Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/444

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XIX. Barometrical Measurements.


By WILLIAM ALLEN, F.R.S


member of the geological society.


[Read 19th November, 1812.]


The following measurements were made with a single Barometer of the construction proposed by Sir Henry Englefield, and have been calculated according to the formula recommended by him in his memoir on the subject, which is inserted in the 14th volume of Nicholson's Journal. I shall give in detail the observations made upon Snowdon; and of the other measurements I shall mention only the results.

Snowdon.
Observ. Hour September 8th, 1806 Therm. Barom.
1 A.M. 9 00 Goat Inn, Beddgelert 61 29.69
2 —— 10 25 Llyn Cader 61 29.162
3 P.M. 1 25 Summit of Snowdon 50 26.164
4 —— 4 00 Llyn Cwellyn 56 29.30
5 —— 4 45 Llyn Cader 57 29.12
6 —— 6 00 High water-mark at Pont-aber-glas-Llyn 55 29.78
7 —— 6 30 Goat Inn at Beddgelert 53 29.6

It appears from observations 1 & 7 that the Barometer had fallen at Beddgelert in 9 hours 0.09 inches, and from observations 2 & 5 that it had fallen at Llyn Cader in 6 hours 0.042 inches. The descent of the mercury may therefore be estimated at about 0.008 inches an hour, for which due correction has been made in each observation on calculating the measurements.