that combination; and he thus invented the method of eudiometry or the ascertainment of the relative purity of different kinds of atmospheric air. In considering the great merits of Priestly as an experimentalist, it must not be forgotten that he had almost to create the apparatus by which his processes were to be performed. He for the most part had to construct his instruments with his own hands, or to make unskilful workmen form them under his own immediate direction. His apparatus, however, and his contrivances for collecting, keeping, transferring gaseous bodies, and for exposing substances to their action, were simple and effectual, and they continue to be still used by chemical philosophers without any material improvement. Although Priestly was the first to discover oxygen, and thus give the basis of the true theory of combustion, he clung all his life with a wonderful pertinacity to the Phlogistic Theory,[54] and nothing in after life would make him give it up. In 1773 Priestly accepted an invitation from Lord Shelbourne (afterwards first Marquis of Lansdowne), to fill the place of librarian and philosophic companion, with a salary of 250_l._, reducible to 150_l._ for life should he quit the employment; 40_l._ a-year was also allowed him for the expense of apparatus and experiments, and homes were provided for his family in the neighbourhood both of Lord Shelbourne's town and country residence. Priestly remained with the Earl of Shelbourne for six or seven years, at the end of which period, in 1780, he settled at Birmingham and became minister of a dissenting body there. While residing at Birmingham he engaged fiercely in polemical writings and discussions, particularly with Gibbon and Bishop Horseley. He also displayed a warm interest in the cause of America at the time of the quarrel with the mother-country, and likewise took an active and not very temperate part in the controversy to which the French Revolution gave rise; and, having published a 'Reply' to Burke's famous pamphlet, he was in 1791 made a citizen of the French Republic. This gave considerable offence to the inhabitants of Birmingham, an ironical and somewhat bitter pamphlet against the high church party still further excited their feelings against him; and a dinner which was given on the 14th of July, to celebrate the anniversary of the attack upon the Bastile, became the signal for a general riot. The tavern where the party were assembled was attacked, and, although Dr. Priestly was not present, his house and chapel were immediately afterwards assailed, he and his family escaped, but his house, library, and manuscripts were burnt. Although his losses were made up to him partially by an action at law and partially by a subscription among his friends, Priestly felt that he could no longer live at Birmingham, he therefore removed to London and succeeded his friend Dr. Price as principal of the Hackney Academy. He, however, still found himself highly unpopular and shunned