PEOOEEDING-S 
OF THE 
Vol. II. MARCH, 1867. No. 3 
GENERAL MEETING. 
Thursday, March 7th, 1867.— Mr. Thomas Pease, F.G.S., Vice- 
President, in the chair. 
Mr. W. L. Carpenter, B.Sc, called the attention of the meeting to 
some fine crystals of Selenite (sulphate of lime) found in the Lias clay 
now being excavated to form the new reservoir for the Bristol Waterworks 
Company, at Barrow. He remarked that the crystals were hemitropes, 
having re-entering angles, and spoke of the optical properties exhibited by 
thin laminae of the substance, when exposed to polarised light. 
The President, Mr. W. Sanders, F.R.S., F.G.S., then read a paper 
upon the Theory of the Mountain Barometer. After some preliminary 
remarks upon the dryness of his subject, especially to the ladies, he asked 
all present to follow him closely in the demonstration he was about to give, 
else, if a step were lost, it would be unintelligible. He would abstain as 
much as possible from technical terms and signs, and when obliged to use 
them, would explain their meaning. A synopsis of the whole was con- 
tained in the formulae attached to the annexed diagram, a large copy of 
which was exhibited, as well as of several formulae, which would not be found 
as such in any book on the subject, because the author had made certain 
corrections and alterations in the form of those taken from different works f 
in order to compare them all together. Copies of these will be found on 
pages 26 and 27. 
