Wilhelm Conrad Röntgen’s Strasbourg Years (1872–1879): W.C. Röntgen – Two Decades before the Discovery of X-rays (with GPX Track “Röntgen in Strasbourg”)

Abstract

Background

Two decades before his groundbreaking discovery of X-rays in 1895, Wilhelm Conrad Röntgen worked from 1872–1879 as an assistant, private lecturer, and finally associate professor at the University of Strasbourg, which was then part of the German Empire. This period was briefly interrupted in 1875/76 by Röntgen’s first professorship at the Agricultural Academy in Hohenheim.

Method

Based on publications about W. C. Röntgen and research in a total of seven archives (Strasbourg, Hohenheim, Remscheid-Lennep, Würzburg), this work describes his professional career and private life during this period.

Results

In addition to his workplaces, a total of seven places of residence were identified for this period, four of which are described for the first time. A GPX track leading past the Strasbourg addresses is available for download. Archival material documenting his career during this period has been compiled. All of Röntgen’s publications from this period are also listed. A detailed exchange of letters between Bertha Röntgen and a friend provides an insight into the Röntgen couple’s private life.

Conclusion

This early period in W. C. Röntgen’s career forms the basis for his successful career with three subsequent full professorships, including his discovery of X-rays in 1895.

Key Points

• After the Franco-Prussian War of 1870/71, the University of Strasbourg was newly founded.

• The University of Strasbourg was heavily subsidized for reasons of power and cultural policy.

• Röntgen worked from 1872–1879 under the direction of the Chair of Physics, Professor August Kundt.

• Röntgen received his first professorship at the Hohenheim Agricultural Academy in 1875.

• In Strasbourg, Röntgen worked as an assistant, private lecturer, and finally as an associate professor.

Citation Format

• Rabe J, Busch U, Michels M et al. Wilhelm Conrad Röntgen’s Strasbourg Years (1872–1879): W.C. Röntgen – Two Decades before the Discovery of X-rays (with GPX Track “Röntgen in Strasbourg”). Rofo 2025; DOI 10.1055/a-2510-9243

Keywords

history - Wilhelm Conrad Roentgen - Strasbourg - Hohenheim - Straßburg

Introduction

“Physics is a highly developed and nearly fully matured science that with the discovery of the principle of conservation of energy will arguably soon take its final stable form. It may yet keep going in one corner or another, scrutinizing or putting in order a jot here and tittle there, but the system as a whole is secured, and theoretical physics is noticeably approaching its completion to the same degree as geometry did centuries ago.”

Philipp von Jolly, 1874

When Philipp von Jolly, professor of physics in Munich, told his prospective student Max Planck in 1874 that he did not foresee any further major breakthroughs in the field of physics, Wilhelm Conrad Röntgen ([Fig. 1]) [2] was 29 years old and a lecturer at the university in Strasbourg, which was part of the then German Empire. Röntgen, who had just completed his postdoctoral work, was concerned primarily with the classical physics that Jolly had outlined to Planck. No one suspected at the time that in the coming decades a door would open to a completely new understanding of physics and that Röntgen would play a major role in these developments.

Fig. 1 W.C. Röntgen, 1874–79, Stuttgart/Hohenheim (German Röntgen Museum, Remscheid [2]).

In the second half of the 19^th century, several discoveries were made in physics that have gradually and totally transformed the way we see world.

In 1868/69, Johann Wilhelm Hittorf discovered cathode radiation during experiments with gas discharge tubes. In 1886, Heinrich Hertz demonstrated the existence of electromagnetic waves, which were predicted by James Maxwell in the 1860s, and discovered the photoelectric effect in 1887.

In 1895, Wilhelm Conrad Röntgen, inspired by William Crookes and Philipp Lenard’s work in the field of cathode radiation, experimented with that very radiation and discovered “X-rays” (Hittorf, Crookes, and Lenard are mentioned by name by Röntgen in the first sentence of his groundbreaking publication). This “new type of radiation” lies on the higher frequency side of the electromagnetic spectrum compared to the low frequency radio waves detected by Hertz.

In 1896, Henri Becquerel observed an intrinsic radiation activity in uranium salts, a discovery investigated further in subsequent years by Marie Sklodowska-Curie and Pierre Curie and named “radioactivity”. Two years after Röntgen’s groundbreaking discovery, Joseph John Thomson discovered the electron in 1897, thereby clarifying the physical nature of cathode radiation. Following preliminary work by Hendrik Antoon Lorentz, Albert Abraham Michelson, Edward Williams Morley, and Henri Poincaré, Albert Einstein developed the special theory of relativity in 1905, which is still categorized as classical physics. In 1900, Max Planck introduced the quantum hypothesis, which states that electromagnetic radiation can only be emitted or absorbed in certain energy portions, the quanta. Quantum theory marks the beginning of modern physics. In 1903, Ernest Rutherford differentiated radioactivity according to alpha, beta, and gamma radiation. In 1911, he developed an atom model with a positively charged nucleus and a negatively charged shell of electrons, a model developed further by Niels Bohr in 1913.

