[35] FRANCIS BAILY, "On the Correction of a Pendulum for the Reduction to a Vacuum, Together with Remarks on Some Anomalies Observed in Pendulum Experiments," _Phil. Trans._ (1832), vol. 122, pp. 399-492. See also _Collection de mémoires_, vol. 4, pp. B-105, B-112, B-115, B-116, and B-117. [36] One was of case brass and the other of rolled iron, 68 in. long, 2 in. wide, and 1/2 in. thick. Triangular knife edges 2 in. long were inserted through triangular apertures 19.7 in. from the center towards each end. These pendulums seem not to have survived. There is, however, in the collection of the U.S. National Museum, a similar brass pendulum, 37-5/8 in. long (fig. 15) stamped with the name of Edward Kübel (1820-96), who maintained an instrument business in Washington, D.C., from about 1849. The history of this instrument is unknown. [37] See Baily's remarks in the _Monthly Notices of the Royal Astronomical Society_ (1839), vol. 4, pp. 141-143. See also letters mentioned in footnote 38. [38] This document, together with certain manuscript notes on the pendulum experiments and six letters between Wilkes and Baily, is in the U.S. National Archives, Navy Records Gp. 37. These were the source materials for the information presented here on the Expedition. We are indebted to Miss Doris Ann Esch and Mr. Joseph Rudmann of the staff of the U.S. National Museum for calling our attention to this early American pendulum work. [39] G. B. AIRY, "Account of Experiments Undertaken in the Harton Colliery, for the Purpose of Determining the Mean Density of the Earth," _Phil. Trans._ (1856), vol. 146, p. 297. [40] T. C. MENDENHALL, "Measurements of the Force of Gravity at Tokyo, and on the Summit of Fujiyama," _Memoirs of the Science Department, University of Tokyo_ (1881), no. 5. [41] J. T. WALKER, _Account of Operations of The Great Trigonometrical Survey of India_ (Calcutta, 1879), vol. 5, app. no. 2. [42] BESSEL, op. cit. (footnote 21), article 31. [43] C. A. F. PETERS, _Briefwechsel zwischen C. F. Gauss und H. C. Schumacher_ (Altona, Germany, 1860), _Band_ 2, p. 3. The correction required if the times of swing are not exactly the same is said to have been given also by Bohnenberger. [44] F. W. BESSEL, "Construction eines symmetrisch geformten Pendels mit reciproken Axen, von Bessel," _Astronomische Nachrichten_ (1849), vol. 30, p. 1. [45] E. PLANTAMOUR, "Expériences faites à Genève avec le pendule à réversion," _Mémoires de la Société de Physique et d'histoire naturelle de Genève, 1865_ (Geneva, 1866), vol. 18, p. 309. [46] Ibid., pp. 309-416. [47] C. CELLÉRIER, "Note sur la Mesure de la Pesanteur par le Pendule," _Mémoires de la Société de Physique et d'histoire naturelle de Genève, 1865_ (Geneva, 1866), vol. 18, pp. 197-218. [48] A. SAWITSCH, "Les variations de la pesanteur dans les provinces occidentales de l'Empire russe," _Memoirs of the Royal Astronomical Society_ (1872), vol. 39, p. 19.