PRIESTLEY, Joseph (1733-1804). Two autograph letters signed ('J. Priestley'), the first to the Secretary of the Philosophical Society of Orleans, Birmingham, 12 May 1785, expressing his appreciation at being elected a member, 'From the labours of so many persons engaged in the same pursuit, we cannot doubt but that the knowledge of nature will be rapidly advanced', one page, folio, the second to Dr Barton in Philadelphia, Northumberland [Pennsylvania], 16 June 1796, 'I ... requested that you would be so good as to correct the press for a pamphlet I wished to publish on the subject of the doctrine of phlogiston', also asking for some samples for experimentation from his correspondent (a botanist), 3 pages, 4to, integral address panel. (2)