THE SMITHSONIAN INSTITUTION. 235 



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 l)roken. 

 Gov, Covered sky ; without any visible spot of blue. 

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

 ard. 



According to this, they are distinguished by their external forms 

 into three kinds : the cirrus^ cumulus, and the stratus, to whicli belong 

 four transition forms, the cirro-cumulus, the cirro-stratus, the cumulo- 

 stratus, and the nimhus. The most remarkable of these forms may 

 be characterized in the following manner : 



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

 the whole of which sometimes resembles a pencil, sometimes 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, form- 

 ing 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 often 

 called fleecy ; when the sky is covered with clouds of that kind it is 

 said to be mottled. 



The cirro-stratus is composed of small bands, formed of closer fila- 

 ments than those of the cirrus, for the rays of the sun often find it 

 difficult to penetrate them. These clouds form horizontal beds, 

 which, at the zenith, seem composed of a great number of loose 

 clouds, while at the horizon a long and very narrow band is seen. 



The cumulo-stratus is a mass of heaped up and dense cumuli. At 

 the horizon they often assume a dark or bluish tint, and pass into the 

 condition of nimbi, or rain clouds. 



The nimbus is distinguished by its uniform grey tint, its fringe and 

 indistinct edges ; the clouds composing it are so blended that it is 

 impossible to distinguish them. 



But besides these principal forms, there are several intermediate, 

 to which it is difficult to assign a name. They must be referred to 

 the form which they most resemble. 



They may be entered in the journal by means of the following 

 abbreviations : 



, St. i. e. Stratus. 



Cu. " Cumulus. 



Cir. " Cirrus. 



Cir. st. " Cirro-stratus. 



Cu. St. " Cumulo-stratus. 



Cir. cu. " Cirro-cumulus. 



Nim. " Nimbus. 



If several of these forms are visible, the most frequent should be 

 underlined, and the others should follow the order of their frequency. 

 The distribution of the clouds in the sky should be noted, whether 



