Book Review: Pendulum: Léon Foucault and the Triumph of Science by Amir D. Aczel

The book traces Leon Foucault’s ingenious approach to solving the problem of providing a terrestrial proof of rotation of the Earth. The pendulum he devised oscillates in a constant plane, and if properly engineered (as he did) can actually show the rotation of the Earth. The demonstration is one the most visually impressive scientific experiments. Also, Foucault gave prediction, an equation which would tell us how the pendulum will behave at different parts of the Earth. The pure mathematicians and physicists alike were taken aback at this simple yet powerful demonstration of the proof which eluded some of the most brilliant minds, which includes likes of Galileo and Newton. Rushed mathematical proofs were generated, some of the mathematicians earlier had claimed that no such movement was possible. That being said, Foucault was seen as an outsider by the elite French Academy due to his lack of training and degree. Yet he was good in designign things and making connections to science. This was presented to the public in 1851, and the very next year in 1852 he created another proof for rotation of the Earth. This was done by him inventing the gyroscope.. Gyroscope now plays immense role in navigation and other technologies. Yet he was denied membership to the Academy, only due to interest of the Emperor Napolean III in his work in 1864. The pendulum is his most famous work, but other works are also of fundamental significance.

  • He was first person to do photomicrography using Daguerreotype
  • Accurate measurment of speed of light using rotating mirrors –
  • Devised carbon arc electric lamp for lighting of micrcoscope
  • One of the first to Daguerreotype the Sun
  • Designed the tracking systems used in telescopes
  • also designed many motors, regulators to control electrical devices

There are a couple of places in the book where Aczel seems to be confused, at one point he states parallax as a proof for rotation of Earth around its axis, whearas it is more of a proof of Earths motion around the Sun. At another place he states that steel was invented in 1800s which perhaps he means to say that it was introduced in the west at the time. Apart from this the parallels between the rise of Napoleon III, a Nephew of Napolean, to form the second Empire in France and Foucault’s own struggle for recognition of his work and worth is brought out nicely.

The Pendulum and The Fixed Points

… And then last year, when I saw the Pen­dulum, I understood everything.”


“Almost everything. You see, Casaubon, even the Pendulum is a false prophet. You look at it, you think it’s the only fixed point in the cosmos, but if you detach it from the ceiling of the Conserva­toire and hang it in a brothel, it works just the same. And there are other pendulums: there’s one in New York, in the UN building, there’s one in the science museum in San Francisco, and God knows how many others. Wherever you put it, Foucault’s Pendulum swings from a motionless point while the earth rotates beneath it. Every point of the universe is a fixed point: all you have to do is hang the Pendulum from it.”

– Umberto Eco, Foucault’s Pendulum