My dear Henry
Thanks for your remarks <1> on Foucaults Pendulum experiment. I have no doubt that if you could suspend a rigid bar as you suggest, it would, remaining unmoved, while the earth revolved, appear to move round, but the experiment is not worth making, it being obviously impossible to satisfy the conditions of the experiment, which would necessarily imply an absence of all friction between the bar and its fulcrum. The practical difficulty to be overcome in the Pendulum experiment is similar in its nature, there being always more or less friction at the point of suspension of the rod.
Yours ever truly
CRM Talbot
3 Cavendish Sq
July 8 1851.
[envelope:]
W. H. F. Talbot Esqe
Lacock Abbey
Chippenham
Orrell Cottage Grasmere
Ambleside
Westmorland
Notes:
1. Remarks on M. Foucault’s Pendulum Experiment by H.F. Talbot, privately printed by Cox and Wyman, London, 1851. In March 1851 Jean Bernard Léon Foucault (1819–1868), French physicist, suspended a metal ball, weighing 28 kg, in a wire from the dome of the Panthéon in Paris. The ball was set in a pendulous motion, and over a span of hours it would exhibit a slow rotation in the direction of the pendulous motion, but what seemed to be the gradual rotation of the direction of the pendulous motion would actually be the rotation of the earth in space. In his paper WHFT suggested a different experiment, in which a horizontal bar balancing on a vertical bar would have to revolve within the span of 24 hours if Foucault’s reasoning was true. WHFT was convinced that this experiment would fail and thereby prove Foucault wrong, and the experiment would have failed, but perhaps not for the reasons WHFT thought. WHFT’s experiment would fail because he operated with an object, which was at rest with respect to the earth, whereas Foucault operated with an object, or rather a movement, which was at rest with respect to the frame defined by the stars. In the defence of WHFT and Christopher Rice Mansel Talbot only the fewest contemporary observers perceived this difference. [See Doc. No: 06438; see also Tobin, William, The Life and Science of Léon Foucault: the man who proved the earth rotates (Cambridge and New York: Cambridge University Press, 2003), pp. 133–172.].