If there were ever any truth in the esoteric tales of Umberto Eco’s bestselling novel Foucault’s Pendulum, it seems that the key to that knowledge has been lost.

The original pendulum, which was used by French scientist Leon Foucault to demonstrate the rotation of the Earth and which forms an integral part of Eco’s novel’s labyrinthine plot, has been irreparably damaged in an accident in Paris.

The pendulum’s cable snapped last month and its sphere crashed to the marble floor of the Musee des Arts et Metiers.

In 1851, Foucault used the pendulum to perform a sensational demonstration in the Paris Pantheon, proving to Napoleon III and the Parisian elite that the Earth revolved around its axis. Such was its success that the experiment was replicated throughout Europe.

Thierry Lalande, the museum’s ancient scientific instruments curator, said that the pendulum’s brass bob had been badly damaged in three places and could not be restored.

“It’s not a loss, because the pendulum is still there, but it’s a failure because we were unable to protect it,” he said. The circumstances surrounding the accident have raised eyebrows in France.

The museum regularly hosts cocktail parties in the chapel that houses the pendulum, and Mr Lalande admitted that several alarming incidents had occurred over the past year. In May 2009, for example, a partygoer grabbed the 28kg instrument and swung it into a security barrier.

Amir D. Aczel, research Fellow in the history of science at Boston University, described the news of the accident as “saddening”.

“It is certainly one of the most important historical instruments of all time. It’s a bit like hearing that one of the statues at the Vatican has been broken,” he said.

Foucault’s experiment involved releasing a pendulum and watching the Earth rotate under its oscillation frame. Dr Aczel said that it brought “closure for Galileo” and led the Church to accept the rotation of the Earth.

William Tobin, a retired astronomy lecturer and biographer of Foucault, said that the accident was embarrassing for the museum, and a blow for academia.

Dr Tobin helped to identify the pendulum used by Foucault from among the other similar instruments held in the museum, and said that examining old instruments in the flesh “tells you more about the development of science than the written record can”.

However, Thibault Damour, professor of theoretical physics at the Paris Institut des Hautes Etudes Scientifiques, said scholars would find comfort in the fact that the legacy of Foucault’s experiment, which asked “fundamental questions about the nature of space and time”, lived on in “Einstein’s thought and in current experiments”.

In particular, he pointed to a recent Nasa mission, Gravity Probe B, which verified Einstein’s theory of relativity, which explains why the oscillation plane of the pendulum does not remain fixed in absolute space, as expected by Foucault, but is slowly dragged by the presence of the rotating Earth.