The custom of making a systematic use of stone, in music, is peculiarly a Chinese institution. In the _Chouking_, one of the most ancient of Chinese chronicles, we read that already in the almost mythological days of Yao and Chun, the Chinese had observed that certain kinds of stone were adapted to giving out musical sounds, and that these tones occupied the place between the sound of metal and of wood, being less sharp and penetrating than the former, and more sonorous than the latter, and more brilliant and sweet than either. Even in those days they carved and shaped the stones, in order to extract from them the regular notes of their scale, and made instruments of them which even to-day are used in China, and are named _king_. These musical stones were highly valued, and received as tribute as early as 2250 B. C. Those found on the surface of the earth, and near the banks of the rivers, were most esteemed, as it was supposed that their exposure gave clearness and purity to their tone. These stones, called _Yu_, are found near the mountain streams and torrents of Yun-nan. They are of extreme hardness and are polished in the same manner as agate and precious stones. Large specimens are extremely rare; those which Amiot saw at the Imperial palace, were three feet by one foot eight inches in size, but they were considered unique. Their weight (specific gravity) is also very wonderful, for stones which seem to be not too heavy a burden for one man, require four men to move them.[109] Those in the palace were of many colors, milk-white, sky-blue, indigo-blue, yellow, orange, pale green, sea-green, red and gray. Those most esteemed were of a single color throughout, though when five colors blended, it was considered a valuable specimen. It may be mentioned in this connection that the number five seems to acquire a mystical significance among the Chinese, for their music has five principal tones, they recognize five elements, five virtues, five senses, five duties, and five principal ceremonies.[110] Some of these stones resemble marble, and others seem to be petrifactions of some sort. We are unaware whether those belonging to the emperor have been examined by any recent geologist. The Duke de Chaulnes in the last century, came to the conclusion that the stone was marble, but that its organization differed in some respects from ours; and that iron entered into its composition. It is very difficult to complete an octave with the best of musical stones. In carving and ornamentation they require most skillful manipulation lest the pitch be endangered.