Tin: (;Kospni:RKs 227 



spheres or s fir I Is of matter in the gaseous, 

 lirjuifj, arifi solid or " trans-solid " states. These 

 Ijave bectri ealJcfJ (ieospheres, viz., the atrnos- 

 [)here, the hy(Jrosf>here, the hthosphere, thr-. 

 biosf)here, the tektos[>fiere, and the great 

 ef:r)trosf>here wfiieli rrjakf:s up \)y far the 

 greatest mass arirl vohirne of the glof^e. 'JV> the 

 interaetion of these gef)S[>heres, and to energy 

 (ierived frcirri internal and external sourees, 

 can be referred all the existing superficial 

 phenomena of the planet. 



'^I'he atrao.rphcrc fc>rms the outer shell, and 

 is efn'efly composed of a mixture of oxygen 

 and nitrogen, together with water- vapour, 

 (•arborjie aeid, and rarer gases like argon, 

 neon, etc. Dust f)artieles may also be con- 

 sidered as a constant (constituent of the atmos- 

 phere. A corrjplete mixture of the oxygen 

 and nitrogen takes place throughout the whole 

 atmosf)herie envelope according to the known 

 laws of gaseous diffusion, but the equilibrium 

 of the aqueous vapour is continually disturbed 

 by the ceaseless f>roeesses of condensation and 

 evaporation, whicth vary in amount with 

 itvcry cJjange of temperature and pressure. 

 When, with a lowering of the temperature, 

 water- vapour becomes rain or ice or snow, 

 great movements are brought about in the 

 atmosphere, warm, moist, and light air 

 generally ascending in cyclonic areas, and 



