had taken possession of the mind of men by a three-fold bond.[402] How greatly he is mistaken in ascribing to the Magians the astrology of the Chaldæans, has been remarked above; the mistake is explained by the fact, that the Avesta includes the astronomical knowledge of the priests of Iran in the books which treated of medicine (p. 52). The astronomical chapters are lost as well as those on medicine. From our fragments we cannot so much as fix the year by which the Avesta reckons. We merely perceive that it counted by nights, not by days. It is from the Bundehesh that we first learn that the year of Eastern Iran is made up of 360 days in twelve months of thirty days, with five additional days. This year is said to have begun with the vernal equinox, _i.e._ the period when the vigour of nature again shows itself. In the last five nights of the old year, and the first five nights of the new one, the spirits of the forefathers, the Fravashis, come to their descendants in the houses; they awake with nature to new life (p. 179). The first month is called Farvardin after these spirits; of the remaining eleven, six are called after the Amesha Çpentas, and the remaining five, which are inserted between the six, after Mithra, Tistrya, the spirits of fire and water, and lastly after the law (Din). The inscriptions of the Achæmenids give us nine names of months entirely different from these. Hence the West had its own calendar, as well as its own alphabet, and made use of it as early as the year 500 B.C. In the East the calendar of the Avesta was in use; and this seems to have been current in the West also in the first half of the fourth century B.C. There is no doubt whatever that it was the standard for all Iran at the time of the Sassanids.[403]