Hendrik Lorentz

Hendrik Antoon Lorentz was born in Arnhem, the Netherlands, on July 18, 1853. His father, Gerrit Frederik Lorentz, ran a nursery, and his mother was Geertruida van Ginkel.⁠[1][2][3]

The Biografisch Woordenboek van Nederland gives the father’s occupation as grower (kweker) and prints the mother’s name as Geertruida Ginkel; A. J. Kox’s biography states that the father ran a market-gardening business (tuindersbedrijf) near Arnhem, and Frits Berends’s article calls him a prosperous horticulturalist. Leiden University’s article on the biography by Berends and Dirk van Delft states instead that a game leg forced the father to give up market gardening, that he then worked as a carpenter and as a grocer and had to close the shop when business was bad, and that the family, which had inherited land but could not live from it, was not well off.⁠[4][5][6][7]

Sources differ on when his mother died and his father remarried. The NobelPrize.org biography states that his mother died when he was four and that his father married Luberta Hupkes in 1862; Kox gives 1857 for the mother’s death and has the father remarry about five years later; Russell McCormmach’s article in the Dictionary of Scientific Biography has the father remarry when the boy was nine. Leiden University’s article states that when Lorentz was eight his three-year-old brother died, followed by his mother six weeks later, and that Berends found in the civil records that the father remarried six months after her death.⁠[1][5][3][7]

Known as “Hentje,” he was a quiet, cheerful child who learned to talk late but showed great intelligence early; at ten he bought a table of logarithms with his pocket money. As a child he fell while playing and broke the bridge of his nose. Aletta Kaiser’s brother later recorded that one of his sisters found the nose “niet passend bij het geheel” (not in keeping with the whole), but that the beaming jet-black eyes behind his gleaming spectacles made up for much.⁠[5]

He went to primary school in Arnhem and then to a so-called Franse school, a form of extended primary education, where his teacher Timmer encouraged independent study, which helped him greatly. The Royal Society’s obituary and MacTutor’s biography state that he attended Mr. Timmer’s primary school until he was thirteen and then entered the newly opened high school. Headmaster Timmer introduced him to the world of mathematics and physics, and Lorentz was grateful to him. His grade school held lessons in the evening as well as in the morning and afternoon, which the NobelPrize.org biography likens in a sense to the Dalton method.⁠[5][8][9][7][1]

When the first high school (H.B.S.) in Arnhem opened in 1866, he was placed directly in its third form. After the fifth form and a year of studying the classics, he entered Leiden University in 1870. The Biografisch Woordenboek van Nederland dates his HBS years to 1866–1869. He passed the entrance examination for Leiden University at the age of 17.⁠[1][4][8]

When he entered the third grade of the H.B.S. there were only two other pupils in it. His physics teacher, van de Stadt, had studied at Leiden, and his chemistry teacher, Van Bemmelen, later introduced him to Heike Kamerlingh Onnes in their early student years.⁠[6]

At the HBS he excelled in every subject, and his final examination became almost legendary: teachers consulted it when they were unsure about other answers. To qualify for university he took separate lessons in Greek and Latin. His first contact with experimental physics also came at school; he recalled running through a concert hall holding up a wind meter tied to a long lath.⁠[5]

At school in Arnhem he was always first in his class. He was drawn to physical science early and also read widely in Victorian novels and the history of the Reformation.⁠[3]

In 1870 he entered Leiden University to study mathematics and physics. The astronomer Frederik Kaiser resumed a lecture course he had stopped, giving Lorentz practically private tuition; Lorentz became a close friend of Kaiser, followed his lectures on theoretical astronomy and also attended the lectures of Pieter Leonhard Rijke, then the only professor of physics there.⁠[1][6][3][5]

In 1871 he obtained the candidate’s degree (kandidaats) in mathematics and physics. Kox states that he passed it magna cum laude at the age of 18, the Biografisch Woordenboek van Nederland dates it to November 1871, McCormmach’s article states that he passed it after a year and a half, and Berends’s article dates it to 1872.⁠[1][5][4][3][6]

In 1872 he returned to his parents’ home in Arnhem, where he taught at an evening school while working on his doctoral thesis on his own; he had taught evening classes in mathematics from the age of 19 and stayed in Arnhem until 1878. The Biografisch Woordenboek van Nederland dates his return to February 1872 and his doctoraal examination to June 1873; McCormmach’s article records that he passed it summa cum laude in 1873 and that he lived at home for seven years, studying on his own and teaching at the evening high school. In this period he bought an edition of Fresnel’s collected works, the first reference work he owned beyond the usual textbooks.⁠[1][6][4][3][5]

On Saturday, December 11, 1875, he received his doctorate magna cum laude from Leiden University under Pieter Rijke with the thesis “Over de theorie der terugkaatsing en breking van het licht,” on the theory of the reflection and refraction of light. The NobelPrize.org biography and the Royal Society’s obituary give his age at the doctorate as 22, McCormmach’s article as 21.⁠[5][4][6][10][1][8][3]

The thesis treated reflection and refraction from the standpoint of James Clerk Maxwell’s electromagnetic theory, which was then new, and concluded that Maxwell’s theory explained these phenomena better than its rivals. He followed Maxwell’s theory as interpreted by Hermann von Helmholtz. BritannicaEncyclopædia BritannicaEncyclopædia Britannica is a general English-language encyclopedia first published in Edinburgh, Scotland, in 1768; the name also refers to its publisher, Chicago-based Encyclopædia Britannica, Inc. (which presents itself as The Britannica Group). The print edition ended in 2012, and the company’s main businesses since then have been the online encyclopedia Britannica.com, digital education products for schools and libraries, and Merriam-Webster dictionaries.Open the full entry describes the thesis as a refinement of Maxwell’s electromagnetic theory; the Biografisch Woordenboek van Nederland counts him among the few physicists on the Continent who understood Maxwell’s papers.⁠[1][6][4][3][11]

For a time he was undecided between physics and mathematics. In 1877 he was offered a chair of mathematics at Utrecht University, which he declined. On Rijke’s advice he applied that year for a teaching post at a gymnasium in Leiden, intending also to become a privaatdocent.⁠[3][5][4]

The higher education law of 1876 turned the Amsterdam Athenaeum into a university and split the physics chair at Leiden University, Rijke keeping experimental physics; Berends’s article calls the new chair the chair of mathematical physics. Rijke first thought of his former student Johannes Diderik van der Waals, but van der Waals opted for Amsterdam, and the choice fell on Lorentz.⁠[6][3][5]

