CLIMATOLOGY. 327 



valleys, or according to the effects of the hypsometrical rela- 

 tions on their own summits, which often spread into elevated 

 plateaux. The division of mountains into chains separates 

 the earth's surface into different basins, which are often nar 

 row and walled in, forming caldron-like valleys, and (as in 

 Greece and in part of Asia Minor) constitute an individual 

 local climate with respect to heat, moisture, transparency of 

 atmosphere, and frequency of winds and storms. These cir- 

 cumstances have at all times exercised a powerful influence 

 on the character and cultivation of natural products, and on 

 the manners and institutions of neighboring nations, and even 

 on the feelings with which they regard one another. This 

 character of geographical individuality attains its maximum, 

 if we may be allowed so to speak, in countries where the dif 

 ferences in the configuration of the soil are the greatest possi- 

 ble, either in a vertical or horizontal direction, both in relief 

 * and in the articulation of the continent. The greatest con- 

 trast to these varieties in the relations of the surface of the 

 earth are manifested in the Steppes of Northern Asia, the 

 grassy plains (savannahs, llanos, and pampas) of the New 

 Continent, the heaths (Ericeta) of Europe, and the sandy and 

 Btony deserts of Africa. 



The law of the decrease of heat with the increase of eleva- 

 tion at different latitudes is one of the most important subjects 

 involved in the study of meteorological processes, of the geog- 

 raphy of plants, of the theory of terrestrial refraction, and of 

 the various hypotheses that relate to the determination of the 

 height of the atmosphere. In the many mountain journeys 

 which I have undertaken, both within and without the trop- 

 ics, the investigation of this law has always formed a special 

 object of ray researches.* 



Since we have acquired a more accurate knowledge of the 

 true relations of the distribution of heat on the surface of the 

 earth, that is to say, of the inflections of isothermal and isoth- 

 eral lines, and their unequal distance apart in the different 

 eastern and western systems of temperature in Asia, Central 

 Europe, and North America, we can no longer ask the gen- 

 eral question, what fraction of the mean annual or summer 

 temperature corresponds to the difference of one degree of 

 geographical latitude, taken in the same meridian ? In each 

 system of isothermal lines of equal curvature there reigns a 



* Humboldt, Recueil d'' Observations Astronomiqnes, t. i., p. 126-140; 

 Relation Hislorique, t. i., p. 119, 141 227; Biot, in Connaissance de» 

 Temps pour Van 1841, p. 90-109. 



