Röntgen was the only son of Friedrich Conrad Röntgen, a cloth manufacturer and merchant of Lennep, who belonged to an old Lutheran Rhineland family. His wife, Charlotte Constanze Frowein, was born in Holland, although her family, too, came originally from Lennep. When their son was three, they moved to Appeldoorn in Holland, and here Röntgen attended a private boarding school, the Institute of Martinus Herman van Doorn.

He seems not to have been a particularly studious boy, preferring to be out-of-doors and to use his hands. There is some doubt concerning the exact course of Röntgen’s education until he entered the Utrecht Technical School in December 1862, at the age of sixteen. Apparently he was expelled from a school in Utrecht for refusing to identify a classmate who had caricatured one of the masters. The continuity of his formal progress toward the university was thus broken, and he was never accepted as a regular student by the University of Utrecht—to his own and his parents’ distress. After two-and-a-half years at the Technical School, and nine months’ attendance at the philosophy classes of the university, he passed an examination to enter the Polytechnic at Zurich, as a student of mechanical engineering.
Röntgen was extremely happy in Switzerland, both in his work and in his social life. He received his diploma as a mechanical engineer in 1868 and his doctor of philosophy degree a year later. With these qualifications he became assistant to the professor of physics, August Kundt, whose friendship and support greatly furthered Röntgen’s career. While working in Zurich, Röntgen met his future wife, Anna Bertha Ludwig, the daughter of a German exile. In 1871 Röntgen accompanied Kundt to the University of Würzburg, and the following year he married Bertha Ludwig. The couple had no children, but they adopted Bertha Röntgen’s niece in 1887.
Würzburg saw the real beginning of Röntgen’s academic career, although at first he was disappointed because the university refused to give him any academic position, since he lacked the formal educational requirements. Shortly after his marriage, he moved to Strasbourg with Kundt, where he became tutor in the very fine Physical Institute. He spent the year 1875 as professor at the Agricultural Academy of Hohenheim, but he missed the excellent equipment at Strasbourg and soon returned there to teach theoretical physics. The series of papers he produced during the next two years resulted in his being offered the chair of physics at the University of Giessen, in Hesse. From 1879 to 1888 he worked at Giessen, building such a reputation that he was offered professorships at both Jena and Utrecht. He was not tempted to move, however, until the Royal University of Würzburg offered him the joint posts of professor of physics and director of the Physical Institute. In 1894 he became rector of the University of Würzburg. The following year Röntgen made his momentous discovery of X-rays, which brought him international fame. He was made an honorary doctor of medicine of Würzburg in 1896, an honorary citizen of his birthplace, Lennep, and a corresponding member of the Berlin and Munich academies. On November 30,1896 the Royal Society of London awarded jointly to Röntgen and Lenard the Rumford Medal. In 1900 Columbia University awarded Röntgen the Barnard Medal. The final accolades for this unassuming scientist were the erection of his statue on the Potsdam Bridge in Berlin, and the award, in 1901, of the first Nobel Prize for physics. He gave his prize money to further scientific studies at the University of Würzburg. In 1900, at the request of the Bavarian government, Röntgen moved from Würzburg to the chair of physics and the directorship of the Physical Institute at Munich.
Röntgen’s last years were shadowed by the distresses and privations of World War I. His wife died after a long illness in 1919, and in 1920 he retired from his chair at Munich. He spent a great deal of his time at his country house at Weilheim, near Munich, where he had an extensive library. He continued to work and to enjoy long country walks until the year before his death, which followed a short illness.
Röntgen’s early training as an engineer and his years as Kundt’s assistant at Würzburg, where there was no laboratory mechanic, formed his lifelong habit of making his own apparatus. He was, indeed, the meticulously conscientious experimenter. Röntgen invariably worked alone in the laboratory, and with nothing to disturb his concentration, he was able to develop acute powers of observation. He was able to detect and measure extremely small effects, for example, the compressibility of liquids and solids and the rotation of the plane of polarisation of light in gases. His reticence caused him to shun public engagements, and he never acquired the requisite lecturer’s skills. He even declined to give the expected lecture when he won the Nobel Prize. Röntgen was well known for his assiduous reading of the scientific literature, yet he never allowed his retiring and studious nature to interfere with his university administrative duties. His attitude to his profession is clearly defined in the address that he gave in 1894, when he became rector of Würzburg University;
The University is a nursery of scientific research and mental education, a place for the cultivation of ideals for students as well as for teachers. Her significance as such is much greater than her practical usefulness, and for this reason one should endeavour, in filling vacant places, to choose men who have distinguished themselves as investigators and promotors of Science, and not only as teachers; for every genuine scientist, whatever his line, who takes his task seriously, fundamentally follows purely ideal goals and is an idealist in the best sense of the word. Teachers and students of the University should consider it a great honour to be members of this organization. Pride in one’s profession is demanded, but not professional conceit, snobbery or academic arrogance, all of which grow from false egotism [Glasser, 1933, p. 100].
In all, Röntgen wrote fifty-eight papers, some with collaborators. Most of them were published in Annalen der Physik und Chemie. The fifteen Strasbourg publications covered such topics as the ratio of the specific heats of gases, the conductivity of heat in crystals, and the rotation of the plane of polarisation of light in gases. Four papers on this last subject were the result of his joint work with Kundt. It was only because of the very high level of their experimental skill that the phenomenon was able to be observed and measured, something that Faraday had not been able to achieve. During Röntgen’s professorship at Giessen, he published eighteen papers. Work on the relation between light and electricity was being done by Röntgen at much the same time as by Kerr, who discovered the effect that bears his name. As part of his lifelong interest in crystals, he studied pyroelectrical and piezoelectrical phenomena. Having constructed a very sensitive air thermometer, he was able to measure the absorption of heat in water vapour, and his flair for experiment was also shown by his work on the compressibility of liquids and solids.
