CHAP. l.8. OF CLOUDS. 65 



in the wonted way. These are circumstances 

 which by the hygrometer I have observed to 

 attend a dry state of the air, 



Previous to Rain, very different appearances 

 frequently present themselves. The cumulus 

 in the lower atmosphere changes its appearance, 

 becomes denser, irregular in shape, and rocklike 

 in its superstructure, with fleecy protuberances 

 about its base ; and, by degrees, is a complete 

 cumulostratus. While this process is going 

 on, cirri, cirfostrati, or cirrocumuli, which have 

 previously appeared above, are lost, to all ap- 

 pearance, as if they had suddenly evaporated. 

 The air will now be found damper, and there is 

 frequently a visible mistiness above ; and the 

 explanation which I have to offer for this 

 phaenomenon is, that the humidity of the air 

 between the clouds affords a means of commu- 

 nication between their different electricities ; 

 and that the cumulus, being the largest body, 

 draws down the cirrus above, and is aggrandized, 

 its previous electric state destroyed, and its 

 structure altered by the change. The sur- 

 rounding air being damp, the process goes on, 

 affecting clouds more distant, and the result is 

 nimbus and Rain. 



A free passage for the electric fluid being 



