from *rhuthmos* and *metron*, an instrument contrived to measure equal portions of sounds in musical performance, and to mark the time, at longer or shorter intervals, according to adjustment of the mechanism. Maczel's metronome is the instrument of this kind most generally in use, although one more simple and less costly might easily be made. Diderot, in the fourth memoir of his mathematical works, suggested a musical chronometer, but added, "Le seul bon chronomètre que l'on puisse avoir, c'est un habile musicien qui sait du goût, qui sait bien lui la musique qu'il doit faire exécuter, et qui sache en battre la mesure." The chief utility of a rhyth- meter consists in the power of fixing the duration of time which a composer wishes to give to the equalized portions of his composition, as indicated by the vibrations of a pendulum, and as marked by relative numerals affixed to characters of musical notation. Almost all pieces of music of classical importance are now printed with indications of the metronome measures of time; and this is a great improvement, inasmuch as before the present century we had nothing but tradition, and often no tradition at all, to guide us in the comparative slowness or quickness with which the notes of a musical composition were to be performed.

(RIAZAN, or RJAZAN, a government of European Russia, bounded on the N. by that of Vladimir, E. and S. by that of Tambov, and W. by those of Tula and Moscow, lying between N. Lat. 53. and 55. 40., E. Long. 38. 18. and 41. 30.; length, from N. to S., 180 miles; greatest breadth, 125.; area, 16,454 square miles. It is in no part mountainous, but the surface is diversified by low hills, undulating champaigns, rivers flowing between elevated banks, small forests, and clumps of trees. The Don and the Oka, an affluent of the Volga, along with their respective tributaries, are the chief rivers of the government; the former traversing for a short distance its S.E. corner, the latter flowing in a curve through the central and northern parts from W. to E. Rocky heights occur on the banks of a few of the rivers, but the soil in general is composed of a thick stratum of black mould of considerable fertility. Stone, clay, marl, and lime are found in some places. North of the Oka the land is low and marshy; the climate, too, is not so healthy as that of the southern part. The summer is generally very hot, and the weather variable for a great part of the year. Cultivation is extensively carried on here. Riazan contained in 1849, 5,161,238 acres of arable land, 1,019,025 acres of meadow land, 2,508,099 acres of wood, and 1,056,088 of waste land. In the same year there were produced 51,217,538 bushels of corn, and 2,653,563 bushels of potatoes. The corn is sufficient to supply the domestic wants, and leave a surplus for exportation. Rye, wheat, oats, and barley are the kinds chiefly raised. Hemp and flax are also cultivated. There are many gardens and orchards, and culinary vegetables are much attended to. Of live stock, the government contained in 1849, 482,095 horses, 366,120 horned cattle, 603,410 sheep, 206,832 swine, and 2817 goats. A large number of bees is also kept. The most important minerals obtained here are ironstone, freestone, clay, marl, lime, and sulphur. The manufactures are neither many nor important. In 1849 the total number of factories was 122, and the number of hands employed 10,963. Among the former there were 34 of leather, 18 of tallow and candles, 14 of cloth, 11 of silk, 11 of glass and crystal, and 5 of sugar. The trade is chiefly carried on through Moscow, except for salt, which is obtained from the banks of the Volga. The inhabitants are nearly all Russians, and belong to the Greek Church, except 5133 Mohammedans, and a few Protestants, Roman Catholics, and Jews. The government is divided into twelve circles as follows:

| Circle | Population | |--------|------------| | Riazan | 135,729 | | Saratov | 112,490 | | Kasimov | 122,852 | | Skopin | 112,637 | | Ramenskoye | 113,460 | | Danilov | 88,515 | | Total | 1,308,472 |

Riazan, the capital, stands in a broad valley at the confluence of the Lebeda with the Trubesh, an affluent of the Oka, 105 miles S.E. of Moscow. It has a cheerful appearance; the streets are broad, though but ill paved, and the houses in general well built. In the centre is a public garden, with a handsome kiosk or pavilion. Of its twenty churches, one of which is a cathedral, none are very remarkable. There are also two convents, several schools, and various charitable institutions. The manufactures of the place include iron, glass, woollen and linen cloth, canvas, &c. Riazan is defended by a fortress, and inclosed with earthen ramparts and palisades. It is the seat of the civil governor, and of the Archbishop of Riazan and Saratov. The name of Riazan was conferred on this town by Catherine II. in 1777, as the former place of that name had fallen into ruins. At that time it had only 1500 inhabitants, but now the population is 21,449.