Jean-Bernard-Léon Foucault, born in Paris on September 19, 1819, was an extremely successful experimental physicist. He, like Galileo, believed experimentation and innovation were the best ways to accurately assess the properties of the natural world.

Originally trained as a physician, Foucault made his living as a highly successful science and mathematics writer, and until he was appointed to a post at the Paris Observatory later in his career, he conducted his experimental work at home. Some of Foucault's most fruitful work was done in collaboration with other prominent scientists of the day, such as French physicist Armand H. Fizeau (1819-1896).

Using the daguerreotype developed by Louis Daguerre, Foucault and Fizeau produced the first photographs of the sun's surface in 1845. Since Daguerre's photos required long exposure times to produce a clear picture, Foucault had to design a device for their solar camera capable of following the sun on its...