1835.] Improvements in Science. 105 



Mean Temperature of the Air. — The mean temperature of 

 different places on the earth's surface, is a point of much 

 importance, in reference particularly to its steadiness, during 

 a given period. Because by such data, we are enabled to 

 determine whether the globe possesses a calorific focus from 

 which heat is continually emanating, or whether, according 

 to some philosophers, it is gradually throwing off the heat, 

 which its whole mass was originally possessed of. 



Laplace has shewn in his observations on the ancient 

 eclipses, that the temperature of the earth has not varied 

 for 2500 years, the^ o of a degree. 



Fourier as has already been mentioned {Records of 

 General Science, vol. i. p. 70,) proved that the cooling 

 cannot have exceeded the ~^ of a degree during a century. 

 And M. Arago demonstrated that during 2001 years, the 

 maxima of cold have not increased. 



Libri {Ann. de Chim. lii. 395,) has drawn the following 

 conclusions from his analysis of different theories. 1 . In 

 the interior of the earth, the temperature of the strata, 

 increases or diminishes with the depth. 2. From direct 

 observations, the calculation of eclipses, and the mathe- 

 matical theory of heat, it appears to be demonstrated, that 

 the mean temperature of the globe has not varied during 

 the historic period. 3. Future observations may perhaps 

 enable us to ascertain if the moon has attained a state of 

 calorific equilibrium, or if its mean temperature varies. 

 4. In a given time the cooling of each stratum in the earth 

 being proportional to the quantity of heat, the cooling will 

 be more rapid in the hottest strata towards the centre of 

 the earth. Hence, in order to study the future variations 

 of the mean temperature of the earth, it will be necessary 

 to make experiments with thermometers, deposited at very 

 considerable depths in the earth. 



It is obvious, however, that we are extremely limited in 

 our means of determining temperatures at great depths, 

 the most distant point from the surface which has yet 

 been attained in this country (250 fathoms,) being a most 

 insignificant fraction of the earth's radius. 



There are several methods of ascertaining the mean 

 temperature of terrestrial localities, which have been 

 employed with considerable success. Registers of the 

 thermometer have been kept during the several days of the 



