64 OF CLOUDS. CHAP. 2. 8. 



SECTION VIII. 



Of Nimbi apparently caused by the interfusion 

 of Moisture between distinct Clouds, 



A CUMULUS arising in the lower atmosphere 

 may be electrified differently from a cirrus, or 

 any other cloud occupying a higher region ; 

 and these may both subside; the upper one, 

 perhaps, by evaporation ; and the lower by the 

 usual vespertine descent, without uniting and 

 forming the compound modifications. This 

 appears to be frequently the case in very dry 

 weather, when cirri may be observed in the 

 higher air, changing then* forms, passing to 

 cirrocumulus and cirrostratus, and eventually 

 subsiding, while cumuli sail leisurely along be- 

 low. And these appearances continue, for many 

 days together, without producingcumulostratus; 

 which, nevertheless, occasionally happens, from 

 the cumulus rising up and meeting with some 

 other cloud descending. This will sometimes 

 produce a nimbus, as I described above. At 

 other times, however, the cumulostratus thus 

 formed proceeds no further, and even reassumes 

 the character of simple cumulus, and subsides 



