About 1825 Eugène Burnouf was engaged in a course of researches on the geographical extent of the Aryan languages in India. After he had defined the limits which divide the races speaking Aryan languages from the native non-brahmanical tribes in the south, he wanted to know if a similar boundary had ever existed in the northwest; and if it is outside of India that the origin of the Indian languages and civilization is to be sought for. He was thus led to study the languages of Persia, and, first of all, the oldest of them, the Zend. But as he tried to read the texts by help of Anquetil's translation, he was surprised to find that this was not the clue he had expected. He saw that two causes had misled Anquetil: on the one hand, his teachers, the Parsi dasturs, either knew little themselves or taught him imperfectly, not only the Zend, but even the Pahlavi intended to explain the meaning of the Zend; so that the tradition on which his work rested, being incorrect in itself, corrupted it from the very beginning; on the other hand, as Sanscrit was unknown to him and comparative grammar did not as yet exist, he could not supply the defects of tradition by their aid. Burnouf, laying aside tradition as found in Anquetil's translation, consulted it as found in a much older and purer form, in a Sanscrit translation of the Yasna made in the fifteenth century by the Parsi Neriosengh in accordance with the old Pahlavi version. The information given by Neriosengh he tested, and either confirmed or corrected, by a comparison of parallel passages and by the help of comparative grammar, which had just been founded by Bopp, and applied by him successfully to the explanation of Zend forms. Thus he succeeded in tracing the general outlines of the Zend lexicon and in fixing its grammatical forms, and founded the only correct method of interpreting the "Avesta." He also gave the first notions of a comparative mythology of the "Avesta" and the "Veda," by showing the identity of the "Vedic Yama" with the "Avesta Yima," and of Traitâna with Thraêtaona and Ferìdûn. Thus he made his "Commentaire sur le Yasna" a marvellous and unparalleled model of critical insight and steady good sense, equally opposed to the narrowness of mind which clings to matters of fact without rising to their cause and connecting them with the series of associated phenomena, and to the wild and uncontrolled spirit of comparison, which, by comparing everything, confounds everything. Never sacrificing either tradition to comparison or comparison to tradition he knew how to pass from the one to the other, and was so enabled both to discover facts and to explain them.