﻿THE ATMOSPHEEB IK RELATION TO HUMAK LIFE AISTD 



HEALTH. 



By Francis Albert Eollo Eussell,* 



Vice-President of the Boyal Meteorological Society, Fellow of the Sanitary Institute of 

 Great Britain, Member of the Boyal Institution of Great Britain. 



[Memoir submitted in the Hodgkins Fund Prize competition of the Smithsonian Institution, and 

 awarded honorable mention with a silver medal.] 



Part I. — Constitution and Conditions of the Air. 



The atmosphere has been compared to a great ocean, at the bottom 

 of which we live. But the comparison gives no idea of the magnitude 

 of this ocean, without definite bounds, and varying incessantly in den- 

 sity and other important qualities from depth to height and from place 

 to place. 



Uninterrupted by emergent continents and islands, the atmosphere 

 freely spreads high above all mountains and flows ever in mighty cur- 

 rents at levels beyond the most elevated regions of the solid earth. 

 What is the composition of this encompassing fluid, and what its char- 

 acter? The work of the present century has gathered in a rich store 

 of knowledge to answer the inquiry. 



The atmosphere consists in the main of two gases, oxygen and nitro- 

 gen, and these are intimately mixed in the proportion of about 20.9 

 of oxygen to 79.1 of nitrogen by volume, and 23.1 of oxygen to 76.9 of 

 nitrogen by weight. ^ These gases, which are each of them chemical ele- 

 ments, are not chemically combined with one another, but only mixed,- 

 each preserves its qualities, modified only by solution in the other. 

 Gases have the property of diffusing among each other so completely, 

 that no portion which could be conveniently taken, however small, 

 would fail to represent the two gases in a proportion corresponding 

 with that which they maintain in the whole atmosphere. 



Another valuable constituent of the atmosphere, though varying 

 greatly in amount at different times and places, is of no less impor- 



' Author of "London Fogs," *' Epidemics, Plagues, and Fevers; their Causes and 

 Prevention," " The Spread of Influenza," *' Observations on Dew and Frosts," etc. 



^M. Leduc gives the weights as follows: Oxygen, 23.58; nitrogen, 76.42. Dumas 

 and Boussingault give the density of nitrogen as 0.09725. (Comptes Rendus, 1890.) 



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