Plates from Royal Society Publications: Illustrating William Roy's Baseline on Hounslow Heath

Plates from Royal Society Publications: Illustrating William Roy's Baseline on Hounslow HeathAuthor(s): Jim BennettSource: Notes and Records of the Royal Society of London, Vol. 60, No. 2 (May 22, 2006), pp.225-230Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/20462582 .Accessed: 16/06/2014 09:09

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NOTES & RECORDS Notes Rec. R. Soc. (2006) 60, 225-230

THE ROYAL doi: 10. 1098/rsnr.2006.0138 SOCIETY Published online 26 April 2006

PLATES FROM ROYAL SOCIETY PUBLICATIONS: ILLUSTRATING WILLIAM ROY'S BASELINE ON HOUNSLOW HEATH

Jim Bennett*, Museum of the History of Science, Broad Street, Oxford OX] 3AZ, UK

These four plates from Philosophical Transactions are among the finest and most detailed precision drawings published in the eighteenth century. They accompany the first of three

long papers by William Roy dealing with his trigonometric survey of southern England. This

was the British contribution to a project to link the observatories of Paris and Greenwich by

triangulation, and it would expand into the national institution of the Ordnance Survey.

Running to 96 pages, the first paper, of 1785, was easily the shortest: in 1787 he published

282 pages and 504 in 1790. The subject of the first paper was also foundational to the entire

project, since the initial and fundamental requirement of such a survey is to establish as

accurate a baseline as possible. The paper was 'An account of the measurement of a base on

Hounslow-Heath', Phil. Trans. R. Soc. 75, 285-480 (1785). The most obvious characteristic of Roy's paper is its painstaking thoroughness-not only

in technical details, but also in its narrative. Roy tells a historical story that begins with the

Jacobite rebellion in Scotland in 1745, and he points to the general truth that large-scale

survey will often depend on military necessity: 'if a country has not actually been surveyed,

or is but little known, a state of warfare generally produces the first improvements in its

geography' (ibid., p. 385). Having played a leading role in the survey of Scotland that

followed the battle of Culloden, Roy gives an account of his subsequent promotion of a

survey for the whole island, the impetus that came from the proposal by Cassini de Thury to

connect the two national observatories, and the choice of Hounslow Heath for the baseline.

The first three plates illustrate three methods for measuring such a line.

'One of the first instruments, which that able artist Mr. Ramsden had orders to prepare, was

a steel chain, one hundred feet in length, the best that he could make' (ibid., p. 394). Jesse

Ramsden was Britain's finest maker of precision instruments, soon himself to become a

Fellow of the Royal Society. Although not intended for the final measurement, this was a

chain constructed 'on the principles of that of a watch' (ibid., p. 394). It is described in great

detail and its parts are illustrated exhaustively and at their actual sizes in the accompanying

plate (plate 1). A surveyor's chain was normally one of the least regarded of everyday

instruments, but it was precisely Roy's intention to elevate mundane measurement, through

obsessive care over every detail. Surveying was to be raised from a routine practical art to a

national project and even the chain could be an object of aesthetic admiration: a flick from

one end was communicated to the other 'in a few seconds... in a beautiful vertical serpentine

line' (ibid., p. 397).

*[email protected]

225 C) 2006 The Royal Society


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But this was only the prelude: the chain was not intended for the final measurement. So

Roy describes in even greater detail his first attempt to measure the line with maximum

precision, using reinforced or 'trussed' deal rods capped with bell-metal end-pieces. Three

of these rods, each 20 ft long, were made and could be used alternatively by abutting them

end-to-end, or by overlapping them and aligning marks close to their ends. The plate

illustrates these alternative methods (plate 2). The descriptive account is exhaustive, but even

so, Roy thinks that the illustrations have the explanatory edge: 'Their [the rods'] general

construction will be better conceived from the plan and elevation, and other representations

of their principal parts, in tab. XVIII. than by any description, however particular, conveyed

