Foucault, Léon

1995/08/02 Azkune Mendia, Iñaki - Elhuyar Fundazioa | Kaltzada, Pili - Elhuyar Zientziaren Komunikazioa

• Biografiak

(1819-1868)

Born in Paris on September 18, 1819. After studying and obtaining the medical degree, he met with physicist Armand Fizeau and decided to deal with physics. He began to investigate the heat and especially the light.

Let us think that a ray of light falls on the mirror A and is reflected with an angle. Suppose the beam of light reflected later hits the B mirror and re-reflects it towards the A mirror. If the two mirrors are standing, the light will not stop bouncing.

If the A mirror rotates quickly when the B is reflected in the ray of light, the ray of light will be reflected elsewhere. Taking into account the rotation speed of the mirror A, the angle of the reflected beam and the distance travelled by the light, Foucault calculated the speed of light with a precision greater than Fizeau.

Foucault used the mirror system to measure the speed of light in the air, water and other transparent media. From the time of Huygens and Newton there were debates on the nature of light. According to some, the light was formed by waves and, according to others, it was particle current. The theory of waves indicated that light should expand more slowly in water, while the theory of corpuscles was intermediate.

Around 1850 Foucault found that light was spreading more slowly in water than in the air, opting for wave theory. All these works were published by Foucault in his doctoral thesis.

However, Foucault's name became famous for other essays made by him, especially thanks to an essay begun in 1851. Foucault knew that despite turning the hanging point, the pendulum tended to remain in the swing plane. If a large pendulum was put into operation, its oscillation plane would remain, although the Earth would turn below. If the pendulum were in the north pole, the Earth would turn under the pendulum for 24 hours. In latitudes lower than the North Pole, the Earth's turn seems slower. This speed would be lower when going south and up to zero in the equator. It would turn back to the south of the equator, but in the opposite direction. On the south pole, on the other hand, the entire tour would be completed in 24 hours.

To those who look at the pendulum (which turns with the Earth), it will seem that the pendulum is changing little by little direction.

The results of the first trial were quite different, since it should be done with a longer pendulum. Aragon then offered him the observatory building and Napoleon III a large Parisian church. Foucault used a two-foot diameter iron ball and a 200-foot long steel wire. The ball, hung from the dome, had at its end a small axis to make marks in the sand deployed on the floor of the church.

They brought the ball to a church wall and tied it with laces. They tried to avoid vibrations and winds. Therefore they did not cut the rope (because they would provoke tremors) and burned it. With the passage of time, the motionless people of the church could verify that the marks of the earth changed direction. The latitude corresponding to Paris was turning on request.

From Galileo the scientists recognized that the Earth was turning, but Foucault put this phenomenon in view of his essay.

In 1852 he quickly rotated an arist thick wheel and studying the effects of gravitation invented the gyroscope. It is also due to the first theory on gyroscopic phenomena.

In 1855 the "Royal Society" of London awarded him the title for his scientific work and offered him a place at the Imperial Observatory of Paris.

In 1857 he invented the mercury switch, which is still used in induction coils.

He noted that Araro's "turning magnetism" was due to the existence of currents induced in metallic masses ("Foucault currents"). That year he began to replace silver glass mirrors in telescopes with metallic mirrors. It also invented improvements in the manufacture of parabolic mirrors. On the other hand, the classic telescopes with a prism of total reflection were devised by himself.

In his hometown, he died in Paris on February 11, 1868.