by Simon Schaffer
© Oxford University Press 2004 All rights reserved
Atwood, George (bap. 1745, d. 1807), mathematician, was baptized at St Clement Danes, Westminster, London, on 15 October 1745, the son of Thomas Atwood, the parish curate, and his wife, Isabella Sells of Inglesham, Wiltshire. He was apparently the eldest son, with at least two younger brothers: James, who followed him to Westminster School and Trinity College, Cambridge, and subsequently became East India Company chaplain in Madras, and Thomas, who after schooling at Westminster eventually succeeded his father as curate at St Margaret's, Westminster. George entered Westminster School as king's scholar in 1759, became captain of the school in 1764, entered Trinity College as a pensioner on 5 June 1765, and was elected a scholar on 2 May 1766. He graduated in 1769 as third wrangler and first Smith's prizeman, gained a fellowship in October 1770, proceeded MA in 1772, and became tutor the next year.
Atwood then took an active part in reviving natural philosophy teaching in Cambridge. On 13 June 1776 he was elected a fellow of the Royal Society. In that year the Cambridge natural philosophy professor Anthony Shepherd finally ceased his rather desultory triennial lectures, and reform proposals by the radical mathematician John Jebb for overhauling teaching were defeated. In November 1776 Atwood published a description of a regular lecture course he had started in the observatory over the great gate of his college, to whose master the pamphlet was dedicated. He demonstrated elementary mechanics and hydrostatics with pulleys, pendulums, and air-pumps, as well as electricity, magnetism, and optics, including Leonhard Euler's principles of achromatic lenses. He also taught astronomy, mentioning recent surveys of the earth's density by the mathematician Charles Hutton and the astronomer royal Nevil Maskelyne, plus Maskelyne's favoured lunar method for longitude. The lectures drew large audiences, including William Pitt, and complemented the reform of 1779 that overhauled the Senate House examination and highlighted mathematical expertise. In November 1779 Atwood gave up his tutorship and sent a copy of his course description to Joseph Banks, president of the Royal Society, as part of an unsuccessful bid for the remunerative secretaryship of the board of longitude.
Atwood's reputation spread beyond his university, principally because of his design of a pulley machine to demonstrate motions of bodies under constant forces. Built by the London instrument maker George Adams the younger, it consisted of a 6 foot column carrying conical pivots for two pairs of brass wheel-bearings to minimize friction at a brass pulley. On the pulley ran a long silk cord, at each end of which was a stack of weights. Fitted to the column was a pendulum clock, and set behind the cord was a rule with movable stops, one to terminate the weights' fall, the other to remove weights instantaneously from the stack as it fell. Demonstrations showed the proportionality of impressed force and change of motion, the innate passivity of matter, and the behaviour of bodies in collision. The first public account of Atwood's machine was published in French in 1780 by Adams's colleague Jean Hyacinthe de Magellan, who dispatched machines to Spain and in the spring of 1781 to Pavia University, where his client was Alessandro Volta, the new natural philosophy professor. Magellan complained of Atwood's delay in printing a description, and in 1781 the mathematics professor Gregorio Fontana, a colleague of Volta's at Pavia, instead adapted Atwood's course outline into Italian, adding sections on mechanics and the treatment of observational errors. In the summer of 1781 Atwood himself sent the Royal Society methods for correcting sightings through sextant mirrors, and commended this work to Banks as an example of the practical application of abstruse geometry.
Atwood became an increasingly public figure in London. In the autumn of 1783 he supported an abortive attack on Banks's Royal Society regime by Hutton, Maskelyne, and other mathematicians. In the spring of 1784 he at last published two accounts of his lectures and machine. One was a lengthier version of his course outline with treatment of his demonstration equipment and new remarks on collision, thermometry, and lightning rods. The other was a treatise published by the university press that based discussions of impact and simple harmonic motion on elementary mechanics, criticized past scientific reliance on conservation principles, then gave a long account and fine picture of his machine. Atwood insisted that geometrical mechanics could be made consistent with practical engineering. In such cases, especially the work on water-wheels by the engineer John Smeaton in 1776, Atwood used estimates of friction to reconcile academic and field trials. He also discussed work by the gunner Benjamin Robins on projectile velocities and by the Scottish natural philosopher Joseph Black on latent heat and fixed air in bodies' cohesion. Atwood's publications helped him to a post in London: in February 1784 his former student Pitt was elected for Cambridge University, and as prime minister soon offered him a lucrative appointment in the customs at £500 per year.
During the 1790s Atwood's machine was widely distributed by London instrument makers to virtuosi and lecturers, while its inventor contributed papers to the Royal Society on the pressing problems of horology and navigation. In each case he relied on comparisons between his own geometrical analysis and scale models of complex artefacts. Maskelyne's tests of marine clocks at the board of longitude provided almost frictionless devices compatible with Atwood's rational mechanics. In 1793-4 Atwood worked with the leading clockmaker Thomas Earnshaw to compare his mathematics of cylindrical balances with the spring-driven watches made by Larcum Kendall, which James Cook had taken on his Pacific voyages. In early 1796 he published a long paper on stable and unstable equilibria in floating bodies, discussed and criticized Euler's work on the problem because it ignored ship displacement through large angles, and repeated that resistance to motion could not be assumed to be proportional to the square of ships' speeds. He won the Royal Society's Copley medal for this essay, then followed it in early 1798 with another lengthy study on ship stability, in which his mathematics of flotation was compared with the performance of an East India Company vessel built by the naval architects Randall and Brent. Atwood also worked on excise problems. In 1790 he was made inspector of tontine certificates, and during violent wartime struggles over corn prices in 1800-01 he compiled a vast survey of the assize of bread, the system of price regulation in force since the thirteenth century, including trials of the grain quantity in standard loaves, and of data on bakers' profits, designed to support the tory government's new policy on price regulation. It was said that this intense work and calculation had broken Atwood's health.
Atwood's last public commission was prompted in April 1801 by a parliamentary enquiry into Thomas Telford's scheme for a single span 600 foot cast-iron bridge across the Thames at Blackfriars. A select committee sent queries to Maskelyne, Hutton, Atwood, and others, and the inconclusive report based on their replies appeared in June 1801. Atwood consulted Telford on bridge loading and in the same year independently issued his own views, with rules for calculating arch thrust based on the assumption that the bridge was made of hard, rigid, separable wedges. He ignored friction, which he reckoned could only increase bridge stability. In a supplement finished in late 1803 and printed the next year, Atwood compared his calculations with a model made by Berge, a London mechanic, using pulleys to estimate bridge thrust. Hutton, who issued his own report, charged that bridge work was obviously a new topic for Atwood, that the Cambridge mathematician claimed results already well known to engineers as his own, and that Atwood's report was a sign of failing powers. Atwood died, unmarried, in Westminster at the age of sixty-one, and was buried at St Margaret's, where his brother was curate, on 11 July 1807.
SIMON SCHAFFER
Sources
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Venn, Alum. Cant.
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Sci. Mus., machine
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