In 1878, at the age of 24, he took up the newly created chair of theoretical physics at Leiden University, the first chair of its kind in the Netherlands; McCormmach’s article calls it one of the first in Europe and Berends’s article one of the first worldwide. Britannica, MacTutor’s biography and the Franklin Institute’s page call the post professor of mathematical physics.⁠[1][2][3][12][7][11][9][13][8][5][6]

He began teaching with the inaugural lecture “De moleculaire theorieën in de natuurkunde” (molecular theories in physics), given when he was not yet 25; Kox dates the lecture to January 28, 1878, while the Biografisch Woordenboek van Nederland gives January 25 and prints the title as “De moleculaire theoriën in de natuurkunde.” In the lecture he described the aim of physical research as finding simple, basic principles from which the phenomena can be deduced, and cautioned against overvaluing the mental images associated with those principles.⁠[5][4][3][6]

Although he later received many invitations to chairs abroad, he always remained at his alma mater.⁠[1]

In 1878 he published an essay on the relation between the velocity of light in a medium and the medium’s density and composition; McCormmach’s article states that a paper of 1878, which modelled molecules as containing charged harmonic oscillators to explain the dispersion of light, began his research programme on dispersion. The Biografisch Woordenboek van Nederland dates the paper that led to the formula, “Over het verband tusschen de voortplantingssnelheid van het licht…” (in the Verhandelingen of the Royal Netherlands Academy), to 1879. The formula is known as the Lorenz–Lorentz formula: the NobelPrize.org biography states that the Danish physicist Ludvig Lorenz proposed it almost simultaneously, while the Biografisch Woordenboek van Nederland states that L. V. Lorenz had derived it by a completely different route in 1869.⁠[1][3][4][8]

Also in 1878 he explained the rotation of the plane of polarization of light in a magnetic field. In 1884 he began studying the effect of magnetization on the polarization of reflected light.⁠[4][9]

In 1886 he published an extensive treatise on stellar aberration, adopting Augustin-Jean Fresnel’s hypothesis of an immovable ether pervading all bodies as the basis for a general theory of the electrical and optical phenomena of moving bodies, and concluding that Fresnel’s ether theory was superior to that of George Gabriel Stokes.⁠[1][3]

From May 10, 1881, he was a member of the physics section (Afd. Natuurkunde) of the Royal Netherlands Academy of Arts and Sciences.⁠[14]

On July 15, 1881, he married Aletta Catharina Kaiser in Amsterdam; the Royal Society’s obituary spells her name Alletta. She was born in Amsterdam in 1858, the youngest daughter among the eight children of Jan Willem Kaiser and Johanna Buisman.⁠[8][15]

Her father, J. W. Kaiser, was a professor at the Academy of Fine Arts, director of the museum that later became the Rijksmuseum in Amsterdam, and designer of the first postage stamps of the Netherlands.⁠[1]

She was a niece of his former teacher, the astronomer Frederik Kaiser (1808–1872). The text of Agnes van Steen’s article states that the two met through Kaiser’s son, while its note says that they met at the home of the Kaiser-Fabius couple; Aletta’s brother had heard that when she first saw Lorentz he was sitting on a merry-go-round.⁠[3][12][15][5]

After the wedding the couple lived at Hooigracht 60 in Leiden, and from 1886 at Hooigracht 48 on the same canal.⁠[15]

He wrote two widely used Dutch textbooks: the Leerboek der differentiaal- en integraalrekening (textbook of differential and integral calculus, 1882), translated into German in 1900, and the Beginselen der natuurkunde (principles of physics, 1888–1890), which reached its ninth edition in 1929. Before 1892 he published on average about one paper a year.⁠[4][3][9]

From 1882 he lectured for many years for the Diligentia society, and he gave a lecture series for the Leiden branch of the Maatschappij tot Nut van ’t Algemeen.⁠[4]

When Heike Kamerlingh Onnes was a candidate for a physics chair the faculty was strongly divided, but Van Bemmelen and Lorentz both favoured him; Kamerlingh Onnes was appointed and began his cryogenic research in 1882. Lorentz took over Kamerlingh Onnes’s heavy teaching load for medical students and carried it for about 20 years, until a third professor of physics was appointed. Berends’s article judges that he proved an ideal colleague to Kamerlingh Onnes.⁠[6]

In 1892 he published the first memoir on his electron theory, “La théorie électromagnétique de Maxwell et son application aux corps mouvants” (Maxwell’s electromagnetic theory and its application to moving bodies), in volume 25 of the Archives néerlandaises (pages 363–551).⁠[8][9][3][2]

The theory held that matter contains minute charged particles, electrons, which conduct electric current and whose oscillations produce light; he proposed this before the existence of electrons had been established. The electron concept allowed molecular theory to be applied to electricity and explained the behavior of light waves in moving transparent bodies; with it he modified and completed Maxwell’s theory of electromagnetism, explaining the electric and magnetic properties of matter by the motion of charged atomic particles. Albert Einstein later called it the “Maxwell–Lorentz theory.”⁠[2][1][9][11][16][6]

In 1892 he used the theory to derive the Fresnel drag coefficient, showing that it arose from the interference of light rather than from a real partial dragging of the ether. The force that a magnetic field exerts on moving charged particles is now called the Lorentz force; Kox dates its introduction to 1892, while McCormmach’s article places the equation in the Versuch of 1895 and calls it Lorentz’s own contribution to electrodynamics.⁠[3][5][16]

The experiment of Albert A. Michelson and Morley failed to detect the earth’s motion relative to the ether, and his electron theory did not account for this result. George Francis FitzGerald had independently suggested that moving bodies contract in the direction of their motion, and in 1892 Lorentz adopted this contraction hypothesis to explain the null result; the effect became known as the FitzGerald–Lorentz contraction. McCormmach’s article states that he gave an exact form of the contraction hypothesis in 1895.⁠[11][5][9][8][3]

In 1895 he published the Versuch einer Theorie der electrischen und optischen Erscheinungen in bewegten Körpern (attempt at a theory of electrical and optical phenomena in moving bodies), the book-length version of his electron theory. MacTutor’s biography judges that the 1892 memoir and this book embodied the first systematic appearance of the electrodynamic principle of relativity.⁠[4][5][9][17]

