a 
lay: 
by the Boiling Point of Water. 293 
At that pressure my thermometer (Adie) shews 210.58 F. 
De Saussure’s stood, therefore, 1°.42 F. higher than mine. 
Now, on the top of Mont Blanc, the barometer stood at 
17.133 English inches. 
The boiling temperature by De Saussure 
was, é ; ; F : 187°.234 Fahr. 
Reduced to Adie, . ! 185°.814 — 
But the boiling point of Adie’s tibiae! 
meter, with the barometer at 30 inches, is 212°.62 
Subtract, ; , : 185°.81 
At Mont Blane, below boiling point at 
30 inches, . : 26°.4 1 
By Galbraith’s Tables, . 30. 000 jens = 29228 feet 
17.1388 — = 14593 
Height uncorrected for temperature, 14635 
Now, by the proportion found empirically above, 
Height uncorrected for temperature = 26.71 x 549.5 = 
14677 feet,—a coincidence really surprising. 
I have already stated, that De Saussure found Deluc’s 
formula to conform accurately to his observation on Mont 
Blane. It may therefore be concluded, that Deluc’s formula 
and mine agree closely. In fact, if we take its conversion 
into English measures, as given by Dr Horsley,* 
ausGu00 log z — 92.804, 
which gives the boiling point, in degrees of Fahrenheit, 
reckoned from 32°, z being the height of the barometer in 
tenths of an English inch, we find that this gives 
544.7 English feet of ascent for 1° Fahr. 
Practically, I consider it sufficient to find the difference of 
height, in feet, between two stations, to multiply the differ- 
ence of the boiling points by 550, and then correct as in 
barometric observations for the temperature of the air. 
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, compared to an imaginary 
* Phil. Trans., vol. Ixiv., p. 226. 
