Régis Catinaud, Histoire et de philosophie des sciences, Université de Genève
The first decades of the existence of the Fribourg’s Institute of Physics witnessed an impassioned opposition between two visions of science, those of Albert Gockel and Joseph Kowalski - the first two ordinary professors to serve there. This confrontation had a substantial impact on the subsequent evolution and the orientation of the institute in the first half of the 20th century.
Some accounts of the early years of Fribourg physical Institute described the distinction between Kowalski and Gockel as a genuine opposition between applied and fundamental physics. There are indeed many differences between Gockel’s and Kowalski’s physics but the "pure" versus "applied" science dichotomy hardly exhausts the description of the deep divide between Gockel’s and Kowalski’s styles of physics.
The creation of the Fribourg Institute of Physics
The University of Fribourg is quite recent. It started in 1889 with three faculties (Law, Humanities, and Theology in 1890); the Faculty of Science was added 7 years later in 1896. The Fribourg University owes much to Georges Python, the State counselor elected in 1886 and in charge of the public instruction between 1886 and 1927 1. In 1895, the project, the building and the founding of the Faculty of Science had all been approved thanks to Python’s strong commitment. The last task, and not the least, as Python stated to the High Council was "to find good professors" 2. This is where Joseph Kowalski (1866-1927) enters the stage.
Kowalski, born in the Russian occupied part of Poland, studied initially in Warsaw. In 1884, he enrolled in Göttingen to study mathematics and physics. He stayed there for four years and obtained his Ph.D. in 1889. He prepared his dissertation on the resistance properties of glass 3 under the supervision of the leading Göttingen physicist Woldemar Voigt 4. As his ensuing career shows, Kowalski did not inherit Voigt’s passion for theoretical physics; however, since his Göttingen years, he kept high respect for German teaching and especially German technical schools – the models that later inspired him to shape the Fribourg Institute of Physics.
In 1889 Kowalski went to Paris to attend the International Electrical Congress. He extended his Parisian stay to visit Gabriel Lippmann’s laboratory on industrial electricity 5. Later this year, he left for Berlin where he worked under the direction of Kundt and Helmholtz. In 1890 he became assistant in the Würzburg physical laboratory 6. He transferred next to Switzerland where, the following two years, he taught successively at the Zürich Polytechnicum and Bern University where he obtained his habilitation in physics and in physical chemistry, in general physics and in analytical mechanics 7.
Joseph Kowalski’s scientific trajectory and merits attracted Python’s attention at the time when he was looking for a competent scientist that could help him build the Faculty of Science. In 1895, after a few exchanges with Kowalski, and impressed with the training that the latter has received in Germany and France, Python went convinced that he held the right man: he hired Kowalski as the first professor of the Faculty of Science 8 and asked him to take care of the recruitment of all the other eleven professors for the new Faculty 9.
Kowalski was certainly a versatile physicist. Judging from his educational trajectory, he could have chosen theoretical as well as experimental physics to shape his career. As Python described him "Joseph de Kowalski is an erudite man, but also a very practical one" 10. It is hence difficult to tell what eventually motivated Kowalski’s choice favoring his practical side over the other. Indeed, when Kowalski came to Fribourg, he took a radical shift toward "applied" physics. Thanks to Kowalski, the Institute became one of the best equipped in Switzerland 11. His researches were devoted mainly to electrical phenomena, which involved, among others the study of capacitors and electrical arcs (Kowalski made also some researches on phosphorescence).
Albert Gockel (1860-1927) is today mostly known for his pioneering role in the discovery of the cosmic rays 12. He started his studies in Konstanz gymnasium. He continued his training in the Universities of Freiburg im Breisgau, Würzburg and Karlsruhe. He obtained his doctorate in 1885 in Heidelberg under the direction of Ferdinand Braun, with his work on the Peltier’s effect 13.
Gockel taught for a few years at the Ladenburg gymnasium in his native Baden state. During that time he investigated extensively the phenomena related to lightning and storm 14. In a series of meticulous measurements he monitored the potential of atmospheric electricity and reported his results in great detail comparing them with the observations of the Karlsruhe’s meteorological station and with other investigations, and especially those of Elster and Geitel 15. Gockel summed up his researches in a book published in 1895 and entitled Das Gewitter 16 that received a warm welcome and which was reedited several times.
