Copy letter, from Sir John Herschel to [A. J. F.] Yvon Villarceau, dated at Collingwood Contemporary copy in sender's hand, signed by sender. 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