decomposition. 
In experimenting upon substances which may be heated above 
3 G 
VOL. IV. 
