22 OP CLOUDS. CHAP. 1. 7. 



be differently electrified, we are led to conclude 

 that the process of nimbification, of which cumu- 

 lostratus is one stage, consists in a neutralization 

 of the electricities of two or more clouds; and 

 that where cumulostratus or nimbus appears, 

 unpreceded by the aforedescribed phenomena, 

 the same kind of change has taken place in the 

 aqueous aggregates, from causes which are in- 

 visible.* 



The cumulostratus varies in appearance; 

 sometimes it overhangs a perpendicular stem, 

 and looks like a great Mushroom; frequently a 

 long range of cumulostrati appear together, 

 which have the appearance of a chain of moun- 

 tains with silvery tops.f Before thunderstorms, 

 it seems frequently reddish, which some people 

 have imagined to arise from its being highly 

 charged with the electric fluid. Of this, how- 

 ever, more in another place. 



* See the experiments of Cavallo with the electrical kite, 

 &c. Camp. Treat. Elect. 2d Ed. p. 370. 



f The simple cumulus sometimes has this appearance ; and 

 as the change to cumulostratus is gradual, it is often difficult 

 to determine to which modification to ascribe it. A continuity 

 of base to several mountainous superstructures, and an in- 

 creasing density of colour which by degrees approximates to 

 black, mark the progress of the change to cumulostratus. 



