419 
of Edinburgh , Session 1868 - 69 . 
increased in a greater ratio than the increase of temperature. 
Hutton’s mathematical deduction has been since proved experi- 
mentally to be true. As the solvent power of atmospheric air 
increases in a greater ratio than that at which the temperature 
rises, when two masses of transparent air of different temperatures 
are mixed together, more moisture is present than suffices to satu- 
rate the mixed air at the intermediate temperature which is pro- 
duced; and hence the excess must separate in the form of either 
mist, if the excess be slight, or rain, if the excess be considerable. 
In the topographical branch of Natural History the early Pro- 
ceedings of the Society present several papers which must have 
possessed at the time much interest, such as an account of the 
Caves of Elephanta by Dr Buchanan, of Prince of Wales’ Island 
by Mr Howison, of the Trinidad Petroleum Lakes by Mr Lochead, 
and of the Natural History of Guiana, and of Madeira, by the same 
gentleman. But these narratives have been rendered obsolete by 
more elaborate descriptions published since. 
It remains for me, under the head of the Natural Sciences, to 
take notice of the early labours of the Boyal Society in Mineralogy 
and Geology. In this department the Society, during the first 
twenty years of its life, shone with a brilliancy unsurpassed by any 
of the scientific academies of Europe ; for during that time were 
produced Hutton’s Theory of the Earth, and the illustrative ex- 
periments of Sir James Hall. 
The Society’s papers on Mineralogy and Geology are eleven in 
number, but of three of them the Proceedings contain not even an 
abstract. 
Colonel Imray, in a well-told description of the “ Mineralogy of 
Gibraltar” in 1797, corrects some prevailing errors as to the species, 
composition, and geological position of the famous deposit of bones 
in various parts of the Kock, and is, I believe, the first to point 
out that the hill must have been at one time for a long period 
covered by the sea to the height of at least 900 feet, as he found at 
that elevation numerous “ pot-holes,” formed by trituration under 
water with shingle-stones kept in motion by currents. 
Dr Bichardson, in 1803, describes three remarkable basalts which 
