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1792 he held a similar appointment in Staffordshire, employing his spare time in experimental research and in preparing a translation of Buffon's Natural History of Birds, which was published in nine 8vo vols. in 1793, and brought him some money. For the next twelve years (passed chiefly in London or at Largo, with an occasional visit to the Continent) he continued his physical studies, which resulted in numerous papers contributed by him to Nicholson's Philosophical Journal, and in the publication (1801) of the Experimental Inquiry into the Nature and Propagation of Heat, a work which gained for its author the Rumford Medal of the Royal Society of London. In 1805 he was elected to succeed Playfair in the chair of mathematics at Edinburgh, not, however, without violent though unsuccessful opposition on the part of a narrow-minded clerical party who accused him of heresy in some thing he had said as to the "unsophisticated notions of mankind" about the relation of cause and effect. During his tenure of this chair he published two volumes of a Course of Mathematics – the first, entitled Elements of Geometry, Geometrical Analysis, and Plane Trigonometry, in 1809, and the second, Geometrical Analysis, and Geometry of Curve Lines, in 1821; the third volume, on "Descriptive Geometry" and the "Theory of Solids" was never completed. With reference to his invention (in 1810) of a process of artificial congelation, he published in 1813 A Short Account of Experiments and Instruments depending on the relations of Air to Heat and Moisture; and in close connexion with the subject of this treatise he also wrote a paper on the æthrioscope, which appeared in 1818 in the Transactions of the Royal Society of Edinburgh. In 1819, on the death of Playfair, he was promoted to the more congenial chair of natural philosophy, which he continued to hold until his death, and in 1823 he published, chiefly for the use of his class, the first volume of his never-completed Elements of Natural Philosophy. Leslie's main contributions to physics were made by the help of the "differential thermometer," an instrument whose invention was contested with him by Count Rumford. By adapting to this instrument various ingenious devices he was enabled to employ it in a great variety of investigations, connected especially with photometry, hygroscopy, and the temperature of space. In 1820 he had been elected a corresponding member of the Royal Institute of France, the only distinction of the kind which he valued, and early in 1832 he was, on the recommendation of Lord Chancellor Brougham, created a knight of the Guelphic order. He died at Coates, a small property which he had acquired near Largo, on November 3 of the same year.
LESLIE, Thomas Edward Cliffe (1827-1882), one of the ablest and most original English economists of the present century, was born in the county of Wexford in (as is believed) the year 1827. He was the second son of the Rev. Edward Leslie, prebendary of Dromore, and rector of Annahilt, in the county of Down. His family was of Scotch descent, but had been connected with Ireland since the reign of Charles I. Amongst his ancestors were that accomplished and energetic prelate, John Leslie, bishop first of Raphoe and afterwards of Clogher, who, when holding the former see, offered so stubborn a resistance to the Cromwellian forces, and the bishop's son Charles, the well-known nonjuror. Cliffe Leslie received his elementary education from his father, who resided in England, though holding church preferment as well as possessing some landed property in Ireland; by him he was taught Latin, Greek, and Hebrew, at an unusually early age; he was afterwards for a short time under the care of a clergyman at Clapham, and was then sent to King William's College, in the Isle of Man, where he remained until, in 1842, being then only fifteen years of age, he entered Trinity College, Dublin. He was a distinguished student there, obtaining, besides other honours, a classical scholarship in 1845, and a senior moderatorship (gold medal) in mental and moral philosophy at his degree examination in 1846. He became a law student at Lincoln's Inn, was for two years a pupil in a conveyancer's chambers in London, and was called to the English bar. But his attention was soon turned from the pursuit of legal practice, for which he seems never to have had much inclination, by his appointment, in 1853, to the professorship of jurisprudence and political economy in Queen's College, Belfast. The duties of this chair requiring only short visits to Ireland in certain terms of each year, he continued to reside and prosecute his studies in London, and became a frequent writer on economic and social questions in the principal reviews and other periodicals. In 1870 he collected a number of his essays, adding several new ones, into a volume entitled Land Systems and Industrial Economy of Ireland, England, and Continental Countries. J. S. Mill gave a full account of the contents of this work in a paper in the Fortnightly Review, in which he pronounced Leslie to be "one of the best living writers on applied political economy." Mill had sought his acquaintance on reading his first article in Macmillan's Magazine; he admired his talents and took pleasure in his society, and treated him with a respect and kindness which Leslie always gratefully acknowledged.
In the frequent visits which Leslie made to the Continent, especially to Belgium and some of the less-known districts of France and Germany, he occupied himself much in economic and social observation, studying the effects of the institutions and system of life which prevailed in each region, on the material and moral condition of its inhabitants. In this way he gained an extensive and accurate acquaintance with Continental rural economy, of which he made excellent use in studying parallel phenomena at home. The accounts he gave of the results of his observations were among his happiest efforts; "no one," said Mill, "was able to write narratives of foreign visits at once so instructive and so interesting." In these excursions he made the acquaintance of several distinguished persons, amongst others of M. Léonce de Lavergne and M. Émile de Laveleye. To the memory of the former of these he afterwards paid a graceful tribute in a biographical sketch (Fortnightly Review, February 1881); and to the close of his life there existed between him and M. de Laveleye relations of mutual esteem and cordial intimacy.
Two essays of Leslie's appeared in volumes published under the auspices of the Cobden Club, one on the "Land System of France" (2d ed., 1870), containing an earnest defence of la petite culture and still more of la petite propriété; the other on "Financial Reform" (1871), in which he exhibited in detail the impediments to production and commerce arising from indirect taxation. Many other articles were contributed by him to reviews between 1875 and 1879, including several discussions of the history of prices and the movements of wages in Europe, and a sketch of life in Auvergne in his best manner; the most important of them, however, related to the philosophical method of political economy, notably a memorable one which appeared in the Dublin University periodical, Hermathena. In 1879 the provost and senior fellows of Trinity College published for him a volume in which a number of these articles were collected under the title of Essays in Political and Moral Philosophy. These and some later essays, which ought one day to be united with them, together with the earlier volume on Land Systems, form the essential contribution of Leslie to our economic literature. He had long contemplated, and had in part written, a work on English economic and legal history, which would have been his magnum opus – a more substantial fruit of his genius and
