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 LEIBNITZ AS A LIBRARIAN. 145 As already stated, Leibnitz's second post in the ducal house was that of historiographer. Of his labours in this respect a contemporary tells us : 'In order to obtain material for writing the history of the House of Brunswick, he undertook journeys through Bavaria, Franconia, Suabia, and other German provinces, to examine books and manu- scripts. He despatched Fridericus Heynius to buy books and rare manuscripts ; he journeyed with Heynius to explore the Imperial Library at Vienna, and from thence he passed into Italy to examine archives and celebrated libraries. He also examined records in Marburg, Frankfort-on-Maine, Munich, and Vienna, and when in Italy he visited Venice, Modena, and Rome. Altogether, he was absent from Hanover on this business from 1687 to 1690. Leibnitz had been librarian to the Duke of Brunswick-Luneburg for many years ; but it is on his return home that we hear of his appointment, in 1690, in the same capacity to the ducal library at Wolfenbiittel, a post he retained for the rest of his life. While still at Rome he had been offered the Keepership of the Vatican Library, but his decision to remain at any rate, nominally within the reformed Church obliged him to decline it. Though without doubt his known experience in everything relating to books was the principal reason for his being approached, it must have been believed that his conversion to Rome would not be very difficult to secure, and there was ground for the belief in the opinions expressed in his c De jure suprematus, 5 and his later work, ' Systema theo- logicum' (1686), written with the view of finding a