CLOUDS AND CLOUD FORMS 



81 



to a push caused by rising swirls of heated air 

 trying to escape up a vortex into cooler regions. 

 The color of the nimbus is always cast in gray, 

 and the darkest portions are usually the ones 

 under deepest shadow. Poet and romancer to 

 the contrary, there is no such thing as a " black " 

 cloud seen in the daytime nor for that mat- 

 ter at any other time. The heavy storm-cloud 

 may border upon purple, and sometimes pre- 

 ceding cyclones it is sea-green, but it is never 

 "black/' 



The different forms and kinds of clouds given 

 above enumerate only certain families. Aside 

 from the large groups there are patches of 

 cloud being continually woven or torn from one 

 family to blend and intermingle with another 

 family, thus making many hybrid varieties. It 

 would be almost impossible to catalogue the dif- 

 ferent cloud forms that one may see on an ordi- 

 nary summer day ; or the parts of clouds such 

 as scud, wrack, wreaths, and sprays wrenched 

 away from the parent body by storms and 

 squalls. 



The form of clouds usually gives the ear-mark 

 of recognition to such families as the cirrus, 

 the stratus, and the cumulus ; and yet this form 

 is never the same for any length of time. It is 