These changes in the way we see the world are fundamental to our modern society, and it is a fascinating period to study. Based on the revolutionary discoveries of that time, technologies were developed for everyday use, such as lasers, GPS, telecommunications, social media, and artificial intelligence that we take for granted today. As far as Wilhelm Conrad Röntgen is concerned, the radiation he discovered not only had groundbreaking medical applications but also enabled us to look into the microcosm and nanocosm (e.g. mapping the molecular structure of DNA, X-ray lasers) and analyze the macrocosm (e.g. supernovae, pulsars, black holes, and dark matter). From this perspective, Röntgen’s discovery plays a central role in scientific research and continues to do so today. His time in Strasbourg was important for further developing his experimental skills, and it paved the way for his discovery of X-rays 20 years later.

Historical background and early days in Würzburg

Röntgen studied mechanical engineering from 1865 to 1868 at the Polytechnic Institute in Zürich. Röntgen had previously been expelled unfairly from the Technical School in Utrecht for disciplinary reasons, and he lacked the necessary high school diploma to study at university. The oft-repeated anecdote, in which Röntgen is said to have refused to reveal the name of the classmate responsible for a teacher’s caricature, comes from the obituary written by his friend Ernst Wölfflin [3], as well as reminisces by Röntgen’s goddaughter [4], both more than 50 years after the event. Based on these sources, we can assume that this incident occurred as described. Regardless of the backstory, this particular high school was unable to issue a university entrance qualification certificate at that time, because Latin was not taught there. However, in Zurich, Röntgen had the opportunity to study even without an official high school diploma. This enabled him to pursue his interests in a course of study with a practical focus. Röntgen completed his studies in 1868 and earned his diploma in engineering. After graduation, Röntgen spent another year attending lectures given by August Kundt, Johannes Scherr, and Gustav Zeuner. Fascinated by the mechanical heat theory of Rudolf Clausius and encouraged by his mentor and sponsor Gustav Zeuner, Röntgen applied for a doctorate at the University of Zurich after graduating from the Polytechnic. In consultation with Zeuner, Röntgen wrote a dissertation in 1869 about the analysis of constants in real gases [5].

Coming into contact with the experimental physicist Kundt marked a major turning point in Röntgen’s life. It inspired him to become interested in physics, which Röntgen had not previously studied in detail. Kundt was so impressed by the experimental talent and conscientiousness of his protégé Dr. Röntgen that he took him along as an assistant after his appointment to the Julius Maximilian University of Würzburg in 1870. However, Würzburg soon turned out to be a dead end for Röntgen’s career. Without an official high school diploma and due to the lack of knowledge of Latin, he was denied the postdoctoral degree he sought, based on the university’s statutes.

1872–75: Lecturer in Strasbourg

Similar to his previously being expelled from school in Utrecht and then getting the chance to study in Zurich, a new door opened again at this time for Röntgen. In 1872, August Kundt was appointed to the prestigious physics chair in Strasbourg. After the Franco-Prussian War in 1871, Alsace-Lorraine was incorporated in the German Empire as the state of Alsace-Lorraine. The newly founded university, named after Kaiser Wilhelm in 1877, was funded heavily by Berlin, for reasons of power and cultural policy, using French reparations payments. At this university, the postdoctoral degree regulations were far less restrictive than in Würzburg. As a result, Röntgen, who followed Kundt again, was once again able to pursue his postdoctoral qualification. This took the form of a cumulative postdoctoral qualification, based on his previous and, in part, highly regarded publications. On March 13, 1874 [6] Röntgen received a “venia legendi” status, “with which he would no longer be asked by even the most tradition-conscious universities for a high school diploma or knowledge of Latin” [7]. In the course catalog for the 1874/75 winter semester, Röntgen’s name appears for the first time under the section titled “Mathematical and Scientific Department – Lecturers” beside the following seminars: “Introduction to Practical Physics” and “Selected Chapters from Physical Chemistry, Particularly on Gasometric Methods”. In addition, he also supervised “Courses in the Physics Laboratory” [8]. Kundt left Röntgen entirely in charge of this physics work in the laboratory, whose equipment and funding had been key points when negotiating his appointment. The students are said to have been very attached to him [9].

However, the new University of Strasbourg was also more modern and progressive than most German universities, even beyond the requirements for a postdoctoral degree. Traditionally, the natural sciences were subordinate to the philosophical departments. In Strasbourg, on the other hand, there were initially two independent “departments,” and from 1875 onwards there were even two separate faculties at the university: a college of mathematics and natural sciences and a college of philosophy [8] [10].

1875/76: Intermezzo in Hohenheim – Röntgen’s first professorship

“Dr. Röntgen is a pale, tall man who knows how to live and moves with ease. […] In conversation, there is now and then a touch of something foreign about him; the Dutchman does not deny himself entirely. He made a pleasant impression on me and, based on my observations and inquiries, he would probably be a good fit for Hohenheim.”

Ludwig Rau, Director of the Hohenheim Agricultural Academy, March 24, 1875

Thanks to his appointment to the Agricultural Academy, housed in Hohenheim Palace near Stuttgart ([Fig. 2]) [11], Röntgen became a civil servant and thus automatically a citizen of the Kingdom of Württemberg at the age of 30 and, by virtue thereof, a citizen of the German Empire. Previously, after his release from the “Prussian Subject Association” in 1848, as part of his family’s move to Holland, he did not have German citizenship but held instead a restricted Dutch citizenship, based on what was known as “equal status”. This included all the rights and duties of a Dutch citizen, except for the right to vote [12].

