The Phenomena of the Atmosphere. 95 



intensely cold, the vapours immediately after 

 condensation are frozen, and the frozen particles 

 in their slow descent unite at a determinate 

 angle, forming the beautiful feathery flakes of 

 snow, each of which is, in fact, a very compli- 

 cated group of little crystals. Hail is sometimes 

 an entire drop frozen in its descent through a 

 colder region, or by means of a rapid evaporation, 

 in which case it is a transparent globule; but 

 much more frequently a common snow flake rolled 

 up in a manner by whirling between two cur- 

 rents forming an opake nucleus, which by its ex- 

 treme coldness encrusts itself with clear ice out 

 of the vapours it meets with in falling. These 

 rolled snow flakes often fall unencrusted before 

 a severe frost. Angular hailstones are the frag- 

 ments of larger spheres which have broken in 

 their fall, probably by the expansion of air en- 

 veloped in the spongy nucleus. 



The dew, which falls in a summer evening, is 

 part of the vapour which is raised in the course 

 of the day by the sun's heat ; but not being com- 

 pletely dissolved or dispersed in the atmosphere, 

 it is condensed, and falls with the evening's cold. 

 In cool nights the dew often becomes frozen in 

 the form of hoarfrost. 



The atmospherical phenomena will be further 

 explained when we treat of electricity. 



