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Harriot's ‘Regiment of the Sun’ and its Background in Sixteenth-Century Navigation

Published online by Cambridge University Press:  05 January 2009

John J. Roche
John J. Roche
Affiliation:
Linacre College, Oxford OX1 3JA.
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Extract

It is well known that Richard Hakluyt in a publication of 1581 congratulated Sir Walter Ralegh for employing Harriot to teach him and his many sea captains the sciences of navigation. Even more important, however, was the navigational research carried out by Harriot on behalf of Ralegh. He made important theoretical advances in map theory and in navigational astronomy, carried out the astronomical observations needed for a reform in navigational tables, and designed and himself tested at sea improved navigational instruments. Harriot had many other responsibilities in connexion with Ralegh's enterprises. From August 1585 to June 1586 Harriot was in Virginia, and in 1589 he was listed as one of Ralegh's colonists in Munster. He collected intelligence concerning America for Ralegh, and his publication of 1588 was effective as propaganda for Virginia. Harriot was also entrusted with financial, and even political responsibilities by Ralegh. Instructing Ralegh and his captains in navigation was an important part of Harriot's work but it is more likely that he did this as the occasion demanded, rather than on a regular basis.

Type
Research Article
Information
The British Journal for the History of Science , Volume 14 , Issue 3 , November 1981 , pp. 245 - 262
Copyright
Copyright © British Society for the History of Science 1981

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References

NOTES

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85 BM Add.MS 6788, ff. 468–9.

86 See below, p. 257.

87 ibid.

88 BM Add.MS 6788, f. 469.

89 ibid.

90 See n. 57, above.

91 HMC 241/11, pp. 2–3. In fact the maximum solar parallax is only about 9″: Smart, , op. cit. (54), p. 420.Google Scholar

92 The calculation of this value has had to be omitted due to cost and lack of space. Full details are available from the author.

93 Bm Add.MS 6788, f. 489.

94 In practice it was usually too small for navigators to bother about; see BM Add.MS 6788, f. 489.

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104 Table 1, below.

105 See n. 92, above.

106 In 3½ hours the sun moves approximately 9′ in longitude.

107 See table 1, below and n. 92, above.

108 BM Add.MS 6788, f. 206.

109 From Table 1, the errors in the equinoxes in 1593 are —3h 29′ and +2h42′ respectively. Half the difference is 23½ minutes.

110 BM Add.MS f. 207v, and plate 2.

111 See nn. 99, 100, 101, above.

112 Roche, , op. cit. (23), p. 35.Google Scholar

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114 BM Add.MS 6788, f. 469.

115 The sun takes only four minutes of time to move one degree of terrestrial longitude. The effect on declination is negligible.

116 Harriot was actively engaged in theoretical as well as in practical cartography; see Shirley, John W. (ed.), op. cit. (2), pp. 48, 54–90Google Scholar; Salisbury MSs, op. cit. (8), pp. 256–7.Google Scholar

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121 See n. 92, above. As was mentioned earlier, it is most unlikely that Harriot calculated the orbital parameters from actual observations of the solstices. However, the accuracy of his predicted times for the solstices of 1593 derived from the accuracy of these parameters. Harriot's declination table was sensitive to a change of 1° in the position of the apogee.

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128 BM Add.MS 6788, f. 469. A latitude error of one degree is an error of 60 nautical miles, or 111 kilometres. One nautical mile= 1.85 kilometres.

129 See next paragraph.

130 P. 264, above.

131 HMC 241/V1b, pp. 31–2.

132 BM Add.MS 6788, ff. 423, 476v, 480–484°; Roche, , op. cit. (23), pp. 116–38.Google Scholar

133 Pepper, , ‘Harriot's earlier work’, op. cit. (2).Google Scholar

134 BM Add.MS 6788, ff. 485–9; HMC 241/V1b, p. 32.

135 ibid., f. 475.

136 ibid., f. 469.

137 Nuñez had earlier drawn attention to this error; op. cit. (24), p. 29.Google Scholar

138 Near the equinoxes the declination varies by about 24′ per day (BM Add.MS 6788, f. 206). At a geographic longitude 180° away from the meridian of the ‘Regiment’ there would be a difference of 12′ in the noon declination on the same day.

139 BM Add.MS 6788, ff. 470–1.

140 Roche, , op. cit. (23), p. 145.Google Scholar