Hippolyte Fizeau

Armand Hippolyte Louis Fizeau (French: [ipɔlit fizo]; 23 September 1819 – 18 September 1896) was a French physicist. He made one of the first accurate measurements of the speed of light. In 1849, Fizeau used a clever method involving a toothed wheel and a mirror to determine how fast light travels. His measurement was within 5% of the true value, which was an amazing achievement for its time.

Two years later, in 1851, Fizeau conducted another important experiment. He wanted to know how the speed of light changes when it moves through water. This experiment, known as the Fizeau experiment, helped scientists understand more about the behavior of light.

Fizeau’s work laid important groundwork for future studies in physics. His measurements were much more precise than earlier attempts, and they showed that light travels at incredible speeds—about 186,000 miles per second. His discoveries continue to influence how we study light and its properties today.

Biography

Hippolyte Fizeau was born in Paris and married into a well-known botanical family. He started his career by improving photographic methods. With suggestions from scientists like François Arago and Léon Foucault, he studied how light and heat interact.

In 1849, Fizeau made an important discovery by measuring the speed of light more accurately than anyone before him. He used a clever experiment with a rotating wheel and a mirror to calculate that light travels about 313,000,000 meters per second, which is very close to the actual speed. Later, he also helped discover how the color of light changes when sources move, known as the Doppler effect. Fizeau’s contributions to science were honored by having his name inscribed on the Eiffel Tower and a crater on the far side of the Moon named after him.