OF ARTS AND SCIENCES. 29 



However slightly the expansion of ascending currents may check 

 the escape of energy, it is certain that the subsequent descent of the 

 air composing them must exhibit more and more of its remaining 

 energy in the form of heat. This phenomenon is generally recognized 

 by recent writers upon meteorology, and there can be little doubt that 

 it powerfully afEects the relative climates of places at different alii- i 



tudes. The climate of an elevated region is colder than that of the 

 sea level, because a smaller part of the atraosj^heric energy appears 

 there as heat, and a larger part as expansion. Whether this is a suffi- i 



cient explanation of the observed difference of climate can scarcely be 

 determined until we have more knowledge with regard to the actual 

 extent and velocity of the convection currents of the atmosphere. 



The considerations above set forth indicate the conclusion, that the 

 effect of conduction, aided by convection currents, is probably an im- 

 portant means of maintaining the present terrestrial temperature, as | 

 well as the present distribution of warmth in different latitudes and at 

 different elevations. If this conclusion should hereafter find a more 

 satisfactory basis in observation and experiment, it would have some 

 interesting applications to the climate of the larger planets. Their 1 

 extensive atmospheres, subjected to a powerful force of gravitation, ; 

 may perhaps enable them to economize very efficiently the compara- j 

 tively small quantity of solar radiation which they receive. Another | 

 branch of inquiry connected with the same general subject relates to . i 

 the conditions of temperature in different parts of the ocean. The | 

 atmospheric and oceanic currents prevailing in former times are also ■• 

 frequently discussed by geologists. If the atmospheric convection 

 currents have the effects here attributed to them, they may help to 

 account for some of the unexplained phenomena of prehistoric climates, 

 the evidences of which have remained to the pi'esent day. 



