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CALDECOTT, JOHN (1800–1849), astronomer and meteorologist, had been acting during about four years as commercial agent to the government of Travancore at the port of Allepey, when, in 1836, he became impressed with the advantages derivable to science from the establishment of an astronomical station in southern India. His views, enforced by the British resident, Colonel Fraser, were at once acceded to by Rama Vurmah, then rajah of Travancore. An observatory (described in the Madras Journal, vi. 56) was built at Trevandrum, Caldecott was appointed its director, and in July 1837 observations were begun with portable instruments, the use of which had long constituted his recreation. The completion of a permanent instrumental outfit, including two mural circles by Simms and Jones respectively, a transit, and 7½-foot equatorial by Dollond, claimed his presence in Europe in December 1838, and while there he fell in with the movement recently set on foot by Humboldt for carrying out a connected scheme of magnetic research all over the world. Authorised by the rajah, he purchased a set of instruments of the pattern devised by Dr. Lloyd for the British stations, and on his return to Trevandrum in April 1841 a magnetic and meteorological observatory was erected for their reception. A great mass of observations was quickly accumulated, copies of which were forwarded to the Royal Society, as well as to the court of directors of the East India Company. Their publication was undertaken by the rajah, after Caldecott had made a journey to England in 1846, with the futile hope of enlisting the aid of some scientific society; and in their laborious preparation for the press he was deeply engaged until his death at Trevandrum, of paralysis, on 16 Dec. 1849.

Caldecott showed great energy in overcoming the difficulties attendant on scientific work in India, and collected materials of value despite inevitable shortcomings. His experiments (1842–5) on the temperature of the ground at various depths possessed a special interest as being the first of the kind made within the tropics (Trans. R. Soc. of Ed. xvi. 369). They showed, contrary to the assertion of Kupffer, that the earth is there 5° to 6° F. hotter than the air, and disproved the invariability of temperature at a depth of one foot, imagined by Boussingault, and used by Poisson to support his mathematical theory of heat. Caldecott presented to the British Association in 1840 a series of horary meteorological observations begun June 1837 in pursuance of a suggestion by Sir John Herschel (Report, 1840, ii. 28); and experimented, with Taylor of the Madras observatory, July to October 1837, on the direction and intensity of the magnetic force in southern India (Madras Journal, ix. 221). He first drew scientific attention to the bi-annual inversion of the law of variation near the magnetic equator, but attributed the change to the influence of the monsoon (see Trans. R. Soc. of Ed. xxiv. 670). He observed and computed elements for the great comet of 1843 (Mem. R. A. Soc. xv. 229); and his observations of that of 1845 proved available for Hind's calculations of its path (Astr. Nach. No. 540; Month. Not. vi. 215). The solar eclipse of 21 Dec. 1843 was observed by him at Parratt, near the source of the Mahé river, where it just fell short of totality, but afforded a striking view of Baily's beads (Mem. R. A. Soc. xv. 171). He was elected a fellow both of the Royal Astronomical and of the Royal Societies in 1840.

[Bombay Times, 2 Jan. 1850; Athenæum, 9 Feb. 1850; Annual Reg. 1849, p. 299; Broun's Report on Trevandrum Observatories; R. Soc. Cat. Sc. Papers.]

A. M. C.