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 asa “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 
Scattering 
cloud 
forms. 
