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ROEMER. 221 ciate of Picard and C'assiui in many investiga- tious and discoveries. Rocnicr was the first to notice that light does not move through space instantaneously, but requires an appi-eciable in- terval of time for its transmission. (See Aher- R.^TiON OF LiGJiT. ) This far-reaching discovery is his principal claim to fame. (See Satel- lites.) In 1081 he returned to Denmark as professor of astronomy at Copenhagen, held sev- eral public positions, and finally became Chan- cellor of the Exchequer. ROENTGEN, rent'gen, Wilhelm Konrad (1S4j— ). A German physicist, born at Lennep, in Rhenish Prussia. He received his doctor's degree in 1869 at the University of Zurich, where he studied under Kundt. He was afterwards pro- fessor at Hohenheim, Strassburg, and Giessen, and in 1885 he became professor at the Univer- sity of Wiirzburg. In 1899 he was appointed pro- fessor of experimental physics at the University of Munich, a position which he now holds. In Xovember, 1895, he read before the Physico- Medical Society of Wiirzburg a paper upon his discovery of the rays which bear his name. For this discovery he received many honors, including the Kumford Medal of the Royal Society of Lon- don and the Barnard iledal of Columbia Univer- sit}', awarded in 1900 for the greatest discovery in science during the preceding five years. ( See X-Rats. ) He published, chiefly in the Annalen <3er Pliysik und Chemie, many articles on various physical subjects, including the properties of crystals, specific heat of gases, absorption of heat ray in vapors and gases, electrostriction, piezo electricity, various other electric and magnetic phenomena, and telephony. ROERMOND, rUur'mrJnt. A town in the Prov- ince of Limbui'g, in the Netherlands, situated at the confluence of the Roer with the Meuse. 28 miles northeast of JIaastricht (Map: Nether- lands, E 3). It contains a thirteenth-century Romanesque cathedral, a seminary, and a fine palace of justice. The manufactures of the town consist of woolens, cotton goods, paper, stone and wood carvings. Population, in 1900, 12.348. ROESKILDE, ros'kilde. or ROSKILDE. A town on the island of Zealand. Denmark, situ- ated at the head of the Roeskilde Fjord, 10 miles west of Copenhagen, at the converging point of the three principal railroad lines of Zealand (Map: Denmark, F 3). It contains a magnifi- cent cathedral, erected 1074-84, rebuilt in the twelfth century, and containing the tombs of Danish kings. "Population, in 1901, 8368. Roes- kilde is one of the oldest towiis of Denmark. Previous to 1443 it was the capital of the king- dom and the residence of the royal family, but its decline was consequent on the rapid growth of Copenhagen, and fire and the ravages of the plague destroyed its prosperity. A treaty was concluded here in 1058 between Denmark and Sweden, in which the former relinquished her possessions beyond the Sound. ROGATION DAYS (Lat. rogatio, supplica- tion, from rofiare. to ask). The Monday. Tues- day, and Wednesday before Ascension Day. so called because on these days the litanies (q.v. ) are appointed to be sung or recited by the clergy and people in public procession. The practice of public supplications on occasions of public danger or calamity is traceable very early in Christian use; but the fixing of the days before Ascension ROGER II. for the purpose is ascribed to .MnniertUH, Bishop of Vienne, in tlie middle of the fifth century, who, on occasion of a threatened earthquake or other public peril in his city, ordered a public proces- sion and prayer, for tlie purpose of averting the divine anger. The usage in the Roman Catliolic Church became general ami pernuinent. The form of prayer employed is that known an the Litany of the Saiiilii. In England, after the Reformation, the recitation of the litanies upon these days was discontinued, but the days remain as days of abstinence and prayer to obtain God'n blessing upon the fruits of the earth ; they form also a brief preparation, somewhat analogous to Advent and Lent, before the great festival of the Ascension. ROGER (roj'er) I. (Roger Guiscard) (c.1031- 1101). Grand Count of Sicily, founder of Nor- man rule in lliat island. He was the younge.st of the sons of the Norman noble Tancred de liaiite- ville (q.v.). In 1158, in answer to the sununons of his brother, Robert Guiscard (q.v.) he went to Italy. On his arrival he was deputed by Robert to concpicr Calabria, an achievement which was speedily executed. In 1000 he set out on an expedition against Sicily, tlien ruled by a number of Saracen cliiefs, and by 1090 he had taken the most important towns, and ousted the Saracens from the eontrolof the island. In 10U2he was invested by his brother with Sicily and part of Calabria under the title of Count. Roger di- vided the country into fiefs, which he distributed among his chief barons, whose relations to their subjects were regulated by him with justice and moderation. Moreover, he extended his own rule in Calabria. About 1096 he took the title of 'grand count,' to distinguish him from Ids vassals. Roger was courted by the most ijowerful princes of Europe. He fostered learning and was very tolerant in religious matters, protecting the Sara- cens within his dominions. He supported Rome against the Greek Church, and in 1098 Pope Urban II., in recompense for his fidelity to the Holy See, conferred the title of Papal legate upon him and his heirs forever. He died at ililcto, in Calabria, in July, 1101. Consult Schack, GcschicJite tier yonitanncii in Sicilicn (Stuttgart, 1889). ROGER II. (C.1097-I154). Grand Count of Sicily from 1101 to 1130 and King of Sicily from 1130 to 1154. He was a son of Roger I. (q.v.). Upon the death of his brother Simon, he became the heir to Sicily, and during his minority the government was administered by his mother, a princess of Montferrat. When Roger had taken the supreme authority into his own hands, his first care was to extend his domin- ions. He compelled his cousin William to yield up the portion of Calabria and of the town of Palermo which Roliert Guiscard had withheld from his father; and after the death of William (1127) he took possession of Apulia itself. Ambitious of the title of king, he supported the anti-pope Anacletus, his wife's uncle, and received from him the title of King of Sicily, with rights of suzerainty over the duchies of Naples and Capua. In return. Roger established . aeletus on the pontifical throne in 1130. His bitter enemy, Inocent II.. fell into his hands in 1139. and wa* compelled to withdraw the excommunications he had pronounced against Roger, and to consent to his retaining the territories he had acquired, obtaining by these means not only his own lib-