To Benjamin Franklin from Nevil Maskelyne, 11 December 1769: résumé
From Nevil Maskelyne
ALS:1 American Philosophical Society
[Greenwich, December 11, 1769. The Astronomer Royal asks Franklin, when he next writes to Philadelphia, to inquire of Owen Biddle about the exact distances between the observation points for the transit of Venus. Maskelyne cannot make Biddle’s two accounts agree with each other, or with the distances given by Mason and Dixon in their survey.2 He is also uncertain about the exact location of the Norriton observatory in relation to the southernmost point of the city of Philadelphia, and wants more exact data. The Pennsylvania observers will likewise send him, he hopes, their observations on the transit of Mercury on November 9, 1769, along with any other observations that will help to establish the difference of longitudes.3
He cannot, until his questions are answered, transmit Biddle’s report to the Royal Society.4 He has transmitted the report from John Winthrop that Franklin sent him, and also Winthrop’s observation of the transit of Mercury in 1743, which had been read to the Society but for some reason was not yet in print.5]
1. The letter is so badly mutilated that even the gist of some passages cannot be conjectured. An abridged version, which omits most of these passages, is in APS Trans., I (1771), 90. Maskelyne repeated much of what he asked in this letter, but without the technical details, in his note to BF below, Dec. 27.
2. For this famous survey, which precisely located points near Philadelphia, see above, XII, 341 and the references there given. Precision was necessary to calculate the times and angles by which the sun’s distance from the earth might be determined.
3. William Smith reported on the location of Norriton in APS Trans., I, app., 5–11, but this report does not seem to have reached the Royal Society; Smith, Biddle, and their colleagues reported on the transit of Mercury in ibid., app., pp. 50–4, and their observations also appeared in Phil. Trans., LX (1771), 504–7.
4. He changed his mind, as indicated by his note to BF below, Dec. 27. Biddle’s first account was read before the Royal Society and printed, with Maskelyne’s comments, in Phil. Trans., LIX (1770), 414–21. Biddle’s corrected account appeared in APS Trans., I, 89–96, but like Smith’s report on Norriton did not, apparently, reach the Royal Society.
5. The report from Winthrop on his own observations of the transit of Venus, rather than his query above about earlier observations, Sept. 6. The report was in the form of a letter to Maskelyne, who must have forwarded it some weeks earlier, because it was read on Dec. 7; it was subsequently printed in Phil. Trans., LIX (1770), 351–8. Winthrop’s observations of the transit of Mercury in 1743 were not reported until twenty years later, were read on Nov. 10, 1763, and were not printed until 1770: ibid., pp. 505–6.