MAC 



MAG 



Gsertner terms these embryos pseudo- 

 monocotyledonous, 



MA'CROCOSM (juaKpof, large, koitixo^, 

 the world). A term employed as synony- 

 mous with universe; while microcosm 

 has been used by some philosophers as 

 a designation of man. 



MACRODA'CTYLES (/iaKpoc, large, 

 daKTuXof, a finger or toe). A tribe of the 

 Grallatores, or wading birds, charac- 

 terized by the extreme length of their 

 feet. 



MACRO'PODAL {fxaKp6<!, large, ttous, 

 7ro369, a foot). Large-footed; a term 

 applied by Richard to a modification of 

 the monocotyledonous embryo, in which 

 the radicle presents an unusual protu- 

 berance, as in wheat. 



MACROPO'DIANS (/uaKpo?, large, 

 TToSf, TTodof, a foot). A tribe of brachyu- 

 rous decapod crustaceans, remarkable for 

 the enormous length of their feet, which 

 has procured for them the name of sea- 

 spiders. 



MACROTRA'CHIA. A tribe of bi- 

 valved mollusca, in which the mantle of 

 the animal is so united and prolonged as 

 to form one or two long siphons or tubes, 

 by which the food is imbibed. 



MACROU'RA ifiaKpoi, large, ovpa, a 

 tail). A family of decapod Crustacea, 

 distinguished by the large size of the tail, 

 as in the common lobster. 



MA'CULiE {macula, a spot). Dark 

 spots frequently seen on the disc of the 

 sun. They change their appearance as 

 the sun revolves on his axis, and appear 

 greater or less to an observer on the 

 earth, as they are turned to or from him. 

 One of these was estimated to be more 

 than six times the size of our earth. 



MA'DREPORE. A genus of corals ; 

 but the term is generally applied to all 

 the corals distinguished by superficial 

 star-shaped cavities. In zoological lan- 

 guage, the madrepores are compound 

 polyps, the common body of which se- 

 cretes calcareous matter on its exterior 

 in arborescent masses, presenting upon 

 their surface multitudes of cells, in each 

 of which, when alive, a polyp existed. 



MA'DREPORITE. Anthraconite. Co- 

 lumnar carbonate of lime, found in Nor- 

 way in transition rocks, in Greenland, &c. 



MAGDEBURG HEMISPHERES. An 

 apparatus for exhibiting the force of the 

 atmospheric pressure. Two hollow me- 

 tallic hemispheres, whose edges fit accu- 

 rately, are placed on each other, and the 

 air is exhausted. Supposing the super- 

 ficial content to be 100 square inches, and 

 205. 



the height of the mercury to be 30 inches, 

 the pressure exerted on the hemispheres 

 will amount to 1475 lbs., and it will re- 

 quire the force of two horses to pull them 

 asunder. 



MAGELLA'NIC CLOUDS. The name 

 of three nebulae in the southern hemi- 

 sphere, two of them about 12° or 13° 

 from the south pole, the third more dis- 

 tant. They were first recorded by the 

 navigator Magellan. 



MAGIC LANTERN. The magic lan- 

 tern is a microscope, on the same prin- 

 ciple as the solar microscope. But in- 

 stead of being used to magnify natural 

 objects, it is commonly employed for 

 amusement, by the casting of shadows 

 of small transparent paintings, done on 

 glass, upon a screen placed at a proper 

 distance. 



MAGIC SQUARE. A series of num- 

 bers in arithmetical progression, so ar- 

 ranged in a square order, that the vertical, 

 horizontal, and diagonal columns give 

 the same sura. Thus : 



MA'GISTERY [magister, a master). 

 A masterly preparation, formerly applied, 

 in Chemistry, to all precipitates, but now 

 restricted to a few substances, as the 

 magistery, or subnitrate, of bismuth^ a 

 brilliant white powder of pearly lustre, 

 composed of microscopic crystalline 

 grains ; the magistery of silver, the alche- 

 mical name of the nitrate ; &c. 



MAGNE'SIA. An alkaline earth, 

 having a metallic base, called magnesium. 

 It has been found native, in the state of 

 a hydrate. The term magnesia was ori- 

 ginally applied to any substance which 

 had the property of attracting some prin- 

 ciple from the air. 



MAGNESIAN LIMESTONE. An 

 extensive series of beds, lying imme- 

 diately above the Coal Measures, and so 

 named from the presence of a large quan- 

 tity of magnesia in the limestone. It 

 contains fossils, and among them a few 

 corals and shells. 



MAGNE'SITE. Carbonate of mag- 

 nesia; a white, hard, compact mineral, 

 found in Moravia, in serpentine rocks. 



MAGNE'SIUM. A metallic substance, 

 resembling silver, fusing at a red heat, 

 and then, on burning in air or oxygen, 



