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BIRD, JOHN (1709–1776), mathematical instrument maker, was a native of the county of Durham, and by trade a cloth-weaver. Finding himself one day in a clockmaker's shop, he was struck with the irregularity of the divisions on a dial-plate, thought out a plan for improving them, and for some time engraved dial-plates for recreation. On the strength of a certain reputation thus gained he came to London about 1740, and was engaged by Sisson to cut the divisions on his instruments. Countenanced and instructed by Graham, he perfected his methods, and by 1745 was carrying on business independently. His well-known premises were situated in the Strand.

As the mechanical coadjutor of Bradley, he acquired European fame. An instrumental refit for the Royal Observatory was sanctioned towards the close of 1748. In February 1749 Bird received an order for a brass quadrant of 8-feet radius, which in June 1750 was ready for use. The construction of this instrument, by rendering possible the consummate accuracy of Bradley's observations, marked an epoch in practical astronomy. It was built with the utmost solidity, weighing about 8 cwt., and bore a double arc, one with ninety, the other with ninety-six divisions, accurately cut by Graham' method of ‘continual bisections.' Its price of 300l. was compensated by sixty-two years of valuable service, and although replaced in 1812 (by which time it had become eccentric with use) by Troughton’s circle, it is still reverently preserved at Greenwich. A half-size model was, by order of the commissioners of longitude, prepared by Bird in 1707, and deposited in the British Museum.

No sooner was the Greenwich quadrant completed than a duplicate was ordered for the observatory of St. Petersburg, another reached Cadiz, and a fourth was used by D’Agelet and Lalande at the École Militaire. With a similar instrument of 3-feet radius, Tobias Mayer made his lunar observations at Göttingen. Indeed, most of the chief continental observatories still possess a Bird’s quadrant, valuable even now as affordiug a measure of the probable errors of earlier observations (Maedler, Gesch. d. Himmelskunde, i. 455). Of their necessarily imperfect kind, these instruments could scarcely be surpassed.

Bird further supplied Bradley, about 1750, with a new transit instrument, as well as with a 40-inch movable quadrant, and put a fresh set of divisions, in 1753, upon the great mural arc constructed by Graham for Halley. The extraordinary value attached to his work is evinced by the fact that a sum of 500l. was paid to him by the commissioners of longitude, on the conditions that he should during seven years instruct an apprentice in his methods, and deliver in writing, upon oath, a full and unreserved account of them. Such was the origin of the two treatises entitled respectively ‘The Method of dividing Astronomical Instruments,' London, 1767, and ‘The Method of constructing Mural Quadrants exemplified by a Description of the Brass Mural Quadrant in the Royal Observatory at Greenwich,' London, 1768, both published by order of the commissioners, and furnished each with a preface by the astronomer-royal (Maskelyne), setting forth the singular circumstances under which they had been composed. They were bound together, so as to form one work, were re-issued in 1785, and supplemented by W. Ludlam's ‘Introduction and Notes on Mr. Bird’s Method of dividing Astronomical Instruments,' solemnly vouched for as accurate by Bird in June 1773, and published at the expense of Alexander Aubert [q. v.] in 1786.

The standard yards of 1758 and 1760, destroyed in the conflagration of the houses of parliament, 16 Oct. 1834, were both constructed by Bird (see Baily, Mem. R. A. Soc. ix. 80–1). He observed the transit of Venus, 6 June 1761, at Greenwich with Bliss and Green, and the annular eclipse of 1 April 1765, using on both occasions reflectors made by himself (Phil. Trans. lii. 175–6, liv. 142). He died, 31 March 1776, aged 67.

[Ludlam’s Preface to Introduction and Notes on Mr. Bird's Method; Bradley’s Miscellaneous Works, passim; Poggendorf's Biog.-Lit. Handwürterbuch; MS. Addit. 5728; Gent. Mag. xlvi. 192; Bromley's Catalogue of Engraved Portraits, p. 398.]

A. M. C.