When Gockel came to Fribourg in 1896 to become Kowalski’s assistant he was already 36 while Kowalski was only 29 17. Over the next four years, Gockel worked on his habilitation work entitled "On the relationship between polarization and current density in solid and molten salts" 18. Such a topic, at odds with Gockel’s actual research interests may appear surprising. It becomes less so when one takes into account how much the director of the habilitation work, in the present case Kowalski, had a say in the choice of the subject and in its orientation 19. Be it as it may, Gockel did never come back to his habilitation topic in his further research. In meanwhile, the acceptance of Gockel’s habilitation gave rise to a first conflict between both men.
The Kowalski – Gockel opposition
The acceptance of Gockel’s habilitation depended on Daniëls’, professor of mathematics, and Kowalski’s reports. While Daniëls judged Gockel’s work "good and appropriate", Kowalski found it too vague and inaccurate 20.
It took Gockel one year to answer Kowalski’s criticisms and see his habilitation finally accepted. Soon after, the Faculty proposed him as extraordinary professor for physics and meteorology 21. He was assigned to teach meteorology and "other selected topics in physics", subjected, of course to the prior approval of Kowalski 22. The latter was definitely not willing to give up his grasp over Fribourg’s physics. Thus, the decision of Gockel’s nomination was shortly supplemented with some official clauses severely restraining Gockel’s status and role in the Institute of Physics: Indeed, in the next protocol Nr 267 of the State council one reads:
"The Faculty wished to clarify the rules applying to the relations between the Institute of Physics and Dr Gockel. The holder of the physics chair, Dr. Kowalski has agreed to the following arrangement: 1. The Institute of Physics concedes to Mr. Gockel the exclusive use of room Nr 24 [...] 3. Mr. Dr. Gockel has the right to use for research or teaching, instruments from the collection of the Physics Institute, but after having made the prior special request to the Director of the Institute of Physics and provided that the latter does not wish to reserve the same equipment for its own research or teaching. [...]" 23
The room Nr 24 was actually a small room secluded from the rest of the physical Institute. Moreover, no assistant or other technical help was attributed to Gockel. Actually, over the years when Kowalski directed the Institute of Physics, and even later on, Gockel was never granted, on a regular basis, the appropriate resources required by his researches. He had instead to write directly to the state education authorities, to ask for more funds for particular researches. While such extra funds were often granted to him, his fixed funds remained the same since his initial nomination as an extraordinary professor in 1903 24; the amount he could invest in his research was actually even less given that a part had to be allocated to his students’ laboratory work. 25
Over the next years Kowalski continued to counter any initiative aiming at strengthening Gockel’s effective situation. When, in December 1909, the Faculty of Science proposed to promote Gockel to an ordinary professorship 26, Kowalski fought back arguing that the Institute of Physics was not intended to have two ordinary professors and that he wanted to remain the only examiner for the physics degree and the doctorate. Significantly, Kowalski wished moreover "that the laboratory of M. Gockel not be named 'a physical institute' at all" 27. Gockel got eventually promoted but again under restrictive clauses: In the Faculty meeting protocol stating his nomination (February 18th, 1910) the Faculty narrows the scope of Gockel’s promotion making clear that " […] there is no question of creating a second ordinary professorship for physics, but to recognize the number and quality of the services that Mr. Gockel did and the considerable amount of his works, while not causing any prejudice to the rights and privileges of the holder of the ordinary professorship of physics […] The title of professor is conferred with rights attached thereto, ad personam, to Dr. Albert Gockel." 28
Thus, in spite of his promotion, Gockel’s effective position and status in the Faculty did not see much improvement. His situation, his salary and the funds granted to his Institute did not change until the 1920’s, more than five years after Kowalski left Fribourg and returned to Poland 29.
Different ideas of physics
Kowalski’s and Gockel’s teachings were not that different and both men were working in rather similar fields. However, and this may explain their problematic relationship, Gockel and Kowalski had very dissimilar visions of science and pursued different objectives in their research. As Schneuwly stated: "with Gockel and Kowalski, we are facing two worlds, two radically different visions of research and science" 30.
In 1905, Kowalski co-authored an article on "the teaching of applied sciences in the Fribourg Institute of physics" 31. In a form of a genuine manifesto, it puts forth Kowalski’s vision of what science is all about and helps to understand how the latter intended to develop the Fribourg Institute of physics.
