CLIMATE. 231 



the isothermal and isobaric lines. If then, in consequence 

 of the situation and conformation of the Antarctic masses 

 of land, no great thermal difference, due to latitude, is to 

 be expected, then the annual difference in temperature 

 must inevitably be all the greater, for, barring a few 

 slight exceptions, all the land masses of the south polar 

 regions lie within the Antarctic circle, and are conse- 

 quently subject every year to a difference in the length 

 of the day of from o to 24 hours on the periphery, and to 

 between 179 x 24 hours' day and 186 x 24 hours' night 

 at the Pole itself. But the supply of heat from the sun 

 depends partly on the inclination of the solar rays, and 

 partly on the duration of daylight, whence it follows that 

 the Antarctic regions must have, in comparison with the 

 ocean to the north of it, an excessive climate independent 

 of its probable continental character. In the winter season, 

 which coincides for the central parts with the long polar 

 night, a supply of heat is wholly excluded, and we are 

 forced to assume a very low degree of temperature, at 

 least for the land. In summer the whole region, and 

 especially the Pole, receives continuously a more abun- 

 dant supply of heat from the sun, which is all the more 

 intense as the sun is in perigee ; but as, according to 

 our present knowledge, those regions are covered by a 

 constant mantle of snow, the summer heat is mainly 

 consumed in melting snow and cannot contribute greatly 

 to a rise of temperature, so that even in summer the air 

 of the ocean must in general be warmer than that of the 

 land, and the sea-breezes can exercise no great influence 

 on the climate of the land. 



Our knowledge finally of the relative position of the 

 south polar regions with respect to the universal circu- 

 lation of the air on the globe and the influence this has 

 on its climate, is as yet purely hypothetical. Hann x 



1 An eminent Austrian astronomer and geographer. — The translator. 