That year he introduced the concept of local time, that is, different rates of time at different places, and showed that the field equations keep their form under uniform motion when local time is used. He formulated his theorem of corresponding states in 1895, improved it in the “Théorie simplifiée” of 1899 and in his 1904 paper, and gave it its final form in the second edition of The Theory of Electrons in 1915; the 1895 version held only for the macroscopic equations and only to first order in v/c, and he later proved an exact version for the microscopic equations. By 1900 Joseph Larmor, in Aether and Matter, had proved the theorem to order v²/c².⁠[11][8][3]

The auxiliary quantities he introduced in 1895, among them “local time,” depended on velocity; in 1899 he changed them so that they satisfied the free Maxwell equations exactly, which brought in a contraction factor matching the FitzGerald–Lorentz contraction hypothesis. In the same year he stated a generalized contraction hypothesis, that material systems contract in the same way as the fields, and his 1899 paper already contained length contraction, time dilation and velocity-dependent forces and masses. In 1900 Henri Poincaré realized that local time is the time registered by co-moving observers who synchronize their clocks with light signals.⁠[3]

In 1896 his student Pieter Zeeman, then an experimental physicist in Leiden, discovered that a magnetic field splits spectral lines. Zeeman made a new attempt at the experiment in September 1896, and the Royal Netherlands Academy of Arts and Sciences made his findings public on October 31, 1896.⁠[16][9][6][2][5]

He at once explained the phenomenon with his electron theory and the Lorentz force, predicting that a single line would be split into three and that the edges would be differently polarized; Zeeman’s further experiments confirmed the circular polarization he had predicted. He concluded that the vibrating particles emitting the light in the atom are negatively charged and have a very small mass. The size of the splitting gave the ratio of their charge to their mass, a thousand times as great as the value then believed; the Biografisch Woordenboek van Nederland states that their mass was more than a thousand times smaller than that of the lightest atom. His theoretical explanation of the simplest type of the effect appeared in volume 43 of the Philosophical Magazine in 1897.⁠[3][6][16][5][8][4]

Britannica presents the sequence as Lorentz’s theory implying that a strong magnetic field should affect the wavelength of the light, and his pupil Zeeman demonstrating this in 1896.⁠[11]

At Ludwig Boltzmann’s invitation he lectured at the Versammlung deutscher Naturforscher und Ärzte (meeting of German natural scientists and physicians) in Düsseldorf, his first congress abroad, which drew him into international physics. McCormmach’s article and Kox date the meeting to 1898; the Biografisch Woordenboek van Nederland and Berends’s article give 1897.⁠[3][5][4][6]

In 1900 he spoke at the international congress of physics in Paris. On December 11 of that year Leiden celebrated the twenty-fifth anniversary of his doctorate, and leading scientists contributed a volume of memoirs in his honour.⁠[5][3][6][8]

In 1901 his lecture series for the Maatschappij tot Nut van ’t Algemeen was published as Zichtbare en onzichtbare bewegingen, which MacTutor’s biography lists as Visible and Invisible Movements.⁠[4][9]

He shared the 1902 Nobel Prize in Physics with Pieter Zeeman, each receiving one half, “in recognition of the extraordinary service they rendered by their researches into the influence of magnetism upon radiation phenomena.” His affiliation at the time of the award was Leiden University.⁠[2][3]

Britannica states that the prize recognized his theory of electromagnetic radiation, which Zeeman’s findings had confirmed; MacTutor’s biography states that he received it for his mathematical theory of the electron. The award ceremony was held on December 10, 1902.⁠[11][9][6]

At the ceremony Hj. Théel, President of the Royal Swedish Academy of Sciences, gave the presentation speech, crediting Lorentz of Leiden and Zeeman of Amsterdam with pioneering work on the connection between optical and electromagnetic phenomena and stating that “The greatest credit for the further development of the electromagnetic theory of light is due to Professor Lorentz.” His theory could explain everything the older theory explained and overcame some of its greatest shortcomings; it explained satisfactorily the phenomena discovered by Zeeman, and details that had escaped Zeeman’s attention, including the polarization of the split lines, could be foreseen and were afterwards confirmed by him. The speech called the Zeeman effect one of the most important experimental advances of recent decades and said that the Academy judged dividing the prize between the two “not only justified, but just.”⁠[18]

On December 11, 1902, he gave his Nobel Lecture, “The Theory of Electrons and the Propagation of Light.” He began by explaining that “Professor Zeeman has been prevented by illness from undertaking the journey to Stockholm.”⁠[19]

In the lecture he described the physical world as made up of ordinary matter, electrons and the ether: electrons are charged particles smaller than atoms, which move freely in conductors and vibrate about fixed positions in insulators; the electric field of light forces bound electrons into vibration, and because electrons have mass they respond differently to different colors, which produces dispersion. He explained the Zeeman effect by the vibrations of electrons in the light source, a magnetic field changing their frequencies and splitting one line into three, and noted that more complex spectra implied more complex atomic structures that his theory had not yet explained.⁠[19]

He further pointed out that the charge-to-mass ratio given by the Zeeman splitting agreed with cathode-ray measurements: the electron’s charge is of the same order as that of an electrolytic ion and its mass only about one eight-hundredth of that of a hydrogen atom, a result J. J. ThomsonJ. J. ThomsonJ. J. Thomson (Sir Joseph John Thomson, 1856–1940) was a British physicist who became Cavendish Professor of Experimental Physics at the University of Cambridge in 1884, discovered the electron, which he called the corpuscle, through his cathode-ray experiments of 1897, and received the whole of the 1906 Nobel Prize in Physics for his theoretical and experimental investigations on the conduction of electricity by gases; he later discovered the isotopes of neon with F. W. Aston and was Master of Trinity College from 1918 until his death.Open the full entry at Cambridge had confirmed by a completely different method. He discussed the apparent mass, depending on velocity, that arises because a moving electron stores energy in the surrounding ether; treated the ether as stationary, the earth moving through it without dragging it along; and reproduced with his electron theory the Fresnel drag coefficient confirmed by Fizeau’s experiment. At the end he suggested that molecular forces might also be basically electromagnetic.⁠[19]