Fig. 2 Hohenheim Agricultural College before 1897. The Physics Institute of the Agricultural College was located on the ground floor, Röntgen’s official residence was on the upper floor of the palace (German Röntgen Museum, Remscheid [11]).

Prior to his appointment, Kundt had recommended his assistant without reservation. In addition to Röntgen’s professional skills, he praised his eloquence and the clarity of his expression. He is not only good-natured and intelligent, but downright well-mannered. During his five years of service not the slightest inconvenience occurred under his leadership [9].

The “Full Professorship for Physics and Mathematics” brought Röntgen a considerable increase in salary from 1,000 marks to 3,200 marks per year [13], as well as very generous free accommodation on the upper floor of the palace [14] [15]. By comparison, the annual salary in the 1870s for other professions was as follows: postman 675 marks, female teacher 1,032–1,376 marks, male teacher 1,376–2,074 marks, high school teacher 2,752–3,612 marks, and government director 5,676–6,880 marks [16]. One mark in 1871 corresponds to approximately 19 euros in 2024 [17] [18] [19].

However, the working conditions in Hohenheim were not at all satisfactory for Röntgen. Physics and mathematics held only secondary importance behind agriculture and forestry at the academy. According to the class schedules, Röntgen had to teach introductory courses on topics such as low-level algebra, geometry of space, trigonometry, as well as experimental physics and meteorology [20]. Röntgen believed that, as a specialist physicist, he was the wrong person to teach these subjects and they could be better taught by a secondary or high school teacher [21]. The very limited laboratory equipment and the lack of any research funding in Hohenheim, which had already been noted by his predecessors and later friends Franz Bauer and Eugen Lommel, may have contributed further to his dissatisfaction. Under these circumstances, Röntgen was unable to continue the physics research he had begun in Strasbourg.

In view of his professional dissatisfaction, it was fortunate that only one year after Röntgen’s departure from Strasbourg, the position of associate professor became vacant there, alongside his mentor and chair August Kundt. Röntgen did not have to think long and returned to the lively and intellectually stimulating atmosphere at the University of Strasbourg in 1876. Röntgen’s Hohenheim personnel file shows that the move back to Strasbourg was not without conflict. During a meeting of Hohenheim faculty, there was a major clash between Röntgen and the director of the academy, Ludwig Rau. Röntgen felt overlooked when it came to filling his professorship at Hohenheim. An exchange of letters between Röntgen and Ludwig Rau reveals their differences. Rau felt that Röntgen’s statements during a meeting had been an insult to his “official dignity rather than his personal honor,” and he demanded that Röntgen retract those statements before witnesses [22].

In the course of this dispute, Röntgen had to admit that during the meeting with the entire Hohenheim teaching faculty he had “allowed himself to exceed the usual level of parliamentary expression and, when expressing views that are objectively completely justified and well-founded, to use expressions that are not readily used in front of an assembly.” Röntgen admitted explicitly that this was an error in form, but he maintained his position and did not yield to the university director, who was 21 years older than him [23].

In retrospect, one wonders why Röntgen accepted the professorship in Hohenheim in the first place. He should have known beforehand about the conditions with regard to the subordinate importance of his subject, the teaching obligations below university level, and the poor laboratory equipment. Yet the situation in Strasbourg was uncertain. Kundt could not offer Röntgen a better position at that time and was also of the opinion that Röntgen was “mature and entitled” to a professorship [9]. Röntgen himself expressed to the director of the Hohenheim Academy his wish for “a more independent and lucrative position” [9]. At least Röntgen’s second wish was granted and he was even able to take advantage of the relatively high Hohenheim salary in the context of return negotiations with the University of Strasbourg. In Strasbourg, Röntgen was granted a supplement of 600 marks on top of his annual salary of 2,400 marks in order to reduce the difference to his salary in Hohenheim [24]. However, he was no longer entitled to free housing.

1876–79: Return to Strasbourg – Röntgen’s second professorship

Only after Röntgen’s return from Hohenheim was a personnel file created for him in Strasbourg ([Fig. 3]) [24]. Emil Warburg, Röntgen’s predecessor as associate professor for theoretical physics at the University of Strasbourg, was appointed full professor at the University of Freiburg in the summer semester of 1876 at just 29 years of age. Röntgen would have been aware of the career potential as second professor alongside Kundt. He knew about the very well-equipped laboratory and the opportunity it presented for running experiments. He also knew his tireless, creative, and innovative boss, who did not want an “extraordinarius perpetuus” but instead considered this position a step in the career of a physicist on the way to full professorship [25].

Fig. 3 Cover sheet of the personnel file for W.C. Röntgen, University of Strasbourg. Only after returning from Hohenheim in 1876 was the file created (Archives d’Alsace, Strasbourg site [24]).

So the course was set for Röntgen. According to the catalog, he was the second “theoretical” physicist to give lectures on “The Theory of Light,” “The Theory of Elasticity and Vibrations of Elastic Bodies,” “Electrostatics and Theory of Electromotive Forces,” “On Capillarity,” “Electrodynamics and Magnetism,” “On Electrostatic Measurements,” “The Theory of Heat,” and “The Kinetic Theory of Gases” [8]. In addition to theory, there was still enough time for experimental physics, which at that time was a prerequisite for obtaining a full professorship. During his second Strasbourg phase, Röntgen published a total of nine articles, including three with Kundt. Through these publications, Röntgen gained increasing prestige and recognition among the influential physicists of his time. This finally led to his appointment as full professor at the University of Giessen in 1879.

