The problem of locating the frets accurately upon the finger board was one of the causes which led to close investigation into the mathematical relation of the tones in the scale; and the directions given for placing them by various Arab and other writers afford precise and valuable information concerning their views of intonation. The lute was made in a great variety of sizes, the largest being what was called the arch lute, which was more than four feet long from bottom to the end of the neck. This was employed by Corelli for the basses of his violin sonatas, and Haendel made similar use of it. A diminutive lute has come down to our own days under the name of Mandolin. It is strung with metal strings, however, and played with a plectrum, whereas the mediaeval lute was played with the fingers. Monteverde employed still another variety of the lute in his orchestra, called the Chitarrone, whence our word guitar. This was a very large lute, with many strings, which were wire, and played, therefore, with a plectrum. The chitarrone in the collection at South Kensington has twelve strings upon the finger board, and eight bass strings tuned by the pegs at the top of the long neck. It was used mainly for basses. The guitar, of which a figure is omitted on account of the familiarity of the instrument, was the Spanish form of the lute, or the Spanish form which the Moorish lute took in that country. The essential feature of the violin is the incitation of the vibration by means of the bow. We do not know when or where this art was discovered, but it is supposed to have been in the remote east, at a very early period. The argument of Fetis, that since the Sanskrit has four terms for bow, according to the material of which it was made, therefore the art of the bow must have been known before the Sanskrit ceased to be a spoken language, has little weight. For while it is true that Sanskrit was not a spoken, or, more properly, a living, language in ordinary life after about 1500 B.C., it is true, on the other hand, that it remained in use as a language of religion and of the learned down to times very recent. In that case there would necessarily be additions made to it from time to time, as new concepts came up for expression, in the same manner as additions were made to Latin during the Middle Ages, and even in modern times. Still, all the nations around Hindostan have the tradition that the art of playing music by means of a bow is very old, the Ceylonese attributing the invention to one of their kings who reigned about 5000 B.C. Their ravanastron is very crude. (See page 72.) A similarly simple instrument is in use to the present day in many parts of the east. The Arab form of it, known as the rebec, is represented on p. 113, Fig. 23. It has two strings of silk, and is played with the point downward, like a 'cello. It is not possible after this lapse of time to determine which was the original form of the violin in Europe. Very