instance of his sagacity that in his letter of 20 Feb. 1770, dealing with education, he specifies as the finest subject for historical study the ‘decline of the Roman Empire,’ lamenting that in English there is nothing on this period that is not superficial. His conjectural restoration of a lost treatise of Apollonius of Perga was printed (1770) at the Clarendon Press. On 30 Nov. 1773 he was elected one of the secretaries of the Royal Society. In the ‘Transactions’ of the society (Phil. Trans. lxiv. 96) is a letter addressed to him (21 Dec. 1773) by Richard Price, D.D., occasioned by Priestley's experiments on gases. On 14 Jan. 1774 he was incorporated B.C.L. at Oxford, proceeding D.C.L. on 18 Jan. In the same month he was presented by the father of his pupil to the rectory of Albury, Surrey, holding it by dispensation along with Newington. Lowth, as soon as he became bishop of London, made him his domestic chaplain, with a prebend at St. Paul's in 1777. At the end of the year he succeeded his father as lecturer at St. Martin's-in-the-Fields. In 1779 Horsley resigned Albury; in 1780 Lowth presented him to Thorley, on the resignation of Archdeacon Eaton; in 1781 Lowth made him archdeacon of St. Albans, and in 1782 presented him to the vicarage of South Weald, Essex, when he resigned Thorley.
Horsley made his first controversial allusion to Priestley in a Good Friday sermon (17 April 1778) on the distinction between moral and physical necessity. Priestley in June published a very courteous letter in reply, treating the difference between his position and Horsley's as merely verbal. On 22 May 1783 Horsley delivered a charge to the clergy of his archdeaconry, in which he submitted to severe criticism the first part of Priestley's ‘History of the Corruptions of Christianity’ (1782), dealing with the development of opinion on the person of our Lord. Almost simultaneously Samuel Badcock [q. v.] attacked Priestley in the ‘Monthly Review’ (June 1783). Into the main argument Horsley declined to enter, though he gave it as his own view that the opinion of the church was uniform on this point during the first three centuries. He restricted his polemic to an endeavour to show that Priestley was ‘altogether unqualified to throw any light upon a question of ecclesiastical antiquity’ (Tracts, 1789, p. 85). Priestley was a pioneer of the modern method of investigating the development of doctrine, but the weak places in his scholarship and his haste in drawing conclusions were exposed by Horsley with much learning and in a style of extraordinary vigour, combining great dignity with an unsparing force of sarcasm. The controversy lasted till 1790; in the course of it Priestley published his maturer work, ‘History of Early Opinions,’ 1786, which Horsley declined to read.
In December 1783 Horsley became a member of the club then established by Johnson at the Essex Head, Essex Street, Strand; he attended Johnson's funeral in the following year. During the session 1783–4 occurred a very acrimonious dispute respecting the management of the Royal Society, in which Horsley took a prominent part against the president, Sir Joseph Banks [q. v.] Horsley at length withdrew from the society. His speech is given in ‘An Authentic Narrative of the Dissensions in the Royal Society,’ 1784. Kippis, in his ‘Observations,’ 1784, criticised Horsley's action and defended Banks. In 1785 Horsley completed his edition of Sir Isaac Newton's works, which he had projected in 1776, and begun in 1779. He had access to Newton's papers in the possession of John Wallop, second earl of Portsmouth, and found ‘a cartload’ of manuscripts on religious topics, but did not deem them fit to be published.
Thurlow's favour promoted Horsley to a prebend at Gloucester 19 April 1787. In 1788 he was raised to the see of St. David's, still retaining the rectory of Newington. His primary charge was delivered in 1790. He did much to improve the condition of his clergy, helping them in their difficulties with his purse as well as his counsel, and raising the minimum stipend for curates from 7l. to 15l. It had been customary for Welsh candidates for orders to receive their whole training at one of the nonconformist academies. Horsley declined to accept certificates from Castle Howel [see Davis, David]. He urged his clergy by letter (24 Aug. 1789) to use their influence at the Carmarthen election against John George Phillips, who had voted for the repeal of the Test and Corporation Acts, and who notwithstanding was re-elected (1790). In the House of Lords, however, he spoke (31 May 1791) in favour of the Catholic bill. He took an active part in 1792 in favour of the measure for the relief of the Scottish episcopal church; the clause requiring the Scottish clergy to signify their assent to the Anglican articles was of his introduction. On 30 Jan. 1793 he preached a remarkable sermon before the House of Lords at Westminster Abbey, depicting the dangers of the revolutionary spirit; as he began his peroration the whole assembly rose in rapt enthusiasm.
In November 1793 Horsley was translated
