His father, John Martyn, was a "captain" or mine-agent at Gwennap. The lad was educated at Truro grammar school under Dr Cardew, entered St John's College, Cambridge, in the autumn of 1797, and was senior wrangler and first Smith's prizeman in 1801. In 1802 he was chosen a fellow of his college. He had intended to go to the bar, but in the October term of 1802 he chanced to hear Charles Simeon speaking of the good done in India by a single missionary, William Carey, and some time afterwards he read the life of David Brainerd, the apostle of the Native Americans.
He resolved, accordingly, to become a Christian missionary. On October 22, 1803, he was ordained deacon at Ely, and afterwards priest, and served as Simeon's curate at the church of Holy Trinity, taking charge of the neighbouring parish of Lolworth. He was about to offer his services to the Church Missionary Society, when a disaster in Cornwall deprived him and his unmarried sister of the provision their father had made for them, and rendered it necessary that he should obtain a salary that would support her as well as himself. He accordingly obtained a chaplaincy under the British East India Company and left for India on July 5 1805. For some months he was stationed at Aldeen, near Serampur; in October 1806 he proceeded to Dinapur, where he was soon able to conduct worship among the locals in the vernacular, and established schools. In April 1809 he was transferred to Cawnpore, where he preached in his own compound, in spite of interruptions and threats.
He occupied himself in linguistic study, and had already, during his residence at Dinapur, been engaged in revising the sheets of his Hindustani version of the New Testament. He now translated the whole of the New Testament into Hindi also, and into Persian twice. He translated the Psalms into Persian, the Gospels into Judaeo-Persic, and the Prayer-book into Hindostani, in spite of ill-health and "the pride, pedantry and fury of his chief munshi Sabat." Ordered by the doctors to take a sea voyage, he obtained leave to go to Persia and correct his Persian New Testament, whence he wished to go to Arabia, and there compose an Arabic version.
Accordingly, on October 1, 1810, having seen his work at Cawnpore crowned on the previous day by the opening of a church, he left for Calcutta, whence he sailed on January 7 1811, for Bombay, which he reached on his thirtieth birthday. From Bombay he set out for Bushire, bearing letters from Sir John Malcolm to men of position there, as also at Shiraz and Isfahan. After an exhausting journey from the coast he reached Shiraz, and was soon plunged into discussion with the disputants of all classes, "Sufi, Mahommedan, Jew, and Jewish Mahommedan, even Armenian, all anxious to test their powers of argument with the first English priest who had visited them."
Having made an unsuccessful journey to Tabriz to present the shah with his translation of the New Testament, he was seized with fever, and after a temporary recovery, had to seek a change of climate. On September 12 1812, he started with two Armenian servants, crossed the Araxes, rode from Tabriz to Erivan, from Erivan to Kars, from Kars to Erzerum, from Erzerum to Chiflik, urged on from place to place by a thoughtless Tatar guide, and, though the plague was raging at Tokat (near Eski-Shehr in Asia Minor), he was compelled by prostration to stop there. On the 6th of October he died. Macaulay's youthful lines, written early in 1813, testify to the impression made by his career.
His Journals and Letters were published by Samuel Wilberforce in 1837. See also Lives by John Sargent (1819; new ed. 1885), and G Smith (1892); and The Church Quarterly Review (Oct. 1881).
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