COMPOSITION OF THE AIR. 221 



suddenly lost the stratum of air that surrounds it and ceased to respire 

 the regular breath of the winds. 



The subtle and transparent air is composed of the same gases which 

 are found in greater abundance in the opaque and solid crust of our 

 globe. The four principal elements of all vegetable or animal organ- 

 ism, oxygen, nitrogen, hydrogen, and carbon, are found likewise in 

 the atmosphere. The two first as constituent elements of the air, the 

 third united with oxygen under the form of watery vapour, and 

 the fourth mixed with the breath expired by animals, and with many 

 other gases resulting from the decomposition of organic matter. Be- 

 tween the action of nature and the eternal movement of the atmo- 

 sphere an exchange is constantly being effected, by which the gases, 

 one instant in the animal, plant, or rock, fixed in an organism or in 

 the terrestrial strata, are disengaged and recompose the atmosphere. 



Animals and plants would soon be all destroyed, for want of neces- 

 s'dYj aliment, if the mixture of vapours and gas were not effected by 

 the incessant movement of the aerial masses. Men and animals would 

 gradually kill themselves by absorbing again the carbonic acid al- 

 ready expelled from their lungs ; and plants plunged in an atmo- 

 sphere too full of oxygen emanating from their leaves would end too 

 by d3dng. Happily, the currents of air, which pass in immense spirals 

 over the surface of the earth, uniformly mix all the gases they carry 

 away with them, and thus favour life over their whole course. To 

 the temperate regions, which are principally the domain of man, 

 they bring the oxygen which the immense forests of the tropical 

 zone have exhaled ; to these same forests they impart the carbon 

 which is life to trees, and would be the death of man. Still more, 

 they animate the globe itself, by carrying immense quantities of 

 vapour to the mountains where the net- work of springs is elabor- 

 ated, and in causing to circulate above the sea a dry air eager to 

 absorb the water which evaporates from its surface. Like the heart 

 in living organisms, the productive zone of the atmospheric currents 

 occupies the central region in the ocean of air, and moves alternately 

 to the north and south. It is thus that a movement of systole and 

 diastole is produced in all the aerial mass, impressing the initiatory 

 speed to the arterial currents which carry fertility to all points of the 

 planet. 



Every particle of gas passes thus continually from life to life, and 

 escapes from death to death ; by turns, wind, wave, earth, animal, or 

 flower, despite its smallness, is the symbol of infinite motion. The air 

 is an inexhaustible source whence all that lives, draws its existence, 