The article starts with a firmly stated premise: science should be at the service of industry. Thus, investigations in physics are to be judged relative to their utility and the latter can be secured linking physics to industrial development. In that respect, he wished physical sciences in Fribourg to develop in full acknowledgment of the growing Swiss industry.
Kowalski distinguished consequently different categories of physicists. The ones he valued most were those professionals that he dubbed Wissenschaftliche Hilfsarbeiter of the industry 32: Their role was to provide assistance to industry and to alleviate its potential development. These were, to his opinion, just the physicists that the Fribourg Institute of Physics was endeavoring to train: "Without competing with our leading Swiss technical schools in Zürich and Lausanne, we provide students with a culture, possibly less technical, but which is nevertheless very useful in industries whose development depends largely on that of physical sciences." 33.
On the opposite side of Kowalski’s categorization there were those physicists that he regarded as least important for the advancement of science. This category, where he undoubtedly situated Gockel, regroups scholars that are investigating the laws of nature for the sake of knowledge for knowledge. The superiority of the Wissenschaftliche Hilfsarbeiter over the latter is made clear in another strong statement where Kowalski concludes that “within an industrial environment [the physicist] no longer appears as an estranged being, looking for laws with no purpose or use. [...] His efforts are constantly aimed at specific needs and his findings are [thus] unlikely to remain buried in the files of some great Academy; they are on the spot magnified by the practical collaboration of which he is part of." 34
One can better grasp Kowalski’s precepts examining how he himself followed them in his and his collaborators’ research on electricity. In 1899, Kowalski found out that "the rate of production of nitrous vapors obtained by electrical discharges in the air increases considerably with the frequency of the alternating current producing the latter" 35. He then asked Ignacy Moscicki (1867-1946), his new assistant who replaced Gockel, to study not the causes of the phenomenon but the actual effects and relations that he could observe. In the following years Moscicki prepared a thesis on "The atmospheric nitrogen and its fixation by the electric arc", and Kowalski, while supervising him, took a deeper look at these effects 36. He investigated what improvements could increase the rate of the nitrous production and realized that more efficient capacitors were needed. Even before Moscicki finished his doctorate in 1903, Kowalski founded with him and Jan Modzelewski (1875-1947), another of his assistants, the Fabrique Suisse de Condensateurs in Fribourg. Another research spin off created at the time that resulted from Kowalski’s team activity was the Societé de l’Acide Nitrique initiated and later run by Moscicki after he left the Fribourg’s institute.
From that moment on the number of Kowalski’s publications decreased sharply. After Moscicki and Modzelewski left the University to run their industries Kowalski kept in touch with his former students until 1915 when he himself left his Institute to come back to Poland.
Gockel wrote conversely quite a large number of papers between 1901 and 1927. These publications report mostly his observations of atmospheric electricity and radioactivity. Gockel’s experimentation proves as meticulous as Kowalski’s, to witness his study "On diurnal variation of the loss of electricity in the atmosphere" 37, where Gockel did several hundreds of measurements over three years at different time of the day before he felt ready to report on his results. In this work he carefully discussed all the circumstances of his experiments and the instruments he used. Indeed, Gockel kept up a correspondence with many physicists over the working of his instruments and was anxious about cases where the latter could prove defective 38. He and Kowalski were both relishing precise measurements.
Gockel versus Kowalski, an opposition between pure and applied physics?
Kowalski’s 1905 manifesto indeed suggests this way to differentiate Kowalski’s and Gockel’s research. But, if we understand "applied" as characterizing the transfer of an existing knowledge, from a theoretical to a practical level, then “applied physics” does not characterize aptly Kowalski’s scientific undertakings.
In Kowalski’s study of the rate of production of nitrous vapors, the discovery of the increase in the vapors production with the frequency of the current was not an application of former knowledge but a genuine creation of knowledge, indeed of practical knowledge. The Fabrique Suisse de Condensateurs, as well as the Societé de l’Acide Nitrique that Kowalski created with his collaborators could indeed be characterized as “applications”, but not the work they did at the Fribourg Faculty of Science. Their research does not appear as more “applied” than Gockel’s.
On the other hand, Gockel’s research displays the same typical experimental moves as found in Kowalski's. Judging from the point of view of Kowalski’s and Gockel’s laboratory practices, there is not much difference either.
Actually, one meets in their case the difficulty which makes contemporary historians and philosophers of science wary of hasty distinctions in terms of "applied" and "pure" science: it is just impossible to draw a clear line between the activities supposedly belonging to one or the other.
Yet, there is a difference between Gockel and Kowalski, a definite polarization in their science views. Gockel was interested in the very causes of natural phenomena, and tried to identify the circumstances and parameters best suited to understand them. Kowalski, on the other hand, aimed mostly at gaining practical knowledge, in a form of rules that enable action, namely handling and manipulating a physical object to one’s advantage.
Thus, in the end, the difference between Kowalski's and Gockel's physics did not lie in their activities or the objects of their investigations. It was primarily a matter of inclination toward explanatory knowledge or useful knowledge that gave a specific turn to their research, and influenced the organization of their inquiry as well as their choice of what they thought relevant arguments, good explanation methods, etc. 39.
In 1915, Kowalski took a leave of absence from the Fribourg Institute to come back to Poland and definitely resigned his chair in 1919. During these years, serving as its first physics professor, he helped to shape Warsaw's new polytechnic school apparently following the same precepts that guided his action in Fribourg. From 1919 on, Kowalski turned to diplomacy; when his former student Moscicki became president of Poland in 1926 40, Kowalski was invited to join the government.
Kowalski’s departure did not enable Gockel to promote at last his own vision of physics. Paul Joye (1881-1955), Kowalski's protégé since 1910, replaced his mentor at the direction of the Fribourg Institute where he remained faithful to Kowalski's ideas and was almost equally successful in enforcing them in the subsequent development of Fribourg physics.
After Gockel's death in 1927 his laboratory was shut down and no effort was done to find a successor. Paul Joye remained the only professor of the Physical Institute until his departure for the Entreprises Electriques Fribourgeoises in 1932. The Physical Institute stayed in line with Kowalski’s ideas until 1943 when a second chair of physics was created. As elsewhere in Switzerland, the post-war years proved decisive in shaping new directions for Fribourg physics: in 1952 André Houriet was thus inaugurating the Fribourg Theoretical Physics Institute founded with the support of the Swiss National Science Foundation 41.
1 Georges Python played a major role in Fribourg’s political landscape from the last decade of the 19th century until his death in 1927. See the article devoted to Python in the Historical Dictionary of Switzerland, also online.
2 For a detailed account of the creation of the Faculty of Science and the political debate it raised at the time, see: Histoire de l'Université de Fribourg Suisse, 1889-1989 : institutions, enseignement, recherches, éd. Roland Ruffieux et al, Fribourg, Ed. universitaires, 1991, vol.2, pp.776-783.
3 Kowalski, J., "Untersuchungen über die Festigkeit des Glases", Wied. Ann., vol. XXXVI, p. 307, 1889, see also a reproduction in Journal de Physique Theorique et Appliquée, vol. 9, 1890, pp.166-167.
4 Voigt joined Göttingen in August 1883 to serve as ordinary professorship for theoretical and mathematical physics, see Jungnickel, C., and McCormmach, R., Intellectual mastery of nature, Theoretical physics from Ohm to Einstein, Chicago: University of Chicago Press, vol.2, pp.115-119.
5 A well-known anecdote reports that he brought Marie Sklodowska, whom he knew from Poland, in touch with her future husband Pierre Curie. Be it as it may, the close ties that he kept since then with the Curies explain that he could later obtain some radium for Gockel’s laboratory.
6 He worked probably under the direction of Röntgen.
7 Curriculum vitae de Joseph Kowalski, Dossier Kowalski, Archives d’Etat de Fribourg (AEF); Notice sur les travaux scientifiques de Joseph Kowalski, Dossier Kowalski, AEF
8 He was actually already teaching at Fribourg University two years before the official creation of the Science Faculty with such general lessons as "Energy and its transformations", "Cosmogonic hypothesis", and "Light" – dispensed in the Faculty of Humanities. Histoire de l'Université de Fribourg Suisse, 1889-1989 : institutions, enseignement, recherches, éd. Roland Ruffieux et al, Fribourg, Ed. universitaires, 1991, vol.2, p.785.
9 Kowalski for physics, H. Baumhauer for mineralogy, M. Arthus for physiology, M. Westermaier for botanic, A. Bistrzycki for chemistry, J. Brunhes for geography, M. F. Daniëls for mathematics, R. de Girard for geology, R. Thomas-Mamert for chemistry, M. Lerch for mathematics, L. Kathariner for zoology, Ibid, pp.783-785.
10 Letter from Python to the State Council, Lettre du 20.11.1915, AEF.
11 "Das hiesige physikalische Institut gehörte zweifellos zu den best eingerichteten der Schweiz, und ich erinnere mich noch wohl wie der später berühmt gewordene Ophthalmologe Vogt den Wunsche äusserte im hiesigen Physikalischen Institut arbeiten zu können, weil er die gewünschten Einrichtungen sonst nicht fand.", Urspung, A., "Ein Tag mit Westermaier", Beitrag zum 50jährigen Bestehen der Universität Freiburg, i.d. Schweiz, 1947
12 An account of Gockel’s crucial role in the cosmis ray discovery and the rivalry that opposed Gockel and the Austrian Hess will be covered in a forthcomming article. The present paper intends rather to put emphasis on the confrontation between Kowalski and Gockel, but see two articles already devoted respectively to Gockel’s and Hess’ investigations in the series “Physics Anecdotes” by Hansruedi Völkle and Peter Maria Schuster in Communications of the SPS, July 2009; see also Schneuwly, H., Albert Gockel et la découverte du rayonnement cosmique, Fribourg, Edition Universitaire de Fribourg, 1990.
13 Actes de la Société Helvétiques des Sciences Naturelles, vol.108, 1827, pp.3-9 / Beziehungen der Peltierwärme zum Nutzeffekt galvanischer Elemente, Annalen der Physik und Chemie, Bd.XXIII, Leipzig 1885.
14 Schneuwly, H., Albert Gockel et la découverte du rayonnement cosmique, Fribourg, Edition Universitaire de Fribourg, 1990, p.6
15 Ibid, p.7; Gockel, A., "Messungen des Potentialgefälles der Luftelectizität in Ladenburg a. Neckar", Meteorologische Zeitschrift, 1898, pp.281-297
16 Gockel, A., Das Gewitter, Köln, Bachem, 1895
17 The exact circumstances of Gockel’s arrival to Fribourg are unclear. Maybe Kowalski knew Gockel’s Das Gewitter, or maybe Gockel chose Fribourg and Kowalski because electrical phenomena were at that time at the focus of the Fribourg institute of physics, but such was also the case for many other institutes. Another reason could be related to religious affinity: Gockel was catholic and the Fribourg University was at the time proudly displaying its status of the only catholic university in Switzerland.
18 Gockel, A., "Über die Beziehungen zwischen Polarisation und Stromdichte in festen und geschmolzenen Salzen", Zeitschrift für Physikalische Chemie, Leipzig, XXXIX/5, 1900, pp.529-559.
19 Règlement relatif à l’examen de doctorat, Protocoles de la Faculté des Sciences, Cahier 1, 1896-1906, Archives de la Faculté des Sciences (AFS).
20 Kowalski’s main griefs were that Gockel’s handling of data was inappropriate and incomplete.
21 This was certainly a welcome decision given Gockel’s recent wedding (1902) with Paula Baumhauer, daughter of Heinrich Baumhauer, Fribourg professor of mineralogy.
22Extrait du protocole du conseil d’Etat n°266, 29 février 1903, Dossier Gockel, AEF.
23 "La Faculté s'est préocupée du règlement des rapports entre l'Institut de physique et M. le Dr Gockel ; le titulaire de la chaire de physique, M. le Dr Kowalski, a donné son adhésion à l'arrangement suivant : 1. L'Institut de physique concède à M. Gockel l'usage exclusif de la salle N°24. [...] 3. M. le Dr Gockel aura le droit de se servir, pour ses recherches ou son enseignement, des instruments de la collection de physique, mais après en avoir formulé, au préalable, la demande spéciale auprès du directeur de l'Institut de physique et pour autant que celui-ci ne désire pas se réserver les mêmes appareils pour ses propres recherches ou son enseignement.", Extrait du protocole du conseil d’état, 267, 29 février 1903.