Physics during Röntgen’s Strasbourg/Hohenheim period

In the world of classical physics that Röntgen was studying in Strasbourg, no one suspected the major changes to come in the field. Röntgen was also a child of his time; he replicated and refined physics experiments with a high degree of skill, conscientiousness, scientific rigor, and powers of observation. It was not his ambition to overturn physics’ understanding of the world, rather he sought, through experimentation, to gain a more precise understanding of the world.

The development of theories was not a priority for Röntgen. His primary interest and passion was experimental physics. There was no reason for him to question the concepts of physics. His aim was to determine natural constants with increasing precision. Over time, Röntgen continually honed his experimental skills until he became a master of the art that is the foundation of scientific knowledge: the development of precise methodology and meticulous observation during its application. Röntgen did not set out to look for “new rays.” During an experiment, he accidentally discovered a previously unknown phenomenon, which he immediately recognized as “new”. He then studied this phenomenon thoroughly through experiments, and finally described it in his groundbreaking publication [26]. This is also consistent with an answer Röntgen provided in the only interview that he ever gave. When asked what he was thinking when he discovered X-rays, he replied: “I didn’t think, I was experimenting” [27]. This ability to deliberately experiment, combined with the willingness to observe without bias, led – some 20 years after his Strasbourg period – to the discovery of a natural phenomenon overlooked by other physicists of his time.

In Strasbourg, Röntgen’s task, together with August Kundt, was to set up a physics institute at the newly formed university. Röntgen’s great talent for experimentation and his technical skill were important reasons why August Kundt brought him, in the first place, to Strasbourg as an assistant and later as an associate professor. It can be assumed that Röntgen’s previous studies in mechanical engineering helped him considerably with planning and carrying out his experiments.

In Strasbourg, Röntgen was also tasked with teaching theoretical and experimental physics in its full scope at that time (i.e. mechanics, acoustics, optics, electrostatics, gas, and heat theory) [8]. He later expanded his teaching to include more “modern” theories that had only been developed about 15 years earlier, such as electrodynamics and magnetism, the theory of light, and the kinetic theory of gases.

An overview at the articles published by Röntgen during his time in Strasbourg (and Hohenheim) ([Table 1]) [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] illustrates the many different areas of physics that he worked on, although some of his publications are related more to the fields of mechanical and electrical engineering. Nevertheless, his focus was always on practical experimental work. The only article published at the Hohenheim Agricultural Academy actually dealt with a natural product – rubber.

Table 1 Röntgen’s Publications in Strasbourg and Hohenheim.

Strasbourg I	Year	Title of publication	Area	Ref.
1	1873	Bestimmung des Verhältnisses der specifischen Wärme bei constantem Druck zu derjenigen bei constantem Volumen für einige Gase. [Determination of the ratio of the specific heat at constant pressure to that at constant volume for some gases]	Thermodynamics	[28]
2	1873	Ueber das Löthen von platinirten Gläsern. [On the soldering of platinum-plated glasses]	Procedural instruction (mechanics)	[29]
3	1874	Über eine Anwendung des Eiscalorimeters zur Bestimmung der Intensität der Sonnenstrahlung. [On the use of ice calorimeters to determine the intensity of solar radiation]	Thermodynamics	[30]
4	1874	Ueber fortführende Entladungen der Elektricität. [On continuing discharges of electricity]	Electrodynamics	[31]
5	1874	Ueber eine Variation der Senarmont’schen Methode zur Bestimmung der isothermen Flächen in Krystallen. [On a variation of Senarmont’s method for determining isothermal surfaces in crystals]	Heat conduction	[32]
Hohenheim
6	1876	Ueber das Verhältniss der Quercontraction zur Längendilatation bei Kautschuk. [On the relationship between transverse contraction and longitudinal dilatation in rubber.]	Elastostatics (mechanics)	[33]
Strasbourg II
7	1877	A telephonic alarum. [A telephonic alarum]	Electrical engineering	[34]
8	1878	Ueber eine Methode zur Erzeugung von Isothermen auf Kristallen. [On a method for generating isotherms on crystals]	Heat conduction	[35]
9	1878	Mittheilung einiger Versuche aus dem Gebiet der Capillarität. [Communication of some experiments in the field of capillarity]	Fluid mechanics	[36]
10	1878	Ueber ein Aneroidbarometer mit Spiegelablesung. [On an aneroid barometer with mirror reading]	Optics/mechanics/thermodynamics	[37]
11	1878	Über Entladungen der Elektricität in Isolatoren. [On discharges of electricity in insulators]	Electrodynamics	[38]
12	1879	Nachweis der electromagnetischen Drehung der Polarisationsebene des Lichtes im Schwefelkohlenstoffdampf. [Detection of the electromagnetic rotation of the polarization plane of light in carbon disulfide vapor]	Electrodynamics	[39]
13	1879	Nachtrag zur Abhandlung über die Drehung der Polarisationsebene im Schwefelkohlenstoffdampf. [Addendum to the treatise on the rotation of the polarization plane in carbon disulfide vapor]	Electrodynamics	[40]
14	1879	Ueber die electromagnetische Drehung der Polarisationsebene des Lichtes in den Gasen. [On the electromagnetic rotation of the polarization plane of light in gases]	Electrodynamics	[41]
15	1880	Ueber die electromagnetische Drehung der Polarisationsebene des Lichtes in Gasen. II. Abhandlung. [On the electromagnetic rotation of the polarization plane of light in gases, 2nd treatise]	Electrodynamics	[42]

August Kundt (1839 -1894): teacher, mentor, colleague, friend

“Do you remember that it was through you that I met Kundt, who introduced me to physics and helped to dispel my uncertainty about my future?”

