MIC 



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MIC 



millionth part of an inch. Mica is 

 easily scratched with a knife, and, 

 commonly, even by the finger-nail. 

 Its surface is smooth to the touch ; 

 its powder is dull, usually grayish, 

 and feels soft. Its colours are 

 silver- white, gray, green, brown, 

 reddish, and black, or nearly black. 

 Specific gravity from 2 '50 to 2 '90. 

 "When rubbed on sealing-wax, it 

 communicates to the wax negative 

 electricity. Before the blow-pipe, 

 it fuses into a grey or black enamel. 

 Its constituents parts are, according 

 to Klaproth, silex 48*0, alumine 

 34-20, potash 8'75, oxide of iron 

 4'5, oxide of manganese 0'5. Ac- 

 cording to others, it is a compound 

 of silicium, potassium, magnesium, 

 calcium, &c., combined with oxy- 

 gen. Mica is one of the component 

 parts of granite, gneiss, and mica- 

 slate ; it occurs also in syenite, 

 porphyry, and other primary rocks. 

 To quartz and limestone it fre- 

 quently communicates a slaty 

 texture. It may always be dis- 

 tinguished from talc by the elasti- 

 city of its plates, talc being only 

 flexible and not elastic ; in its want 

 of unctuosity, and by its communi- 

 cating negative electricity to seal- 

 ing-wax. There are several varie- 

 ties, or sub-species; Jameson enu- 

 merates ten. Mica has been 

 employed, instead of glass, in the 

 windows of dwelling-houses. In 

 lanterns it is superior to horn, 

 being more transparent, and not so 

 easily injured by the flame. Mica 

 is a doubly refracting substance, 

 with two optic axes, along which, 

 light is refracted in one pencil. 

 MICA'CEOUS IKON OEE. A variety of 

 oxide of iron. This occurs generally 

 in amorphous masses, composed of 

 thin six-sided laminae. Colour 

 iron-black, or steel-grey. Lustre 

 metallic. Opaque. Feel greasy. 

 Hardness 5 to 7. Specific gravity 

 from 4'5 to 5'7. It is said to yield 

 nearly 70 per cent, of iron. 



MI'CA SCHIST. | A metamorphic rock, 



MI'CA SLATE, j composed of mica 

 and quartz ; it passes by insensible 

 gradations into clay-slate, and its 

 texture is slaty. Sometimes the 

 mica and quartz alternate, though 

 commonly they are more or less 

 intimately mingled, the mica 

 usually predominating. 



MI'CAKELLE. The Finite of Kirwan. 

 See Finite. 



MICROCHO'NCHAS CARBON A'RIUS. A mi- 

 croscopic spiral shell with but few 

 volutions, which when young touch 

 one another, but when old are 

 extended into a free tube, resem- 

 bling vermetus or vermillia. The 

 shell is sinistral. The lines of 

 growth are strong, somewhat irreg- 

 ular, deficient in parallelism, and 

 oblique to the axis of the tube. 

 Spiral striae may be perceived, 

 though but faintly. The Microchon- 

 chas Carbonarius is a fossil shell of 

 the coal measures. 



MfcROpYLE. (from juicpos, small, 

 and 77-vXos, gate, Gr.) A botanical 

 term for the foramen in the perfect 

 seed ; this foramen is often visible, 

 as in the pea and bean. 



MI'CROSCOPE. (from ytu/c/>o?, small, 

 and ffKOTrew, to behold, Gr. micro- 

 scope, Fr. microscopic, It.) A mi- 

 croscope is an optical instrument for 

 examining and magnifying minute 

 objects. Jansen and Drebell are 

 supposed to have separately in- 

 vented the single microscope, and 

 Fontana and Galileo seem to have 

 been the first who constructed the 

 instrument in its compound form. 

 The single microscope is nothing 

 more than a lens or sphere of any 

 transparent substance, in the focus 

 of which minute objects are placed. 

 The best single microscopes are 

 minute lenses ground and polished 

 on a concave tool ; but as the per- 

 fect execution of these requires 

 considerable skill, small spheres 

 have often been constructed as a 

 substitute. The most perfect single 



