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Rh feature that has not been already illustrated. Among higher religions orthodox Islam has never had real priests, doing religious acts on behalf of others, though it has, like Protestant churches, leaders of public devotion (imāms) and an important class of privileged religious teachers (‘ulemā). But a distinction of grades of holiness gained by ascetic life has never been entirely foreign to the Eastern mind, and in the popular faith of Mahommedan peoples something very like priesthood has crept in by this channel. For where holiness is associated with ascetic practices the masses can never attain to a perfect life, and naturally tend to lean on the professors of special sanctity as the mediators of their religious welfare. The best example, however, of a full-blown priestly system with a monastic hierarchy grafted in this way on a religion originally not priestly is found in Tibetan Buddhism (see ), and similar causes undoubtedly had their share in the development of sacerdotalism in the Christian Church. The idea of priestly asceticism expressed in the celibacy of the clergy belongs also to certain types of heathen and especially Semitic priesthood, to those above all in which the priestly service is held to have a magical or theurgic quality.

 PRIESTLEY, JOSEPH (1733–1804), English chemist and Nonconformist minister, was born on the 13th of March 1733 at Fieldhead, a hamlet near Birstal in the West Riding of Yorkshire. He was the eldest of a family of six. His father, Jonas Priestley, a woollen-cloth dresser of moderate means, was the son of a member of the Established Church, but both he and his wife, the only daughter of a farmer named Swift, were Nonconformists. Three years after the death of Mrs Priestley in 1739, Joseph's father's sister, Mrs Keighley, took him to live with her, and sent him at the age of twelve to a neighbouring grammar school. In his holidays he learned Hebrew from Mr Kirkby, a dissenting minister at Heckmondwike, who subsequently took entire charge of his education. From the age of sixteen to nearly twenty his health was so unsatisfactory that he attended neither school nor college, but worked at Chaldee and Syriac, began to read Arabic, and mastered &rsquo;S Gravesande's Natural Philosophy, together with various textbooks of logic and metaphysics. An uncle having promised him a place in a counting-house at Lisbon, he also learned French, German and Italian to fit himself for the post. But his aunt was anxious for him to be a minister, as he himself desired, and therefore in 1752, when his health had improved, he went to Daventry to attend the Nonconformist academy formerly carried on by Dr P. Doddridge at Northampton. There he stayed three years, exchanging his early Calvinism for a system of “necessarianism” under the influence of D. Hartley's Observations on Man and A. Collins's Philosophical Enquiry concerning Human Liberty. In 1755 he was appointed to a small congregation at Needham Market, in Suffolk, where he was not very successful. In 1758 he obtained a more congenial congregation at Nantwich, where he opened a school at which the elementary lessons were varied with experiments in natural philosophy. Three years later he removed to Warrington as classical tutor in a new academy, and there he attended lectures on chemistry by Dr Matthew Turner of Liverpool and pursued those studies in electricity which gained him the fellowship of the Royal Society in 1766 and supplied him with material for his History of Electricity. In 1762 he had married the daughter of Isaac Wilkinson, a Wrexham ironmaster. In 1767 he was appointed to the charge of Mill Hill Chapel at Leeds, where he again changed his religious opinions from a loose Arianism to definite Socinianism and wrote many political tracts hostile to the attitude of the government towards the American colonies. He also began his researches into “different kinds of airs,” getting a plentiful supply of “fixed air” from a brewery next door to his house. By the end of 1771 his scientific reputation was such that he was suggested for the post of “astronomer” to Captain Cook's second expedition to the South Seas, but his unorthodox opinions were objectionable to certain members of the board of longitude and the appointment was not ratified. In 1772, the year in which he was chosen a foreign associate of the French Academy of

