[Fr., from Gk. air, air; aein, to blow.] The gaseous fluid which we breathe and which surrounds the earth. It is a mixture of oxygen and nitrogen, with a small amount of carbon dioxide, the average proportions being, by volume: oxygen, 20.96 per cent.; nitrogen, 79.00 per cent.; carbon dioxide, 0.04 percent. (See Atmosphere; Compressed Air ; Liquid Air.)