Léon Foucault and His Contribution To The Study of Light
Updated: Dec 16, 2020
The Big Breakthrough Into Spectrometry.
Jean Bernard Léon Foucault was born in 1819 as the son of a book publisher. He was mostly homeschooled and then went to study medicine. However due to a phobia of blood he quit this path and took an interest in the development of existing practical methodology in photography and photo development. This took him into microscopic photography where he started his journey into science as an experimental assistant in taking photos of microscopic anatomy.
It was during his time as an assistant that he chanced upon someone studying light waves. They took a primary look at the comparison between the light of the sun and a carbon arc lamp and the lime in an oxyhydrogen flame. Going back to our last post, he also took from Herschel’s work and studied the interference of infrared radiation in this light.
One of the first experiments into spectrometry was done by Foucault in 1849 where he experimentally demonstrated absorption and emission lines of a flame appearing at the same wavelength. You may notice that these terms are still in used today in the flame photometer and many other spectrometers as being classed as emission and absorption spectrometers. He also critically noted that the difference between these emission lines were from the temperature of the light source.
Whilst his early days were based in measuring light and its spectrum, he then went on to analyse more physical constants. He made the first reasonably accurate measurement of the speed of light, and this was considered by the scientific community to put to rest Isaac Newtons theory of corpuscular theory of light, which we will touch on next week when looking at the work done by Isaac Newton.
His experiment was done by having a beam of light shine into a rotating mirror, then through a lens and onto a stationary mirror. The time taken to bounce the beam of light back to the rotated mirror would result in the return angle of the light being picked up in a new direction, and then by measuring the angle of the lights path changing the speed can be measured. However, this is not anyway near close to the accuracy on the speed of light measurements we have today. He thought the speed of light to be 298,000km/s only 10,000km/s from out currently accepted speed of light (a 0.6% margin in error).
Foucault went on with his study of physics and invented the gyroscope. A device that was later installed into planes for navigation, still finding a use for it over 100 years later. He also had an interest in lenses and invented a test to look at the curvature of a lens or mirror.
Later in his life he discovered how to polarize light, which was initially used so that people can look at the sun without damaging their eyes, however he did not understand the mechanism behind this phenomenon. In 1868 he died to multiple sclerosis and his name is now inscribed on the Eiffel tower.
We at BWB Tech are glad for Foucault’s study into light, and it was his base theory that prompted our work here to begin in the first place.