Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/272

256 1C M I C by alignment, and that all this results from the unaided labour of a single observer, we find that our ideas of the possible have to be modi fied, when such a man undertakes a work with persistent unity of purpose for more than twenty years (1860-83). Berlin There is an ingenious mode of registering differences of declination decline- that has been in use at the Berlin Observatory since 1879, and is graph. described by Dr Knarre in the Zeitschrift fiir Instrumentcnkunde for July 1881. The instrument is called a declinograph. It has a web moved in declination by a quick-acting screw ; the same screw carries a travelling pricker or point. The observer having bisected a star by the wire has simply to compress an india-rubber ball con nected by a flexible tube with a thin metal box made on the prin ciple of the vacuum chamber of an aneroid barometer. The ex pansion of this box so produced brings a sheet of paper in contact with two prickers, one the movable pricker before mentioned, the other a fixed pricker. The action of the vacuum box also automatically shifts the paper (a long roll) by a small quantity at each observation, so that successive observations are recorded in regular order. To obtain the observed differences of declination it is then only necessary to measure with a glass scale (divided for the special telescope to 10") the distance of each record of the moving pricker from the fixed pricker. It is found, with this declinograph on the Berlin equatorial, that the observed declina tions have only a probable error of 0" 9. It is obvious that by using a chronograph in conjunction with this instrument both right ascensions and declinations could be recorded with great accuracy and rapidity. Miscellaneous Micrometers. Parallel Clausen in 1841 (Ast. Nach., No. 414) proposed a form of micro- glass meter consisting of a divided plate of parallel glass placed within micro- the cone of rays from the object-glass at right angles to the meter. telescope axis. One half of this plane remains fixed, the other half is movable. When the inclination of the movable half with respect to the axis of the telescope is changed by rotation about an axis at right angles to the plane of division, two images are pro duced. The amount of separation is very small, and depends on the thickness of the glass, the index of refraction, and the focal length of the telescope. Secchi (Comptcs llcndus, xli., 1855, p. 906) gives an account of some experiments with a similar micro meter ; and Porro (Comptcs Rendus, xli. p. 1058) claims the original invention and construction of such a micrometer in 1842. Clausen, however, has undoubted priority. Helmholtz in his " Ophthalmo- meter " has employed Clausen s principle, but arranges the plates so that both move symmetrically in opposite directions with respect to the telescope axis. Should Clausen s micrometer be employed as an astronomical instrument it would be well to adopt the im provement of Helmholtz. Ghost Burton and Grubb (Monthly Notices, vol. xli. p. 59), after calling micro- attention to Lamont s paper (Jahrbueh dcr K. S. b. Mimclicn, p. meter. 187) and Littrow s paper (Proc. of Vienna, Acctd. of Sciences, vol. xx. p. 253) on a like subject, proceed to describe a most ingenious form of " Ghost Micrometer," in which the image of a fine line or lines ruled in (or rather cut through) a silver film deposited on glass is formed at the common focus of an object-glass and eye-piece of a telescope. A faint light being thrown on the outside of the silvered plate, there appear bright lines in the field of view. We have not had an opportunity of testing this, nor Grubb s more recent models ; but, should it be found possible to produce such images satisfactorily, without distortion and with an apparatus convenient and rigid in form, such micrometers will probably supersede the filar micrometer. Their absolute freedom from diffraction, the perfect control of the illumination and thickness of the lines, and the accuracy with which it will be possible to construct scales for zone observations will be important features of the new method. For the use of micrometers in connexion with the microscope, see p. 277 of the present volume. (D. GI. ) MICRONESIA. The term "Micronesia" embraces that region of the Pacific north of the great Melanesian islands, where, either perhaps from a greater or more rapid subsidence, or from the decreasing activity northwards of the coral builders, the islands become, generally speaking, smaller and fewer, and finally cease. Accordingly, except ing the Marianas or Ladrones, which are of volcanic origin, and a few isolated instances of elevation in the Carolines, the Micronesian islands, though many of the groups cover a vast area, are almost without exception very small low coral (atoll) formations. Besides the LADRONE and CAROLINE ISLANDS (q.v.) Micronesia includes the Marshall and Gilbert groups, and some geographers include the Anson group, a number of small widely- scattered islets to the west of Hawaii, the Magellan group farther west, and the Bonin Islands north of the Ladrones. 1 North-easterly winds prevail during the winter months over the Marshalls, Ladrones, and Carolines, except in the extreme west, while between May and September the influence of the monsoon causes unsettled weather from the west, with heavy gales. In the Gilberts the south-east trade- wind brings fine weather at this season. The ethnological features of Micronesia are much more definite than the geographical, for its populations form one great branch of the fair Polynesian race, distinguished from the other by well-marked differences in appearance, language, and institutions. Its ethnological relations are not thoroughly understood. The proximity of Japan and the Philippines on the west and of the Papuan and South Polynesian islands on the south and south-east suggests, what in fact we find, a combination of elements in different degrees of fusion. In some places the oblique Mongolian eye is noticed, and (along with certain Indo-Chinese customs) there is often a scantiness of beard and general " Malay " look which increases westwards, and seems to imply relations with the archipelago subsequent to the departure thence of the pure Polynesians. In the Gilberts the traces of Polynesian (Samoan) influences are evident, and are confirmed by tradition. Among the Carolines and the Marshalls darker and more savage communities are found, suggesting a Melanesian element, which is further traceable in the Ebon (Marshall) and other languages. Each of the four groups, from long isolation, has devel oped peculiarities of its own. The most advanced were the " Chamorros " of the Ladrones, owing to the greater natural resources of the islands, and perhaps more frequent contact with influences from the west ; but as a separate people they no longer exist, having been nearly extermin ated by the Spaniards in the 17th century. Next in advancement come the Carolines. The general type is a well-proportioned rather slightly built figure, with small and regular features ; head high and well-proportioned, but forehead rather retreating, and narrow at the temples ; cheek bones and chin slightly prominent ; colour somewhat darker than the Polynesians, the Marshalls being darker and more vigorous than the Carolines, while the Gilbert type is still darker and coarser. The upper class greatly surpasses the common people in physique and intelligence. There is a peculiar division of society into septs or clans, the membership of which constitutes the closest tie. Persons of the same sept must not intermarry, and when two islands or communities meet in war the members of one sept, however widely separated by distance of space or time, will not injure or fight with each other. Each community is usually composed (but there are local differ ences) of (1) an upper class of chiefs, from among whom the head (tamol or iros) is chosen ; (2) a lower but still noble class ; and (3) common people, mostly without rights of property. These last are only allowed one wife. Assemblies of the chiefs everywhere limit the kingly authority. In the Marshalls the sovereign has lost his control over many of the atolls, and in the Gilberts the above distinctions have nearly disappeared; the headship has lapsed, and, especially in the southern islands, the man of largest substance is the most powerful, and sometimes establishes a local supremacy. Here and there are traces, as in Tonga, of a spiritual sovereign, the descendants probably of a conquered dynasty. Succession is through the female side, which assures to women a certain position, 1 These islands, which contain a mixed immigrant population, are claimed, and have been recently surveyed, by Japan. But they were amiexed to England by Captain Beechey in 1827. (See Von Kittlitz,

Denkwiirdiykeiten einer Rcisc nach .... Mikroncsicn, &c., vol. ii.)