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XXXI. On the Ebullition of Water at Specific Temperatures, 
as the Measure of Altitude. By Joun Murray, F.S.A. 
ELS. FILS. F.G.S. &c. &c.* 
i is known that water boils in the attenuated atmosphere 
of the air-pump, at an inferior temperature, and that this 
point and period of ebullition has some ratio comparatively 
with the density of the incumbent air. Theodore de Saussure 
found that water boiled on the summit of Mont Blanc at 187° 
Fahr. It was Fahrenheit that first proposed this application 
of the thermometric expression of boiling water as a measure 
of altitude. In the Philosophical Transactions for 1817, the 
Rev. Francis Wollaston has described an instrument for this 
purpose, most ingeniously constructed, and no doubt accurate. 
enough for minor elevations. 
During last summer, on my excursion in Switzerland, Italy, 
&c., I made several experiments on the ebullition of water at 
different elevations. A few of these I beg leave to submit to 
you. The thermometer was graduated by a diamond on the 
stem; the bulb was small, and the divisions only indicated 
the entire degree of Fahrenheit’s scale. 
At the Hospice of the Great St. Bernard, on the 30th of 
July 1825, at eight o’clock P.M., the barometer indicated 
21°08 inches. Thermometer without, 52° Fahr., and within 
the Hospice 59° Fahr. Water boiled at 186° Fahr. 
At the village of Simplon on the Simplon, 13th of August, 
at ten o’clock P.M.; air 62°. 
Lxp. 1.—Water boiled, ball touching the surface 197° 5! 
Ditto, entirely immersed  . 2 eg 202 
tte motto nk as ke. Cie cf OS'S 
Exp. 2.—Ball touching the surface . . . . 197 5 
Ball immersed and at the centre . , 203 5 
Ditto at bottom . . . 205 
3d of August. At Brieg, in the Valais, at 45 30' A.M.; 
air 56° Fahr. Water boiled at 204° 5! Fahr. 
15th of August. At Sion in the Valais, at ten o’clock P.M.; 
air 69° Fahr. Water boiled at 206° 5! Fahr. 
17th August. At Martigny in the Valais, six: o’clock 
A.M. ; air 57° Fahr. Water boiled at 110° Fahr. 
Ist of September. At the inn on the Mountain Righi, 
at 9" 45' A.M.; air 63° Fahr. Water boiled at 201° 
Fahr. 
Ist of September. At Lucerne, at 8" 15! P.M. 3; air 70° 5! 
Fahr. Water boiled at 206° Fahr. 
* Communicated by the Author. 
Vol. 67. No. 335. March 1826, 20 It 