24 Namely 500 francs per year, protocole n°266, ibid.
25 Some studies suggest that this lack of funding was one of the major reasons why Gockel “lost” the run for the cosmic ray discovery against Hess: "[Gockel] didn’t have the material means to challenge and compete with [Hess]", Schneuwly, H., Albert Gockel et la découverte du rayonnement cosmique, Fribourg, Edition Universitaire de Fribourg, 1990.
26 Réunion de la Faculté des Sciences, 4 décembre1909, Protocole de la Faculté des Sciences, Cahier 2, Archives de la Faculté des Sciences (AFS)
27 The proposal to promote Gockel and Kowalski’s reactions to it are stated in a letter from the Faculty of science dean (Dr. Daniëls) to the director of Fribourg’s State education dated December 9, 1909. Correspondance du doyen de la Faculté des Sciences, AFS.
28 "Il est réservé qu'il n'est pas question de créer un second ordinariat pour la physique, mais bien de reconnaître le nombre et la qualité des services rendus par M. le Dr Gockel, ainsi que la quantité considérable de ses travaux sans porter aucun préjudice aux droits et prérogatives du titulaire de l'ordinariat de physique. […] Le titre de professeur est conféré avec les droits qui s’y rattachent, à titre personnel, à M. le Dr Albert Gockel". Extrait du protocole du conseil d’Etat n°284, 18 février 1910, Dossier Gockel, AEF.
29 Kowalski kept his influence over the Faculty of Science even years after his departure. It can be witnessed for example in the controversy between his successor Paul Joye and Gockel.
30 Schneuwly, H., Albert Gockel et la découverte du rayonnement cosmique, Fribourg, Edition Universitaire de Fribourg, 1990.
31 Kowalski, J., and Dalemont, J., "L’enseignement des sciences appliquées à l’Institut de Physique de l’Université de Fribourg", Revue Générale des sciences pures et appliquées, n°17, 15 septembre 1905, pp.773-776.
32 In French :"Savants associés à l'oeuvre industrielle", ibid, p.774.
33 "Sans donc faire concurrence à nos grandes écoles techniques suisses de Zürich et de Lausanne, nous donnons aux étudiants une culture moins technique, sans doute, mais qui est néanmoins d'une grande utilité dans les industries dont le développement dépend en grande partie de celui de la science physique." ibid, p.776.
34 "Ainsi placé au milieu d'un organisme industriel en pleine activité, le savant n'apparaît plus comme un être hors cadre, cherchant des lois sans utilité ou sans utilisation. Son effort est orienté sans cesse par des besoins précis et ses découvertes ne risquent pas de rester enfermées dans les dossiers de quelque grande Académie; elles sont imédiatement mises en valeur par la collaboration pratique dont il est entouré.", ibid, p.775.
35 "Déjà, en 1899, j'avais remarqué que le rendement des vapeurs nitreuses produites dans l'air par des décharges électriques augmente beaucoup avec la fréquence du courant alternatif employé pour produire ces décharges. Cette influence de la fréquence sur la quantité des vapeurs nitreuses produites par les décharges, qui n'a été, que je sache, remarqué par aucun autre chercheur, peut être expliquée de différentes manières." Kowalski, J., «Production de l’acide nitrique par des décharges éléctriques», Société Internationale des Electriciens. Extrait du Bulletin, 2e série, tome III n°26, p.3.
36 Kowalski, J., "Quelques applications des oscillations électriques lentes", Congrès de l’Association française pour l’avancement des sciences, Angers, 4 au 11 Août 1903.
37 Gockel, A., "Sur la variation diurne de la déperdition de l’électricité dans l’atmosphère", Archives des sciences physiques et naturelles, 1904.
38 See Schneuwly, H., Albert Gockel et la découverte du rayonnement cosmique, Fribourg, Edition Universitaire de Fribourg, 1990.
39 One could say that their « styles of scientific thinking » were ultimately opposed, see Crombie, A. C., Styles of scientific thinking in the European tradition, London, Duckworth, vol.1-3, 1994.
40 Moscicki returned to Poland in 1913.
41 It might be comforting to know that between 1927 and 1952 Friedrich Dessauer, that held the Fribourg chair of physics between 1937 and 1953 took genuine interest in Gockel’s life and work, see Histoire de l'Université de Fribourg Suisse, 1889-1989 : institutions, enseignement, recherches, éd. Roland Ruffieux et al, Fribourg, Ed. universitaires, 1991, vol.2, pp.806-808.
[Released: January 2012]