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BRADLEY, James A letter to the Right Honourable George, Earl of Macclesfield, concerning an apparent motion observed in some of the fixed stars. London  1747

4to. 43 pp. Bound in paneled calf à l’antique. Macclesfield library stamps on initial leaves. A fresh copy, excellent.

First edition, separately printed, of Bradley’s letter announcing his discovery of nutation of the earth’s axis, and the dedicatee’s copy, bearing stamps from the library of the Earl of Macclesfield, himself a keen amateur astronomer. Halley’s successor as astronomer royal, Bradley was “a brilliant original thinker, a very skillful observer, and a thoroughly practical astronomer” (DSB II.389). His “discoveries of aberration and nutation first rendered possible exact knowledge of the places of the fixed stars, and thereby of the movements of the other celestial bodies” (DNB II.1079). Nutation of the earth, “a ‘nodding’ movement of the axis due to the moon’s unequal action upon the equatorial parts of the earth, was more than suspected early in 1732; but Bradley did not consider the proof complete until he had tracked each star through an entire revolution of the moon’s nodes (18.6 years) back to its mean place… In September 1747 he was at length fully satisfied of the correspondence of his hypothesis with facts; and 14 Feb. 1748 a letter to his friend and patron the Earl of Macclesfield, in which he set forth the upshot of his twenty years’ watching and waiting, was read before the Royal Society” (DNB II.1077). The letter contains geometrical discussion and tables of precession, aberration and nutation for several stars from 1727 to 1747.Bradley (1693?-1762), a vicar who became the Savilian chair of astronomy at Oxford, ranks “as one of the most eminent astronomers of the eighteenth century” (Henry Smith Williams, A History Of Science, 1904). He made his other great discovery—of stellar aberration (1728)—in attempting to explain the peculiar motion of the pole-star, which resulted in the first direct observational evidence that the earth really was orbiting the sun, and the first accurate measurement of the speed of light (within 2% of the currently accepted value). After winning the Copley medal for his work on nutation, he was able to obtain important new instruments for the Royal Observatory, consequently laying “the firm foundation of modern practical astronomy” (ibid.)Bradley’s Letter was also published in the Philosophical transactions of the Royal Society of London (1748, v. 45, p. 1-43); based on the imprint date of 1747, and the practice of providing offprints to their authors prior to distribution of the journal issues, it seems likely that this separate edition appeared first.
* Sparrow, Milestones of Science, 28; DSB II.388; DNB II.1074-79.

$US3300

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