Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/644

620 R O E R O G remarkable suspension bridge over the Ohio river at Cincinnati, with a clear span of 1057 feet (see CINCINNATI, vol. v. p. 782), added to Roebling's reputation, and his de- sign for the great bridge spanning the East River between New York and Brooklyn was accepted. 1 While personally engaged in laying out the towers for the bridge, Roebling received an accidental injury, which resulted in his death, at Brooklyn, from tetanus, 22d July 1869. At the time of his death Roebling's work on Long and Short Span Bridges (New York, 1869) was in the press. It is devoted to an exposition of his belief that " the principle of suspension will of necessity become the main feature in our future long span railway bridges, " and was intended as the initial volume of a series relating to his general theory of bridge construction, with detailed plans and descriptions of the larger works erected by him. ROEMER, OLE (Latinized OLAUS) (1644-1710), Danish astronomer, was born at Aarhuus in Jutland, 25th Septem- ber 1644. He studied mathematics at the university of Copenhagen until 1671, when he assisted Picard in de- termining the geographical position of Tycho Brahe's observatory (Uranienburg on the island of Huen). In 1672 he accompanied Picard to Paris, where he remained nine years, occupied with observations at the new royal observatory and hydraulic works at Versailles and Marly. In 1675 he read a paper before the Academy on the suc- cessive propagation of light as revealed by a certain in- equality in the motion of the first of Jupiter's satellites (see PARALLAX, vol. xviii. p. 251). In 1681 he returned to Copenhagen, where he spent the remainder of his days as professor of astronomy, but his great ability and prac- tical talents were made use of in several other public employments. He died on 23d September 1710. Roemer's name is now best known by his discovery of the finite velocity of light. Most of his contemporaries doubted the reality of this discovery, chiefly because the eclipses of the three outer satellites of Jupiter did not show similar irregularities to those exhibited by the first satellite. This is not surprising, as the mutual attraction of the satellites makes their motions far more complicated than astronomers imagined before the development of the theory of gravitation, and it should perhaps be chiefly ascribed to chance that Roemer brought forward his theory, which Bradley's discovery of the aberration of light about fifty years later proved to be a true one. Roemer's ingenuity has, however, appeared very pro- minently in the important improvements which he carried out in the construction of astronomical instruments. The large "armil- lary spheres," first constructed by the astronomers of Alexandria and also used by Tycho Brahe, had been superseded by the meridian or mural quadrant for measuring meridian zenith distances, and by the sextant for measuring distances between stars in order to find their difference of right ascension by solving the spherical triangle between the pole and the two stars. Both these instruments were introduced by Tycho Brahe. Roemer, however, saw that Tycho's idea of making the rotating earth itself an astronomical instrument by observing the transits of stars across the meridian could be carried out better by fixing a telescope at right angles to a hori- zontal axis placed exactly east and west, so that the telescope could only move in the meridian. The first transit instrument was con- structed in 1689 and erected in Roemer's house in 1690. In the same year he erected in the university observatory an instrument with altitude and azimuth circles (for observing equal altitudes on both sides of the meridian) and an equatorial instrument In 1704 he constructed a private observatory at Vridlbsemagle, a few miles west of Copenhagen, and mounted a meridian circle (the transit instrument and vertical circle combined) and a transit instrument n:oving in the prime vertical. Roemer may thus be considered the inventor of nearly all our modern instruments of precision, and it is much to be regretted that his ideas were not adopted by astro- nomers until about a century later. All the results of his observa- tions were destroyed in a great conflagration in 1728, except three days' work, which has been discussed by Oalle (0. Roemeri triduum observationum astronomicarum a. 1706 institutarum, Berlin, 1845). His disciple Horrebow has left us a very detailed description of Roemer's instruments and ideas in his Opera mathematico-physica (3 vols., Copenhagen, 1740-41). Grant's History of Physical Astro- nomy (London, 1852) gives a very correct account of Roemer and his inventions. About his life see also an article by Philipsen in Nordisk Universitets Tidsskrift, vol. v., 1860. 