204 On the Propagation of Sound. 
thermometer a corresponding dilatation of the air equal to 
002078 is produced. 
According to the researches of Sir George Shuckburgh, the 
mean annual range of the barometer at the surface of the sea is 
30°04 inches, and this elevation is constant in every degree 
of latitude. In calculating the temperature, we have followed 
the formula invented by that great philosopher Tobias Mayer of 
Gottingen. From these data we find the mean annual tempera- 
ture at the surface of the sea in latitude 45° equal. to 57°5 of 
Fahrenheit ; and the mean density of the air -0012353 ; and by 
making use of the numbers ascertained by Mr. Tralles for the 
density of mercury, we find it in the same latitude and tempera- 
ture 13°59043. “Then to find the elevation of a column of air of 
equal weight, we have 
aces X we = 27540-98 feet, or 4590-163 fathoms 
for the height of the atmosphere. 
Now to find the pressure of the air, or, in other terms, at what 
elevation the mercury in the barometer would stand, if taken to 
the height of 4590:163 fathoms, is an important part of what we 
require. 
In order to approach as near to accuracy as possible, it will be 
requisite to determine the precise decrease of temperature for 
every increase of altitude in the atmosphere. Saussure has found 
a decrease of one degree of Fahrenheit for every 289 feet. 
Daubuisson* found, under the same circumstances, an elevation of 
319 feet corresponding to 1° npon the same scale. The best ob- 
servations for deciding this question, we think, are those ob- 
tained from the journals of the Monks residing in the venerable 
priory situated upon Mount St. Gothard in Switzerland. The 
mean annual height of the barometer kept in this place is 21°77 
inches, and of Fahrenheit’s thermometer 29°'8. Now the lati- 
tude of the place is about 46° 30’ North; and the mean annual 
temperature of this latitude at the level of the sea, as appears 
from Mayer’s formula before mentioned, is 56°1. Calculating 
the height of the priory from these data, by De Luc’s method 
for ascertaining the altitudes of mountains by the barometer, we 
find it equal to 8557 feet. 
Then 56°] —29°8=26°-3, and ~ eon =325 feet 
of elevation, corresponding to a depression of Ie aes Fahren- 
heit’s scale. 
From these deductions we shall be able to find the detglie of 
the mercury in the barometer, at any determinate altitude, by 
applying the following calculation to that purpose. 
* Nicholson’s Journal, vol. xviii. p. 150. 
27540°98 