W. C. Röntgen to his university friend E. L. Albert in December 1922

August Kundt ([Fig. 4]) [44] was certainly the most important person, professionally, for Röntgen. Kundt, who was only six years older than Röntgen, was professor of physics at the Polytechnic in Zurich from 1868–70. After Röntgen received his diploma in mechanical engineering, Kundt recognized his talent at a difficult time when Röntgen was still finding his way. Kundt awakened his passion for experimental physics, and later intensively promoted his development. In the following years, Kundt took the recently graduated Röntgen as an assistant, first to Würzburg in 1870 and then to Strasbourg in 1872. Kundt brought Röntgen back to Strasbourg from Hohenheim as an associate professor in 1876. The relationship between the two men developed from that of a student to a colleague and finally to a friend with whom the Röntgens remained close personally throughout their lives. The special characteristic of Kundt’s research drive was the constant search for new, unexpected effects. In this way, he also showed his student Röntgen the way to be constantly alert to new and unforeseen things.

Fig. 4 August Kundt, 1872–1888, Strasbourg (German Röntgen Museum, Remscheid [44]).

However, Kundt’s importance for physics goes far beyond promoting Röntgen. His charisma and service can be measured by looking at the careers of his students and colleagues. At least twenty-two of his students occupied a total of thirty chairs and professorships between 1879 and 1906 [45] [46]. In addition to Röntgen (1901), Kundt’s former extraordinarius professor Ferdinand Braun was also awarded the Nobel Prize in Physics (1909). Making sound waves visible as dust figures in Kundt’s tube to determine the speed of sound is still a classic in physics lessons today. In 1976, a crater on the moon was named in his honor.

In 1888, August Kundt was appointed to the chair of experimental physics in Berlin, succeeding Hermann von Helmholtz. He did not live to see the discovery of X-rays by his former student, assistant, and associate professor. The outstanding experimenter and charismatic teacher had died a year and a half earlier in 1894 at the age of just 54 from heart disease. His grave is in Berlin’s famous Dorotheenstadt Cemetery.

Röntgen’s life, residences, and workplace in Strasbourg (and Hohenheim)

“Six years of marriage – and we’ve moved six times! But it’s best to take things lightly, and then things get better; the main thing is to stay healthy, and thank God we have our health.”

Bertha Röntgen, October 17, 1877

Röntgen’s residences and workplace in Strasbourg are listed in [Table 2] and mapped in [Fig. 5].

Table 2 Röntgen’s Residences and Workplaces in Strasbourg and Hohenheim.

Historical address	Contemporary address	Registration date	Source	Number on GPX Track ([Fig. 5])
Strasbourg (1872–1875)
No. 2 Ballspielgasse	2 Rue du Jeu de Paume (building demolished)	May 29, 1872	[48]	4
No. 16 Militärlazarettstrasse	1b Rue de l’Hôpital Militaire	January 29, 1875	[48]	5
No. 5 Militärlazarettstrasse	5 Rue de l’Hôpital Militaire	March 25, 1875	[48]	6
Hohenheim 1875/76
Official apartment in Hohenheim Palace		April 28, 1875 – October 25, 1876	[14] [15]	–
Strasbourg (1876–1879)
No. 15 Waisengasse	15 Rue des Orphelins	December 1, 1876	[48]	3
No. 11 Schiffleutstaden	11 Quai des Bateliers		[49] [50]	2
No. 11 Gutenbergplatz	11 Place Gutenberg	–	[51] [52]	1
Address for the Mathematical and Natural Sciences department at the University of Strasbourg, 1872–82
No. 4 Akademiestrasse	4 Rue de l’Académie	–	[10]	7

Fig. 5 Detail of the Strasbourg city map with GPX track “Röntgen in Strasbourg” (numbering per [Table 2]).
Map by OSM & Locus Map.

Physics Institute

After the founding of the “Imperial University” in 1872, the Physics Institute was not housed in the main building in the palace on the Ill (today Palais Rohan), but rather in a somewhat remote, provisional building in the old Académie (Akademiestrasse 4, Rue de l’Académie) ([Fig. 6] and [Fig. 7]) [53]. Since 1991 the building has housed the Lycée Jean-Frédéric Oberlin. The new building for the Physics Institute on the present university grounds, negotiated by August Kundt, was not occupied until 1882, three years after Röntgen’s move to Giessen [10].

Fig. 6 Former Physics Institute, now Lycée Oberlin.

