138 Mr. T. Hopkins on the Formation 



part of the atmosphere which is near to the surface of the 

 earth, and causes it to ascend to a greater elevation ; this fact 

 was previously known, and is, I presume, generally admitted. 

 The part of the atmosphere near the earth which thus ascends 

 has within it some certain quantity of steam or elastic aqueous 

 vapour. When the air rises to an adequate height, and is 

 consequently sufficiently cooled, a part of this steam is con- 

 densed. A new process now takes place. Upon the conden- 

 sation of this portion of steam, latent caloric, or caloric of elas- 

 ticity, is liberated, and this caloric attaches itself to surround- 

 ing bodies, and raises their temperature. In this way beds 

 or strata of warm air are formed at different heights in the 

 atmosphere. 



But if liberated caloric raises the temperature of masses of 

 air floating high up in the atmosphere, we know that those 

 masses will expand through the increase of their elasticity. 

 The additional elastic force thus acquired must be exerted in 

 all directions, but as there will be the least resistance from 

 above the force will be first developed principally in a vertical 

 direction, and the whole column above will be raised, and 

 caused to expand laterally in the higher regions of the atmo- 

 sphere. On this second heating power, arising from conden- 

 sation, being exerted, and a part of the atmosphere raised and 

 thrown off laterally, the air below, relieved from a portion of 

 the incumbent pressure, will spring upwards, and the sur- 

 rounding air near the surface of the earth will flow in to re- 

 store the equilibrium of atmospheric pressure. Thus a local 

 and temporary upward current will be created; and this 

 upward current taking with it steam from near the sur- 

 face of the earth, successive condensations take place — suc- 

 cessive expansions follow; and the condensed steam, taking 

 the shape of cloud, becomes a cumulus, and swells and grows 

 in the way that has just been attempted to be described. 

 The generally slow formation of the cloud, and the slight re- 

 sults which ordinarily follow, are, it is presumed, attributable 

 to the limited portion of steam that is in the atmosphere. 

 When steam is deficienfin the raised air, no cloud is formed ; 

 when it is plentiful, clouds are freely formed ; and when it is 

 very abundant/ the clouds are heavy and rain falls. The libe- 

 ration of caloric by condensation it is evident may be effected 

 in the smallest degree conceivable, and the process described 

 may be slow, and the result only the elevation of the tem- 

 perature of limited portions of the upper atmosphere, in the 

 way in which the temperature of the tropical atmosphere is 

 raised. Evaporation in the tropical regions furnishes a full 

 supply of steam to the atmosphere, which steam being carried 



