PHENOMENA OF EAIX. 285 



particles of the clouds appear to lose their 

 mutual repulsion, and several unite into one, 

 probably in consequence of some change in 

 their electric relations, a drop is thus formed, 

 and its gravity causes it at once to fall towards 

 the earth. As the drop falls, being formed in 

 higher strata, it is colder than the air through 

 which it traverses in its passage to the earth; 

 it therefore condenses more and more vapour 

 around it, and thus increases in size until it 

 finally reaches the earth. Even the altitude of 

 an observatory will make a difference in the 

 size of a rain-drop, for it is constantly remarked 

 that rain-gauges at the summit of such a place 

 never indicate so great a fall of rain as others 

 placed at the basement, the drops in falling this 

 height undergoing an increase of size which 

 became sensible by means of this instrument. 

 Other explanations of the increase of rain near 

 the ground are given. Perhaps this is the most 

 simple and correct. 



Although it is not difficult to assign the ulti- 

 mate cause of rain to a change of temperature, 

 or to define the process by which vapour be- 

 comes rain, it must be confessed that great 

 obscurity still rests upon the laws which in- 

 fluence its occurrence, and upon the actual 

 nature of the phenomenon. Rain occasionally 

 falls from a sky clear as crystal, and altogether 



