144 
Proceedings of the Royal Society 
Monday , 3 d April 1876. 
Sir WILLIAM THOMSON, President, in the Chair. 
The following Communications were read : — 
1. Chapters on the Mineralogy of Scotland. By Professor 
Heddle. Chapter I. —On the Bhombohedral Carbonates. 
Communicated by Professor Tait. 
Professor Heddle read a paper on the 11 Bhombohedral Carbonates 
occurring in Scotland,” the first of a series of Chapters intended to 
embrace the analytical results of an investigation of all unknown 
or insufficiently determined Scottish species. 
In this paper many analyses of the carbonates were submitted ; 
and the pseudomorphic changes taking place in these were referred 
to in a special manner. 
2. On Thermo-Dynamic Motivity, By Sir W. Thomson. 
3. On the Vortex Theory of Gases, of the Condensation of 
Gases on Solids, and of the Continuity between the 
Gaseous and Liquid State of Matter. By Sir W. 
Thomson. 
4. On two new Laboratory Apparatus. By William Dittmar. 
The object of this communication is to submit to the notice of 
the Society two little inventions of mine, which, whatever may be 
the degree of originality which they can claim, will, I venture to 
hope, prove useful additions to the catalogue of chemical-laboratory 
appliances. The one is a new form of the precision balance, 
which pretends to execute exact weighings with a hitherto un- 
attained degree of rapidity ; the other is a contrivance for main- 
taining a constant pressure in a supply of gas, and thus making it 
possible, with comparative facility, to keep, say an air-bath, for 
any length of time, at a constant temperature. 
The new balance differs from the instrument in its customary 
