AIR-Trunk, the name of a contrivance by Dr Hales, to prevent the stagnation of putrid effluvia in jails and other places, where a great number of people are crowded together in a small space. It consists only of a long square trunk open at both ends, one of which is inserted into the ceiling of the room, the air of which is required to be kept pure, and the other extends a good way beyond the roof. Through this trunk a continued circulation is carried on; and the reason is, that the putrid effluvia which do so much mischief when collected, being much lighter than the pure atmosphere, arise to the top of the room, and, if they there find a vent, will continually go out through it. These effluvia arise in very considerable quantity, being calculated by Dr Keil at no less than 39 ounces from one man in 24 hours.

AIR-Vessels are spiral ducts in the leaves, &c. of plants, supposed to be analogous to the lungs of animals, in supplying the different parts of a plant with air.