In the lecture he also noted that “electrons” was the name introduced later by Johnstone Stoney; suggested that an atom is in the last resort some sort of local modification of the omnipresent ether; mentioned that soon after Zeeman’s discovery the Russian physicists Egorov and Georgievsky found that a sodium flame in a magnetic field emits partially polarized light; discussed Voigt’s theory and the work of Kaufmann and Abraham on apparent mass; and gave Fresnel’s drag coefficient for water as 0.44. He closed with the hope “to play a modest part in the solution of the problems which next present themselves to us.”⁠[19]

In 1903 he put forward an electron theory of metals and derived from it a formula for black-body radiation valid only in the long-wavelength limit. That year he published his Principle of Correlation in volume 6 of the Proc. Amst. Acad.⁠[3][8]

In 1904 he published “Electromagnetic Phenomena in a System Moving With Any Velocity Smaller Than That of Light,” putting forward what became known as the Lorentz transformation, a name proposed by Henri Poincaré. It rests on slight changes in electromagnetic forces caused by motion, which produce a minute contraction of moving bodies; it accounted for the failure of Michelson and Morley’s experiments to detect the earth’s motion relative to the ether, described the changes in mass, length and time of moving bodies, and paved the way for, and formed the basis of, Albert Einstein’s special theory of relativity. Berends’s article describes it as a transformation of the frame of reference from a moving to a stationary observer in which time as well as length is modified, which “repaired” classical theory, while Einstein’s 1905 theory later made it a logical consequence.⁠[1][11][9][6][5][3][3]

In 1904 he lectured in Berlin on the electron theory and other topics of current interest in physics, and in 1905 in Paris.⁠[3]

In 1905 he considered moving to the University of Munich as professor of theoretical physics; he agreed to stay only after Leiden University relieved him of introductory lectures by appointing a third professor of physics. In 1906 J. P. Kuenen was appointed to this third chair to teach the first-year students, partly for fear that Lorentz would leave for Munich.⁠[3][4][6][5]

In 1906 he traveled to the United StatesUnited StatesThe United States is a federal country in North America made up of 50 states, the District of Columbia as the seat of government, and territories such as Puerto Rico and Guam; its capital is Washington, D.C. The Continental Congress adopted the Declaration of Independence on July 4, 1776. The 2020 census (April 1, 2020) counted a resident population of 331,449,281, and the 435 seats of the House of Representatives are apportioned among the states on the basis of the census.Open the full entry to lecture on the electron theory at Columbia UniversityColumbia UniversityColumbia University, formally Columbia University in the City of New York, is a private research university in New York City and a member of the Ivy League. Founded in 1754 by royal charter from King George II as King's College, it is the oldest institution of higher education in New York State and the fifth oldest in the United States. It was renamed Columbia College in 1784 and adopted the university name and moved to Manhattan's Morningside Heights in 1896. It has 17 schools and four affiliated colleges, with 35,978 students enrolled in fall 2025. Legal scholar Jennifer L. Mnookin became president on July 1, 2026.Open the full entry in New York City as Earnest Kempton Adams lecturer; the lectures, expanded, were published in Leipzig in 1909 as The Theory of Electrons. He visited the United States four times, in 1906, 1922, 1924 and 1926.⁠[5][3][9][17][4]

In 1908 he lectured at the Fourth International Congress of Mathematicians in Rome, using Gibbsian statistical mechanics to conclude that the Rayleigh–Jeans law was the only radiation law compatible with classical molecular mechanics and that equipartition must hold, which ended his hope of explaining the experiments favouring Planck’s law by a breakdown of equipartition; he adopted James Jeans’s suggestion that the discrepancy came from a lack of true equilibrium between radiation and matter. Immediately afterwards Wilhelm Wien, among others, objected on experimental grounds: by the Rayleigh–Jeans law a silver bar at room temperature would be clearly visible in the dark. He quickly and publicly retracted the conclusion and accepted the experimental validity of Planck’s law.⁠[3][9]

Leiden University’s article states that in the Rome lecture he said Max Planck’s hypothesis conflicted with contemporary physics, and that the Nobel physics committee had just nominated Planck but Gösta Mittag-Leffler, who heard the lecture, changed his mind about Planck, so that Planck did not receive the prize. McCormmach’s article states instead that in 1908 Lorentz spoke out in favour of Planck’s quantum theory as the only theory capable of explaining the complete spectrum of black-body radiation, one of the first to do so, and emphasized the deep antithesis between the quantum hypotheses and those of the electron theory. His friendship with Planck continued: Planck lectured in Leiden the day before the Nobel Prize he had missed was awarded and stayed at Lorentz’s house on the Hooigracht.⁠[7][3]

He rejected Einstein’s light-quantum hypothesis, because interference and diffraction seemed impossible to reconcile with a particulate nature of light and estimates of the size of a quantum gave absurd results; he accepted Planck’s radiation law but remained skeptical, and in his Paris lecture “l’Ancienne et la nouvelle mécanique” of December 10, 1923, he still said that quantum theory was not understood. His correspondence with Planck and Einstein shows his continued search for a classical interpretation of quanta. The Biografisch Woordenboek van Nederland states that he was extremely cautious toward the newest developments such as Planck’s radiation theory, Einstein’s relativity and quantum theory, but was willing to accept the new axioms of quantum theory; MacTutor’s biography states that he never fully accepted quantum theory and hoped to incorporate it into the classical approach; McCormmach’s article states that he deeply regretted the passing of classical physics.⁠[3][4][9][3]

His correspondence with Einstein began in 1908. In 1909 Einstein wrote to him that he was impressed by his work, and Lorentz replied that he had long admired Einstein.⁠[20][7]

From 1909 to 1921 he was president of the physics section of the Royal Netherlands Academy of Arts and Sciences.⁠[3]

Sources differ on when his post at Teylers in Haarlem began: Kox dates his appointment as curator of the physics cabinet (Fysisch Kabinet) of Teyler’s Stichting to January 1910, and Leiden University’s article also gives 1910; the Teylers Museum’s page on him and Einstein calls him director of the museum’s physics laboratory from 1909 to 1928; the NobelPrize.org biography, the Biografisch Woordenboek van Nederland, the Digitaal Wetenschapshistorisch Centrum’s membership record and another Teylers Museum page give 1912.⁠[5][7][20][1][4][14][12]

In 1910 he gave a series of lectures in Göttingen, and that year a free public library opened in Leiden on his initiative.⁠[5][4]

