Paul Langévin (1872 -- 1946)
 Paul Langévin was born in Paris on 23 January 1872. He attended the Ecole Lavoisier and the Ecole de Physique et de Chimie Industrielles, where he was supervised by Pierre Curie (1859-1906) during his laboratory classes. In 1891 he entered the Sorbonne, but his studies were interrupted for a year in 1893 by his military service. In 1894, Langévin entered the Ecole Normale Superieure, where he studied under Jean Perrin (1870-1942). Langévin joined the Collage de France in 1902, and was made Professor of Physics there in 1904, a post he held until 1909 when he was offered a similar position at the Sorbonne. Contemporary to Marie Curie, Albert Eienstein and Hendrik Lorentz, he was noted for his work on the molecular structure of gases, analysis of secondary emission of X-rays from metals exposed to radiation and for his theory of magnetism. He suggested that the alignment of molecular moments in a paramagnetic substance would be random in the absence of an externally applied magnetic field, but would be non-random in its presence. The greater the temperature, however, the greater the thermal motion of the molecules and thus the greater the disturbance to their alignment by the magnetic field.
 
Langévin further postulated that the magnetic properties of a substance are determined by the valence electrons, a suggestion which influenced Niels Bohr (I885-1962) in the construction of his classic model describing the structure of the atom. He was able to extend his description of magnetism in terms of electron theory to account for diamagnetism. He showed how a magnetic field would affect the motion of electrons in the molecules to produce a moment that is opposed to the field. This enabled predictions to be made concerning the temperature-independence of this phenomenon and furthermore to allow estimates to be made of the size of electron orbits.  
 
He published his work on the atomic theory of paramagnetism in 1905. In the same year Albert Einstein correctly identified Brownian motion (such motion, visible only under a microscope, is the incessant, random movement of micrometre-sized particles immersed in a liquid) as due to imbalances in the forces on a particle resulting from molecular impacts from the liquid. Shortly thereafter, Langévin formulated a theory in which the minute fluctuations in the position of the particle were due explicitly to a random force. Langevin's approach proved to have great utility in describing molecular fluctuations in other systems, including nonequilibrium thermodynamics.
 
In the later years, Langévin became increasingly involved with the study of Einstein's work on space and time. He was a firm supporter of the theory of the equivalence of energy and mass. Einstein later wrote that Langévin had all the tools for the development of the special theory of relativity at his disposal before Einstein proposed it himself and that if he had not proposed the theory, Langévin would have done so.
 
Langévin was responsible for some of the most important work on piezoelectricity and on piezoceramics for which he was generally remembered. He was the inventor of the underwater Sonar for submarine detection during World War I, where his theories and researches were extensively ultilised by the French and the Americans. In 1916 he was able to obtain echoes from the bottom and from a sheet of metal at a distance of 200 meters. In 1917 Langevin started to use the piezoelectric effect, rather than the electrostatic projector and carbon-button microphone used in 1916. He also started the use of vacuum tube amplifiers in underwater sounding equipment, this is thought to be the first use of electronics in this manner. With this new technology echoes were received from a submarine for the first time, in 1918, as deep as 1500 meters. Their transducer was a mosaic of thin quartz crystals glued between two steel plates (the composite having a resonant frequency of about 50 KHz), mounted in a housing suitable for submersion. Working on past the end of the war, they did achieve their goal of emitting a high frequency "chirp" underwater and measuring depth by timing the return echo. The strategic importance of their achievement was not overlooked by any industrial nation, however, and since that time the development of sonar transducers, circuits, systems, and materials has never ceased.  
 
After world war I his echo sounding devices were employed in many French ocean-liners, starting with the Ile de France in 1928. He was soon arrested by the Nazis for his outspoken antifascist views. He was first imprisoned in Fresnes, and later placed under house arrest in Troyes. The execution of his son-in-law and the deportation of his daughter to Auschwitz (which she survived) forced Langévin to escape to Switzerland in 1944. He returned to Paris later that year and was restored to the Directorship of his old school, but died soon after, in Paris on 19 December 1946

Philippe PASSELECQ [Parents] est né le 3 avril 1675 à 73, St Ghislain, SAVOIE. Il est décédé le 18 novembre 1744 à 73, St Ghislain, SAVOIE. Philippe a épousé Anne Marie Josèph RAPAILLIERE le 29 août 1712 à 73, St Ghislain, SAVOIE.