Letter, from [A. J. F.] Yvon Villarceau to Sir John Herschel, dated at Paris Autograph letter signed by sender. Is sending a communication to John Frederick William Herschel for insertion in the Monthly Notices of the Royal Astronomical Society Seems to be some problem with understanding Yvon Villarceau's calculations of the orbits of double stars, so Yvon Villarceau explains his method. 18 May 1849