The adjustment of the solar year to correspond with the lunar year and of the two with the civil year dates from this period. The month was still composed of thirty days, but the solar years were grouped into quinquennial periods, in the middle and at the end of which the lunar month was doubled. Combining these quinquennial periods with the revolutions of the planet _Brihaspati_ (Jupiter), which was calculated as occupying about twelve years, the Indian astronomers computed an astronomical cycle of sixty solar years. As the same cycle is found with the Chaldeans, where, according to Berosus, it was called the _Sossos_, we have to inquire how far Brahmanic astronomy was influenced by the systems which were originally formed in ancient Chaldea. The presumption of such an influence furnishes a simpler and more probable hypothesis than the effort to trace the earliest astronomical ideas of the Hindus, as M. W. Brennand has recently suggested, to a period when the ancestors of the Aryans, the Semites, and the Chinese were wandering together over the plateaus of central Asia! We know now, from the cuneiform inscriptions, that the Chaldeans had, at a period far anterior to the entrance of the Aryans into India, invented a double calendar, solar and lunar, with intercalary periods; discovered the proper motion of the planets; calculated the return of eclipses; and constituted a double metrical system, decimal and sexagesimal; and, as was done, too, in India, had divided the circumference into three hundred and sixty degrees of sixty minutes each. It is impossible to draw the lines exactly between the astronomical discoveries which the Hindus borrowed from abroad and those which they drew from their own resources prior to the invasion of the Greeks, but we need in no case go farther than Mesopotamia for the source of the borrowed data. The ancient literature of India contains observations of the positions or conjunctions of some of the stars that carry us back to positive dates in the history of the sky. The astronomers Bailly, Colebrooke, and Bentley, and, more recently, M. Brennand, have found notes relative to astronomical phenomena that took place in the twelfth, fourteenth, fifteenth, and even the twenty-first centuries B. C. Max Müller, however, advises prudence and reserve in accepting these calculations, some of which may have been afterthoughts, and others offer only apparent agreements.