SUMMAKY. ix] 



clear sky, or in one overcast with mist. General summary of the causes 

 which yield a more genial climate to the greater portion of Europe 

 considered as the western peninsula of Asia p. 333. Determination 

 of the changes in the mean annual and summer temperature, which 

 correspond to one degree of geographical latitude. Equality of the 

 mean temperature of a mountain station, and of the polar distance of 

 any point lying at the level of the sea. Decrease of temperature with 

 the decrease in elevation. Limits of perpetual snow, and the fluctua- 

 tions in these limits. Causes of disturbance in the regularity of the 

 phenomenon. Northern and southern chains of the Himalaya ; habita- 

 bility of the elevated plateaux of Thibet p. 338. Quantity of moisture 

 in the atmosphere according to the hours of the day, the seasons of the 

 year, degrees of latitude, and elevation. Greatest dryness of the atmo- 

 sphere observed in Northern Asia between the river districts of the 

 Irtysch and the Obi. Dew, a consequence of radiation. Quantity of 

 rain p. 342. Electricity of the atmosphere, and disturbance of the 

 electric tension. Geographical distribution of storms. Predetermina- 

 tion of atmospheric changes. The most important climatic disturbances 

 cannot be traced at the place of observation to any local cause, but are 

 rather the consequence of some occurrence by which the equilibrium in the 

 atmospheric currents has been destroyed at some considerable distance. 

 i. Physical geography is not limited to elementary inorganic terres- 

 trial life, but, elevated to a higher point of view, it embraces the sphere 

 of organic life, and the numerous gradations of its typical development. 

 Animal and vegetable life. General diffusion of life in the sea and on 

 the land ; microscopic vital forms discovered in the polar ice no less than 

 in the depths of the ocean within the tropics. Extension imparted to the 

 horizon of life by Ehrenberg's discoveries. Estimation of the mass 

 (volume) of animal and vegetable organisms pp. 347-356. Geography 

 of plants and animals. Migrations of organisms in the ovum, or by 

 means of organs capable of spontaneous motion. Spheres of distribution 

 depending on climatic relations. Regions of vegetation, and classification 

 of the genera of animals. Isolated and social living plants and animals. 

 The character of floras and faunas is not determined so much by the 

 predominance of separate families in certain parallels of latitude as by 

 the highly complicated relations of the association of many families, and 

 the relative numerical value of their species. The forms of natural 

 families which increase or decrease from the equator to the poles. Inves- 

 tigations into the numerical relation existing in different districts of the 

 earth between each one of the large families to the whole mass of phane- 

 rogamia pp. 356-560. The human race considered according to its 

 physical gradations, and the geographical distribution of its simultane- 

 ously occurring types. Races and varieties. All races of men are forms 

 of one single species. Unity of the human race. Languages considered 

 as the intellectual creations of mankind, or as portions of the history of 

 mental activity manifest a character of nationality, although certain his- 

 torical occurrences have been the means of diffusing idioms of the 

 same family of languages amongst nations of wholly different descent 

 pp. 360-369. 