On Saturday, February 11, 1911, he and Einstein met for the first time. He had invited Einstein to lecture in Leiden, and the Einsteins stayed at his house; that day he took Einstein and Mileva Marić to the Teylers Museum, where John Hulk (1855–1913), curator of the art collection, showed them paintings and drawings, and Lorentz probably also showed them his new, well-equipped laboratory; the day before, he had written to Hulk that he hoped to come to the museum with Mr. and Mrs. Einstein at about two o’clock. The Teylers Museum’s page states that shortly before the visit Einstein wrote to a friend that he admired Lorentz like no other, and Kox records that in 1911 Einstein called Lorentz a “levend kunstwerk” (living work of art).⁠[20][7][5]

In the autumn of 1911 he chaired the first Solvay Conference in Brussels, which examined classical physics and the quantum theory; in his opening address he compared Planck’s hypothesis of energy elements to a wonderful ray of light that had opened unexpected vistas. In a letter from the conference Heike Kamerlingh Onnes wrote that Lorentz “has won everyone’s heart” and praised the “exceptional clarity, facility and friendliness” of his chairmanship.⁠[9][6][5]

In 1912 Ernest Solvay founded the Institut International de Physique in cooperation with him.⁠[5]

Around 1910 he decided to leave Leiden, as his many duties left too little time for research and his teaching had become a heavy burden; in 1912, after 35 years of lecturing on all branches of theoretical physics, he resigned his chair at Leiden University. He had wanted Einstein to succeed him, but Einstein had just accepted a post at the Eidgenössische Technische Hochschule in Zurich; he then proposed Paul Ehrenfest (1880–1933), 27 years his junior, whom he described as an “inspiring, passionate and witty lecturer.” Ehrenfest took up the chair in the autumn of 1912, and despite their differences in character the two established a congenial relationship.⁠[3][8][9][6][7][5]

Shortly after Ehrenfest arrived, he moved with his family to Haarlem, where he became curator of the physics cabinet of Teyler’s Stichting and secretary of the Hollandsche Maatschappij der Wetenschappen while remaining extraordinary professor (Britannica: honorary professor) at Leiden University; for the rest of his life he gave a lecture on recent developments in physics in Leiden every Monday morning. The laboratory at Teylers was remodeled after that of the Royal Institution in London for his use, and for the first time he had a laboratory of his own, where an assistant could carry out experiments under his direction, fulfilling a long-held wish. The NobelPrize.org biography and the American Institute of Physics’ record date his secretaryship of the society from 1912, the Digitaal Wetenschapshistorisch Centrum’s record gives 1920–1928, and Berends’s article also places it later.⁠[1][5][15][4][3][11][17][14][6]

His Monday lectures covered most new developments in physics: in 1913–1914 he lectured on Einstein’s theory of gravitation while it was still being developed, and he discussed Heisenberg’s matrix mechanics in 1925–1926 and Schrödinger’s theory in 1927, about a year after each appeared, when he was already over seventy.⁠[6]

In 1912 he lectured at the Collège de France on statistical theories in thermodynamics; the lectures were published in French at Leipzig in 1916.⁠[9]

During 1914–1918 he initiated a scientific advisory committee from which the Dutch organization for applied scientific research TNO later grew. Through his standing with the government he convinced officials of the value of science for national production.⁠[4][1][17]

During the war his correspondence with Einstein intensified, dealing with the relation between the electron theory and special relativity and leaving hundreds of pages of calculations. On August 2, 1915, Einstein wrote to him of his bitter disappointment at the narrow national feeling of even eminent people. He followed closely Einstein’s completion of his theory of gravitation in 1915–1916, discussed its problems with him in long letters and made some important contributions himself; McCormmach’s article places his fundamental contributions to general relativity in 1914–1917 and describes him as strongly sympathetic to the theory. An article of his from 1915 shows that he had mastered the brand-new theory; a letter from Einstein in January 1916 removed his last doubts, and in a letter of January 10–11, 1916, he wrote to Ehrenfest that he now understood the theory and had congratulated Einstein on his brilliant results. Einstein was pleased by Lorentz’s compliments, as a letter of January 17, 1916, shows; Ehrenfest replied that the exchange meant to him what it means when one freemason recognizes another by a secret sign, and asked Lorentz to devote a Monday lecture to general relativity, which Willem de Sitter attended before publishing on the subject himself.⁠[20][6][5][3]

After large parts of North Holland above Amsterdam were flooded in January 1916, a law for closing the Zuiderzee was passed in June 1918, and he chaired the state committee, made up of engineers, oceanographers and meteorologists, that prepared the closure and studied the effects of the closing dike (Afsluitdijk) on the water levels and currents of the Wadden Sea. The NobelPrize.org biography dates his appointment as chairman to 1919; McCormmach’s article states that in 1920 he took charge of the calculations for the height of the closing dike.⁠[4][5][6][1][3]

He introduced a new, scientifically based method for calculating the required dike heights. The final report, more than half of which he wrote himself, was published by the Algemeene Landsdrukkerij in November 1926. His theoretical calculations, the result of eight years of pioneering work, were later confirmed in practice in the most striking manner, and the dikes proved high enough during the floods of 1953 elsewhere in the country.⁠[6][4][1]

In 1919 two British expeditions observed the solar eclipse. On September 22 of that year he informed Einstein by telegram that the observations of Arthur Eddington and others had confirmed an important part of the general theory of relativity. On December 21 of that year Einstein sounded him out about a special professorship in Leiden; in 1920 Einstein became professor by special appointment at Leiden University and gave his inaugural lecture.⁠[6][20][7]

From 1919 he was a member of the newly founded Dutch education council (Onderwijsraad), and from 1921 to 1926 he chaired its department of higher education; together with the Leiden professor Cornelis van Vollenhoven he was largely responsible for the new academic statute regulating university examinations, and he was one of the founders and for many years a curator of the Nederlands Lyceum in The Hague.⁠[4]

From 1919 to 1925 his lectures at Leiden University, edited by several of his students, were published in eight parts as Lessen over theoretische natuurkunde (lessons on theoretical physics), followed by German and English editions, the English Lectures on Theoretical Physics appearing in eight volumes in London in 1931. In 1920 he published The Einstein Theory of Relativity: A Concise Statement.⁠[4][3][9]

