68 OF CLOUDS. CHAP. 2. 9. 



the cause of the nimbus unpreceded by other 

 clouds. For if the air, from unknown causes, 

 can so deposit watery particles, which may be 

 diffused through a large mass of air, if the said 

 large tracts of air, before dry, and consequently 

 an electric, should have a plus and minus state, 

 the watery particles diffused in it would also 

 receive such a division of electricity ; but these 

 electricities having now, by the general humi- 

 dity, a communication almost as soon as formed, 

 they might unite, so as to form Rain. This is a 

 process which would be comparatively slow and 

 progressive: and thus we may account for 

 what has been called, by some, the spontaneous 

 formation of nimbi ;* and, by others, the gradual 

 condensation of the air into Rain,f which lasts 

 whole days, and affords an example of the 

 more slow and gentle operation of the same 

 causes, which, when effected rapidly by the 

 sudden union of clouds, produce the more 

 temporary and violent phaenomena of showers 

 and thunderstorms. 



* M. I. A. De Luc mentions having observed this spon- 

 taneous nimbification, unpreceded by cirri, when he was at 

 the top of high mountains. See some curious observations in 

 his " Idees sur la Meteorologie," 2 vol. 8vo. London, 1 786. 



t In nimbum cogitur aer 



