r 3S3 .] 



they mufc be in the fuperior regions of the atmofphere prevents: 

 their coalefcence in any but the extreme degrees of cold. 



Hence we fee that in the warmer latitudes and feafons, various 

 ftrata of clouds may be formed one above the other ; Mufchen- 

 broock attefts, that even in Holland, in Auguft 1748, he diftindly 

 difcerned three. Thefe diflinit ftrata, varioufly eledrified and 

 otherwife circumftanced, give occafion to various phasnomena, the 

 detail of which would here be mifplaced. 



The clouds which commonly crown the fummits even of low 

 mountains, and often announce rain, are caufed by the near ap- 

 proach to faturation at thofe elevations, and its adtual attainment 

 through the evaporation from thofe fummits. But the fummits 

 of the loftieft mountains ever crowned with fnow, are generally 

 fhrouded in clouds from the cold they impart to the air in contail 

 with them, and the lofs of eledlricity conduded away from the 

 vapours contained in that air, by the mountain. 



The heights at which the loweft clouds are formed are various 

 in various latitudes and feafons ; greater in the warmer and fmailer 

 in the colder. In latitude 54*^ in Cumberland, Mr. Crofthv/aite 

 obferved none lower than 2700 feet, and none higher than 3150 



in 



