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Rh years for their reduction. The published results of these observations appeared in several volumes which he prepared. While Prof. Rogers had sev- ered his connection with Harvard, he still retained supervision of his unfinished work at the obser- vatory. One of the earliest diflieulties that he met with was the finding of micrometer spider- webs that were suitable for his work. After nu- merous experiments he succeeded in etching glass plates with the moist fumes of hydrofluoric acid so satisfactorily that the U.S. government ordered the plates, which were used by the expeditions that were sent out from this country to observe the transit of Venus. His study of this subject, extending over sixteen years, had made him a universally acknowledged authority in all that per- tains to micrometrical work. He hud specially studied the construction of comparators for the determination of differences in length, and had established useful working standards of measure- ment for practical mechanical work, resulting in the Rogers-Bond universal comparator, built by the Pratt and Whitney company of Hartford, who were thus enabled to make their system of standard gauges. In 1880 he was sent abroad to obtain authorized copies of the English and French standards of length. These were used as the basis of comparison for the bars that he con- structed and that now serve as standards of length for Harvard, Yale, Columbia, Princeton, the U. S. signal service, the Lick observatory, and other im- portant institutions. Prof. Rogers's micrometer rulings, both on metal and glass, are known to microscopists for their accuracy as regards divis- ions, and also for the character and beauty of the lines. In 188U he was made a fellow of the Royal siiriety of London, and he had since been advanced to the grade of honorary fellow. He was elected in 1885 to the National academy of sciences, and was vice-president of the American association for the advancement of science in 1882-'3, presiding over the section in mathematics and astronomy. In 1886 he was chosen president of the American society of microscopists. The degree of A. 51. was conferred on him by Yale in 1880, and that of Ph. D. in 1886 by Alfred university. His pub- lished papers, nearly fifty in number, relate to his specialties, and have been published in scien- tific journals or in the transactions of the learned societies of which he was a member.

ROGERS, Woodes, English navigator, _b. in Derbyshire, England, about 16G5 ; d. in Nassau in 1732. He was a commander in the navy when he was chosen in 1708 as captain of an expedition that was sent by merchants of Bristol, at the sug- gestion of William Dampier, to explore the Pacific ocean. He sailed from Bristol on 1 Aug., with two ships, with Dampier as pilot. After advancing far to the south, disappointed in not finding a great southern continent, they steered to the north, and landing, 1 Feb., 1709, at Juan Fernandez island, rescuecl Alexander Selkirk (q. i:). On the sout hern coast of Peru, Rogers secured some rich Spanish prizes, attacked the city of Guayaquil, exacting from the citizens an enormous ransom, and sailed along the coast as far as Cape San Lucas in Lower California. After visiting Batavia he passed the Cape of Good Hope, and anchored in the Downs, 2 Oct., 1711. In 1717 he was commissioned gov- ernor of New Providence in the Bahamas, and was sent with a division against the pirates that had ravaged the neighboring islands. He published " Narrative of a Cruise around the World " (Lon- don, 1712). Edward Cook, who commanded one of the ships in Rogers's expedition, published " Voy- age in the South Sea and Around the World, made in tin- Years 1708-'9-'10-'ll"(1712).

ROHBE, Lewin Jürgen (ro'-deh), West Indian naval officer, b. in St. Thomas, 28 Oct.. 1786 ; d. in Copenhagen, Denmark, 2 Aug., 1857. He was the son of a governor of St. Thomas, entered the Copenhagen naval school in 1803, and served cred- itably at the bombardment of that city. In 1821 lie was promoted harbor-master of St. Thomas, and sent to make a nautical survey of the coast of the colony. His charts are still considered standards. In 1835 he was retired with the rank of captain. His works include " Historic og befolkning af Oeen St. Thomas" (2 vols., Copenhagen. 1822), and " Ful- staendig Signal System til Brug for alle nationers Skibe " (1835 ; revised ed., 1846), which has been translated into all European languages.

ROJAS, Gabriel de (ro'-has). Spanish soldier, b. in Cuellar in the 15th century; d. in Charcas, Peru, 17 Dec., 1548. He came to South America in 1514 with Pedrarias Davila. in 1524 took part in the con- quest of Nicaragua with Cordova, commanded in the campaign against Gil Gonzalez Davila, and assisted in the discovery of the Desaguadero, and the foun- dation of Gracias a Dios. In 1533 his old friend, Francisco Pizarro, solicited his aid, and Rojas armed two ships and 200 men ; but Pedro Alvarado, who was planning an expedition of his own, took possession of the ships and the forces. Rojas es- caped with only a few followers and sailed to Peru, landing at San Miguel de Piura. With an escort that was provided by Sebastian de Yelalcazar, he joined Pizarro in the valley of Pachacamac, took part in the foundation of Jauja, and was appointed 1 irutenant-governor of the town. He assisted after- ward in the defence of Cuzco, during the siege by Manco Inca Yupanqni (q. '.), and in the civil wars between the Pizarros and the Almagros. He was then commissioned by Vaca de Castro to settle Charcas, and when, on his return to Cuzco, he found Gonzalo Pizarro at the head of a rebellion, he fled to Lima. On his arrival the viceroy Nunez de Vela was already imprisoned, and Rojas narrow- ly escaped being killed by Francisco de Carvajal, but Gonzalo Pizarro pardoned him on account of his former services. When President De la Gasca ar- rived, Rojas joined the royal forces, and was ap- pointed commander of the artillery, which he di- rectedat thebattlesof Huarinas and Xaquixaguana. In recompense he was appointed magistrate of Potosi, but he died shortly afterward.

ROJAS, Juan Ramon, Argentine poet, b. in Buenos Ayres in 1784: died at sea, 9 Sept., 1824. He studied in the College of San Carlos, and as an officer of artillery was present at the sieges of Mon- tevideo in 1812 and 1816. In 1813. he was pro- moted commander of the squadron of grenadiers, and as such took part in the battle of Sipe-Sipe. He served in the staff of the armies of the United Provinces in 1818. In the first days of the revolu- tion he began to write poetry, and published " ( 'an- cion heroicaal sitio de Montevideo" (1811), and A laaperturadelaSociedad patriotica " (1812). In the collection of " Poesias patrias" (Buenos Ayres, 1820) his best patriotic compositions were published. He perished in a shipwreck.

ROLANDER, Daniel (ro'-lan-dair), Swedish naturalist, b. in the province of Smaaland in 1720 : d. in Lund in 1774. After receiving his education in Upsala he became preceptor of the children of Linmeus. and engaged later in botanical researches under the direction of the great naturalist. At Linnaeus's suggestion, he accompanied to Surinam a wealthy citizen of the colony, and on his arrival, 20 June, 1755, began immediately to explore the