ARISING FROM DIFFERENCE OF ELEVATION. 
13 
been lately taken with great care at the Grey Lock Observatory on Saddle Mountain in 
Massachusetts, and at Williams College. The distance in a direct line between the two 
stations is about 5J miles, and the difference in level 2767 feet; the lower station being 
about 800 feet above the level of the sea. The observations were taken at intervals of 
two hours from five o’clock in the morning till nine in the evening, and continued on 
three successive days. The mean result shows a diminution in temperature of 1° for every 
337 feet of ascent. 
The above are all the direct observations that I have been able to obtain to determine 
the law in question ;* and arranged in tabular form, they stand as follows : 
PLACES 
OF OBSERVATION. 
Difference of level 
in feet. 
Diff. for lo 
in feet. 
Number of 
observations 
Balloons. 
1500 to 22897 
378 
14 
Andes and Cordilleras . 
16404 
351 
Numerous. 
Alps. 
7822 to 14351 
262 
6 
Teneriffe . 
12234 
412 
1 
Etna . 
10620 
312 
1 
Pyrenees . 
1841 to 10227 
305 
21 
Clermont, France .... 
1247 to 3466 
267 
7 
Williams College .... 
2767 
337 
28 
The rule commonly laid down, is to allow 1° for every 300 feet of ascent; but from the 
above table, that would seem to be too much, and that 1° to 325 feet would be nearer the 
truth. It ought, however, to be noticed that all the observations I have quoted were 
taken, so far as I can learn, in the warmer part of the year. Observations taken in 
winter might modify the result. 
It has been thought that where the slope of the country is gradual, the diminution of 
temperature from elevation is less than when you compare it on isolated peaks of precipi¬ 
tous mountains with the plains below, or when you ascend in a balloon. Mr. Kirwan 
estimated that when the rise was not more than six or seven feet per mile, the decrease was 
not more than 1° in 800 feet; and for any ordinary rise, not more than 1° in 400 feet. 
By the experiments of Dr. Hutton, near Edinburgh in Scotland, it was 1° in 270 feet; but 
I do not think his data so satisfactory as those which are furnished by the observations 
taken at the academies in your State. The latter have been taken for a considerable 
number of years, according to fixed and uniform rules, and at the same time of day; and 
though it is possible there may be cases where the observers may not have been as careful 
* Since writing the above, I have noticed a series of observations taken at Ithaca (New-York), by Messrs. Cogswell 
and Eddy, in the year 1837. The distance between the stations was about half a mile, and the difference of level 300 
feet. The observations were continued daily through the year, and the result is very remarkable, showing a difference 
in the mean temperature of 3°.99, which is about 1° to every 75 feet of ascent. There appears to be some mistake 
in the record, typographical or otherwise, as the annual result does not agree with the average of the semi-monthly 
results. If the localities are favorable, I hope the experiment will be repeated. 
