ROCKY MOUNTAIN                                1623

ROENTGEN RAYS

Rocky Mountain or White Goat, an

American goat-antelope, as a rule is found in the mountains just above the timber-line, in high, inaccessible spots where only the boldest hunter can follow ; but in British Columbia it comes toward the coast. In appearance clumsy, it is remarkably agile, an expert in climbing rocks and icy steeps. Its weight is about that of the common deer. In form it resembles the bison, the body thick-set, legs stocky, hind-quarters low, shoulders high, head carried low. The dense coat is all yellowish white, the hair next the skin fine, the outer hair long and coarse. The Indians used to make blankets of the long silky hair, and now the hides are valued. The horns are small, black, smooth and sharp-pointed, having little beauty to attract the trophy-hunter. It is found sparingly in Alaska and British Columbia, in Idaho, Montana and Washington, but the well-beaten trails tell of great numbers that once existed.

Ro'dents, or the order of Rodentia, form the largest order among mammals, and include upwards of 2,000 species. They range in size from the mouse to the South American capybara, which is almost as large as an ordinary hog. They are characterized chiefly by the nature of their teeth. They have no canine teeth; but have long, curved, very sharp incisors, which are separated from the molars by a considerable gap. The molars are few; and are moved sideways with the jaw in the characteristic gnawing of animals of the order. Among well-known rodents may be mentioned (besides the many familiar species of rats and mice) the beaver, hare, agouti, jerboa, guinea-pig, muskrat, mole-rat, rabbit, marmot, squirrel, woodchuck, porcupine, capybara and lemming. Rodents live almost absolutely upon vegetable food. They often are cunning and are guided by elaborate instincts, as in the case of the beaver. Some of them make great migrations, as, e. g., the lemmings. The furs of some of the group are of value, and some are edible. The ordinary rats and mice, however, are pernicious and destructive; and it has recently been demonstrated that rats are chiefly responsible for the spread of the bubonic plague in India and elsewhere.

Rodg'ers, John, an American naval officer, was born in Maryland, Aug. 8, 1812, his father being the Capt. John Rodgers who distinguished himself by firing the first gun on the British during the War of 1812. He entered the navy in 1828, and was commissioned captain in 1862. Next year, while in command of the monitor Weehaw-ken, he captured the Confederate Atlanta, and was promoted to be commodore. He became rear-admiral in 1869, and was superintendent of the United States Naval Observatory at Washington from 1877 until his death, May 5, 1882.

Rodin (ro'dan') Auguste, a French sculptor, was born at Paris in 1840. In 1875 he exhibited in the Salon He disregards the conventionalities of classic style, and expresses the first feeling or act of a subject. So his sculptures are fantastic and rugged. Though he has a power of execution that is said to be worthy of the best artists of the Renaissance, he tries to express things beyond the scope of sculpture. Among his creations are a bust, of Hugo, a statue of Balzac and The Burghers of Calais.

Rod'man, Thomas J., was born at Salem, Ind., in 181, and after graduating at the United States Military Academy was commissioned lieutenant of ordnance in 1841. To him belongs the honor of inventing a method of casting large guns about a hollow core and cooling the metal from the m side. He died at Rock Island, 111., June 7, 1871,

Rodrigues (ro-drē'gĕs) is a volcanic island 375 miles east by north of Mauritius, of which it is a dependency. Its area is 42 square miles, population 3,200, of whom less than 200 are pupils in the government-schools. The Portuguese discovered the island in 1Ŏ45, the British took possession in 1814, and its isolation in the Indian Ocean, which prevents changes among its animais and plants, makes it important to zoologists and botanists. The solitarie, a bird now extinct, survived here almost until 1700. The chief export is cocoa-oil.

Roem'er, Ole, a Danish astronomer, is known principally as the man who first discovered that light travels with a finite speed. Born in 1644, he died in 1710. He was educated at the University of Copenhagen. The years from 1672 to 1681 he spent in the Paris Observatory. Then he returned to Copenhagen as professor of astronomy, a position which he held until death. During his Parisian residence he studied the motion of Jupiter's satellites and showed from inequalities in the motion of the first satellite that the speed of light across the orbit of the earth is approximately 309,000,000 meters a second, a result which is not so very far — perhaps three per cent.— from the best modern measures. Roemer devised the transit instrument, the meridian circle and the altazimuth instrument; but he was in advance of his times and adoption of his inventions was delayed until many years after his death. See Grant's History of Physical Astronomy.

Roentgen (rent'gĕn) Rays. About the beginning of 1896 Roentgen, a German physicist long and favorably known to the scientific world, discovered that rays which in many respects are similar to Lenard's can be observed through a very large region outside of an ordinary Crooke's tube. These are the so-called X-rays. Among the most important properties of these rays are the following: