Copy letter, from Sir John Herschel to [A. J. F.] Yvon Villarceau, dated at Collingwood Copy of a letter, copied as part of the correspondence project led by Colonel John Herschel FRS following the death of his father. Has passed Yvon Villarceau's memoirs on the calculation of orbits on to G. B. Airy for publication; copies will be sent [see Yvon Villarceau's 1849-4-1]. Notes that Yvon Villarceau's methods are similar to those of U. J. J. Leverrier. 19 April 1849