Fig. 7 Physics laboratory in the provisional Physics Institute at the Academy, probably 1879. Experimental setup by Kundt and Röntgen to demonstrate the Faraday effect in gases. The pumping device is on the right. In the middle is the magnetic coil with light source on the right and the polarimeter on the left. The tube with the sample of the pressurized gas is inside the electromagnet. Handwritten note by Röntgen: “Physics Institute of the University of Strasbourg“ (University Archive, Würzburg [53]). [rerif]

Places of residence

All four of the registered Strasbourg addresses in the registration card index of the city archives ([Fig. 8]) [48] (and that of the provisional Physics Institute) are located only a few hundred meters apart in what is today the Krutenau district, southeast of the Ill River.

Fig. 8 Registration card for W.C. and B. Röntgen with four addresses: No. 2 Ballspielgasse, No. 16 Militärlazarettstrasse, No. 5 Militärlazarettstrasse, and No. 15 Waisengasse (Archives de la Ville et de l’Eurométropole de Strasbourg [48]).

After their wedding in January 1872, the Röntgens lived together in Würzburg for a short time [54]. In May 1872, they moved to Strasbourg. After comparing historical city maps and today’s city layout, we can be certain that the address at No. 2 Ballspielgasse, which they moved into on May 29, 1872, no longer exists. Today, there is a small parking lot with trees at this location ([Fig. 9]). The street now starts with a building at number 4. Shortly before moving to Hohenheim, the Röntgens made two more moves. The house inhabited by Röntgen at “No. 16bis Militärlazarettstrasse (Rue de l’Hôpital Militaire)” ([Fig. 10]) [55], was demolished in 1980. Today, there is a modern building here with the house number 1b. Only two months later, the young couple moved a few houses down to No. 5 Militärlazarettstrasse. The house still stands today, but an additional floor was added in 1969 ([Fig. 11]) [56].

Fig. 9 View of Ballspielgasse (Rue du Jeu de Paume) (at center). The building at no. 2 was formerly on the small open space in the foreground.

Fig. 10 No. 16 Militärlazarettstrasse (16bis Rue de l’Hôpital Militaire) in 1972 (arrow). The buildings were completely demolished in 1980 and replaced by a new construction (Archives de la Ville et de l’Eurométropole de Strasbourg [55]). [rerif]

Fig. 11 No. 5 Militärlazarettstrasse (Rue de l’Hôpital Militaire) in 1959. Built originally in 1862, a third floor was added in 1969 (Archives de la Ville et de l’Eurométropole de Strasbourg [56]). [rerif]

After returning to Strasbourg from Hohenheim, the Röntgens moved into No. 15 Waisengasse (Rue des Orphelins), the house ([Fig. 12]), in which his parents, who had also lived in Strasbourg since 1873, were registered before their Hohenheim period together [57]. However, the situation there was difficult apparently for several reasons. On the one hand, the landlord soon reclaimed the bedroom for himself [47], and on the other hand, her doctor found this bedroom to be unhealthy due to bad air. Bertha Röntgen suspects in a letter [50] that the dampness there led to pain in her right shoulder. As a further reason for the subsequent change of residence, Bertha Röntgen stated in the same letter, “we were walking on eggshells around our housemates.” Apparently, there were tensions between the landlord and the Röntgens.

Fig. 12 No. 15 Waisengasse (Rue des Orphelins).

Other places of residence are not included in the registration file. However, two other apartments are described in Bertha Röntgen’s letters.

The unknown residence

In two letters from 1877/78, Bertha Röntgen provides detailed information about a home that does not match any of their known places of residence [49] [50]. The following clues emerge from this letter:

• view of the Ill River

• “across from us are the palace and cathedral”

• “near the palace bridge” (there was no Palace Bridge at that time, and she likely means the bridge “at the palace,” which was formerly Magdalene Bridge and today is known as Pont Sainte Madeleine)

• building with bay windows

• apart from the Röntgens, only “the owner” lives in the house.

Based on this description, this address is most likely No. 11 Schiffleutstaden (Quai des Bateliers). The drawing from 1842 by F. Piton ([Fig. 13]) [58] provides a good overview of the layout described from the perspective of the cathedral tower. At that time, there was only one house with a bay window. The address book of 1878 [59] lists only one resident (“landlord”) in two buildings at this location. The other house had no bay window and was therefore eliminated. Presumably, the Röntgens are not listed because they only lived there for a few months. The street today still looks very much the same ([Fig. 14]).

Fig. 13 Drawing by F. Piton, 1842: View from the Cathedral looking southwest to the Krutenau neighborhood. The building at No. 11 Schiffleutstaden (now 11 Quai des Bateliers) on the Ill with its bay windows and peaked roof can be seen clearly (arrow). In the foreground at left is the former palace (now Palais Rohan). The bridge across the Ill river leading to the Palais Rohan is obscured by the palace. “(Archives de la Ville et de l’Eurométropole de Strasbourg [58])”.

Fig. 14 View from Strasbourg Cathedral to the southeast in 2024. The Schiffleutstaden building (no. 11 Quai des Bateliers) with its bay windows and peaked roof is virtually unchanged (arrow).

Bertha Röntgen’s subjective assessment that this was the “prettiest and friendliest location” [50] in Strasbourg can be confirmed from today’s perspective. In this and another letter [15], she writes that the apartment is quite small (“miniature”). However, considering that there are four large rooms, a small room and a dressing room, as well as a kitchen and a maid’s room outside the apartment, this seems to be a surprising amount of space for a married couple. Yet the wish for a larger apartment would be fulfilled with the couple’s next move.

