too exhausted to bring forth something better.
Oldenburg remained at the university until May 1667, when he accompanied his pupil Jones on a long journey to the continent. From Saumur, where they spent the first year, Oldenburg sent letters to Milton and Boyle. In the second year he and his pupil visited other parts of France and Germany, and in May 1669 he wrote from Paris, where they remained until their return to England in 1660.
In November 1660 the society which afterwards became the Royal Society, and which had existed in a more or less nebulous condition since 1646, took definite shape. Among the first members proposed and elected (26 Dec.) were Oldenburg and his pupil Ranelagh. Oldenburg was elected a member of the first council and he and Dr. John Wilkins were appointed the first secretaries (22 April 1663); but he received no salary until 1669. In the Birch MSS. at the British Museum (4441, f. 27) is preserved, in Oldenburg's handwriting, an account of the duties of the 'Secretary of ye R. Soc' 'He attends constantly,' the paper recites, 'the meetings both of ye Society and Councill; noteth the observables, said and done there; digesteth ym in private; takes care to have ym entred in the Journal- and Register-books; reads over and corrects all entrys; sollicites the performances of taskes recommended and undertaken; writes all Letters abroad and answers the returns made to ym, entertaining a corresp. wth at least 30 psons [not fifty, as in Weld's 'History']; employes a great deal of time and takes much pains in satisfying forran demands about philosophicall matters, disperseth farr and near store of directions and inquiries for the society's purpose, and sees them well recommended, etc. Q. Whether such a person ought to be left vn-assisted?' It was with the intention that the sale should procure him a remuneration for his gratuitous services that he was authorised in 1664 to publish the ' Transactions of the Society;' but the net profit seldom amounted to 40l. a year. From June 1666 to the following March the sittings of the Royal Society were suspended, owing to the plague. Oldenburg and his family remained in London, but escaped the infection. In September 1666 the great fire of London ruined most of the booksellers, and greatly obstructed the publication of Oldenburg's 'Transactions.' Boyle made vain endeavours to secure for Oldenburg, who was suffering much pecuniary distress, the post of Latin secretary formerly held by Milton.
While he held the secretaryship of the Royal Society, Oldenburg's foreign correspondence grew very large. He could not have coped with it, he said, had it not been his habit to answer every letter the moment he received it. His aim is tersely expressed in his letter to Governor Winthrop (1667): 'Sir, you will please to remember that we have taken to taske the whole Vniverse, and that we were obliged to doe so by the nature of our Dessein. It will therefore be requisite that we purchase and entertain a commerce in all parts of ye world wth the most philosophicall and curious persons, to be found everywhere.' Among his correspondents was Spinoza. Oldenburg had visited Spinoza at Rijnsburg (Rhynsburg) in 1661, and numerous letters passed between them from that year to 1676. At first Oldenburg enthusiastically urged Spinoza to publish his writings: 'Surely, my excellent friend, I believe that nothing can be published more pleasant or acceptable to men of learning and discernment than such a treatise as yours. This is what a man of your wit and temper should regard more than what pleases theologians of the present age and fashion, for by them truth is less regarded than their own advantage.' But afterwards he became cautious, complaining that Spinoza confused God with nature, and that his teaching was fatalistic. In these letters Oldenburg defines his relations to both speculative philosophy and exact science.
The vastness of Oldenburg's foreign correspondence, which, though mainly scientific, was in part political, excited suspicion at the English court, and, under warrants dated 20 June 1667, he was imprisoned in the Tower (cf. Pepys, 28 June 1667). He was in the Tower for more than two months, and Evelyn visited him there on 8 Aug. On 3 Sept. Oldenburg wrote to Boyle that he had been stifled by the prison air, and had recruited his health on his release at Crayford in Kent, and was now falling again to his old trade.
The publisher threatened at the time to discontinue printing the 'Transactions,' and Oldenburg, in a letter to Boyle, expressed a wish that he had 'other means of gaining a living.' From the beginning of 1670 he accordingly undertook many translations. His 'Prodromus to a Dissertation by Nicholas Steno concerning Solids naturally contained within Solids,' 8vo, appeared in the following year. 'A genuine Explication of the Book of the Revelation,' by A. B. Piganius, 8vo, 1671 ; 'The History of the late Revolution of the Empire of the Great Mogol,' by F. Bernier, 8vo, 1671; and 'The Life of the Duchess of Mazarine,' followed