AIR AND LIFE. 191 



of the atmosphere, or at least its homogeneity. If the atmosphere 

 were motionless, the air in cities would be perpetually vitiated, and nil 

 the carbonic acid which originates there would be delayed in its travel 

 toward the country, the fields, and the forests, in whose biology it plays 

 so important a part; the vicinity of volcanoes, and even of cities, would 

 be uu in habitable, and life in cities impossible. 



Again, from a biological standpoint, the movements of the atmos- 

 phere are useful in another way. They prevent the air from remain- 

 ing excessively dry in some regions and inordinately damp in others. 

 The air which has accumulated a large amount of humidity while above 

 an ocean, a lake, a' river, a forest, does not remain there. It travels 

 farther, and carries the aqueous vapor it contains inland, up moun- 

 tains, and over plains. It transports the clouds, and carries the water 

 drawn from the Pacific Ocean to fall in rain on the American con- 

 tinent; through the same agency the water drawn from the Atlantic 

 falls on Europe, and the water of oceans is carried through the atmos- 

 phere to enormous distances to provide the continents with the rain 

 essential to plants, animals, and man, both that immediately used and 

 that which, sinking through the soil, comes to light again, sometimes at 

 considerable distances, under the form of springs, which help to make 

 the streams and rivers. If winds did not occur as they do, if the aerial 

 ocean were motionless, the vapors which arise'above the oceans and 

 masses of water would not travel so fast, so far, nor in such quantity, 

 and a great part of our globe would be condemned to drought and 

 sterility. The other part would hardly be pleasanter; in an atmosphere 

 saturated with vapor, as that would be, perspiration evaporates most 

 slowly, and if the temperature were even moderately high, man would 

 lead a sluggish life, shunning effort as inducing an uncomfortable con- 

 dition, and living in a laziness and/ar niente which have never conduced 

 to moral, mental, or physical advancement. Truly wind is no unimport- 

 ant agency in civilization and in the general evolution of mankind. 



Again, the movements of the atmosphere play an important part in 

 the regulation of temperature, as they do in the regulation of humidity. 

 If they did not occur, air would be i^erpetually warm in some x>laces 

 and perpetually cold in others, the radiation and diffusion of heat acting 

 but slowly. The wind is beneficent in that it carries warm air to cold 

 regions and cold air to warm ones, tempering the climate of each. 



To end this chapter, a word must be said of the part which wind 

 plays in the biology of many species of plants, by providing them with 

 important means of dispersion. Many plants possess light seeds, which 

 are, moreover, provided with appendages in the form of wings, or of 

 feathery hairs, and such seeds are very easily carried to considerable 

 distances over plains, over rivers, and even over narrow sea channels. 

 Through the wind's agency, these species are transported to new habi- 

 tats, where they may settle and thrive, spreading gradually over large 

 tracts. Numbers of insects and birds are thus carried to great distances 



