ATMOSPHERE

gaseous envelope surrounding a heavenly body, in the earth po ibly to height of 200 miles; air pre ure at sea-level, or at 760 mm. of mercurial barometer, 14.7 Ib. per sa. inch. Air is a mixture, not a compound, averaging 77.12% nitrogen, 20.66% oxygen, c. 1.4% aqueous vapor, c. 0.79% argon, 0.03% carbon dioxide, and traces of hydrogen, krypton, neon, xenon, and helium, besides dust.