The Röntgens’ last residence in Strasbourg

The Röntgens last address in Strasbourg was No. 11 Gutenbergplatz ([Fig. 15]), only 150 m from his parents’ apartment at No. 9 Münsterplatz (Place de la Cathédrale) [57]. The exact date of the move is unclear, but it must have taken place in the summer of 1878. In a letter dated November 11, 1878, Bertha sketches a detailed floor plan of the very spacious apartment (eight rooms plus kitchen and a maid’s room) that clearly indicates the location ([Fig. 16] ) [51]. This address also appears in the university’s personnel directory from 1878 [52]. In contrast to the other residences, Bertha Röntgen’s description (“80 steps high”) and her sketch [51] make it possible to identify even the specific apartment on the 3rd floor with Röntgen’s study at the corner of Gutenbergplatz and Schlossergasse (Place Gutenberg/Rue des Serruriers).

Fig. 15 View from Strasbourg Cathedral to the southwest: 11 Gutenbergplatz (Place Gutenberg). Röntgens study was on the 4th floor at the corner of Schlossergasse/Rue des Serruriers (arrow). Bertha Röntgen writes in a letter that, from his desk, he enjoys a wonderful view of the cathedral [51].

Fig. 16 Letter, B. Röntgen: Sketch with rooms labeled in the apartment on Gutenbergplatz. The study is marked at the lower right at the corner of the building. Additional rooms in clockwise direction: dining room, guest room, spare room, housemaid’s room, kitchen, bedroom, closet room, my room, visiting room. Upper left: courtyard. Streets: Guttenbergplatz (at right), Schlossergasse (at bottom). (Archive of the German Röntgen Museum, Remscheid [51]).

The Röntgens’ personal life

Very little is known about the Röntgens’ personal life in Strasbourg and Hohenheim. There is virtually no information about the first period in Strasbourg. We owe a little information about the time after their return from Hohenheim to the correspondence between Bertha Röntgen and her friend Ernestine Baur, the wife of the Hohenheim professor of forestry Franz Baur. In these letters, Bertha almost always refers to her husband as “Willy.” However, the information remains fragmentary and subjective, as it is written from Bertha Röntgen’s perspective. We can also refer to a few remarks from this period made by Röntgen’s mother Charlotte Constance Röntgen-Frowein [60].

Since 1873, Röntgen’s parents also lived in Strasbourg [57]. They followed him to Hohenheim (living in Stuttgart) and later back to Strasbourg. In one of the letters from 1878, Bertha writes somewhat wistfully that out of consideration for her parents-in-law, her travel options are somewhat restricted [61]. And a few months later: “But you understand it well, and feel similar to us that our duty is to stay with our old folks” [62]. However, the Röntgens also enjoyed the closeness and the time they spent with their parents, for example, when celebrating Christmas together in 1878 [63]. The letters mention a shared holiday in the nearby Black Forest (Durbach) [15].

Röntgen’s mother describes her daughter-in-law as follows: “Bertha is a very well-suited wife for Willem and a warm-hearted and caring daughter for us. I have never met anyone who [...] makes such a good impression on everyone who meets her and who, although she has not much schooling or knowledge, yet judges all the affairs, objects, and circumstances of life with knowledge and thereby makes a pleasant housewife and companion” [60]. However, she also writes: “Her temper is a bit fierce, which is unfortunate, but our Willem has the tact to manage it.” In 1879, after her son was appointed to the chair in Giessen, shortly before the move, she wrote proudly: “Our WILLEM is now 34 years old; we can only be grateful that he has had such a good career. He owes this to his own diligence and work, blessed as he is by the Almighty” [60].

Shortly after moving to Giessen in 1879 she writes: “Willem is very happy with his position, I believe he is seen and loved. He has a good income and a large audience. You no longer recognize the tall, thin, pale young man; he has become a broad-shouldered, strong man. He is a good son.” She adds: “We would like him to be a little more talkative in everyday life, at least for my husband that would be more pleasant, but that’s just not his style, and he means well. He is good, yes, very good, and they are very happy, but he has to have his way, and he is keenly aware of his surroundings; he loves order and cleanliness, in the laboratory, the study, and the household” [60].

The childless Röntgen couple enjoyed the company of young people. In a letter to her friend Ernestine Baur, Bertha writes about her daughter: “I don’t want to explain to you here how much we like having Johanna with us, suffice it to say that since we have had this lovely and cheerful creature with us, we have become completely different people, we are so happy and feel much better in general too” [64].

The letters show that Röntgen worked an enormous amount and had little time for his wife. Bertha Röntgen does not explicitly complain about this situation, but mentions it several times [50] [61] [65], but always with understanding for her husband. (“[...] because I don’t hold loud conversations with myself, and a certain someone else has neither the inclination nor the time to listen to my chatter” [65]. “I cannot and must not torture Willy to make him spend more time with me, as he has so much work to do, he is often (rightly so) up to his ears in books” [50]. She also speaks several times about “silence, loneliness, and boredom” [50] [61] [64] [66] and remembers happy times in Hohenheim [15]. “I miss the friendly atmosphere that I had in Hohenheim!” [50]. Bertha Röntgen’s letters from this time show that they felt more comfortable in Hohenheim than in Strasbourg. After returning to Strasbourg she writes: “In a word, my dear, we hardly have any close contact with local families. I’ve always said the way people interact here strikes me as a bit frosty, and this seems truer than ever after we had such dear friends in Hohenheim who were so friendly to us. I don’t blame the people here, because they are still the same as before, but we are changed, we are spoiled” [67].

