580 HISTORY OF THERMOTICS. 



the air with a horizontal base ; the stratus grows 

 from below, and spreads along the earth; the cirrus 

 consists of fibres in the higher regions of the atmo- 

 sphere, which grow every way. Between these 

 simple modifications are intermediate ones, cirro- 

 cumulus and cirro-stratus; and, again, compound 

 ones, the cumulo-stratus and the nimbus, or rain- 

 cloud. These distinctions have been generally ac- 

 cepted all over Europe : and have rendered a 

 description of the processes which go on in the 

 atmosphere far more definite and clear than it could 

 be made before their use. 



I omit a vast mass of facts and opinions, sup- 

 posed laws of phenomena and assigned causes, 

 which abound in meteorology more than in any 

 other science. The slightest consideration will show 

 us what a vast amount of labour, of persevering 

 and combined observation, the progress of this 

 branch of knowledge requires. I do not even speak 

 of the condition of the more elevated parts of the 

 atmosphere. The diminution of temperature as we 

 ascend, one of the most marked of atmospheric facts, 

 has been variously explained by different writers. 

 Thus Dalton 24 (1808) refers it to a principle "that 

 each atom of air, in the same perpendicular column, 

 is possessed of the same degree of heat," which 

 principle he conceives to be entirely empirical in 

 this case. Fourier says s5 (1817), "This phenomenon 



24 New Syst. of Chem. vol. i. p. 125. 



25 Ann. Chim. vi. 286. 



