Person: Foucault, Jean Bernard Léon
Léon Foucault was a French mathematician and astronomer who is best known for his invention of a pendulum which demonstrates the rotation of the earth.
Mathematical Profile (Excerpt):
- It gave him a rather awkward appearance and this was made worse by the fact that Léon became self-conscious about his appearance, tending to prefer being by himself.
- Foucault did, however, make a good friend of one of the students at the Collège Stanislas, namely Hippolyte Fizeau.
- If academic school work was not to Foucault's liking, he did begin to exhibit other talents.
- Just before starting work as Donné's assistant, Foucault had attended talks by Daguerre on his photographic methods.
- Foucault's friend Fizeau had been with him and the two experimented, improving the photographic process.
- Foucault combined his new photographic skills with his work for Donné and devised a method of taking photographs through a microscope.
- In 1845 Foucault and Donné published A course of microscopy which contained 80 photographs of objects under a microscope.
- He retired from this position in 1845 handing over the task to Foucault.
- Always polite, yet seeking the truth, Foucault applied carefully considered judgements.
- Arago had learnt of Foucault's expertise with photography through a microscope on the publication of his book with Donné.
- He approached Foucault and Fizeau, whom he knew personally, in 1845 and asked if they could try to take photographs of the sun.
- Arago was delighted and saw the potential Foucault had to carry out other experiments for the Academy of Sciences.
- He next suggested that Foucault and Fizeau try to measure the speed of light in water.
- Shortly after beginning work using Arago's methods, Foucault and Fizeau had an argument.
- Foucault now devised his own methods to approach the problem of measurement, building a steam engine to drive a spinning mirror.
- Foucault's next idea was that if he was able to design the support for a pendulum which allowed it to freely move in any direction without any resistance, then once set in motion it would retain its plane of swing in space while the Earth rotated beneath it.
- A paper by Foucault on his pendulum was read by Arago to the Academy of Sciences on the same day as the experiment was carried out in the Observatory.
- Plana presented a paper to the Academy of Sciences of Turin on Foucault's pendulum in March.
- Poisson had, deplorably quickly, decided its was not worth considering; and it was Foucault, without and help or assistance, who was the first to propose it.
- Foucault next invented the gyroscope, which he did to demonstrate in yet another way the motion of the Earth.
- It was an invention which was of little significance in Foucault's time, but of course today we recognise its widespread use in airplanes, guiding of telescopes, the Hubble space telescope etc.
- Political events in France now worked to Foucault's advantage.
- On 2 December 1851 there was a coup d'état in France with Louis-Napoléon Bonaparte assuming absolute power and dissolving the National Assembly.
- He greatly supported science in general and Foucault in particular so he arranged the post of Physicist Attached to the Imperial Observatory to be specially created for Foucault.
- Soon Foucault was creating superb telescopes for the Observatory with many innovative features.
- Foucault accompanied Le Verrier on an expedition to Spain in 1860 to observe the eclipse on 18 July.
- By October 1867 Foucault began to feel numbness in his hands.
- It is likely that the illness was the result of the chemicals, in particular mercury, that Foucault had experimented with all his life.
Born 18 September 1819, Paris, France. Died 11 February 1868, Paris, France.
View full biography at MacTutor
Tags relevant for this person:
Physics
Thank you to the contributors under CC BY-SA 4.0! 
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- @J-J-O'Connor
- @E-F-Robertson
References
Adapted from other CC BY-SA 4.0 Sources:
- O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive
