The treatment of the calendar among the Bataks of Sumatra is of great interest. The calendar indeed originates in India: the days of the months shew the familiar names of planets in corrupted Sanskrit forms, four times repeated and distinguished by various additions. Only the 28th and 29th or the 29th and 30th days, as the case may be, have names of another kind, so as to equalise the number of the days of the moon-month. The week is therefore not shifting but is immovably fitted into the month. The months are regulated by Scorpio, the largest star of which is Antares. The year begins with the new moon at the morning setting of Orion and the contemporary morning rising of Scorpio in May. The full moon fourteen days later then stands in the constellation Scorpio. In the first half of the year the full moon goes farther from Scorpio every month, and in the second half gets nearer and nearer to it. In the Batak calendar, which has 12, sometimes 13, × 30 squares, the sign of Scorpio is registered at the proper day, and the month is decided by it. As a means of control the soothsayer uses a buffalo rib with 12 × 30 holes (four times repeated), and every day he draws a string through one hole in order to keep account of the days. It is clear that the calendar can give no certain help in the establishing of the month, and that the means of control must be directly misleading, since the moon-months vary between 29 and 30 days. For this reason the soothsayer is often uncertain in his reckoning of the months, and refers to the natural phases in order to correct it[905]. Hence in his selection of days he looks not only to the current month, but also to the preceding. Our authority says that the surplus month is no intercalary month in the European sense, although it is likely that to it originally fell the task of equalising the lunar and the solar years. This is indeed the only correct explanation. When, presumably in the twelfth month, a following month is involved in the decision, the thirteenth is also included so that an intercalation takes place. If the thirteenth month is not available, the first is taken, we are told. But an intercalation is necessary all the same: the observation of the natural phases and of the morning rising of Orion serves for the correction. And this can happen just because the people are uncertain in the reckoning, and act according to circumstances. The Batak calendar is a product of decay, and is used exclusively for divination, not as a genuine calendar[906]; but it is of great interest to observe how the soothsayers, since they do not possess the knowledge necessary for a proper management of the calendar, fall back upon primitive methods. It is significant that the indispensable thirteenth month has often been lost: the people do not even understand the difference between the months and the year, and yet they cannot avoid the necessity of the intercalation.