AIR 



ALA 



called the American agone, is in the 

 western hemisphere ; the other, or Asia- 

 tic, is in the eastern hemisphere. They 

 extend from south to north, but they do 

 not coincide with the meridians ; for they 

 both, especially the Asiatic, intersect the 

 latter lines under different angles. See 

 Isogonic lines. 



AIR (ci>7p, aer). The general designa- 

 tion of a gas, or permanently elastic 

 fluid. Ethereal air, or ether, is an ima- 

 ginary fluid, supposed to fill all space 

 beyond the atmospheres of the earth and 

 other planets. Atmospheric air is the 

 gaseous fluid which surrounds the earth, 

 consisting, when pure, of 20 parts of 

 oxygen, and 80 of nitrogen, with a por- 

 tion of carbonic acid, varying from 3 to 8 

 parts in 10,000 by weight. Air which is 

 expanded, or rendered less dense than 

 usual, is said to be rarefied; that which 

 has been subjected to pressure, is said to 

 be condensed. 



AIR-CELLS. A term applied to cavi- 

 ties in the stems and leaves of plants, 

 which, being filled with air, enable the 

 plants to float in water ; also to mem- 

 branous receptacles in birds, by means of 

 which their bodies, being permeated by 

 the atmospheric air, are adapted for 

 flight. 



AIR-GUN. An instrument for pro- 

 jecting bullets, resembling a common 

 gun, with the addition of a hollow ball 

 or reservoir, into which air is introduced 

 and condensed by means of a syringe. 

 The effects of the apparatus depend on 

 the elasticity and compression of the 

 air. 



AIR-PLANTS. Plants which grow 

 without having their roo^s within the 

 earth. It was supposed that they were 

 nourished by the air ; but their locality 

 in a damp atmosphere, or in contact with 

 other vegetables, rather suggests the 

 usual mode of existence There are 

 two tribes of air-plants, viz., the Brome- 

 liacece and the Orchidacece. 



AIR-PUMP. An exhausting syringe, 

 or pneumatic apparatus for rarefying the 

 atmospheric air and reducing it to any 

 required degree of tenuity, and at the 

 same time exhibiting the circumstances 

 which attend this change of condition as 

 displayed in other bodies. 



AIR-TIGHT. That degree of close- 

 ness, in any vessel or tube, which pre- 

 vents the passage of air. 



AIR-VESSEL. A vessel in which air 

 is condensed by pressure, for the pur- 

 pose of employing the reaction of its 

 13 



elasticity as a moving or a regulating 

 power. The term has also been applied 

 to the spiral vessels of plants and to the 

 trachea of insects. 



A'LA. The Latin term for a wing. 

 In Ornithology, it denotes the pectoral 

 extremity, the bones of which support 

 broad folds of skin, covered with feathers, 

 and adapted for flight. In Botany, it is 

 the lateral petal of a papilionaceous 

 corolla. 



A'LABASTER {dXd^aarTpov, a calca- 

 reous spar). A stone usually white, re- 

 sembling marble, but soft enough to be 

 scratched by iron. The term is said to 

 be derived from Alabastron, a town of 

 Egypt. 1. Gypseous alabaster is a natural 

 semi-crystalline sulphate of lime, forming 

 a compact gypsum of various colours, 

 and employed for making statues and 

 vases. 2. Calcareous alabaster is a car- 

 bnnale of lime, deposited by the dripping 

 of water in stalactitic caves, and fre- 

 quently found as a yellowish-white de- 

 posit in certain fountains. The oriental 

 alabaster is of this kind. 



A'LALITE. Another name for diop' 

 side or mussite, a sub-species of oblique- 

 edged augite. It is found at Piedmont, in 

 the black rock at Musa, near Ali, in veins, 

 along with epidote or pistacite, and hya- 

 cinth-red garnets. 



ALA'NGIA'CEiE. An order of Dico- 

 tyledonous plants, named ixoxn Alangium, 

 tlie Malabar name of one of the genera. 

 Large trees, with leaves alternate ; petals 

 5-10; stamens 2A times as numerous as 

 the petals; fruit drupaceous, esculent; 

 seeds album.inous, fleshy, pendulous. 



A'LANTINE. An amylaceous sub- 

 stance, procured from the root of the 

 Angelica Archangelica, an umbelliferous 

 plant. 



ALASMODO'NTINiE. A sub-family 

 of the Unionidce, unios, or river mussels, 

 named from the genus alasmodon. 



ALA'TE {ala, a wing). Winged ; a 

 term applied to any body, as a stem or 

 seed of a plant, which is bordered by a 

 leafy or membranous expansion resem- 

 bling a wing. 



ALAU'DINiE (alauda, a lark). Alau- 

 dine birds, or larks ; a family of the 

 Cantatrices of Macgillivray, intimately 

 allied to the Wagtails on the one hand, 

 and to the Thrushes on the other. They 

 do not belong, according to this author, 

 to the Conirostral or Thick-billed birds, 

 as generally supposed ; for their bill i'a 

 differently formed, and they never shell 

 or husk seeds, but swallow them entire. 