Sciences, he accepted the position of librarian and literary companion to Lord Shelburne (afterwards 1st Marquess of Landsdowne) at Calne, with a salary of £250 a year and a house. With that nobleman he travelled on the Continent; the month of October 1774 he spent in Paris, and meeting Lavoisier and his friends, gave them an account of the experiment by which on the previous 1st of August he had prepared “dephlogisticated air” (oxygen). In 1780 he parted company with his patron, who allowed him an annuity of £150 for life, and settling at Birmingham was appointed junior minister of the New Meeting Society. There he continued his literary and scientific labours, enjoying congenial intercourse with such men as Matthew Boulton, James Keir, James Watt and Erasmus Darwin at the periodical dinners of the Lunar Society. On the 14th of July 1791 the Constitutional Society of Birmingham arranged a dinner to celebrate the anniversary of the fall of the Bastille. Priestley, according to his own account, “had little to do with it.” But his predilections in favour of the revolutionists were notorious, and the mob seized the occasion to burn his chapel and sack his house at Fairhill. He and his family escaped, but his material possessions were destroyed and the labour of years annihilated. He retreated to London, where he felt safe, though he continued to be an object of “troublesome attention,” and even the fellows of the Royal Society shunned him. But he received an invitation to become morning preacher at Gravel Pit Chapel, Hackney. This he accepted, and performed the duties of the charge till 1794, when he determined to follow his three sons, who had emigrated to America in the previous year. On the 7th of April he embarked with his wife at Gravesend and reached New York on the 4th of June. Finally settling at Northumberland, Pennsylvania, he lived there for nearly ten years, until on the 6th of February 1804, after clearly and audibly dictating a few changes he wished made in some of his writings, he quietly expired.

Priestley was a most voluminous writer, and his works (excluding his scientific writings) as collected and edited by his friend J. T. Rutt in 1817–1832 fill 25 octavo volumes. (The first volume, containing his life and correspondence, was issued separately in two parts, 1831–1832.) His first appearance as an author was in 1761, when he published the Scripture Doctrine of Remission and the Rudiments of English Grammar. His chief theological and philosophical works were Institutes of Natural and Revealed Religion (3 vols., 1772–1774); History of the Corruption of Christianity (2 vols., 1782); General History of the Christian Church to the Fall of the Western Empire, vols. i. and ii. (1790), vols. iii. and iv. (1802–1803); Disquisitions relating to Matter and Spirit (1777), and various essays and letters on necessarianism. But his theological writings are forgotten, and he is chiefly remembered as a scientific investigator who contributed especially to the chemistry of gases. Yet judged by modern standards he had an inadequate conception of the meaning of ordered research. In reference to his preparation of oxygen he says, “It provides a striking illustration of a remark I have more than once made in my philosophical writings and which can hardly be too often repeated, viz. that more is owing to what we call chance—that is, philosophically speaking, to the observation of events arising from unknown causes—than to any proper design or preconceived theory in this business.” If in this sentence he scarcely does justice to the powers of logical inference and inductive reasoning displayed in much of his work, it remains true that blind experiment heating a substance, or treating it with some reagent, to see what would happen was his characteristic method of inquiry. Thus by heating spirits of salt he obtained “marine acid air” (hydrochloric acid gas), and he was able to collect it because he happened to use mercury, instead of water, in his pneumatic trough. Then he treated oil of vitriol in the same way, but got nothing until by accident he dropped some mercury into the liquid, when “vitriolic acid air” (sulphur dioxide) was evolved. Again he heated fluorspar with oil of vitriol, as K. W. Scheele had done, and because he was employing a glass vessel he got “fluor acid air” (silicon fluoride). Heating spirits of hartshorn, he was able to collect “alkaline air” (gaseous ammonia), again because he was using mercury in his pneumatic trough; then, trying what would happen if he passed electric sparks through the gas, he decomposed it into nitrogen and hydrogen, and “having a notion” that mixed with hydrochloric acid gas it would produce a “neutral air,” perhaps much the same as common air, he synthesized sal ammoniac. Dephlogisticated air (oxygen) he prepared in August 1774 by heating red oxide of mercury with a burning-glass, and he found that in it a candle burnt with a remarkably vigorous flame and mice lived well. He concluded that it was not common air, but the substance, “in much greater perfection,” that rendered common air respirable