XXU SUMMARY OF THE CONTENTS. 



cultivated plants, going down from the vanilla, cacoa, and musaceee, to 

 citrons and olives, and to vines yielding potable wines. The influence 

 which these scales exercise on the geographical distribution of culti- 

 vated plants. The favorable ripening and the immaturity of fruits are 

 essentially influenced by the difierence in the action of direct or scat- 

 tered light in a clear sky or in one overcast with mist. General sum- 

 mary of the causes which yield a more genial climate to the greater 

 portion of Europe considered as the western peninsula of Asia — ^p. 326. 

 Determination of the changes in the mean annual and summer temper- 

 ature, which correspond to one degree of geographical latitude. Equal- 

 ity of the mean temperature of a mountain station, and of the polar dis- 

 tance of any point lying at the level of the sea. Decrease of tempera- 

 ture with the decrease in elevation. Limits of perpetual snow, and the 

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

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

 itability of the elevated plateaux of Thibet — p. 331. Quantity of moist- 

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

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

 atmosphere observed in Northern Asia, between the river districts of 

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

 of rain — p. 335. Electricity of the atmosphere, and disturbance of the 

 electric tension. Geographical distribution of storms. Predetefmina 

 tion of atmospheric changes. The most important climatic disturbances 

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

 rather the consequence of some occurrence by which the equihbrium 

 in the atmospheric currents has been destroyed at some considerable 

 distance— p. 335-339. 



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 diSusion 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 — p. 339-346. Geog- 

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

 by means of organs capable of spontaneous motion. Spheres of distri- 

 bution 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. Investigations into the numerical relation existing in difierent 

 districts of the earth between each one of the large families to the 

 whole mass of phanerogamia — p. 346-351. The human race considered 

 according to its physical gradations, and the geographical distribution 

 of its simultaneously 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 histoiy of mental activity, manifest a character of nation- 

 ality, although certain historical occurrences have been the means of 

 difflising idioms of the same family of languages among nations of wholly 

 different descent — p. 351-359. 



