Sir William Thomson (Lord Kelvin) and Peter Guthrie Tait, Treatise on Natural Philosophy, 2nd ed. (Cambridge, England: Cambridge University Press, 1879), vol. 1, part 1, page 227 (页面存档备份,存于互联网档案馆).
William L. Laurence, "'Cosmic pendulum' for clock planned," New York Times, 21 January 1945, page 34. Reprinted on page 77 of: Lombardi, Michael A.; Heavner, Thomas P.; and Jefferts, Steven R. (December 2007) "NIST primary frequency standards and the realization of the SI second," (页面存档备份,存于互联网档案馆) NCSLI Measure, vol. 2, no. 4, pages 74-89.
Sir William Thomson (Lord Kelvin) and Peter Guthrie Tait, Treatise on Natural Philosophy, 2nd ed. (Cambridge, England: Cambridge University Press, 1879), vol. 1, part 1, page 227 (页面存档备份,存于互联网档案馆).
William L. Laurence, "'Cosmic pendulum' for clock planned," New York Times, 21 January 1945, page 34. Reprinted on page 77 of: Lombardi, Michael A.; Heavner, Thomas P.; and Jefferts, Steven R. (December 2007) "NIST primary frequency standards and the realization of the SI second," (页面存档备份,存于互联网档案馆) NCSLI Measure, vol. 2, no. 4, pages 74-89.