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.
In any case, the advent of Buddhism, by depreciating the religious practices and astrological speculations of the Brahmans, contributed to bringing on a decline of astronomy at the very time it was taking its most vigorous stand among the Greeks. We learn from a passage in Strabo that the Pramnai regarded the Brahmans as boasters and mad because they were interested in physiology and astronomy. Now, there really exists an ancient Buddhist treatise in which the predictions by the Brahmans of eclipses of the sun and of the conjunctions and oppositions of the planets, and their discussions of the appearance of comets and meteors, are treated as despicable arts and lies.
It was just at this age that Hellenic culture was developed in northwest India. It held astronomy, and astrology too, in great esteem. The Milinda Panda mentions the royal astrologer as one of the principal functionaries of Menander. No doubt there were, among the Gavanas (Ionians) of Taxila and Euthydêmia, minds versed in the knowledge of the principal cosmological systems formulated among the Greeks from Thales to Aristotle, and also acquainted with all the progress in the physical and mathematical sciences that had been achieved by the Alexandrian astronomers in the last centuries before Christ. To comprehend the extent of the influence of Hellenic science, we have only to inquire what Hindu astronomy had become again at the time of the restoration of the Brahmans in the sixth century A. D. Aryabhatta teaches the rotation of the earth around its axis; maintains that the moon, naturally dark, owes its light to the rays of the sun; formulates the true theory of eclipses; assigns an elliptical form to the planetary epicycles; and demonstrates the displacement of the equinoctial and solstitial points. Varâha-Mihira devotes himself especially to astrological labors, but also has the merit of having condensed into a vast encyclopædia the Pantcha Siddhântikâ, the principal astronomical treatises that were current in India. And Brahmazoupta is especially famous for his revision of an older treatise, the Brahma Siddhânta.
In the opinion of the most competent critics, these works, which are chiefly empirical methods of determining the positions of the stars, are inferior to those which the Alexandrians have left us. Yet, in matters relating to the measurement of arcs and to spherical trigonometry, they reveal a more advanced state of the science. It is impossible to determine at what period this new astronomical science was constituted in India. Some of its theories squarely betray their indebtedness to Greek science, as, for instance, that of the displacement of the equinoctial and solstitial points by a periodical vibration or tremor. We can also say as much of the solar zodiac, the names of the constellations of which strikingly resemble the Greek names in form as well as in significance, and the same of the names of the chief planets. Other expressions are found, notably in the works of Varâha-Mihira, which indicate, if not a borrowing, a contact, at least, with the works of the Greek astronomy, of which Mr. Burgess gives a fairly complete list in his Notes on Hindu Astronomy and the History of our Knowledge of it, in the Journal of the Royal Asiatic Society. Among these terms, some are Greek words which have been utilized in naming constellations or astronomical measures; others have retained the special significations which they had in the works of the Alexandrian astronomers. It would certainly be an exaggeration to insist that the adoption of a foreign term of necessity implies the borrowing of the idea which it expresses. It is, nevertheless, probable that the Sanskrit writers would not have made use of so many of these exotic denominations if the ideas they represent had already found their expression in the languages of India.
Further, among the fine Siddântas which Varâha-Mihira collected and condensed as including all the astronomical science of his time, there are two, the Romaka and the Pauliça, the names of which suggest directly—the first the scientific culture of the Roman world, and the other Paulus, a celebrated Alexandrian astronomer of the third century A. D.[8]
We apparently find, likewise, the names of Manetho (fourth century A. D.) in Manittha or Manimda; of Spensippus in Sporedjivadja; and of Ptolemy in Asoura Maya, whom the Sounya Siddhânta designates as the founder of astronomy, and who another treatise says was born at Romakapouri, "the city of the Romans."
In this order of ideas the natives of India have never tried to deny their sources. The Gavanas, we read in the Gargí Samhitâ, are barbarians; but this science (astrology) has been constituted by them, and they must be revered as saints. M. Weber affirms that a treatise on astrology bearing their name, the Gavana Çastra, was reputed to have been written in the land of the Gavanas by the god Sourya in person, when, expelled from heaven by the resentment of his divine rivals, he came down and was born again in the city of the Romans.[9]
We find, further, that the Greek calendar appears to have survived Hellenic domination in northern India. General Cunningham, in 1862, read in the inscriptions of the Indo-Scythians the names of the Macedonian months Artemisios and Appellaios. Since then the names of two other months of that calendar—Panemos and Daisios—have been found in inscriptions in the Kharosthis character.
Another era of Grecian origin, that of the Seleucidæ, seems likewise to have furnished the Hindus their first historical computation.[10] It should be observed, in fact, that their most ancient era, that of the Mauryas, dates from the year 312 B. C., or the beginning of the era of the Seleucidæ. This had been adopted by the Grecian sovereigns of India, as is attested by a coin of Plato, struck in the year 166 B. C.