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Zeeman : His Life and Works

Pieter Zeeman (25 May 1865 – 9 October 1943) was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Hendrik Lorentz for his discovery of the Zeeman effect.

 

Pieter Zeeman was born on May  25, 1865, at Zonnemaire, a small village in the isle of Schouwen,  Zeeland, The Netherlands, as the son of the local clergyman  Catharinus Forandinus Zeeman and his wife, née   Wilhelmina Worst. After having finished his secondary school  education at Zierikzee, the main town of the island, he went to  Delft for two years to receive tuition in the classical  languages, an adequate knowledge of which was required at that  time for entrance to the university. Taking up his abode at the  house of Dr. J.W. Lely, conrector of the Gymnasium and brother of  Dr. C. Lely (Minister of Public Works and known for initiating  and developing the work for reclamation of the Zuyderzee), Zeeman  came into an environment which was beneficial for the development  of his scientific talents. It was here also that he came into  contact with Kamerlingh Onnes (Nobel  Prize in Physics for 1913), who was twelve years his senior.  Zeeman's wide reading, which included a proper mastery of works  such as Maxwell's Heat, and his passion for performing  experiments amazed Kamerlingh Onnes in no small degree, and  formed the basis for a fruitful friendship between the two  scientists.

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Zeeman entered Leyden University in 1885 and became mainly a  pupil of Kamerlingh Onnes (mechanics) and Lorentz (experimental  physics): the latter was later to share the Nobel Prize with him.  An early reward came in 1890 when he was appointed assistant to  Lorentz, enabling him to participate in an extensive research  programme which included the study of the Kerr effect - an  important foundation for his future great work. He obtained his  doctor's degree in 1893, after which he left for F. Kohlrausch's  institute at Strasbourg, where for one semester he carried out  work under E. Cohn. He returned to Leyden in 1894 and became  "privaat-docent" (extra-mural lecturer) from 1895 to 1897.

In 1897, the year following his great discovery of the magnetic  splitting of spectral lines, he was called to a lectureship at  the University of  Amsterdam; in 1900 came his appointment as Extraordinary  Professor. In 1908 Van der Waals  (Nobel Prize in Physics for 1910) reached the retiring age of  70 and Zeeman was chosen as his successor, at the same time  functioning as Director of the Physics Laboratory. In 1923 a new  laboratory, specially erected for him, was put at his disposal, a  prominent feature being a concrete block weighing a quarter of a  million kilograms, erected free from the floor, as a suitable  platform for vibration-free experiments. The institute is now  known as the Zeeman Laboratory of Amsterdam University. Many  world-famous scientists have visited Zeeman there or worked with  him for some time. He remained in this dual function for 35 years  - on numerous occasions refusing an invitation to occupy a Chair  abroad - until in 1935 he had to resign on account of his  pensionable age. An accomplished teacher and of kind disposition  he was much loved by his pupils. One of these was C.J. Bakker,  who was from 1955 until his untimely death in an aircraft  accident in 1960 the General Director of the Organisation Européenne pour la Recherche Nucléaire (CERN) at Geneva. Another worker  in his laboratory was S. Goudsmit, who in 1925 with G.E.  Uhlenbeck originated the concept of electron spin.

Zeeman's talent for natural science first became apparent in  1883, when, while still attending the secondary school, he gave  an apt description and drawing of an aurora borealis - then  clearly to be observed in his country - which was published in   Nature. (The Editor praised the meticulous observations of   «Professor Zeeman in his observatory at  Zonnemaire»!)

Zeeman's main theme of investigation has always concerned optical  phenomena. His first treatise Mesures relatives du  phénomène de Kerr, written in 1892, was rewarded  with a Gold Medal from the Dutch Society of Sciences at Haarlem;  his doctor's thesis dealt with the same subject. In Strasbourg he  studied the propagation and absorption of electrical waves in  fluids. His principal work, however, was the study of the  influence of magnetism on the nature of light radiation, started  by him in the summer of 1896, which formed a logical continuation  of his investigation into the Kerr effect. The discovery of the  so-called Zeeman effect, for which he has been awarded the Nobel  Prize, was communicated to the Royal Academy of Sciences in  Amsterdam - through H. Kamerlingh Onnes (1896) and J.D. van der  Waals (1897) - in the form of papers entitled Over den Invloed  eener Magnetisatie op den Aard van het door een Stof uitgezonden  Licht (On the influence of a magnetization on the nature of  light emitted by a substance) and Over Doubletten en  Tripletten in het Spectrum teweeggebracht door Uitwendige  Magnetische Krachten (On doublets and triplets in the  spectrum caused by external magnetic forces) I, II and III. (The  English translations of these papers appeared in The  Philosophical Magazine; of the first paper a French version  appeared in Archives Néerlandaises des Sciences Exactes  et Naturelles, and in a short form in German in   Verhandlungen der Physikalischen Gesellschaft zu  Berlin.)

