Page:1902 Encyclopædia Britannica - Volume 27 - CHI-ELD.pdf/89

 CHRISTMAS

ISLAND—CHRONOGRAPHS

down to extreme old age, died at Edinburgh on 23rd January 1882. Christmas Island, a British possession under the government of the Straits Settlements, situated in the eastern part of the Indian Ocean (in 10° 25' S. lat., 105° 42' E. long.), about 190 miles S. of Java. It is not known when and by whom the island was discovered, but under the name of Moni it appears on a Dutch chart of 1666. It was first visited in 1688 by Dampier, who found it uninhabited. In 1886 Captain Maclear of H.M.S. Flying Fish, having discovered an anchorage in a bay which he named Flying Fish Cove, landed a party and made a small but interesting collection of the flora and fauna. In the following year Captain Aldrich on H.M.S. Egeria visited it, accompanied by Mr J. J. Lister, F.B.S., who formed a larger biological and mineralogical collection. Among the rocks then obtained and submitted to Sir John Murray for examination there were detected specimens of nearly pure phosphate of lime, a discovery which eventually led, in June 1888, to the annexation of the island to the British Crown. Soon afterwards a small settlement was established in Flying Fish Cove by Mr G. Clunies Ross, the owner of the Keeling Islands, which lie about 750 miles to the westward. In 1891 Mr Ross and Sir John Murray were granted a lease, but on the further discovery of phosphatic deposits they disposed of their rights in 1897 to the company now in possession. In the same year a thorough scientific exploration was made, at the cost of Sir John Murray, by Mr C. W. Andrews, of the British Museum. Physical Features and Geology.—The island is a quadrilateral with hollowed sides, about 12 miles in greatest length and 9 in extreme breadth. It is about 190 miles from the nearest land, and is probably the only tropical island that had never been inhabited by man. When the first settlers arrived, in 1897, it was covered with a dense forest of great trees and luxuriant undershrubbery. The settlement in Flying Fish Cove now numbers some 250 inhabitants, consisting of Europeans, Sikhs, Malays, and Chinese, by whom roads are being cut and patches of cleared ground cultivated. The island is the flat summit of a submarine mountain more than 15,000 feet high, the depth of the platform from which it rises being about 14,000 feet, and its height above the sea being upwards of 1000 feet. The submarine slopes are steep, and within 20 miles of the shore the depth of the sea reaches 2400 fathoms. It consists of a central plateau descending to the water in three terraces, each with its “tread” and “rise.” The shore terrace descends by a steep cliff to the sea, forming the “ rise ” of a submarine “tread ” in the form of fringing reef which surrounds the island and is never uncovered, even at low water, except in Flying Fish Cove, where the only landing-place exists. The central plateau is a plain whose surface presents “rounded, flat-topped hills and low ridges and reefs of limestone,” with narrow intervening valleys. On its northern aspect this plateau has a raised rim having all the appearances of being once the margin of an atoll. On these rounded hills occurs the deposit of Kate of lime which gives the island its commercial value. osphatic deposit has doubtless been produced by the longcontinued action of a thick bed of sea-fowl dung, which converted the carbonate of the underlying limestone into phosphate. The flat summit is formed by a succession of limestones — all deposited in shallow water—from the Eocene (or Oligocene) up to recent deposits in the above-mentioned atoll with islands on its reef. The geological sequence of events appears to have been the following :—After the deposition of the Eocene (or Oligocene) limestone—which reposes upon a floor of basalts and trachytes— basalts and basic tuffs were ejected, over which, during a period of very slow depression, orbitoidal limestones of Miocene age— which seem to make up the great mass of the island—were deposited ; then elapsed a long period of rest, during which the atoll condition existed and the guano deposit was formed ; from then down to the present time there has succeeded a series of sea-level subsidences, resulting in the formation of the terraces and the accumulation of the detritus now seen on the first inland cliff, the old submarine slope of the island. The occurrence of such a series of Tertiary deposits appears to be unknown elsewhere. The whole series was evidently deposited in shallow water on the summit of a submarine volcano standing in its present isolation, and round which the ocean floor has probably altered but a few hundred feet since the Eocene age. Thus