After the war he worked to restore international scientific relations, especially between scientists of the former belligerents. For years after the war German researchers were not invited to conferences, and French and Belgian researchers refused to attend if Germans were present. He sought to repeal the clauses excluding the Central Powers from international organizations and, as president of the academy’s physics section, worked to bring the Netherlands into the postwar scientific bodies; in the Conseil International de Recherches, founded in 1918, he worked to have German scientists admitted, succeeding in 1925. McCormmach’s article states that the continuing divisions in science were a source of great unhappiness to him.⁠[8][3][4][7]

In 1923 he was elected to the League of NationsLeague of NationsThe League of Nations was an international organization established under the Covenant of the League of Nations after the First World War. It existed from 1920 to 1946 with its seat in Geneva, Switzerland, and a total of 63 states became members; the United States never joined.Open the full entry’ International Committee of Intellectual Cooperation, made up of only seven of the world’s most eminent scholars; he took the place of Einstein, who had resigned in disagreement with the way the committee worked. The committee’s aims included rebuilding relations in postwar Europe and restoring cordial relations among scientists of all countries, and it was a predecessor of UNESCO. From 1923 to 1928 he was first a member and then chairman; the Digitaal Wetenschapshistorisch Centrum’s record lists his posts on the committee as secretary in 1923 and chairman in 1925.⁠[1][3][5][6][7][14]

On his seventieth birthday in 1923 his extraordinary professorship at Leiden University was converted into a special chair funded by the Leidsch Universiteits-Fonds, so that he could go on lecturing until his death. He formally retired that year and continued his Monday lectures as special professor.⁠[4][5]

That year he lectured at the Royal Institution in London and at the University of CambridgeUniversity of CambridgeThe University of Cambridge is a university in Cambridge, England, United Kingdom. It gives 1209 as its founding date, is made up of Schools, Faculties, Departments and autonomous Colleges, and is a member of the Russell Group.Open the full entry received an honorary degree and gave the Rede Lecture, on Clerk Maxwell’s Electromagnetic Theory. He also received an honorary doctorate from the University of Paris.⁠[8][3]

Leiden University’s article shows a photograph taken at the Leiden Observatory in 1923 of Einstein, Ehrenfest, Willem de Sitter, Eddington and Lorentz.⁠[7]

In 1925 he succeeded Henri Bergson as president of the League of Nations’ International Committee of Intellectual Cooperation. That year he gave an address to the Institute of Metals on “The Motion of Electricity in Metallic Bodies.”⁠[1][5][4][3][8]

On December 11, 1925, Leiden celebrated the fiftieth anniversary of his doctorate in the university’s Great Auditorium, an occasion documented in volume 6 of Physica (1925). Those present included Prince Hendrik, Niels Bohr, Marie Curie, Einstein and the prime minister, Colijn, the last three of whom gave speeches. At the celebration Heike Kamerlingh Onnes announced the Lorentz Fund to promote theoretical physics and foster contacts between Dutch and foreign scientists, which had raised 100,000 guilders, a considerable sum at the time, from two thousand people, one thousand in the Netherlands and one thousand from nineteen other countries; the fund still exists. The Royal Society’s obituary dates the fund to 1926, calls it the Lorentz Foundation and describes its purpose as sending young Dutch physicists abroad and inviting young foreigners to Dutch universities. The national weekly De Haagse Post published a cartoon about the event.⁠[5][4][6][8]

Leiden University awarded him an honorary doctorate in medicine in gratitude for his devotion to teaching medical students; Kox places the award at the 1925 celebration, while the Royal Society’s obituary dates it to 1926, by decision of the university’s senate.⁠[5][8]

For a booklet made for the celebration, Einstein contributed a handwritten note stating that the Germans were beginning to see that Lorentz’s efforts to reconcile scientists of the Allied countries and Germany were guided by the best and noblest intentions. His former assistant Hendrika Johanna van Leeuwen attended the celebration and afterward described his “beminnelijke eenvoud en warme belangstelling voor allen om hem heen” (amiable simplicity and warm interest in everyone around him). Leiden University’s article shows a photograph of him walking in the procession in 1925.⁠[20][12][7]

In 1926 he lectured on quantum mechanics at Cornell UniversityCornell UniversityCornell University is a private research university in Ithaca, New York, and a member of the Ivy League. It is New York State's federal land-grant university, a distinction unique within the Ivy League. Ezra Cornell and Andrew Dickson White founded the university in 1865, and it opened in 1868. In addition to its Ithaca campus, Cornell operates Weill Cornell Medicine and Cornell Tech in New York City and a medical college in Qatar. It enrolled 26,793 students in fall 2024. Its president is Michael I. Kotlikoff.Open the full entry in the United States.⁠[17]

In 1927 he himself presented the first Lorentz Medal to Max Planck. That year his lectures at the Institute of Technology at Pasadena were published in Boston as Problems of Modern Physics, edited by H. Bateman.⁠[5][3][17]

He presided over the first five Solvay Conferences, in 1911, 1913, 1921, 1924 and 1927, held in Brussels every three years; the NobelPrize.org biography states that he chaired all Solvay Congresses until his death. After the war the Solvay meetings excluded German and Austrian physicists, and no German physicist was invited to the first postwar conference in 1921; as chairman of the Solvay Council he worked to annul the ban and in 1927 succeeded in having them invited again. The fifth conference, in October 1927, dealt with quantum mechanics.⁠[4][1][6][7][8][5]

In 1927, shortly before the fifth Solvay Conference, he chaired a congress devoted to quantum theory at Como, where he had gone for the celebration of the centenary of Alessandro Volta’s death.⁠[5][8]

He fell ill on January 16, 1928, and a few weeks later, on February 4, died in Haarlem, aged 74, after a short and happily painless illness; his death was sudden and unexpected. The Netherlands observed national mourning. January 28, 1928, would have marked fifty years as a professor, a date he did not live to celebrate.⁠[5][1][11][3][8]

The funeral took place in Haarlem at noon on Friday, February 10, 1928. At twelve o’clock the State telegraph and telephone services of the Netherlands were suspended for three minutes in tribute. The procession had fifteen carriages, one entirely covered in wreaths, and many thousands watched it pass. Representatives of the Dutch royal house, the government and science, as well as of scientific academies around the world, attended, together with many colleagues and distinguished foreign physicists.⁠[8][9][3][6][5]