Röntgen’s fame rests on two pieces of work, both of which were far outside his normal field of research. The discovery of X-rays is the more famous, but the earlier one concerned the magnetic effects produced in a dielectric, such as a glass plate, when it is moved between two electrically charged condenser plates. He set himself to test the electromagnetic theory of Maxwell, which implies that there will be a magnetic field in a dielectric whenever the electric field changes. In 1878 Rowland claimed to have detected the magnetic effect caused by the motion of electrostatic charges, but others could not repeat the experiments. For Röntgen here was a challenge. In a paper published in 1888 he demonstrated beyond doubt both the reality of the effect and the ability of Maxwell’s theory to explain it quantitatively. H. A. Lorentz named the effect the “roentgen current,” and Röntgen himself considered it as having as much importance as his discovery of X-rays because it led to the theories of Lorentz and is the basis for modern theories of electricity.
During the eleven years which he spent at Würzburg, Röntgen published eighteen papers, the final three embodying the discovery of X-rays. The earlier papers dealt with the effects of pressure on the physical properties of solids and liquids. While professor at Munich, administrative work took up so much of his time that only seven papers were produced between 1900 and 1921. These were concerned with the physical properties of crystals, their electrical conductivity, and the influence of radiation on them. The investigations published in 1914 on pyroelectricity and piezoelectricity proved of particular significance in clarifying the real nature of these effects.
It is, of course, for the discovery of X rays, as he called them, that Röntgen is known to the general public. In Germany, the name given to the rays is more usually Röntgenstrahlen. It is now known that X-rays are part of the electromagnetic spectrum, as is light. The wavelengths of X-rays are very short, occupying the region 0.01 to 50 angstroms.
On Friday November 8, 1895, Röntgen first suspected the existence of a new phenomenon when he observed that crystals of barium platinocyanide fluoresced at some distance from a Crookes tube with which he was experimenting. Again, this investigation into gas discharges was outside his normal field of interest. Hertz and Lenard had published on the penetrating powers of cathode rays (electrons), and Röntgen thought that there were unsolved problems worth investigation. He found time to begin his repetition of their experiments in October 1895. As a preliminary to viewing the cathode rays on a fluorescent screen, Röntgen completely covered his discharge tube with a black card, and then chanced to notice that such a screen lying on a bench some distance away was glowing brightly. Although others had operated Crookes tubes in laboratories for over thirty years, it was Röntgen who found that X-rays are emitted by the part of the glass wall of the tube that is opposite the cathode and that receives the beam of cathode rays. He spent six weeks in absolute concentration, repeating and extending his observations on the properties of the new rays. He found that they travel in straight lines, cannot be refracted or reflected, are not deviated by a magnet, and can travel about two metres in air. He soon discovered the penetrating properties of the rays, and was able to produce photographs of balance-weights in a closed box, the chamber of a shotgun, and a piece of non-homogeneous metal; he also noticed the outlines of the bones in his fingers on these photographs. The apparent magical nature of the new rays was something of a shock even to Röntgen, and he, naturally, wished to be absolutely sure of the repeatability of the effects before publishing. On December 22 he brought his wife into the laboratory and made an X-ray photograph of her hand. It was no doubt the possibility of seeing living skeletons, thus pandering to man’s morbid curiosity that contributed to the peculiarly rapid worldwide dissemination of the discovery. The first communication on the rays, on December 28, was to the editors of the Physical and Medical Society of Würzburg, and by 1 January 1896 Röntgen was able to send reprints and, in some cases, photographs to his friends and colleagues. Emil Warburg displayed some of the photographs at a meeting of the Berlin Physical Society on 4 January. The Wiener Presse carried the story of the discovery on January 5, and on the following day the news broke around the world. The world’s response was remarkably swift, both the general public and the scientific community reacting in their characteristic ways. For the former, the apparent magic caught the imagination, and for the latter, Crookes tubes and generators were promptly sold in great numbers.
After a royal summons, Röntgen demonstrated the effects of X rays to the Kaiser and the court on January 13. He was immediately awarded the Prussian Order of the Crown, Second Class.
In March 1896, a second paper on X-rays was published, and there followed a third in 1897, after which Röntgen returned to the study of the physics of solids. He had shown clearly the uses of the new rays for medicine and metallurgy, and so founded radiology, but the discovery of the nature of the rays and other applications he left to others. The hypothesis that X-rays were transverse electromagnetic rays was proved by the experiments of Friedrich and Knipping, based on Laue’s idea of using a crystal as a diffraction grating. The possibility of an X-ray spectrometer was developed brilliantly by Moseley, whose papers of 1913 and 1914 showed the physical significance of atomic numbers and predicted the existence of three undiscovered elements.
X-rays must have been produced by others long before Röntgen, probably with some of the electrical apparatus used during the eighteenth century. Crookes himself, in 1879, complained of fogged photographic plates that happened to be stored near his cathode-ray tubes. A. W. Goodspeed and W. N. Jennings in Philadelphia in 1890 noticed a peculiar blackening of photographic plates after having demonstrated a Crookes tube, but they failed to follow up their observation. Lenard and some other German physicists had noticed the fluorescence near Crookes tubes, but since they were concentrating on studying the properties of cathode rays, the strange side effects were not examined.