BY THE BOILING POINT OF WATER. 415 



If the barometer at one station is to be compared with the boiling point at 

 another, the simplest way is to find what elevation the barometer expresses, com- 

 pared to an imaginary station, where the barometer stands at 30 inches, the boiling 

 point at 212. Then the height of the station, where the thermometer has been 

 observed, above the imaginary station, is found by the preceding rule. 



For example : The corrected boiling point on the Col d'Erin between Evolena 

 and Zermatt, in the Vallais, on the 19th August 1842, was 19F.93, the external 

 thermometer 34., the barometer (English) at Geneva was 28.73, ^and the tempera- 

 ture 72, required the height. 



Then, by GALBRAITH'S table, for 30 inches, . . . 29228 feet. 



28.73 28098 



Difference, . . 1130 



Consequently, supposing the atmospheric temperature 32, the barometer stood at 

 30 inches, at a level 1130 feet below Geneva. The boiling point at the upper 

 station was 20.07 below 212. TheCold'Erin was, therefore, 20.07 x 549.5 = 11028 

 feet above that imaginary sattion, or 9898 feet above Geneva. Corrected for 

 temperature, this gives 10377 ; and Geneva being 1343 feet above the sea, the 

 height of the Col d'Erin is 11720 feet. 



This is purposely given as a complex case ; but let us suppose that the boil- 

 ing point, at the level of the sea, is assumed to be 212, then the approximate 

 height of the Col d'Erin is 549.5 x 20.07 = 11028 feet; and supposing the mean 

 temperature of the column 54, the height will be 11586 feet above the sea. 



