CLOUDS. 29 



can be easily estimated, in accordance with the following scale. 

 Thus, we understand by 



0. A clear sky, entirely free from clouds; 



10. The whole sky covered with clouds, or a dense fog, or 

 rain ; and by 1, 2, 3, 4, 5, 6, 7, 8, 9, the different degrees 

 of cloudiness which lie between these : 



1. Denotes, for instance, nine times as much blue sky as clouds ; 



5. An equal amount of clouds and blue sky ; 



9. Nine times more clouds than blue sky. 



If, on account of the locality, it is impossible for the observer 

 to estimate the quantity of clouds in this way, he can make use 

 of the following expressions, which will mark at the same time 

 the medium character of the aspect of the sky during each day : 



Wcl. Wholly clear; a sky entirely free from clouds. 



Cl. Clear; when at least two-thirds of the sky is unclouded. 



M. Medium ; the clouded part of the sky nearly equal to 

 the blue. 



C. Cloudy ; a larger part cloudy than clear. 



Ov. Overcast ; the clouds rarely broken. 



Cov. Covered sky; without any visible spot of blue. 



The form of the clouds will be indicated by the terminology of 

 Howard. 



According to this, they are distinguished by their external 

 forms into three kinds : the cirrus, cumulus, and the stratus, to 

 which belong four transition forms, the cirro-cumulus, the cirro- 

 stratus, the cumulo-stratus, and the nimbus. The most remark- 

 able of these forms may be characterized in the following man- 

 ner: 



The cirrus, or cat-tail of the sailors, is composed of loose fila- 

 ments, the whole of which sometimes resembles a pencil, some- 

 times curly hair, sometimes a fine net, or a spider's web. 



The cumulus, or summer cloud, the cotton-bale of the sailors, 

 often shows itself under the form of a hemisphere resting on a 

 horizontal base. Sometimes these half spheres are piled upon 

 one another, forming those large accumulated clouds in the 

 horizon which resemble, at a distance, mountains covered with 

 snow. 



The stratus is a horizontal band, which is formed at sunset 

 and disappears at sunrise. 



The cirro-cumulus are those small rounded clouds, which are 