Ehrenfest, Ernest Rutherford, Paul Langevin and Einstein addressed the mourners; Rutherford, as President of the Royal Society, represented the society and gave an oration at the graveside. McCormmach’s article records that Einstein, speaking at the graveside, called him the greatest and noblest man of our times.⁠[6][8][9][3]

His wife, Aletta Lorentz-Kaiser (1858–1931), was active in the women’s movement in Leiden from 1881 to 1912: in 1885 she became secretary of the Vereeniging tot verzorging van kleine kinderen, whose crèche opened on November 11 of that year, leaving its board in 1893; in 1900 she became treasurer of the Leiden women’s suffrage association and set her sights on the university’s professors; in 1902 she took the chair of the Leiden branch of the Vereeniging Onderlinge Vrouwenbescherming; at the end of 1904 she initiated a public playground on the Raamland and sat on its board; in 1907 she helped Lizzy van Dorp and others found the Nederlandsche Bond voor Vrouwenkiesrecht, became vice-president of its national board with responsibility for propaganda, and chaired its Leiden branch, founded in November 1907, until 1911; and in 1910 she chaired the Leiden reception committee of the Nationale Vrouwenraad. She moved with her husband to Haarlem in 1912 and died in Amsterdam in 1931.⁠[12][15][15]

In a letter to Lizzy van Dorp of February 5, 1907, she wrote “Ik wilde dadelijk op de proffenjacht gaan” (I wanted to go straight out on the professor hunt) and listed professors who would tentatively support the Bond, among them Lorentz; the Teylers Museum’s page likewise says that she recruited members among her husband’s colleagues and called it a proffenjacht. Lorentz regularly helped the women’s movement: Jacoba Elisabeth Vreede recalled that most of the journals of the Leiden women students’ reading circle had been kindly given by Professor Lorentz and Professor H. L. Drucker. His student Adriaan Fokker wrote in 1946 that Aletta was an “ingetogen vrouw” (a reserved woman), perhaps somewhat strict in her views, and “een overtuigde voorstandster en verdedigster” (a convinced supporter and defender) of women’s emancipation.⁠[15][12]

Sources differ on the number of children: the NobelPrize.org biography and Kox give two daughters and a son, the Royal Society’s obituary states that he was survived by his widow and three children, and the Biografisch Woordenboek van Nederland gives two sons and two daughters. McCormmach’s article names the elder daughter, Geertruida Luberta (born 1885), the younger, Johanna Wilhelmina (born 1889), a first son who died in infancy, and a second son, Rudolf, born in 1895; Agnes van Steen’s article states that this son was born in 1893 and died within a year, and that Rudolf, too, was sickly.⁠[1][5][8][4][3][15]

His elder daughter, Geertruida Luberta, known as Berta (1885–1973), studied physics and in 1912 took her doctorate under her father with a thesis on the theory of Brownian motion and related phenomena, described as the first research on the Brownian motion of electrons; Berends remarks that such supervision “would not be allowed today.” As a student she joined the Bond voor Vrouwenkiesrecht and from 1907 to 1910 sat on the board of the Leiden women students’ association. In 1910 she married the physicist Wander Johannes de Haas (1878–1957), later director of the cryogenic laboratory (Kamerlingh Onnes Laboratory) of Leiden University. Her father tried, unsuccessfully, to arrange translation work for her.⁠[12][15][1][17][7]

His younger daughter, Johanna Wilhelmina, known as Hanny, married the lawyer H. C. Leemhorst in 1912; his son Rudolf, still too young to marry in 1912, later married M. C. van Vollenhoven and became librarian of both Teylers and the Hollandsche Maatschappij der Wetenschappen, which Berends says “nepotism is too big a word” for, calling it a product of a time without social security. Berta’s biography of her father says nothing of her mother’s work in the women’s movement but records that her parents helped a poor family: her mother prepared bottles of milk for twins in the family, and her father made sure that one of its sons could become a bricklayer.⁠[15][7]

McCormmach’s article describes him as having none of the mannerisms of the eccentric genius or the bookish ascetic but as a disciplined scholar of regular habits, with a marked sense of humor and a gift for conversation, who always enjoyed a cigar and a glass of wine with friends; he grew up in Protestant circles but was a freethinker in religious matters. To all who knew him he seemed a man of remarkable inner harmony. He was unusually quick with foreign languages, inferring grammar and idiom from context, and regularly attended the local French church to improve his French.⁠[3]

He spoke German, French and English fluently. The NobelPrize.org biography describes him as a man of immense personal charm, the very picture of unselfishness and full of genuine interest in everyone who crossed his path, who endeared himself both to the leaders of his age and to the ordinary citizen and presided over international gatherings with exceptional skill; the Royal Society’s obituary speaks of his indescribable charm and surprising modesty and of a kind and appropriate word of encouragement for every student. Kox notes that those who knew him praised his warmth and his interest in other people’s problems and often mentioned his mildness and his somewhat ironic detachment, and that however busy he was he always found time to receive a guest over a cigar and a glass of wine.⁠[5][1][8]

Berends describes him as a very well-mannered person who kept people at a certain distance and says that he comes across in the sources as “Mr Perfect,” so that a biographer looks for the odd blemish. The Biografisch Woordenboek van Nederland describes him as a clear and original lecturer and a gifted popularizer, diplomatic and fluent in several languages and therefore a natural chairman of international congresses, with a strong interest in education and in young people of modest background.⁠[7][4]

From 1912 he supervised the first four women doctoral students in physics at Leiden: Johanna Reudler (1880–1962), Eva Bruins (1885–1966), Hendrika Johanna van Leeuwen (1887–1974) and his own daughter Berta. Van Leeuwen nearly gave up her post as his assistant in 1917 because some held that it should go to a man, Adriaan Fokker; Lorentz disagreed. She completed her thesis on magnetism, “Vraagstukken uit de Electronentheorie van het Magnetisme,” in 1919, became an assistant at the Technische Hogeschool Delft (now Delft University of Technology) in 1920 and in 1947 its first woman lecturer in theoretical and applied physics. Fokker took his doctorate under Lorentz in 1913.⁠[12]

The students he advised at Leiden included Johannes Droste, A. D. Fokker, L. S. Ornstein and P. Zeeman, and Balthasar van der Pol worked with him at Teylers as a postdoctoral student; his own teachers were Frederik Kaiser and P. L. Rijke. Young physicists came to Leiden from all over the world to hear his lectures, and Einstein and other young theorists made frequent journeys to Leiden to discuss their ideas with him.⁠[17][3][4]

