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 is a 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 



