In spite of the talk about music by the Greek writers, musical theory, in an exact form, occupies but a small place in the volume of their works. The earliest theorist of whom we have any account was Pythagoras, who lived about 580 B.C. He was one of the first of the Greek wise men to avail himself of the opening of Egypt to foreigners, which took place by Psammeticus I in the year 600 B.C. Pythagoras lived there twenty years in connection with one of the temples, where he seems to have gained the confidence of the priesthood and learned much of his philosophy and so-called musical science. He defined the mathematical relation of the octave as produced by half of a given string, the fifth produced by two-thirds and the fourth by three-fourths. He also found the ratio of the major step by subtracting the fourth from the fifth. This was the ratio 9:8. With this as a measure he attempted to place the tones of the tetrachord, or Greek scale of four tones, which was the unit of their tonal system. This gave him two major steps, and a half step somewhat too small, being equal to the ratio of 256:243. The most important part of Pythagoras' influence upon the art of music was of a sentimental character. From Egypt he acquired many ideas of a musical nature, such as that certain tones represented the planets, and that time was the essence of all things. It was one of the laws of his religion that before retiring at night his disciples should sing a hymn in order to compose their spirits and prepare them for rest. The verses selected for this use were probably of a devotional character, like what are now known as the Orphic hymns, of which the lines upon the next page may be taken as a specimen. Ambros well remarks that such hymns could only have been sung appropriately to melodies of a choral-like character. "Thou ruler of the sea, the sky, and vast abyss, Thou who shatterest the heavens with Thy thunder peals; Thou before whom spirits fall in awe, and gods do tremble; Thou to whom fates belong, so wise, so unrelenting Thou; Draw near and shine in us."