Lorentz was 25 years older than Einstein. Einstein regarded him as his mentor and great example and said he was indebted to the groundwork Lorentz had laid, and in its early years the theory of relativity was called the Lorentz–Einstein theory. On the mantelpiece of his study in his house in Haarlem stood a photograph of Einstein. Einstein was his collaborator, colleague and friend.⁠[20][7][17]

McCormmach’s article states that Einstein said Lorentz had been the greatest influence in his life; Berends’s article records Einstein’s words that Lorentz meant more to him personally than anyone else he had met on his life’s journey.⁠[3][6]

In 1905 Einstein argued that the ether of the electron theory and the related notions of absolute space and time were superfluous. McCormmach’s article states that Lorentz admired this reinterpretation but never embraced it, regarding the choice between the two interpretations, which had the same observable consequences, as a matter of taste, and believing in the ether and in absolute space and time until his death; he did not use the term “principle of relativity” for his own theory until after Einstein’s 1905 paper, and he treated time dilation as a mathematical artifice but length contraction as a real effect of molecular forces. The supplementary article by Janssen and Kox states that after 1905 he realized that the auxiliary quantities of his theory were the quantities measured by a moving observer, but still regarded Lorentz invariance as a feature accidentally shared by the laws of Newtonian space and time rather than as a symmetry of relativistic space-time. The Biografisch Woordenboek van Nederland states that Einstein’s theory of relativity of 1905 postulated for all phenomena the hypothesis that Lorentz had derived as a conclusion.⁠[3][4]

His honours included honorary membership of the London Mathematical Society (1898); foreign membership of the Royal Society (May 11, 1905); the Royal Society’s Rumford Medal (1908) and Copley Medal (1918); the Franklin Institute’s Franklin award in physics (1917) “For researches which have contributed to our knowledge of the nature of light and the ultimate constitution of matter”; and fellowship of the Royal Society of Edinburgh (1920). He was also a foreign member of the German Physical Society, received the French Legion of Honour and was made a commander of the Order of Orange-Nassau.⁠[9][17][14][8][11][13][3][5]

He was a member of the Nederlands Natuur- en Geneeskundig Congres (Dutch congress of natural science and medicine) before 1890.⁠[14]

In 1924 he published Clerk Maxwell’s Electromagnetic Theory. After his death Pieter Zeeman and A. D. Fokker edited his Collected Papers in nine volumes, published in The Hague in 1935–1939.⁠[9][3]

His papers and correspondence are held in several places: the Museum Boerhaave holds his papers of 1869–1928, the Algemeen Rijksarchief his papers of 1888–1928, Columbia University his lecture notes The Quantum Theory of 1926, and the Niels Bohr Library & Archives of the American Institute of Physics Einstein’s correspondence with him and Kamerlingh Onnes (1901–1926, on microform), with further holdings at the Library of CongressLibrary of CongressThe Library of Congress is the library of the United States Congress. Founded in 1800 and housed on Capitol Hill in Washington, D.C., it answers reference requests from Congress, the public and other federal agencies.Open the full entry, the Deutsches Museum and elsewhere.⁠[17][4]

A. J. Kox edited his Selected Scientific Correspondence, the first volume of which appeared in 2008.⁠[3]

After his death a national committee of one hundred prominent Dutch citizens was formed to see to the monuments, and a design competition was considered inappropriate. The main monument, by the sculptor Wenckebach, was inaugurated in Arnhem in 1931 and shows Lorentz flanked by Huygens, Fresnel and Maxwell and by Planck, Einstein and Bohr; Leiden and Haarlem received more modest public memorials. In 2008 the visual artist van Houwelingen proposed carving the names of twentieth-century Nobel laureates in physics on the monument’s blank walls.⁠[6]

The house at Hooigracht 48 in Leiden where he lived bears a gable stone with the name Lorentz, and the formula for the Lorentz force is painted on a wall opposite his house. A crater on the moon is named Lorentz. Stained-glass windows by Harm Kamerlingh Onnes, a nephew of the physicist, at the Instituut-Lorentz depict Zeeman’s experimental discovery and Lorentz’s theoretical explanation, and the logo of the Lorentz Foundation is abstracted from them.⁠[15][16][9]

On October 25, 2019, Prometheus published the biography by Frits Berends and Dirk van Delft, Lorentz. Gevierd fysicus, geboren verzoener (Lorentz: celebrated physicist, born mediator), and in October 2019 A. J. Kox published a separate biography, Een levend kunstwerk. Leiden University’s article states that there had been no real biography of Lorentz before then.⁠[7]

The NobelPrize.org biography judges that his work revolutionized contemporary conceptions of the nature of matter and that all theoretical physicists regarded him as the world’s leading spirit, who completed what his predecessors had left unfinished and prepared the ground for the fruitful reception of the new ideas based on the quantum theory. The Royal Society’s obituary calls him “one of the greatest scientific figures of our time,” regards his theory, complete, exact and unambiguous within classical physics, as the culmination of the classical philosophy, and, describing the tribute on the day of the funeral, calls him the greatest man Holland had produced in that time; it quotes Joseph Larmor’s remark that “a survey of his whole life’s work is a liberal education in the history of physical science during the past half century.”⁠[1][8]

MacTutor’s biography quotes O. W. Richardson’s view of him as a man of remarkable intellectual powers, noted for the singular clearness of his writings and for the wisdom to lead discussion into fruitful channels. Britannica judges his work in physics to have been wide in scope, its central aim a single theory linking electricity, magnetism and light. The Biografisch Woordenboek van Nederland calls him the last representative of the great physicists of the classical period, and Berends likewise calls him the last great representative of classical physics, who also took part in the new ideas. McCormmach’s article quotes Einstein’s description of Lorentz’s separation of field and matter as an “act of intellectual liberation” and judges that his work carried classical physics to its “furthest stage of clarity, precision, and unity.” Berends also notes that the Lorentz force keeps particles circulating in accelerators and that the Lorentz transformation is still used daily at CERN.⁠[9][11][4][6][3][7]

Leiden University: Official website: https://www.universiteitleiden.nl/en (opens in a new window).⁠[21]

Teylers Museum: Official website: https://teylersmuseum.nl/nl (opens in a new window).⁠[22]