Letter, from [Gottfried Leibniz] to [Henry Oldenburg], dated in Paris Letter in Leibniz' hand, addressed to "Monsieur Oldenburg [Counsel of the King and Secretary of the Royal Society]", and carried "[by a friend]". Dated 15 July using Gregorian calendar by Leibniz. Titled "Monsr Leibniz concerning his new Arithmetical Instrument and some geometrical discoveries" in Henry Oldenburg's hand on the last page. Describes an arithmetical instrument that allows him to perform multiplications - [clarification: likely the stepped reckoner]. Lays out his method to express the area of a circle using infinite series and mentions his general analytical method in a paragraph underlined in red to mark its inclusion in the printed 'Commercium Epistolicum' 1722 edition, page 115, XXXII Mentions [Robert] Boyle, [John] Wallis, and [Robert] Hooke in the closing of the letter. Two postscripts which include his forwarding address in Paris and mention Pascal and Cassini. Noted "received in London 12 July 1674 by M. Walter, responded 15 July". Endorsed 'No. 32: p. 114' 5 July 1674