These statements by Bertha Röntgen stand in contrast to recollections by the Röntgens’ goddaughter, Margret Boveri, who more than 50 years later in 1931: “The Röntgens always had the worst memories of their time in Hohenheim and did not like to talk about it. They missed the stimulating company of young friends who were present in large numbers at the newly founded University of Strasbourg and who were great company for outings and get-togethers” [4].

Röntgen was also able to hunt in Hohenheim, but not in Strasbourg. Bertha Röntgen wrote: “How good it [a rabbit] will taste to us, since it comes from Hohenheim, where of course all rabbits are better than anywhere else! – I can certainly say that my husband looked at it wistfully, for the poor fellow longs so much to roam through the fields and forests with his gun once again. I fear there will be no more hunting here [in Strasbourg] this winter, because he has a lot of work to do and he hasn’t met anyone who could take him hunting” [68].

The Röntgens employed – at least during the second Strasbourg period – a maid. The name “Marie” appears again and again in the letters. Marie lived in her own room, partly in the attic, partly in the apartment ([Fig. 16]) [51]. Her tasks included housework, but also hauling water, wood, and coal [51].

Both in Strasbourg and in Hohenheim there were problems with vermin, as W.C. Röntgen wrote in his memoirs in 1922: “We had rats in Hohenheim and had already become relatively friendly with them: they got their daily food in the gutter drain from the kitchen and otherwise left us alone! We had bedbugs and cockroaches in our apartment in Strasbourg, but my wife soon got rid of them. We were young and so we could deal with setbacks and laugh about them” [69].

In their free time, the Röntgen couple went to the theater or concerts [61]. In a letter, Bertha Röntgen complains that no social gatherings were held in the winter of 1877/78 due to bereavements (including the death of the Kundts’ youngest child). However, they stayed away from a student ball of their own accord, because they ”feared they would not know anyone there, as well as a party given by the university’s president von Möller” [61]. This leads one to the conclusion that they both may have been a bit shy.

The letters also mention some books that Bertha has read, including several historical novels by the Egyptologist and writer Georg Ebers (“The King’s Daughter”, “Uarda,” and “Homo sum”). Bertha found these books “wonderful, I only regretted that I could not talk to anyone about them, which is something one likes to do so that one can hear what others think about them. […], because my dear, good Willy has so much work to do that we rarely get to have a really pleasant conversation” [61]. But occasionally both seem to have read the same material. “Willy and I read a travelogue about the dark continent (Africa) by Henri M. Stanley. I cannot tell you with what interest and excitement we followed his story about all his discoveries and adventures” [51]. During Christmas 1876, the couple gave each other – “after agreeing together” – the works of Goethe, Lessing, and Shakespeare [67].

In Hohenheim, the Röntgen couple apparently had a small allotment garden at their disposal. In 1877, back in Strasbourg, Bertha Röntgen mentioned with regret that she no longer had such a “garden plot” [70].

In 1878, Bertha writes that ”Willy, her little man” had to turn down several hunting invitations, because he did not have a properly warm “outfit” [68]. This was obviously meant ironically, because other sources know that Röntgen was “tall” [9] [60], according to Röntgen’s Dutch ID card he was 1.86 m [71] . He was “very pleased” to receive the “jacket” he ordered from friends in Hohenheim in Munich for Christmas [63].

Apparently, the Röntgens were price-conscious when choosing their travel destinations, because the prices are mentioned several times in the context of holidays in Durbach (Black Forest) and Fly (Switzerland) (“cheap” and “inexpensive”) [15] [65].

1879: Farewell to Strasbourg

“It is particularly hard to bid farewell to the Alsace, especially Strasbourg, which is very dear to me, as I experienced the founding of the university there with such great enthusiasm and spent one of the most beautiful, most industrious periods of my life there. Sometimes I look at the picture of Strasbourg that hangs in my room and hum to myself the old song ‘O Strasbourg, O Strasbourg, you beautiful city.’”

W.C. Röntgen, November 19, 1918

In the spring of 1879, W.C. Röntgen was appointed chair of physics at the University of Giessen. This marked the end of his time in Strasbourg. In retrospect, Röntgen’s period in Strasbourg (and Hohenheim) can be seen as the foundation for his impressive career with three professorships. In just seven years, he rose from assistant to lecturer, then to associate professor, and finally to full professor. Thanks to his hard work, his meticulous experimentation, and a total of fifteen highly regarded publications, he gained an outstanding reputation as a physicist and experimenter during this time, which led to appointments to chairs for physics in Giessen, Würzburg, and lastly Munich. The inspiring spirit of optimism at the newly founded university, described by Röntgen himself, certainly contributed significantly to his development in Strasbourg.

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Publication History

Received: 17 May 2024

Accepted after revision: 20 December 2024

Article published online:
20 February 2025