1 For description of this the largest wire suspension bridge in the world, see NEW YORK CITY, vol. xvii. p. 465. ROERMOND or ROERMONDE (i.e., " Roer-Mouth "), a town of the Netherlands in the province of Lhnlmrg (formerly Guelderland), on the right bank of the Maas (Meuse) at the mouth of the Roer, which separates it from the suburb of St Jacob. It is 29 1 miles from Maastricht by the railway to Venlo (opened" 1865). The old forti- fications were dismantled in 1819 and have been partly turned into promenades. At this point the Maas is crossed by a bridge erected in 1866-67, and the Roer by one dating from 1771 and replacing the older structure destroyed in 1764. The finest building in the town is the Romanesque minster church, begun in 1218, and dedicated by Arch- bishop Engelbert of Cologne. In the middle of the nave is the tomb of Count Gerhard III. of Guelderland and his wife Margaret. The cathedral of St Christopher is also of note ; on the top of the tower (246 feet) is a copper statue of the saint and the interior is adorned with paint- ings by Rubens, Jacob de Wit, &c. The Reformed church was once the chapel of the monastery of the Minorites. The old bishop's palace is now the court-house, and the old Jesuits' monastery with its fine gardens is now occu- pied as a higher burgher school. Woollen, cotton, silk, and mixed stuffs, paper, flour, and beer are manufactured at Roermond. The population of the town was 5712 in 1840 and 8797 in 1870; and that of the commune has increased from 6005 in 1840 to 10,470 in 1879. Till the 13th century Roermond was only a village with a hunt- ing lodge known as Pot. The erection of the monastic church in 1218 was followed by the building of town walls in 1231 by Count Otho II. In 1543 Roermond was occupied by the troops of Charles V., and in the course of the Eighty Years' War few places more frequently changed hands. The peace of Minister (1648) left it in the Spanish Netherlands ; but between 1702 and 1716 it was held by the forces of the United Provinces. ROGATION DAYS, the Monday, Tuesday, and Wednes- day before Ascension Day. The week in which they occur is sometimes called Rogation Week. See LITANY, vol. xiv. pp. 695-696. ROGER I., " grand count " of Sicily, the twelfth and youngest son of Tancred de Hauteville in Normandy, was born about 1031. He joined his brother ROBERT Gu ISCARD (q.v.) in Italy in 1058, and after taking part with him in his conquests on the mainland passed over to Sicily in 1061. There such success attended his arms that in 1071 he took the title of count; in 1089 he became "grand count" and in 1098 received from the pope for himself and his suc- cessors the title of " legate apostolical " in Sicily. He died in 1101. See SICILY. ROGER II., count of Sicily, son of the preceding, was born about 1093 and died in 1154. He obtained from the antipope Anacletus II. the title of king of Sicily in 1130, and was crowned in the same year. The title was afterwards confirmed in 1139 by Innocent II. See SICILY. ROGER OF HOVEDON. See HOVEDON, vol. xii. p. 319. ROGER OF WENDOVER, who was a monk in the abbey of St Albans, and who died prior of Belvoir in 1237, was long regarded as the sole author of a Latin chronicle entitled Flores ffistoriarum, being a history of the world from the creation down to the year 1235. Recent investi- gation, however, has disclosed that only the portion from 1189 onwards is from his pen, and that the remainder must be attributed to John de Cella, who was abbot of St Albans from 1195 to 1214. See vol. xv. p. 634. ROGERS, JOHN (c. 1500-1555), editor of the English Bible known as Matthew's. See vol. viii. p. 386. ROGERS, SAMUEL (1763-1855), the "melodious Rogers " of Byron, the " memory Rogers " of the general reader, has a unique reputation among English men of letters. Not only was he a poet of sufficient mark to be hailed by Byron with perverse but sincere admiration as one of the few men of genuine weight in an age of