in words' (ibid., p. 399). The exhaustive account is particularly remarkable, because it was

eventually decided that the deal rods were not sufficiently stable and that method was

abandoned. Wooden rods were replaced by three glass tubes (plate 3). The magnificent plate shows the

cases that contained them, set on their stands, the central case open to reveal the tube, the

covers of the cases to either side showing the horizontal stems of thermometers whose bulbs

hung inside, close to the tubes. The final plate (plate 4) is an outstanding visual account of the

pyrometer designed by Ramsden to determine the temperature corrections to be applied to

measurements with the steel chain and glass tubes. The engraver of the plates is identified as

the leading practitioner of the time, James Basire, who was engraver to the Royal Society, but

there is no attribution on the plates of the original draughtsman; perhaps we are to assume that

it was Roy himself.

Why all this obsessive detail? Roy explained that he had 'given a very minute account of

the actual operations in the field, that the Public, being informed of every circumstance, might

be better enabled to judge of the accuracy of the result' (ibid., p. 461). Clearly they were

meant to judge the result sufficiently accurate to bear a national survey, and the plates were to

play their part in this persuasion. Their quality and detail had a rhetorical as well as an

informative purpose. They were part of the assurance that every detail had been carefully considered and every source of uncertainty minimized. In a sense the paper, with its

impressive plates, was to play a role analogous to the baseline itself: its integrity and the

confidence it could command had to be sufficient to sustain the entire project-not just

linking the observatories but also Roy's greater ambitions for a national survey. The baseline

measurement was indeed a public event. The King paid a visit, and the President of the Royal

Society, Sir Joseph Banks, set up what we might call a hospitality tent, 'where his immediate

guests, and the numerous visitors whom curiosity drew to the spot, met with the most

hospitable supply of every necessary and even elegant refreshment' (ibid., pp. 425-426).

It was appropriate that Roy's conclusion was simply a number, but one towards which all

the resources of his project and his paper had been directed. The final calculated figure for the

length of the baseline, reduced to sea level, was 27 404.7219 feet.

It will doubtless be allowed, that infinite pains have been taken in the field and otherwise, throughout the whole of this operation, to obtain a just conclusion; but as the most accurate measurement imaginable is still more liable to err in excess than in defect, we will throw away some useless decimals, and establish the ultimate length of the base at 27 404 feet and seven-tenths. (ibid., p. 478)



Article Contentsp. 225p. 226p. 227p. 228p. 229p. 230

Issue Table of ContentsNotes and Records of the Royal Society of London, Vol. 60, No. 2 (May 22, 2006), pp. 135-230Front Matter[Illustration]: Frontispiece Shows a Photograph of James Prescott Joule Frs (1818-89)[Editorial]: The Palace of Westminster Frescoes, Kelvin's Secretary and the Calcutta School of Tropical Medicine [pp. 135-137]Arthur Herbert Church FRS and the Palace of Westminster Frescoes [pp. 139-159]Dr. Thomas Carver and Lord Kelvin [pp. 161-170]Leonard Rogers KCSI FRCP FRS (1868-1962) and the Founding of the Calcutta School of Tropical Medicine [pp. 171-181]ReportHistory and Philosophy of Science at Leeds [pp. 183-192]An Unpublished Letter by Charles Darwin in the Royal Society's Archives [pp. 193-197]Edmond Halley's Last Portrait [pp. 199-201]

Essay ReviewReview: Temperature: A Showcase for Complementary Science? [pp. 203-214]

Book ReviewReview: The Many Images of Isaac Newton [pp. 215-216]Review: A Beguiling Story [pp. 217-218]Review: The Dutch Galileo? The Greatness of Huygens' Science [pp. 219-220]Review: Laplace: The Man [pp. 221-223]

Plates from Royal Society Publications: Illustrating William Roy's Baseline on Hounslow Heath [pp. 225-230]Back Matter

Plates from Royal Society Publications: Illustrating William Roy's Baseline on Hounslow Heath

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