63

although the rocks of the southern coast of Java in their general characters and succession resemble those of Christmas Island, there lies between them an abysmal trough 18,000 feet in depth, which renders it scarcely possible that they were deposited in a continuous area, for such an enormous depression of the sea-floor could hardly have occurred since Miocene times without involving also Christmas Island. One of the main purposes of the exploration was to obtain light on the question of the foundation of atolls. As a result of the investigation it has been found that “the great thickness of reef limestone required by the Darwinian theory of atoll formation” does not exist, and “although there may be some evidence that subsidence did occur in the earlier history of the island, it is clear that it was neither continuous for any long period nor of any great extent ” {Andrews). If Christmas Island cannot, perhaps, be proved to have been a typical atoll, it can, however, ‘ ‘ be shown that at one time it must have consisted of reefs and islands approximating very nearly to those seen on atolls which are regarded as typical, and the determination of the nature of the foundation upon which those reefs and islands rested is, at least, a step in the right direction ” {Andrews). Flora and Fauna.—The flora consists of 129 species of angiosperms, 1 Cycas, 22 ferns, and a few mosses, lichens, and fungi, 17 of which are endemic, while a considerable number — not specifically distinct—form local varieties nearly all presenting Indo-Malayan affinities, as do the single Cycas, the ferns, and the cryptogams. As to its fauna, the island contains 319 species of animals—54 only being vertebrates—145 of which are endemic. A very remarkable distributional fact in regard to them, and one not yet fully explained, is that a large number show affinity with species in the Austro-Malayan rather than in the Indo-Malayan, their nearer, region. The ocean currents, the trade-winds blowing from the Australian mainland, and north-westerly storms from the Malayan islands, are no doubt responsible for the introduction of many, but not all, of these Malayan and Australasian species. Climate.—The climate is healthy, the temperature varying from 75° to 84° F. The prevailing wind is the S.E. trade, which blows the greater part of the year. The rainfall in the wet season is heavy, but not excessive, and during the dry season the ground is refreshed with occasional showers and heavy dews. Malarial fever is not prevalent, and it is interesting to note that there are no swamps or standing waters on the island. See Andrews, C. W. A Monograph of Christmas Island {Indian Ocean), London, 1900, to which the present writer has been greatly indebted. (h. O. F.) Chronographs.—In the article Gunnery (Ency. Brit. vol. xi.) descriptions were given of some chronographs adapted for the determination of the velocities of projectiles. Some additional forms of instruments both for this and for other purposes are here described. Gun Chronographs.—Probably the earliest forms of chronographs, not based on the ballistic pendulum method, are due to Colonel Grobert, 1804, and Colonel Dabooz, 1818, both officers of the French army. In the instrument by Grobert two large discs, attached to the same axle 13 ft. apart, were rapidly rotated ; the shot pierced each disc, the angle between two holes giving the time of flight of the ball, when the angular velocity of the discs was known. In the instrument by Colonel Dabooz a cord passing over two light pulleys, one close to the gun, the other at a given distance from it, was stretched by a weight at the gun end and by a heavy screen at the other end. Behind this screen there was a fixed screen. The shot cut the cord and liberated the screen, which was perforated during its fall. The height of fall was measured by superposing the hole in the moving screen upon that in the fixed one. This gave the approximate time of flight of the shot over a given distance, and hence its velocity. In the early form of chronoscope invented by Wheatstone in 1840 the period of time was measured by means of a species of clock, driven by a weight; the dial pointer was started and stopped by the action of an electromagnet which moved a pawl engaging with a toothed wheel fixed on the axle to which the dial pointer was attached. The instrument applied to the determination of the velocity of shot is described thus by Wheatstone :— “A wooden ring embraced the mouth of the gun, and a wire connected the opposite sides of the ring. At a proper distance the target was erected, and so arranged that the least motion given to it would establish a permanent contact between two metal points. One of the extremities of the wire of the electromagnet (before mentioned) was attached to one pole of a small battery ; to the other extremity of the electromagnet were attached two wires, one of which communicated with the contact piece of the target, and the other with one of the ends of the wire stretched across the mouth of the gun ; from the other extremity of the voltaic battery