[49] J. J. BAEYER, _Über die Grösse und Figur der Erde_ (Berlin, 1861). [50] _Comptes-rendus de la Conférence Géodésique Internationale réunie à Berlin du 15-22 Octobre 1864_ (Neuchâtel, 1865). [51] Ibid., part III, subpart E. [52] _Bericht über die Verhandlungen der vom 30 September bis 7 October 1867 zu Berlin abgehaltenen allgemeinen Conferenz der Europäischen Gradmessung_ (Berlin, 1868). See report of fourth session, October 3, 1867. [53] C. BRUHNS and ALBRECHT, "Bestimmung der Länge des Secundenpendels in Bonn, Leiden und Mannheim," _Astronomisch-Geodätische Arbeiten im Jahre 1870_ (Leipzig: Veröffentlichungen des Königlichen Preussischen Geodätischen Instituts, 1871). [54] _Bericht über die Verhandlungen der vom 23 bis 28 September 1874 in Dresden abgehaltenen vierten allgemeinen Conferenz der Europäischen Gradmessung_ (Berlin, 1875). See report of second session, September 24, 1874. [55] CAROLYN EISELE, "Charles S. Peirce--Nineteenth-Century Man of Science," _Scripta Mathematica_ (1959), vol 24, p. 305. For the account of the work of Peirce, the authors are greatly indebted to this pioneer paper on Peirce's work on gravity. It is worth noting that the history of pendulum work in North America goes back to the celebrated Mason and Dixon, who made observations of "the going rate of a clock" at "the forks of the river Brandiwine in Pennsylvania," in 1766-67. These observations were published in _Phil. Trans._ (1768), vol. 58, pp. 329-335. [56] The pendulums with conical bobs are described and illustrated in E. D. PRESTON, "Determinations of Gravity and the Magnetic Elements in Connection with the United States Scientific Expedition to the West Coast of Africa, 1889-90," _Report of the Superintendent of the Coast and Geodetic Survey for 1889-90_ (Washington, 1891), app. no. 12. [57] EISELE, op. cit. (footnote 55), p. 311. [58] The record of Peirce's observations in Europe during 1875-76 is given in C. S. PEIRCE, "Measurements of Gravity at Initial Stations in America and Europe," _Report of the Superintendent of the Coast Survey for 1875-76_ (Washington, 1879), pp. 202-337 and 410-416. Peirce's report is dated December 13, 1878, by which time the name of the Survey had been changed to U.S. Coast and Geodetic Survey. [59] _Verhandlungen der vom 20 bis 29 September 1875 in Paris Vereinigten Permanenten Commission der Europäischen Gradmessung_ (Berlin, 1876). [60] Ibid. See report for fifth session, September 25, 1875.