Air-engine

(-in'jin.) (Engin.) A machine somewhat analogous to the steam-engine, in which heated air is the motive power, united by the vapor of water. The advantages of such a machine would be, freedom from the danger of explosion, absence of a boiler and the nece ity for water, and a more economical expenditure of heat. But, in practice, it is complicated, and has not been found to answer, particularly on a large scale. Air'-gun, an instrument for projecting bullets or other mi iles, the moving power being the elastic force of condensed air, some of which is liberated at each discharge of the trigger. [s. 14] Air -plant. (Bot.) A name given to plant Air -plant. (Bot.) A name given to plants of any kind which grow without their roots penetrating the earth, all the materials required for their growth being derived from the atmosphere. The Orchid aceæ of warm climates are examples. [s. 14] Air -pump. (Phy.) A pneumatic machine fo Air -pump. (Phy.) A pneumatic machine for removing the air from a ve el. Its operation depends on the elasticity of the air: for, by working the pump, the air in the receiver (E, Fig. 14) will expand itself; by which means part of it will be forced by the opening C into the cylinders PP, from which it escapes into the atmosphere by means of properly constructed valves. By thus continuing to work the pump, the air in the re-| ce iver will be gradually exhausted; but can never be wholly drawn out, so as to leave a perfect vacuum within the ve el; for it must be considered, that the air which is exhausted, is only pushed out by the spring of that which remains behind. In practice the machine will E cease to act when the air is so rarefied as to be unable by its elasticity to open the valves; though they are of extreme lightne , being generally formed of oiled silk. (Steam - engine.) A pump worked by the en-Fig. 14.-AIR-PUMP. gine for removing the air disengaged from the cold water in the condenser, and the water thus collects at the bottom of that ve el. Air'- threads. (Nat. Hist) See GOSSAMER. [s. 14] Air - ve els. (Comp. Anat.) In insects Air - ve els. (Comp. Anat.) In insects, the atmospheric air is conveyed through all parts of the body, for the purposes of respiration, chiefly by means of air ve els or tr acheæ. [s. 15] IMG:plate0032.jpg:Gravür