TABLE of mean temperature at tJte lecel of the sea in different latitude?, 

 calculated from Leslie's formula. 



Mean temperature of London, as observed at the apartments of the 

 Royal Society for 20 years, from 1790 to 1809, = 50" 94. The greatest an- 

 nual temperature during that time was 53o. 2, the least 48o. 5. 



18. In ascending from the level of the sea, this mean temperature de- 

 creases nearly uniformly, though accurately the decrease seems some- 

 what slower as we ascend. Playfair calculates the diminution of heat at 

 the rate of 1 for 270 feet nearly, when not far from the surface of the 

 earth. Leslie allows 300 feet at the earth's surface ; and at I, 2, 3, 4, and 

 5 miles altitude, 295, 277, 252, 223, and 192 feet respectively, for every de- 

 gree of Fahrenheit. 



Hence to find the mean temperature at any height 7i above the level of 



the sea, we must subtract from the formulae in the last Art. -p^r- accord- 



ing to Playfair, - according to Leslie, and 



A 



accord- 



ing to Atkinson. r 200 



19. The temperature of profuse fountains gives very accurately the 

 mean temperature of any place ; and by this method the altitude of any 

 place above the level of the sea may be nearly ascertained. Thus sup- 

 pose t temperature of the spring (Fahrenheit), T = mean temperature 

 due to that parallel, found by the above Table or formulae, then 



(T t} x 300 = height above the level of the sea in feet. If the 

 altitude be very considerable, 300 is too large a multiplier, and a correc. 



34 



