own, and to the latter a number of halakic discourses. [Jewish Encyclopedia] Works His main work of responsa, titled Noda Biyhudah (נודע ביהודה, "Known in Judah", a reference to Psalms 76:2 and his father's name), is one of the principal sources of Jewish law of his age. Famous decisions include those limiting autopsy to prevent a clear and present danger in known others. This collection was esteemed by rabbis and scholars, both for its logic and for its independence with regard to the rulings of other Acharonim as well as its simultaneous adherence to the writings of the Rishonim. Other works Dagul Mervavah on the Shulkhan Arukh (cf. Song of Solomon 5:10) Tziyun le-Nefesh Chayah (abbreviated as Tzelach, named in reference to his mother, whose name was Chayah) on the Talmud. Drushei HaTzlach, a collection of sermons. Ahavas Tzion Doresh LeTzion Notable views Returning to the Talmud Landau was disturbed by the increasing influence of non-Talmudic sources on the Jewish community. He believed that many kabbalistic concepts were being understood in a heretical fashion, and was especially concerned with the prospect of the kabbalistic ideology of the Sabbatean movement infiltrating the populace. Landau frequently spoke against teaching Kabbalah to the masses, and was echoed in this regard by his student, Elazar Fleckeles, who praised the government for instituting laws limiting the study of kabbalah. In his responsa, when asked about matters that had no source in the Talmud, Landau would often respond, "it is not my way to study any issue which is not discussed in the Talmud". He responded in such a manner to inquiries about the ethical will of Rabbi Yehuda haChasid, which contains various instructions not found in the Talmud, a question about the proper manner of writing certain letters in the Torah scroll according to kabbalistic literature, and other similar questions. Opinion on the Zohar In his sefer Derushei HaTzlach, Landau argued that the Zohar can not be considered reliable, since it only came into the hands of the Jewish people many hundreds of years after Rashbi's death, and thus lacks an unbroken mesorah as to its authenticity, among other reasons. Clashes with the haskalah movement Landau condemned the haskalah movement in harsh terms. In numerous public sermons, he campaigned against the study of heretical philosophy. He particularly singled out Hartwig Wessely for criticism after the publication of the latter's Divrei Shalom V'emes, which advocated abandoning