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Issue No.01 - January-March (2003 vol.25)
pp: 34-47
Michael R. Williams , Computer History Museum
Erwin Tomash , Charles Babbage Institute
<p>The sector-also known as the proportional, geometric, or military compass-was an analog calculating instrument used widely from the late 16th century until modern times. The origins and usage of this commonly encountered instrument are not well known. This article provides historical background on the sector's invention and on its precursor instruments, and describes the uses for many of the scales commonly found on these instruments.</p>
Michael R. Williams, Erwin Tomash, "The Sector: Its History, Scales, and Uses", IEEE Annals of the History of Computing, vol.25, no. 1, pp. 34-47, January-March 2003, doi:10.1109/MAHC.2003.1179877
1. The illustration inFigure 1high res imageis a case in point. It is the frontispiece of the work by D. Henrion (in this case the edition published by J. Deshayes); L' usage du compas de proportion,Paris, 1681.
2. See in particular H. Coggeshall, The art of practical measuring, by the sliding rule…, J. Ham, ed., London, 1767.
3. J. Werner, Joannis Verneri de triangulis shpaericis libre quatuor, A.A. Bjornbo, ed., Leipzig, 1907.
4. N. Raimarus Ursus, Fundamentum astronomicum…, Strasbourg, 1599.
5. N. Tartaglia, La nova scienta inventa da Nicolo Tartalea B.,Venice, 1537.
6. See G. Galilei, Operations of the geometric and military compass, S. Drake, translator, Washington, D.C., 1978.
7. Incidentally, Joost Bürgi, a highly talented instrument maker, must be credited, along with John Napier, with the independent discovery of logarithms.
8. See, for example, S. Drake, "Galileo and the First Mechanical Computing Device," Scientific Am., Apr. 1976, pp. 104-113, and other works by the same author.
9. J. Errard, La geometrie et practique generalle d'icelle,Paris 1594, p. 2.
10. Further information on Errard can be found in M.D. Pollak, Military Architecture, Cartography and the Representation of the Early Modern European City, Newberry Library, Chicago, 1991.
11. T. Hood, The making and use of the geometricall instrument, called a sector,London, 1598.
12. Scientific Instrument Soc., Bull. of the Scientific Instrument Soc., no. 38, 1993, p. 28.
13. A. Turner, Early Scientific Instruments, Sotheby's, 1987, p. 159.
14. See, for example, J. Ward, The Lives of the professors of Gresham College,London, 1740.
15. Although Gunter's book ( The description and use of the sector ) was only published in 1624, it is clear that a manuscript version was available as early as 1606.
16. J. Napier, Rabdologiae seu numerationis per virgulas,Edinburgh, 1617.
17. From the dedicatory epistle in the English translation of Napier's Rabdologia : "Rabdology by John Napier," W.F. Richardson, translator, Tomash Publishers, 1990, p. 3.
18. G. Galilei, Le operazioni del compasso geometrico et militare,Padua, 1606.
19. B. Capra, Usus et fabrica circini cuiusdam proportionis,Padua, 1607.
20. G. Galilei, Difesa di Galileo Galilei…, Venice, 1607.
21. M. Bernegger, translator, De proportionum instrumento…, Strasbourg, 1613.
22. For example, see G. Galilei, Tractatus de proportionum instrumento, quod merito compendium universægeometriædixeris, M. Bernegger, translator, Strasbourg, 1635.
23. Thomas Hood's first sector also had a quadrant arc.
24. The radius is usually the length of the line of lines, but occasionally a sector is inscribed with another line, usually labeled as a line of 6 or 60, which is the defining radius. In the latter case the other scales, such as those for dialing, may also be related to this line.
25. This scale was first devised by Samuel Forster and published in E. Gunter, The Works of that Famous Mathematician Mr. Edmund Gunter, fifth edition, London, 1673.
26. See, for example, F. Edward Hulme, Mathematical drawing instruments and how to use them,London, 1880.
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