Natural Philosophy Collection

Foucault’s Pendulum

We do not have Léon Foucault’s original Pendulum, now safely displayed in a glass case in the great hall of the Conservatoire des Arts et Métiers, formerly the church of Saint-Martin-les-Champs. This hall, and the impression of Foucault’s swinging pendulum, sets the opening scene in Umberto’s Eco’s novel Foucault’s Pendulum. In 1851, when Foucault swung his 64 metre long pendulum from the dome of the Panthéon in Paris, crowds watched its slow mesmeric swing in awe. When the weighty pendulum bob was set off it kept swinging in the same plane while the earth turned beneath. The watching crowds standing on the earth saw the plane of the pendulum slowly counter-rotating, the rotation being seen by the tip of the pendulum cutting different lines in piles of moist sand placed at either end of the swing. This was visible proof, in a closed room, that the earth does indeed rotate under the heavens and not the heavens about the earth. Natural Philosophy students of King’s College were taken by Professor Thomson in 1859 to see a re-enactment of Foucault’s experiment from the high ceiling of St. Machar’s Cathedral. The experiment was described in the reminiscences of that class as the most memorable of the year. Church and Science have clashed over celebrated issues in the past but over Foucault’s pendulum there seems to have been collaboration. Our heavy, lead pendulum bob, weighing 22 kilos, is likely to be a 19^th century relic, which could, perhaps, go back to the St. Machar’s Cathedral demonstration.

John S. Reid