MAN 



MAR 



MANU'RES. Animal, vegetable, or 

 mineral matters, deposited in the soil, to 

 accelerate vegetation and increase the 

 production of crops. 



MAP {mappa, a napkin). A repre- 

 sentation, upon a plane, of some portion 

 of the surface of a sphere, on which are 

 traced the particulars intended to be ex- 

 pressed, whether they be continuous out- 

 lines or points. The projections chiefly 

 used in maps are the orthographic, the 

 stereographic, and Mercator's. See Pro- 

 jection. 



MARBLE. A term applied to every 

 limestone which is finely coloured and 

 capable of receiving a high polish, or of 

 being worked into statuary; the pure 

 "White crystalline kinds being those em- 

 ployed for the latter purpose. Forest 

 marble is a coarse laminated shelly oolite, 

 interposed between beds of clay, sand, 

 and grit. 



MARCEL'S BLOWPIPE. An appa- 

 ratus for increasing temperature, by urg- 

 ing the flame of an alcohol lamp by a 

 blowpipe supplied with oxygen gas. 



MA'RGARIC ACID (fxapyapl^, a 

 pearl). An acid obtained from human 

 fat and vegetable flxed oils, and also 

 produced by the dry distillation of ox 

 and mutton suet, and of stearic acid. Its 

 name is derived from its pearly lustre. 



MA'RGARIN. Margarate of glyceryl ; 

 a i)eculiar fatty matter contained in vege- 

 table oils and animal fats. 



MA'RGARITE. A greyish-white mine- 

 ral, resembling silvery mica. 



MARGARI'TIC ACID. One of the 

 fatty acids produced by the saponifica- 

 tion of castor oil. The other acids ob- 

 tained by this process are the ricinic and 

 the elceodic. 



MA'RGARONE. A solid white fatty 

 matter, crystallizing in pearly scales, ob- 

 tained by dry distillation of margaric 

 acid. 



MARGINELLI'NiE. Date-shells; an 

 aberrant sub-family of the Volutidce, or 

 volutes, named from the typical genus 

 marginella, having plaits upon the pillar, 

 and crenated teeth on the thickened 

 outer lip; the foot very large, but the 

 mantle not lobed nor reflected. 



MARINE ACID. Spirit of salt. Mu- 

 riatic or hydrochloric acid, procured from 

 common salt by distilling it with sul- 

 phuric acid and water over a water-bath 



MARINE CONGLOMERATES. De 



posits formed by sand thrown by the sea 



upon its shores, mixed with remains of 



shells and corals, which are agglutinated 



210 



by a calcareous cement, finally acquiring 

 a tolerably firm consistence. Rocks of 

 this kind are daily forming on the shores 

 of Sicily, and are very abundant in the 

 West Indies. 



MARINER'S COMPASS. An instru- 

 ment consisting of a small magnetic bar, 

 called a needle, poised on its centre of 

 gravity, so as to be enabled to turn 

 readilyevery wayin a horizontal direction. 

 After a few vibrating motions, during 

 which it is said to traverse, the needle 

 takes its direction nearly north and south, 

 which direction is said to be in the plane 

 of the magnetic meridian of the place 

 where the compass happens to be. 



Compass variation. A term expressive 

 of the angle, which the magnetic meri- 

 dian is east or west from the geogra- 

 phical, or true north and south. It varies 

 in different places and at different timesr. 

 MARIOTTE'S LAW. Boyle and Ma- 

 riotte experimentally investigated the 

 ratio subsisting between the density of 

 the air, its elasticity, and the space it 

 occupies, when the following law was 

 detected : — that the density and elasticity 

 of atmospheric air are directly, but the 

 space it occupies is inversely, as the force 

 of compression. 



MA'RKAB. A star of the second 

 magnitude in the northern constellation 

 Pegasus. 



MARL. An argillaceous rock, con- 

 sisting of clay mixed with lime ; soft, 

 friable, but not forming a tenacious paste 

 with water; it is grey, yellow, green, 

 blue, or red. The variegated marls, or 

 keuper, are red, greenish-grey, and 

 bluish, and contain subordinate beds of 

 sandstone and dolomite, deposits of 

 brown coal, masses of gypsum, and salt. 

 These marls are covered with a white 

 quartz sandstone, which connects them 

 with the lias. 



MARLSTONE. A constituent of the 

 lias formation, consisting of arenaceous 

 and calcareous layers, with nodules of 

 ironstone. This rock is well developed 

 in Yorkshire and Leicestershire. 



MA'RMOLITE. A variety of serpen- 

 tine, found at Hoboken, in New Jersey. 



MARS. ^ The planet which imme- 

 diately follows our earth in respect of 

 distance from the sun, from which he is 

 separated by 146 millions of miles. His 

 diameter appears to be sometimes 18", 

 sometimes 19". He revolves on his axis 

 in 24*', 31' 22", and completes his orbit 

 round the sun in 686^, 23^, 30' 41", 4. 

 MARSH'S APPARATUS. An appa- 



