Page:The New International Encyclopædia 1st ed. v. 13.djvu/499

MICROMETER. 451 MICROSCOPE. reading is inacU', and the difference of tlic two reailin^s gives the distanec between the points upon the image. By phicing a known scale, for example a tenth of a millimeter, upon the stage iif the mierosoopc, and measuring the image as ahove. the magnifying power of the microscope objective is obtained, and it is possible to cal- culate what distance upon the stage, or in the object, corresponds to one revolution of the mi- crometer screw. The whole number of revolu- tions of the screw is sometimes read by means of a second wheel, so geared to H that it makes one revolution for twenty or thirty revolutions of the screw S. In other cases a' strip of metal with small teeth like saw teeth, and as far apart as the threads of the screw S, is placed across the side of the opening so that the double spider- line appears to move over it from tooth to tooth, each tooth corresponding to one complete revo- lution of the screw. Such micrometers are used in measuring objects under the microscope, in most accurate linear and angular determinations, and in telescopes for obtaining star distances, and for a great variety of measurements. A very elaborate and delicate micrometer attached to the eye end of the telescope and used in star work is called a position micrometer. A special form of micrometer is used for measuring the star distances on the photographic plates that are taken of star groups and clusters. See !Ml- CRoscoPE ; Telescope. MICROMETER CALIPERS. See Calipers ami MLlUdMETKIi. MI'CRONE'SIA (Xeo-Lat., from Gk. ^lkpU. viil.riis, small + fijaos, iirsos, island). A name of Greek origin, meaning 'small islands.' It is used to designate that part of Oceanica which consists of the Ladrone and Caroline islands, Marshall Islands, the Gilbert group, and many others of small size. All of these lie northwest of Polynesia, north of Melanesia, and east of the Philippines, being all north of the equator, and between longitudes 130° and 180° E. The group also forms an ethnological division of Oceanica. (See ^Iichoxe-stans.) The most im- portant of the groups are described under the I'nipcr tides. MICRONE'SIANS. The inhabitants of Micrimesia (q.v.). They belong undoubtedly to the Malayo-Polyncsian race, although the autlior- itics ilirt'cr concerning their ethnic purity. The languages of Jlicronesia are luobahly Melanc- sian, but the natives are extremely nii.ed, show- ing all shades of color and transitional forms be- tween the Papuan, Malay, and Polynesian types. The mass diller in type slightly from the Poly- nesians; they are more hairy, are shorter, their head is more elongated, and they possess some ethnic characters apart. They use rope armor, and have weapons of sharks' teeth, special money, and other distinguishing marks. The i.adrone, Pelew, Marshall, Caroline, and Gilbert groujjs, collectively called Micronesia, would ap- pear to have been originally peopled by Papuans from ilelanesia, and to have afterwards received numerous colonists from both Polynesia and ilalaysia (the Philippines), besides occasional settlers from Japan and China. But the extent of the Papuan element in Micronesia has yet to be determined and has probably been over- estimated. The Gilbert group form the natural transition to Polynesia proper. For information in detail concerning the ilicronesians, the follow- ing works may be consulted: Kubary, Ethiio- firophische lieitriige ^hc Kenntnis dcs KaroUnen- Archipcls ( Leyden. lSS'J-95) : Meinicke, Die In- srln. dcs Stilleii Oceans (Leipzig, 1875) ; Cabeza Pereira, Estudios sobre las Carolinas (Manila,. 1895): Heinsheim, Siidsee Erinnerungen (Ber- lin, 1883) : id., Beitrag zur Sprache der Mar- ■•duill-Inseln (Leipzig, 1880) : Bastian, Die mik- ronesischen Colonicn aus ethnologischen tftand- punktcn (Berlin, 1899) ; Christian, "On Miero- nesian Weapons," in the Journal of the Anthro- pological Institute (London) for 1899, and The Caroline Islands (London, 1899); Bartolis, Las Carolinas (Barcelona, 1885). See Polynesians. MI'CROPHONE. See Telephone. MI'CROPYIiE (from Gk. iui!p6s, mikros,. small -f- Tr6ri. pglC. gate) (in plants). In an ovule, the passageway left by the integument or integuments, through which the pollen-tube passes to the nuccllus. It also marks the point in the seed at wdiich the escaping plantlct first emerges. See Ovi'LE. MI'CROSCOPE (from Gk. iuKp6s, mikros, small + a-KoweTv, skopein, to view). An instru- ment by which objects are made to appear of greater magnitude. LTndoubtedly the oldest mi- croscope on record is a plano-convex lens of quartz found by A. H. Layard amid the ruins of Nineveh, surrounded b.y articles of bronze and other materials. It is now in the British Mu- seum, and is 0.5 cm. (less than 0.2 inch) in thickness, 3.5 cm. (1.4 inches) in diameter, and its focal len.gth is 10.7 cm. (about 4 inches). Many authorities believe with good reason that this lens was used as a burning glass, as similar ones were used for that purpose at the time of Socrates. On the other hand, there can be no doubt that such lenses were used as simple micro- scopes, or magnifying glasses, inasmuch as the ap- parent increase of size of an object seen through them must inevitably have attracted the atten- tion of such goo<l observers, and moreover the elaborate and delicate engraving on many of the- seals and gems of that period furnish sufficient evidence that some means must have been era- idoyed to aid the eye in executing this work. Spherical glass vessels filled with water would also have called attention to their employment as magnifiers; spherical drops of glass would act similarlv.