1823.] Cx)L Beaufoy's Astronomical Observations. 259 



It appears from these experiments, that this white saUne 

 matter is pm-e, or nearly pure, chloride of potassium. 



I am inchned to attribute its introduction into the lava to 

 subHmation. 



As chloride of potassium is a new species in mineralogy, I 

 shall send the specimen to the British Museum. 



Article V. 



Astronomical Observation s, 1823. 

 By Col. Beaufoy, FRS. 



Bushey Heath, near Stanmore. 

 Latitude 5P 37' 44*3" North. Longitude West in time 1' 20*93". 



Sept. 2. Immersion of Jupiter's first els'* 24' 5S*7"Mean Time at Bushey. 



satellite ^15 26 19*6 Mean Time at Greenwich. 



Sept. 7. Immersion of Jupiter's second C 15 05 21 Mean Time at Bushey. 



satellite ..^15 06 42 Mean Time at Greenwich. 



Sept. 19. Immersion of Jupiter's first f 15 40 01 Mean Time at Bushey. 



)l5 



satellite ; 1 5 41 22 Mean Time at Greenwich. 



Article VI. 



An Abridged Translation of M, Ramond's Instructions for the 

 Application of the Barometer to the Measurement of Heights, 

 with a Selection from his Tables for facilitating those Opera- 

 tions, reduced {lohere necessary) to Englisli Measures^ By 

 Baden Powell, MA. of Oriel College, Oxford. 



{Continued from p. 177.) 



The configuration of the place where the barometer is situated 

 is far from being a matter of indifference to the accuracy of the 

 measurements. We have just seen what influence it has on the 

 temperature ; it appears not to have less on the pressure of 

 the atmosphere. A dry and strongly heated plain gives greater 

 velocity to the ascending currents, which is not done by a ver- 

 dant hill ; upon all sides of which the sun does not shine at the 

 same time. Here the barometer will be proportionally higher ; 

 in the other case lower. On an insulated peak all currents have 

 an ascending motion given them from passing along its acclivi- 

 ties : they all acquire a compressing power in a narrow and 

 deep valley where they engulph themselves : and the mercury 

 sustains itself constantly above the point at which it would 

 stand in an open plain at the same absolute elevation. I have 

 measured several hundred times the height of Bareges above 

 Tarbes. The town of Tarbes is situated on an extensive plain. 

 The valley of Bareges is a very narrow gorge, surrounded on all 



s2 



