The pendulum suspended from the ceiling of the Panthéon.
Image © F. Giovannangeli; used with permission.
Spinning Foucault's Pendulum at the Panthéon
Paris Kiosque - November 1996 - Volume 3, Number 11
Copyright (c) November 1996 Françoise; Giovannangeli - used with permission
"Vous êtes invités à venir voir tourner la terre ..." were the words printed on
a huge banner hanging outside the Panthéon, that great French memorial to the
nation's most distinguished minds.
In 1851, Léon Foucault used the same words to invite scientists of the day to
come and witness his revolutionary experiment which would provide proof that the
earth does indeed spin on its axis.
With a little time on my hands and an outstanding curiosity to assuage I climbed
the monumental steps and made my way towards the promised event: the opportunity
to directly observe the rotation of the earth.
I had been disappointed by my first attempt to view the magical pendulum at the
Conservatoire des Arts et Métiers, its official home since 1855. Intrigued by
Umberto Eco's account of Foucault's pendulum in his novel of the same name, I
had set out in quest of it in the hopes of partaking in the supreme
transcendental experience the narrator describes while watching it. But the
Conservatoire has been undergoing a major renovation in recent years and at the
time, the nef was closed and the pendulum inaccessible.
Recently, museum officials decided to find a temporary location to show off the
famous gold-coloured sphere -- and what better place than under the dome of the
Panthéon, where the first public demonstration of Foucault's experiment was held
nearly 150 years ago.
Inside I watched the pendulum slowly sway to and fro beneath the dome of the
former church, tracing its invisible path against the hour table below. Attached
to the "eye of God" in the centre of the painted dome, a 67-metre wire connects
the pendulum to an imaginary fixed point in the universe. On the ground, a large
white ring surrounding the area of oscillation is marked with a series of
numerals to reflect a period of 24 hours. As time passes, the path of
oscillation appears to shift progressively around the circle.
I wandered about the building, whose four nefs form a Greek cross, but couldn't
find a spot from which the celestial point was visible. The Panthéon is badly in
need of repair, and since bits of stone and tile have been breaking away, the
central area is now cordoned off.
Foucault first presented his experiment to his colleagues on 3 February 1851.
The event, held at the Observatoire, had such an impact that Prince Louis
Napoléon Bonaparte, the future Napoléon III, asked him to give a public
demonstration on 26 March of the same year.
Next to a column, a short audio-visual display was relating the story: it told
viewers to imagine for a moment that their feet were no longer touching the
ground, something which seemed simple enough. Then, it continued, consider that
the pendulum's plane of oscillation, which also doesn't touch the ground,
remains unchanged with respect to the stars even as the earth rotates -- here is
the proof that the Panthéon moves around the pendulum and not vice-versa.
I decided to think about all of this later, as a small crowd was starting to
gather, eager to receive the knowledge imparted by the video. For now, I was
content to admire the pendulum and its appeasing motion.
Outside, the sun had gone down, or rather the earth had moved up -- or, had it
moved round? As I headed down the rue Soufflot towards the busy boulevard Saint
Michel I wondered what Léon Foucault would have replied.
Françoise Giovannangeli is a Canadian freelance writer who lives in Paris. She
can be contacted via
this link.
