By means of laws like that of the Correspondence of Letters, discovered by Rask and Grimm, it has been possible to determine the exact form of words in Gothic, in cases where no trace of them occurred in the literary documents of the Gothic nation. Single words which were not to be found in Ulfilas have been recovered by applying certain laws to their corresponding forms in Latin or Old High-German, and thus retranslating them into Gothic. But a much greater conquest was achieved in Persia. Here comparative philology has actually had to create and reanimate all the materials of language on which it was afterwards to work. Little was known of the language of Persia and Media previous to the Shahnameh of Firdusi, composed about 1000 A.D., and it is due entirely to the inductive method of comparative philology that we have now before us contemporaneous documents of three periods of Persian language, deciphered, translated, and explained. We have the language of the Zoroastrians, the language of the Achæmenians, and the language of the Sassanians, which represent the history of the Persian tongue in three successive periods--all now rendered intelligible by the aid of comparative philology, while but fifty years ago their very name and existence were questioned. The labours of Anquetil Duperron, who first translated the Zend-Avesta, were those of a bold adventurer--not of a scholar. Rask was the first who, with the materials collected by Duperron and himself, analysed the language of the Avesta scientifically. He proved-- 1. That Zend was not a corrupted Sanskrit, as supposed by W. Erskine, but that it differed from it as Greek, Latin, or Lithuanian differed from one another and from Sanskrit. 2. That the modern Persian was really derived from Zend as Italian was from Latin; and 3. That the Avesta, or the works of Zoroaster, must have been reduced to writing at least previously to Alexander's conquest. The opinion that Zend was an artificial language (an opinion held by men of great eminence in Oriental philology, beginning with Sir W. Jones) is passed over by Rask as not deserving of refutation.