Henri Abraham

Henri Abraham in 1935, photo byStudio Harcourt

Henri Abraham(1868–1943) was a French physicist who made important contributions to the science ofradio waves.He performed some of the first measurements of the propagation velocity of radio waves, helped develop France's firsttriodevacuum tube,and withEugene Blochinvented theastable multivibrator.He was murdered atAuschwitzduringthe Holocaust.

Life

Henri Abraham was born on 12 July 1868 in the1st arrondissement of Paris.After brilliant studies atChaptal secondary school,from 1886 to 1889 he pursued scientific graduate studies at theÉcole Normale Supérieure,where he attended the lectures of physics professorsJules ViolleandMarcel Brillouin,and the Faculty of Paris, where he studied physics withGabriel Lippmannand Edmond Bouty and obtained degrees in physical sciences and in mathematical sciences. He was then appointed for one year preparer physics laboratory of the École Normale Supérieure, then led by Jules Violle, where he wrote his thesis for the doctorate in physical sciences: "New determination of the ratio between electromagnetic and electrostatic units", which he received in 1892. He served as professor atCollège Chaptal(November 1890 – September 1894), then at theLycée Louis-le-Grand(September 1894 – November 1900).

Lecturer at the École Normale Supérieure from 1897 (1899–1900 3rd year), he was appointed lecturer in physics in November 1900, then the conference's second year with Marcel Brillouin, then it supports the Conferences 1st year. He also succeeded Jules Violle as director of the physics laboratory of the school. He served as director of the laboratory at theÉcole pratique des hautes étudesfrom 1904 to 1905. After the annexation of the École Normale Supérieure by theUniversity of Paris,he was appointed on 1 November 1904 Lecturer of Physics at the Faculty of Paris, delegate to the École Normale Supérieure, then professor of physics in 1912. He served a term as exchange professor to Brazil in 1922. He retired in October 1937, when he received an honorary award.Eugene Blochsucceeded him as director of the physics laboratory, whilePierre Augerwas his successor for physics conferences.

He was Secretary General of theSociété Française de Physiquefrom 1900 to 1912 and its president in 1922. WithGustave-Auguste Ferrié,he founded the League of Radioélectriciens in 1921, and succeeded him as president in 1934. He was also president of the Society of clotting France in 1932, and in 1934 Secretary General of theInternational Union of Pure and Applied Physics(IUPAP).

Arrested by the militia on the night of 23 June 1943 inAix-en-Provence,he was delivered to theGestapoand taken toMarseilleon 7 December at Drancy before being deported from theBobignystation on "Convoy No. 63" 17 December 1943 toAuschwitz concentration camp,where he was probably murdered on arrival, on 22 December 1943.TheThree Physicists Prizewas named to honour him, Bloch and Georges Bruhat, who also were murdered in Nazi concentration camps.

Scientific work

One of Abraham and Bloch's early astable multivibrators(small box, left)being used to calibrate a wavemeter(center)

As a student at the ENS, Henri Abraham was fascinated by the pioneering experiments ofHeinrich Hertzin 1888 onradio waveswhich confirmed the predictions of Maxwell's equations, established in 1864. His entire scientific career was devoted to developing applications of electromagnetic theory. In his thesis, he created a new measure of the relationship between units ofelectric chargeused at that time in the electrostatic and the electromagnetic CGS systems of units. The ratio of these units was equal to the speed of wave propagationc,according to Maxwell. His work inferred a value of this speed with an uncertainty of 1/2000 that of experiments performed by the best physicists of the time.

In 1899–1900, he measured very short time constants of theKerr effect,a few billionths of a second, or about the time it takes light to travel one meter. Between 1911 and 1914, he made the first measurements of the actual speed of electromagnetic wave propagation, measuring the propagation times between remote stations (in collaboration with Alexandre Dufour and G. Ferrie). Mobilized in 1914 in the Department of Military Telegraphy, under the direction of Commander Ferrie, in collaboration with Eugene Bloch he developed the first Frenchtriodeamplifyingvacuum tubefor radio reception. He and Bloch also invented theastable multivibrator.The harmonics produced by this device provided the first accurate technique for measuring radio frequencies, which was employed in 1916 in the French and British armies, and in the U.S. Army after 1917.

After the war, Abraham helped his former pupil Alexandre Dufour achieve the first devices foreshadowing our modern CRT oscilloscopes, and to record the oscillations of high frequency radio waves. He also directed the thesis of Peter Fleury (1921).

In the thesis of his pupil Jean Mercier (in 1923 ), a method is described which allows accurate measure of the frequency f of a radio wave and its wavelength L (distance traveled by the wave during the time period T = 1 / f). This measure allows deduction of the speed of light c = L / T = Lf with an unparalleled accuracy of 1:10,000. The same measurement method, applied with modern techniques after the Second World War in 1973, achieved a precision of nine significant digits, leading to a change in the definition of the meter.

Legacy

TheThree Physicists Prizeand the Henri Abraham Awardare awarded in the memory of Abraham.

Publications

• Recueil d'Expériences de Physique par H. Abraham avec la collaboration de nombreux physiciens; édition 1904, édition 1923, chez Gautier-Villard
• Recueil de Constantes Physiques par H. Abraham et P. Sacerdote, éditions Gautier-Villard 1913