(17421830), geographer, born in 1742, was son of John Rennell, captain in the royal artillery, by Anne Clarke of Chudleigh in Devonshire. Losing both parents when quite a boy, the one killed in battle, the other making a poor second marriage, young Rennell found a guardian, who remained a true friend through life, in the Rev. Gilbert Burrington, vicar of Chudleigh. Rennell entered the navy in 1756, at the age of fourteen, and was present at the disastrous action of St. Cast on the coast of Brittany. In 1760 he went out to the East Indian station, and served in the Grafton under Captain Hyde Parker (17141782) [q.v.] during the three following years, when he saw some active service, including a cutting-out expedition at Pondicherry. He soon mastered the theory and practice of marine surveying, and, on account of his proficiency in this regard, Parker lent his services to the East India Company. He served for a year on board one of the company's ships bound to the Philippine Islands, with the object of establishing new branches of trade with the natives of the intervening places. During this cruise Rennell drew several charts and plans of harbours, some of which have been engraved by Dalrymple.
At the end of the seven years' war there appeared to be no chance of promotion for a youth without interest. So, acting upon his captain's advice, Rennell obtained his discharge from the navy at Madras, and applied for employment in the East India Company's sea service. He at once received command of a vessel of two hundred tons; but she was destroyed by a hurricane in Madras roads in March 1763, with all hands. Fortunately, her captain was on shore, and he was at once appointed to command a small yacht called the Neptune, in which he executed surveys of the Palk Strait and Pamben Channel. His next cruise was to Bengal, and he arrived at Calcutta at the time when Governor Vansittart was anxious to initiate a survey of the British territory. Owing to the friendship of an old messmate, who had become the governor's secretary, Rennell was appointed surveyor-general of the East India Company's dominions in Bengal, with a commission in the Bengal engineers, dated 9 April 1764. He was only twenty-one years of age when he met with this extraordinary piece of good fortune.
Rennell's survey of Bengal, which was commenced in the autumn of 1764, was the first ever prepared. The headquarters of the surveyor-general were at Dacca, and in the successive working seasons he gradually completed his difficult, laborious, and dangerous task. In 1776, when on the frontier of Bhutam, his party was attacked by some Sanashi fakirs, and Rennell himself was desperately wounded. He never entirely recovered from the effects of his injuries, and was thenceforth less able to withstand the effects of the climate. He received the rank of major of Bengal engineers on 5 April 1776, and retired from active service in 1777, after having been engaged on the survey for thirteen years. The government of Warren Hastings granted him a pension, which the East India Company somewhat tardily confirmed. The remainder of Rennell's long life was devoted to the study of geography. His Bengal Atlas was published in 1779, and was a work of the first importance for strategical as well as administrative purposes. He was elected a fellow of the Royal Society in 1781, and took up his residence in Suffolk Street, near Portland Place, where his house became a place of meeting for travellers from all parts of the world. His second great work was the construction of the first approximately correct map of India. It was accompanied by a memoir containing a full account of the plan on which the map was executed, and of his authorities. The first edition was published in 1783; the third, with both map and memoir considerably enlarged, in 1793. In 1791 Rennell received the Copley medal of the Royal Society; and from this time he was frequently consulted by the East India Company on geographical questions. After the completion of the map of India, Rennell gave his attention to comparative geography, and conceived a comprehensive scheme for a great work on western Asia. His geography of Herodotus, which occupied him during many years, only formed a part of his whole project. It was published in two volumes, a monument of laborious research and acute and lucid criticism. Sir Edward Bunbury recorded his opinion that Rennell's Herodotus remains of the greatest value. In 1814 Rennell published his Observations on the Topography of the Plain of Troy, and in 1816 his Illustrations of the Retreat of the Ten Thousand; while after his death his daughter published two volumes, entitled A Treatise on the Comparative Geography of Western Asia (London, 1831, with atlas), which may be looked upon as the great geographer's workshop, displaying his critical methods and his treatment of the materials he collected.
Rennell gave much of his attention to the geography of Africa, and, among other results of his researches, he has the merit of having first established the true view of the voyage of Hanno and its southern limit. In 1790 he constructed a new map of the northern half of Africa for the African Association, accompanied by a very able memoir on the materials for compiling such a map. On the return of Mungo Park in 1797 all his materials were placed in the hands of Rennell, who worked out the ardent young traveller's routes with great care. Rennell's geographical illustrations were published with a map of Park's route, which was afterwards used to illustrate Park's book.
Rennell was before all things a sailor. He never forgot that he had been a surveying midshipman. He showed this in the enormous amount of labour and trouble he devoted to the study of winds and currents, collecting a great mass of materials from the logs of his numerous friends and correspondents, and prosecuting his inquiries with untiring zeal. About 1810 he began to reduce his collections to one general system. His current charts of the Atlantic and his memoirs were completed by him, although they were not published in his lifetime. He was the first to explain the causes of the occasional northerly set to the southward of the Scilly Islands, which has since been known as Rennell's Current. He did this in two papers read before the Royal Society on 6 June 1793 and 13 April 1815. His current charts and memoirs were invaluable at the time, and he was offered the post of first hydrographer to the admiralty, but he declined it because the work would interfere with his literary pursuits. Among minor publications Rennell wrote papers in the Archæologia on the ruins of Babylon, the identity of Jerash, the shipwreck of St. Paul, and the landing of Cæsar.
After the death of Sir Joseph Banks, Rennell was for the next ten years the acknowledged head of British geographers. Travellers and explorers came to him with their rough work, projects were submitted for his opinion, and reports were sent to him from all parts of the world. In 1801 he had become an associate of the Institute of France, and in 1825 he received the gold medal of the Royal Society of Literature. He died on 29 March 1830. He was interred in the nave of Westminster Abbey, and there is a tablet to his memory, with a bust, near the western door. The year of his death saw the foundation of the Royal Geographical Society.
Rennell married, at Calcutta, in 1772, Jane, daughter of Dr. Thomas Thackeray, headmaster of Harrow, and great-aunt of the novelist, William Makepeace Thackeray. His wife died in 1810. His second son, William, was in the Bengal civil service, and died in 1819, leaving no children; the eldest, Thomas, was unmarried, and survived until 1846. His talented daughter Jane was married, in 1809, to Admiral Sir John Tremayne Rodd, K.C.B. Lady Rodd devoted several years to the pious labour of publishing her father's current charts and revising new editions of his principal works. She died in December 1863.
Rennell was of middle height, well proportioned, with a grave yet sweet expression of countenance. The miniature painted for Lord Spencer represents him sitting in his chair, with folded arms, as in reflection. He was diffident and unassuming, but ever ready to impart information. His conversation was interesting, and he had a remarkable flow of spirits. In all his discussions he was candid and ingenuous.
Sir Henry Yule's Memoir in the Royal Engineers' Journal, 1881; Mrs. Bayne's Thackeray Family History, privately printed; Markham's Life of Rennell in the Century Science Series, 1895; Rennell's Works.
C. R. M.
Original date of publication: 1896