CHEMISTRY OF THE EIGHTEENTH CENTURY. 355 



and others, by whom he was encouraged to undertake the composition 

 of "A History of Electricity," which work first brought him into notice 

 as a scientific man, for many of his own experiments are described in 

 the book. In 1767 he removed from Warrington to take charge of a 

 chapel at Leeds, and for another six years he remained at Leeds, 

 where he wrote many works, and began his career as a chemist, which 

 soon raised him to the highest position in the ranks of British men of 

 science. It was while residing in Leeds that Priestley discovered 

 oxygen, and this discovery is the brightest jewel of his scientific crown. 

 His researches on carbonic acid and nitrous oxide were also of high 

 importance. Priestley's mental activity was by no means entirely ab- 

 sorbed by his chemical investigations ; he was also engaged in meta- 

 physical disputations and theological polemics, and wrote besides a 

 " History of Optics." Priestley's career at this time is a fine instance 

 of a man's inner power triumphing over his circumstances. His posi- 

 tion was a contrast to that of Cavendish: an obscure dissenting minister 

 struggling to maintain a family on the slenderest of incomes, his pro- 

 gress in his profession checked by a defect of his voice and the un- 

 popularity of his theological opinions. His invention, however, was 

 stimulated to obviate the smallness of the means he could command 

 in the purchase of apparatus by ingenuity in the construction of new 

 and cheap instruments of investigation. His methodical regularity 

 rendered it easy for him to register every new fact he observed, and 

 the ardour of his scientific curiosity made him a watchful observer. 

 He wrote with care, and his experience in teaching had trained him 

 to a certain clearness of expression, 



The scientific celebrity which our dissenting minister had acquired 

 induced Lord Shelburn (afterwards Marquis of Lansdowne) to invite 

 Priestley to take up his residence with him nominally as librarian, with 

 a salary of ^250 a year. He accepted, and accordingly left Leeds for 

 Wiltshire, where he completed his experiments on the different kinds 

 of air. His controversial publications on divinity and metaphysics 

 were not suspended, and some of his treatises found for their refuta- 

 tion active employment for theologians of a polemical turn. 



It was probably on account of Priestley's religious and political 

 opinions that the relations between his patron and himself soon came 

 to an end. Priestley had been elected to the membership of the 

 Royal Society in 1767, and the Copley Medal was awarded to him 

 in 1772. On leaving Wiltshire, he took charge of a chapel at Bir- 

 mingham, and at this place associated on terms of intimate friend- 

 ship with Watt and Wedgwood. He was one of the small band of 

 illuminati who called themselves the " Lunar Society." Priestley, 

 when denouncing in his works the selfish passions that corrupt society, 

 often maintained that a high ideal morality must make men better ; 

 and in reviewing the progress which had been made in natural science 

 during the years of the eighteenth century that lay behind him, he 



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