"The Schools teach the air to be a warm and moist element, and consequently a simple and homohenous body. Many modern philosophers have, indeed, justly given up this elementary purity in the air, yet few seem to think it a body so greatly compounded as it really appears to be. The atmosphere, they allow, is not absolutely pure, but with them it differs from true and simple air only as turbid water from clear. Our atmosphere, in my opinion, consists not wholly of purer aether, or subtile matter which is diffused thro' the universe, but in great number of numberless exhalations of the terraqueous globe; and the various materials that go to compose it, with perhaps some substantial emenations from the celestial bodies, make up together, not a bare indetermined feculency, but a confused aggregate of different effluvia. One principal sort of these effluvia in the atmopshere I take to be saline, which float variously among the rest in that vast ocean; for they seem not to be equally mixed therin, but are to be found of different kinds, in different quantities and places, in different seasons.... Many men talk much of a volatile nitre in the air, as the only salt wherewith that fluid is impregnated. I must own
