MID 



MICA SLATE. A transition slate, ' 

 full of bright specks of mica mixed 

 with quartz. 



MICROMETER. An instrument 

 afTixed to microscopes and telescopes 

 for measuring the size of objects. 



MICROPYLE. In botany, a small 

 hole over the apex of the nucleus of 



o cppH 



MICROSCOSMIC SALT. Phos- 

 phate of ammonia and soda, used in 

 blowpipe analysis. 



MICROSCOPE {horn fiiKpoc, small, 

 and oKo-eu, I view). An optical in- 

 strument which enables us to see and 

 examine objects which are too mi- 

 nute to be seen by the naked eye. 

 Microscopes are single or compound, 

 according to the nature of their con- 

 struction ; a single microscope being 

 one through which, whether it con- 

 sists of a single lens or a combina- 

 tion of lenses, the object is viewed 

 directly ; and a compound microscope 

 one in which two or more lenses are 

 so arranged that an enlarged image 

 of the object formed by one of them 

 is magnified by the second, or by the 

 others, if there are more than two, 

 and seen as if it were the object it- 

 self. A single microscope is no more 

 than a magnifying glass. 



MIDDEN. A dung heap. 



MIDDLE RAIL. The central rail 

 of the door, on which the lock is 

 placed. 



MIDRIB OF A LEAF. The cen- 

 tral collection of woody fibres and 

 vessels ; the prolongation of the leaf 

 stem. 



MIDRIFF. The diaphragm; the 

 muscle which divides the cavity of 

 the chest from the abdomen. 



Fig.l. 



MIL 



MIGNONETTE. Reseda odorata 

 An annual, but may become peren- 

 nial by keeping in a hot-house during 

 winter and prunmg. 



MIGRATORY. Of the habit of 

 migrating or moving with the season 

 to the north or south, as numerous 

 birds and fishes. 



MILDEW. This is a thin and whi- 

 tish coating with which the leaves 

 of vegetables are sometimes covered, 

 occasioning their decay and death, 

 and injuring the health of the plant. 

 It is frequently found on the leaves 

 of hop, pea, hazel, fruit-trees, and 

 the white and yellow dead-nettle ; it 

 is found also on wheat, in the shape 

 of a glutinous exudation, particularly 

 when the days are hot and the nights 

 without dew. J. Robertson {Hort. 

 Trans., v., 178) considers it as a mi- 

 nute fungus, of which different spe- 

 cies attack different plants. Sulphur 

 he has found to be a specific cure. 

 In cultivated crops mildew is said to 

 be prevented by manuring with soot ; 

 though by some this is denied, and 

 soot, by rendering the crop more lux- 

 uriant, is said to be an encourager of 

 mildew, the richest parts of a field 

 being always most infected by it. As 

 it is least common in airy situations, 

 thinning and ventilation may be con- 

 sidered as preventives. 



Liming, the use of salt, and saline 

 manures generally act as prevent- 

 atives. The varieties of mildew are 

 many, the Pucania graminis being 

 that" affecting wheat and grasses. 

 See Uredo. The effects of mildew and 

 bhght have sometimes been averted 

 by lighting fires to windward, so that 

 I the smoke swept over the field, and 



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