David Gans, who was born in Westphalia in 1541, and died in Prague in 1613, was a great scholar and writer. He began his studies at Cracow, in a Rabbinical seminary, but after a while he gave up the learning of the Talmud, and devoted himself to the study of astronomy and history and geography. He wrote, in Hebrew, a chronological History, עֶמַח דָּוִד, in two parts, consisting of Jewish history and general history. His chief works besides were מָנֵן דָּוִד (Shield of David), an arithmetic guide; מִנְדַּל דָּוִד (Tower of David), a geometrical work; and נֶחְמָד וְנָעִים (Pleasant and Desirable), an astronomical volume. In the introduction to the last, Gans gives a short account of astronomy up to his own time, including a sketch of the astronomer Copernicus, with whom he was personally acquainted. David Oppenheim, Rabbi of Prague (born 1664, died 1736), is famous as the owner of a valuable Hebrew library. The history of the books which he collected is, perhaps, more interesting than a summary of the contents of them might be. The nucleus of the collection was made by a certain Samuel Oppenheim, who, an agent at the court of Vienna, asked and received, as a reward for some financial transaction, a number of valuable Hebrew books, which Prince Eugene had looted during the Turkish war. These were left by will to Rabbi David Oppenheim, who largely added to the collection. He made out a list of missing and desirable volumes, and sent it in all directions, with orders to buy for him. In this way he raised his number of printed books to 7,000, and of MSS. to 1,000. Being afraid that the censor in Prague might mutilate or confiscate some of the books, Rabbi Oppenheim kept his beloved library at Hanover, in the house of his father-in-law, Lipman Cohen. After Rabbi David Oppenheim’s death, his son, Herschel Isaac Oppenheim, Rabbi at Hildesheim, got the collection. After his death (1770) it was sent to Hamburg, and pledged to a senator there for 50,000 marks. It subsequently came into the hands of a certain Isaac Cohen in Hamburg, and was valued by Moses Mendelssohn as worth 50,000 thalers.[57] After some negotiations with Jewish merchants and German princes, the library was bought by the Bodleian Library at Oxford, in 1829, for 9,000 thalers, and there it is at the present time.