The chronology of these periods varies according to the systems of different orientalists. It is, however, admitted that the Vedas are the first literary productions of India, and that their origin cannot be later than the fifteenth century B.C. The period of the Vedas embraces the other sacred books, or commentaries founded upon them, though written several centuries afterwards. The second period, to which belong the two great epic poems, the "Ramayana" and the "Mahabharata," according to the best authorities ends with the sixth or seventh century B.C. The third period embraces all the poetical and scientific works written from that time to the third or fourth century B.C., when the language, having been progressively refined, became fixed in the writings of Kalidasa, Jayadeva, and other poets. A fourth period, including the tenth century A.D., may be added, distinguished by its erudition, grammatical, rhetorical, and scientific disquisitions, which, however, is not considered as belonging to the classical age. From the Hindu languages, originating in the Sanskrit, new literatures have sprung; but they are essentially founded on the ancient literature, which far surpasses them in extent and importance, and is the great model of them all. Indeed, its influence has not been limited to India; all the poetical and scientific works of Asia, China, and Japan included, have borrowed largely from it, and in Southern Russia the scanty literature of the Kalmucks is derived entirely from Hindu sources. The Sanskrit literature, known to Europe only recently, through the researches of the English and German orientalists, has now become the auxiliary and foundation of all philological studies. 4. THE VEDAS AND OTHER SACRED BOOKS.--The Vedas (knowledge or science) are the Bible of the Hindus, the most ancient book of the Aryan family, and contain the revelation of Brahm which was preserved by tradition and collected by Vyasa, a name which means compiler. The word Veda, however, should be taken, as a collective name for the sacred literature of the Vedic age which forms the background of the whole Indian world. Many works belonging to that age are lost, though a large number still exists. The most important of the Vedas are three in number. First, The "Rig- Veda," which is the great literary memorial of the settlement of the Aryans in the Punjaub, and of their religious hymns and songs. Second, The "Yajur-Veda." Third, The "Sama-Veda." Each Veda divided into two parts: the first contains prayers and invocations, most of which are of a rhythmical character; the second records the precepts relative to those prayers and to the ceremonies of the sacrifices, and describes the religious myths and symbols. There are many commentaries on the Vedas of an ancient date, which are considered as sacred books, and relate to medicine, music, astronomy, astrology, grammar, philosophy, jurisprudence, and, indeed, to the whole circle of Hindu science.