XXIX. Barometrical Measurements, 

 By WILLIAM ALLEN, f.r.s. 



MEMBER OF THE GEOLOGICAL SOCIETY, 



[Read 19th NoTember, 1812.] 



_l. HE 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. 



H,: 



A.M. 9 



10 25 



P.M. 1 25 



4 



4 45 



6 



6 30 



September 8th, 1805. 



Goat Inn, Beddgelert . 



Llyn Cader 



Summit of Snowdon 



Llyn Cwellyn 



Llyn Cader 



High water-mark at Pont-aber-glas-Llyn 

 Goat Inn at Beddgelert 



61 



29.69 



61 



29.162 



50 



26.164 



56 



29.30 



57 



29.12 



55 



29.78 



53 



29.6 



It appears from observations 1 & 7 that the Barometer had fallen 

 at Beddgelert in 9f 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 ob- 

 servation on calculating the measurements. 