The importance of the discovery can at once be judged by the fact  that at one stroke the phenomenon not only confirmed Lorentz'  theoretical conclusions with regard to the state of polarization  of the light emitted by flames, but also demonstrated the  negative nature of the oscillating particles, as well as the  unexpectedly high ratio of their charge and mass (e/m).  Thus, when in the following year the discovery of the existence  of free electrons in the form of cathode rays was established by   J.J. Thomson, the identity of  electrons and the oscillating light particles could be  established from the negative nature and the e/m ratio of  the particles. The growing number of observations made by other  investigators on studying the effects of using various substances  as light emitters - not all of them explicable by Lorentz'  original theory (the so-called «anomalous Zeeman  effect» could only adequately be explained at a later date,  with the advent of Bohr's atomic theory, quantum wave mechanics,  and the concept of the electron spin) - was assembled by him in  his book Researches in Magneto-Optics (London 1913, German  translation in 1914). Not only has the Zeeman effect thrown much  light on the mechanism of light radiation and on the nature of  matter and electricity, but its immense importance lies in the  fact that even to this day it offers the ultimate means for  revealing the intimate structure of the atom and the nature and  behaviour of its components. It still serves as the final test in  any new theory of the atom.

Already in his second communication Zeeman expressed the opinion  that the accepted existence of strong magnetic fields on the  surface of the sun could be verified, since these should alter  spectral lines derived from the celestial body. (It is typical of  Zeeman to extend physical concepts into the realm of celestial  phenomena.) In a letter to him (1908) the astronomer G.E. Hale,  Director of Mount Wilson Observatory, corroborated this opinion  by means of photographs which indicated that in solar vortices  the spectral lines indeed appeared to be affected by magnetic  fields. Even the theoretical prediction concerning the probable  interrelationship between the directions of polarization and  those of the magnetic fields was subsequently confirmed by  Hale.

With regard to Zeeman's activities outside the field of the  magnetic splitting of spectral lines, mention should first be  made of his work on the Doppler effect in optics and in canal  rays (laboratory tests). A second field of study was that on the  propagation of light in moving media (justification of the  existence of the Lorentz-term in the Fresnel drag coefficient).  Other investigations were those into the influence of the  magnetic moment of the nucleus on the hyperfine structure of  spectral lines. He also succeeded, with J. de Gier, in  discovering a number of new isotopes (38Ar,   64Ni, amongst others) by means of Thomson's parabola  mass spectrograph. Zeeman's predilection for testing fundamental  laws also found expression in his verification - carried out with  an accuracy of < 1: 107 - of the equality of heavy  and inert masses.

Zeeman was Honorary Doctor of the Universities of Göttingen, Oxford, Philadelphia, Strasbourg,  Liège,  Ghent, Glasgow, Brussels and Paris. He was also a member or honorary  member of numerous learned academies, including the very rare  distinction of Associé Etranger of the Académie des  Sciences of Paris. He was also member and Chairman of the  Commission Internationale des Poids et Mesures, Paris. Appointed  member of the Royal Academy of Sciences of Amsterdam in 1898, he  served as the Secretary of the Mathematical-Physical Section from  1912 to 1920. Among the other distinctions may be mentioned the  Rumford Medal of the Royal Society of London, the Prix Wilde of  the Academie des Sciences of Paris, the Baumgartner-Preis of the  Akademie der Wissenschaften of Vienna, the Matteucci Medal of the  Italian Society of Sciences, the Franklin Medal of the Franklin Institute of  Philadelphia, the Henry Draper Medal of the National Academy of  Sciences of Washington. He was also made a Knight of the  Order of Orange-Nassau and Commander of the Order of the  Netherlands Lion.

Outside his field of study Zeeman showed much interest in  literature and the stage. An entertaining host, he loved to  invite his collaborators and pupils to dine with him at his home,  an event preceded by a learned talk in his study and followed by  a gathering in the family circle.

Zeeman married Johanna Elisabeth Lebret in 1895; they had one son  and three daughters. During the last year of his professorship he  suffered from ill-health. He died after a short illness on  October 9, 1943.

 

 

Source : From Nobel Lectures, Physics 1901-1921, Elsevier Publishing Company, Amsterdam, 1967


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