CLOUDS AND CLOUD FORMS 
73 
and are more capable of reflecting light than 
the ordinary vapor clouds. Certainly their 
luminosity is their strongest feature aside from 
their peculiar spray-like or feathery form, 
though their color is often remarkable. At 
dawn they are the first ones to catch the light 
from below and reflect it in yellow or pink, and 
at twilight they are the last ones to fling back 
the scarlets of the sinking sun. These clouds 
are apparent in all countries and in all skies, 
and are ever tenants of the upper region, though 
some of their branches or manifestations appear 
in connection with clouds of the middle region. 
The cirro-stratus (a) is a mixed or composite 
cloud made up from the cirrus and the stratus. 
It is not one of the four large classes, but rather 
a hybrid variety that must figure under a sub- 
division. In reality it isa part of the cirrus, 
which has become slightly changed in its form 
and elevation by a sudden increase in its moist- 
ure. Grown heavier and denser, it has de- 
scended and woven itself into long, thread-like 
lines resembling a net or veil stretched across 
the sky. Its appearance is usually thought to 
be indicative of approaching storm, and the di- 
rection it takes shows whence the storm is com- 
ing. It is a frost cloud, is frequently seen at 
Color of the 
cirrus. 
The cirro~ 
stratus, 
