Alfred Potier (born Paris, May 11, 1840 – died May 8, 1905) was a French polymath

Polymath

A polymath is a person whose expertise spans a significant number of different subject areas. In less formal terms, a polymath may simply be someone who is very knowledgeable...

 who contributed to many theoretical and practical fields of science when this was rapidly expanding. His interests covered mainly mathematical physics

Mathematical physics

Mathematical physics refers to development of mathematical methods for application to problems in physics. The Journal of Mathematical Physics defines this area as: "the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and...

, the nature of light and the ether, geology

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

, electricity

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 and magnetism

Magnetism

Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...

 and their practical applications in industry. His name’s claim to fame rests, however, on a little explored footnote inserted by Michelson and Morley in their famous paper “On the Relative Motion of the Earth and the Luminiferous Ether”.

Biography

Born in 1840, Potier entered the École Polytechnique

École Polytechnique

The École Polytechnique is a state-run institution of higher education and research in Palaiseau, Essonne, France, near Paris. Polytechnique is renowned for its four year undergraduate/graduate Master's program...

 at age 17, where in 1867 he became a physics teacher, and then in 1881 full Professor of Physics, succeeding Jamin and preceding Nobel Laureate Henri Becquerel

Henri Becquerel

Antoine Henri Becquerel was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics.-Early life:...

. At the same time, he was member of the State Mining Engineers Corps, occupying the chair of Physics in the École des Mines where he taught Henri Poincaré

Henri Poincaré

Jules Henri Poincaré was a French mathematician, theoretical physicist, engineer, and a philosopher of science...

. Geological works included revisions of the geological map of France and submarine topographies in Pas-de-Calais in order to examine the feasibility of a tunnel to England. These, and his valor during the German siege of Paris in 1870, earned him the Légion d'honneur

Légion d'honneur

The Legion of Honour, or in full the National Order of the Legion of Honour is a French order established by Napoleon Bonaparte, First Consul of the Consulat which succeeded to the First Republic, on 19 May 1802...

. His other publications concerned Fresnel’s theories of light and the ether, diffraction of polarized light, elliptical reflection, magnetic rotational forces, or interference fringes. He contributed extensive notes to JC Maxwell’s treatise on electromagnetism, facilitating its reading in France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

.

Potier was a member of many committees at the famous 1881 Universal Exposition in Paris

International Exposition of Electricity, Paris

The first International Exposition of Electricity in Paris ran from August 15, 1881 through to November 15, 1881 at the Palais de l'Industrie on the Champs-Elysees. It served to display the advances in electrical technology since the small electrical display at the 1878 Universal Exposition...

, including the one that set the standards for units in electricity. The French Physics Society appointed Potier as president in 1884; the International Electricians Society did the same in 1895. In 1891 he was accepted into the French Academy of Science.

Speed of light

Following Thomas Young’s ideas, light was regarded in the 19th century to move as vibrations (undulations) in a substance called the Luminiferous aether

Luminiferous aether

In the late 19th century, luminiferous aether or ether, meaning light-bearing aether, was the term used to describe a medium for the propagation of light....

, contrary to Newton’s ideas that light itself was made of substantive corpuscles. Exploring the nature of this aether, Albert Michelson published in 1881 his laboratory experiments where he had light travel in the direction of the earth’s motion and perpendicular to it. Thus measured on the moving earth, he found no difference in the speed of light traveling with the earth or perpendicular to it. It would have fully conformed to rules prevailing in a Galilean invariance system of coordinates, also called Newtonian inertial system, which apply to moving material particles.

In the 1887 paper, written with Edward Morley, Michelson amended the route of the perpendicular light from ab1 to ab: “It may be mentioned here that the error was pointed out to the author of the former paper by M.A. Potier, of Paris, in the winter of 1881.” When the instrument on the moving earth is observed from a stationary point outside earth, the mirror at b1 already moved to b while light was traveling there from a. “This meant that Michelson had overestimated by a factor of two the fringe shifts originally expected.” The mirror at c also moved forward at the same time, but this was not taken into account. It thus seemed that light traveled different distances at the same time, which led George FitzGerald and Hendrik Lorentz (Lorentz ether theory) to postulate that distances shorted and time dilated in direction of motion (Fitzgerald-Lorentz contraction).