Microscopes vary much in price, from 5s. to upwards of £100. A good serviceable dissecting simple microscope may be had from any philosophical-instrument maker for from 9s. to 15s. Compound microscopes are more expensive, but a wonderfully good instrument for beginners can be had at 30s. It has one eye-glass and three object-glasses, and magnifies from 70 to 200 diameters. If a superior instrument is wished-one suited for most purposes of observation and research-any one of the following will be found well worth the price: The microscope of Hartnack, with a joint, so that it may be inclined at any angle, has two eye-pieces, two object-glasses, magnifies from 50 to 450 diameters, and costs about £7; Nachet's microscope has three eye-pieces, three objectglasses, magnifies from 50 to 750 diameters, and costs £10; Smith and Beck's educational microscope has two eye-pieces, two object-glasses, magnifies from 50 to 350 diameters, and costs £10; Ross supplies microscopes from £5 to £100, with various number of glasses.

For a more complete account of the different kinds of microscopes, and the various purposes to which they are applied, see Quekett On the Microscope (1855); Carpenter On the Microscope (1862); Hogg On the Microscope (1855); and How to work with the Micro scope (1864), by Beale.

MICROSCOPIC ANIMALS. See ANIMALCULE.

MICROTASIMETER, an instrument invented by Mr. Thomas A. Edison for the purpose of measuring very minute variations of pressure caused by the expansion or contraction of any given body, from whatever causes, heat, moisture, etc. A part of the apparatus is constructed upon the principle of the pyrometer, and when the expansion is caused by moisture, upon that of some forms of hygrometer. But the novel and unique part of the invention consists in the effect which the pressure of the expanding rod has upon the electric resistance of a piece of carbon placed in the circuit of a gal vanic battery. A rod of vulcanite is used as the expanding element when it is desired to use the instrument to ascertain slight variations in the heat vibrations coming from any object, as the sun, or a gas, or electric light. This rod is adjusted in a strong frame kept at an equable temperature, so that no expansions or contractions shall exert any influence, except those which take place in the vulcanite rod itself. In the chamber which receives one end of this rod, or plate, there is placed under a follower, or slide, a piece of carbon, which becomes compressed with great force upon the expansion of the vulcanite rod. If radiant heat is to be measured, a large funnel is placed in front of the apparatus to gather the rays and throw them upon the rod or plate. When the rays increase in intensity the rod expands, compresses the button, and changes its conducting capacity, which at every moment is indicated by a galvanometer. The instrument has been used successfully to ascertain the variations in the radiation from the sun during an eclipse. It may also be used to note the variations taking place on a day when clouds are passing across the sun's disk, or when the transmission of his rays differs from increase or decrease of moisture. It may be used as a delicate hygrometer by substituting in place of the vulcanite rod a body containing gelatine, which expands under the influence of moisture.

MICROZA MIA, a genus of plants of the natural order cycadacea. They are widely diffused over Australia. The fronds resemble those of palms, and are used in the Roman Catholic church on Palm Sunday. The underground stem is large and turnip-like, but covered with scales or leaf-scars, and contains a substance resembling tragacanth. The nuts of M. spiralis are edible, but are only used in times of scarcity.

MIDAS, a genus of platyrhine monkeys belonging to the family hapalidæ, which also contains the marmosets. The common name for the different species is tamarin. It has the following characters: Muzzle short, facial angle 60°; forehead with an appearance of prominence, arising from the great angle of the upper edge of the orbits; upper incisors contiguous, under incisors of the same size as upper; nails like claws, excepting those of the thumbs behind; tail the same as in the marmoset, or jacchus of Geoffroy, and dental formula the same, except that in the latter the incisors are more irregular. There are seven species, the typical one being midas rosalia, the marakina or silky tamarin. This very beautiful little monkey is of a golden yellow color, varying to a redder tint, rather paler on the back and thighs. The long and silky hair about the head and neck forms a kind of mane, on account of which it has sometimes been called the lion-monkey. Its beauty and gentleness render it a great pet; but it is delicate, and requires to be kept warm and dry. It is squirrel-like in its habits, a native of Guayana and the south of Brazil, from Rio Janeiro to cape Frio. There is a black and red variety, and one of a bright, shining red. The species should not be confounded with M. leonina of Humboldt, which is probably the smallest monkey known. It is brownish, and has a well-developed mane of that color which bristles up when the animal is angry so as to look like a little lion. It has a black face, a white mouth, and a tail black above and white below. It inhabits the plains bordering on the eastern slope of the Cordilleras, and is rare.

MIDAS, a common name of the more ancient Phrygian kings, of whom Midas, the son of Gordius and Cybele, is the most famous. He was a pupil of Orpheus. Among the many legends regarding him is one that Bacchus granted his wish that whatever

actites. 5. Quartz-crystals. 6. Cluster of crystals. Formations: 7. Tree-formed sulphate of iron). dar (pea-stone). 13. Kidney-shaped (hematite). 14. Meteoric iron. 15. Coral-formed (aragonite).