LESSON XIX. 



ON ErAPORATION, RATN, HAIL, SNOW, MISTS, 

 AND DEW. 



Th' effusive south 



Warms the wide air, and o'er the void of heav'A 

 Breathes the big clouds with vernal show'rs distent, 

 At first a dusky wreath they seem to rise, 

 Scarce staining aether; but by swift degrees, 

 In heaps on heaps, the doubling vapour sails 

 Along the clouded sky. THOMSON. 



t \ 



OUR next business is to reflect upon the means 

 by which the most usual meteors, as Rain, Hail, 

 Snow, and the all-enlivening Dew, are produced : 

 and in order to this, the first thing we are to con- 

 sider is the process of Evaporation. To have a 

 precise idea of evaporation, some persons distin- 

 guish it from exha ation, and say that the former 

 is the act of dissipating the humidity of a body in 

 fumes or vapour ; while the latter, they say, is' 

 properly a dispersion of dry particles issuing from 

 a body. Others say there is no need of any such 

 distinction, exhalation (properly signifying a 

 Ireathing forth) being applicable to all bodies 

 "capable of being respired, whether moist or dry. 

 The term commonly used by chemists for the 

 wising of the minute panicles of bodies in a dry 



form* 



