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Barometric Measurement of the Height of Beri-Lomond, and 

 mi the Quantity of Water annually discharged by the Ri- 

 ver Leven, jrom the Basin of Loch-Lomond. By Mr Wil- 

 liam Galbraith, a. M. (Communicated by the Author.) 



Dear Sir, 



In a former number of this Journal were inserted two tables, 

 for the purpose of faciUtating barometric measurements, which 

 form a part of a series drawn up by me with that view, and will 

 appear in a new edition of my Mathematical Tables, now in the 

 press. By means of these, I had some hopes that greater accu- 

 racy would l)e attained than usual, by this method of determin- 

 ing the heights of mountains ; and was desirous of ascertaining 

 this fact in a satisfactory manner, by a direct appeal to observa- 

 tion. I mentioned this proposal to my friend Mr John Adie, 

 optician, who cordially entered into my views, and provided 

 two very excellent mountain barometers of the best construc- 

 tion. They were of the kind called syphon barometers, their 

 cisterns were provided with an apparatus for complete adjust- 

 ment, by which means the effect of capillary action was obvia- 

 ted, and their verniers shewed the height of the mercury in the 

 tubes, when read by microscopes, to one thousandth part of an 

 inch. Before applying them to the measurement of any 

 height, their index errors were uniformly determined with great 

 care. There were also attached thermometers set in the brass 

 tubes surrounding the glass, the bulbs of which were bent so as 

 to approach the barometer tube rather closely, that the mer- 

 cury in the ball of the thermometer and barometer tube might 

 be equally affected with changes of temperature. 



One considerable difficulty has always attended barometric 

 measurements, namely, the quantity of aqueous vapour mixed 

 up with the air at the time of observation, the effects of which 

 on the resulting height are known to be considerable. In the 

 24th and 26th Numbers of the Edinburgh Philosophical Jour- 

 nal, Dr Anderson, of the Academy of Perth, treats this subject 

 with considerable address; and, from experiments that he liad 

 made, found differences of 40 or 50 feet in 1000 feet, even 

 when the formula of Laplace was employed, though this for- 



