It was while at Leeds, in the year 1771, that Dr. Priestley was invited by Sir Joseph Banks, who had charge of the scientific arrangements, to accompany Captain Cook's second expedition to the South Seas, in the capacity of astronomer, and accepted the invitation. He was, however, rejected by the Board of Longitude, on account of his religious opinions, which called from him the following pointed letter to Sir Joseph Banks:

After six years' stay at Leeds, Dr. Priestley left, and entered into a relation with Lord Shelburne, afterward Marquis of Lansdowne, the arrangement being brought about by Dr. Price. Priestley was to be librarian and companion to his lordship, with a salary of $1,250 a year, and a house, and a life-pension of $750 a year in case of separation. His family was situated near Lord Shelburne's country-seat, where he spent his summers, but a great part of the winter was passed in his lordship's house in London. Priestley traveled with Shelburne on the Continent, and spent some time in Paris, where he says he found "all the philosophical persons, to whom I was introduced at Paris, unbelievers in Christianity, and even professed atheists. As I chose on all occasions to appear as a Christian, I was told by some of them that I was the only person they had ever met with, of whose understanding they had any opinion, who professed to believe in Christianity. But, on interrogating them on the subject, I soon found that they had given no proper attention to it, and did not really know what Christianity was. This was also the case with a great part of the company that I saw at Lord Shelburne's." While in this situation, Dr. Priestley had much leisure for scientific research, and was active in