Jean Foucault, a French physicist, who created the gyroscope and Foucault pendulum, was born on September 18, 1819.

Night. 1851. Paris. Cellar. The French physicist Jean Bernard Leon Foucault cannot sleep: the experiment is underway. A load is swinging on a two-meter wire. The physicist watches in silence, and after a while he rubs his palms contentedly and goes to bed knowing that proof of the Earth’s rotation has been obtained. That was how the Foucault pendulum was invented and then glorified its creator's name. 

The planet Earth rotates around its axis at a breakneck speed: at the equator, it reaches 1674 kilometers per hour, and at the latitude of Moscow – 936 kilometers. Foucault found confirmation oft this by observing a pendulum with an unchanged plane of oscillation. It is amazing that every second the Earth turns in relation to the stars, while the pendulum is stable – the oscillations occur in the same plane. And it seems to the observer that the plane turns in the direction opposite to the movement of the planet. In fact, it also turns with the Earth, although it is stationery in its coordinate system, while the load is constantly shifting. 

маятник Фуко

But this is not the physicist's only achievement. Here are some other Foucault's achievements: 

– measuring the speed of light when it passes through air and water. According to the scientist, it equals to 298,000 km/s in the air and even less in water. After that, physicists of that era began to assert the wave nature of light. Foucault's experiment was impressive: his installation of mirrors and lenses helped to determine the speed of light almost perfectly;

– an automatic light controller for an arc electric lamp. It became a light source thanks to using electric arc – a certain type of discharge in a gas;

– a new way of making mirrors for large reflectors. The scientist suggested that instead of metal mirrors, glass mirrors with silver coating should be used. They were much lighter and cheaper;

– studying eddy currents and the discovery of heating of metal bodies rotated in a magnetic field by eddy currents. Works in this field are still used in electric (electrodynamic) retarder brakes.

a scheme of Foucault's experiment

a scheme of Foucault's experiment



Jean Bernard Leon Foucault was also a theoretician – he wrote several hundred scientific articles published in Journal des débats in 1845-1862. 

The scientist was a member of the Royal Society of London, the Berlin Academy of Sciences and a corresponding member of the St. Petersburg Academy of Sciences. He was also elected a member of the Paris Academy. And in 1855, his experimental research was awarded the Copley Medal – a prestigious award of the Royal Society of London. 

Foucault made a great contribution to the development of the science of physics. Now his name is engraved on the Eiffel Tower among other 72 names of outstanding French scientists, engineers and industrialists for the period from 1789 to 1889.

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