Wilhelm Foerster

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Wilhelm Foerster, around 1905

Wilhelm Julius Foerster (born December 16, 1832 in Grünberg in Silesia , † January 18, 1921 in Bornim ) was a German astronomer , science organizer, science journalist and pacifist .

From 1865 to 1903 he was director of the Berlin observatory and taught from 1858 to 1920 at the Berlin University .

On his initiative, the Astrophysical Observatory and later the Einstein Tower in Potsdam, the Astronomical Computing Institute, which calculated the orbits of a large number of asteroids, and the Royal Prussian Geodetic Institute in Berlin. He was a co-founder of the Physikalisch-Technische Reichsanstalt, the predecessor institution of today's Physikalisch-Technische Bundesanstalt . He was significantly involved in the establishment of the International Broad Service , the introduction of the metric systemand a European metrology and calibration system. He was a member from 1869 and from 1891 to 1920 chairman of the international measurement and weight committee. From 1870 he was director of the normal calibration commission, the supreme calibration authority of the North German Confederation and from 1871 of the German Empire.

Förster was among other things a co-founder of the international astronomical society and the Berlin society URANIA .

Live and act

Wilhelm Foerster


Foerster was the second son of the cloth manufacturer Friedrich Foerster and his wife Hulda Foerster, née Seydel.

Since 1868 he was married to Ina Foerster (1848–1908), the youngest daughter of the geodesist Friedrich Paschen . They had three sons and two daughters. Her first son was the philosopher and pacifist Friedrich Wilhelm Foerster (1869–1966), an opponent of National Socialism . The second son was the perennial grower and natural philosopher Karl Foerster (1874–1970). The third son, Ernst Foerster (1876–1955), was a ship designer at Blohm & Voss , head of shipping for the Hamburg-America Line and publisher of the magazine “Werft, Reederei, Hafen”.

Memories of their parents' house have come down to us from Friedrich Wilhelm and Karl Foerster.

Training and military service

Wilhelm Foerster attended the Maria-Magdalenen-Gymnasium in Breslau from 1847 . From 1850 to 1854 he studied mathematics , physics , art history and later astronomy at the University of Bonn under Friedrich Wilhelm August Argelander . He obtained his doctorate in 1854. rer. nat.

After graduating, he did a year of military service. He later commented: “The military nature and spirit are now more than ever overrated from some quarters. As an institution of the bloody struggle between nations, these institutions will and must disappear in the cultural world. "

Friedrich Wilhelm University of Berlin

In 1858 Foerster qualified as a professor at Berlin University and was appointed associate professor for astronomy in 1863, and then full professor in 1875 .

He taught astronomy at Berlin University for 62 years, from 1858 to 1920.

In 1891/92 he was its rector. His rector's speech dealt with the topic "On the position of astronomy within the natural sciences and on the humanities in university teaching".

As rector, Foerster was committed to student self-government and to suppressing the influence of the incorporated students . Years later (1910) he looked back at this endeavor in a speech to the Finkenschaft , an association of non-incorporated students:

“When an attempt was made eight years ago at the Berlin University to come closer to the organization of a more comprehensive representation of the student body and a kind of self-administration of common student affairs, the attempt failed because of the extraordinary passion with which at that time opposing political-social party directions were the student body took their position on it. "

Worked at the Berlin observatory

From 1855 onwards Foerster worked as the second assistant and from 1860 as the first assistant to Johann Franz Encke , the director of the Berlin observatory . Together with Otto Lesser , he discovered the asteroid (62) Erato in 1860 .

In 1858, after Encke fell ill, he became his deputy. After Encke's death, he took over the position of director in 1865, which he held until 1903

One of his first tasks as head of the observatory was the renewal and modernization of the instruments. So the Fraunhofer was refractor , with the Johann Gottfried Galle in 1846 the planet Neptune was discovered, revised and a 7 " - Meridian - telescope . Commissioned and placed His other tasks, the organization was one of the time service, the exact depth measurement ( Longitude and latitude ) and the monitoring of geomagnetism . Foerster had the watch of the observatory fitted with electrical contacts and sent precise time signals to the Berlin central telegraph station via cables .

During two stays in England in 1851 and 1859 he got to know the system of electrical time transmission from Jones' godfather. He used this for the precise display on the Berlin normal clocks. Every two seconds the pendulums of the public clocks received an electrical impulse from the precision clock in the observatory.

But he continued to strive for the accuracy and financing of normal clocks. In 1883 he suggested the installation of further normal clocks and the establishment of a Central Clock Company , a year later the installation of non-profit URANIA columns , "small clock towers with displays for weather forecasts and the position of the moon as well as instructive information about astronomy, meteorology, hydrology and geology", entirely in keeping with his popular scientific endeavors. "In addition, the pillars provided space for the railway timetable or information on the way to the nearest fire alarm station, post office or 'medical station'." They began to be set up in 1891.

After all, it was Normal-Zeit GmbH (later Telefonbau and Normalzeit or Telenorma ) that was responsible for the public clocks in Berlin and whose headquarters had a direct cable connection to the Royal Observatory, which Foerster, like the historian Johannes Graf (* 1963 ) emphasized, “ensured” “that the public clocks remained committed to the ideal of the highest precision even after his resignation as director of the Royal Observatory.”

Wilhelm Foerster played a decisive role in researching the Luminous Night Clouds , which were observed from 1885. His colleague Otto Jesse studied it for several years.

The Royal Observatory belonged to the Prussian Academy of Sciences until 1889, but was then attached to the Friedrich Wilhelm University, which has been using the observatory since it was founded.

In 1890, Friedrich Simon Archenhold became an employee of the observatory and, on behalf of Foerster, set up a photographic branch at Halensee in Grunewald for taking pictures of cosmic nebulae .

Science organizational initiatives

Foerster published a memorandum in 1871 for the establishment of an observatory for observing the sun. This gave the impetus to found the astrophysical observatory and later to erect the Einstein Tower in Potsdam. In 1874 he founded the Astronomical Computing Institute , which among other things. calculated the orbits of a variety of asteroids.

Together with Johann Jacob Baeyer , Foerster produced a memorandum “Promemoria concerning the organization of an institute for higher measurement science”. They submitted this to the Prussian Ministry of Culture on March 16, 1867; this led to the establishment of the Royal Prussian Geodetic Institute in Berlin in 1870 . In 1899 he founded the International Broad Service with Carl Theodor Albrecht and Friedrich Robert Helmert .

Berlin memorial plaque on the house at Ahornallee 32, in Berlin-Westend

In 1870 Foerster was appointed director of the normal calibration commission , the supreme calibration authority of the North German Confederation and, in 1871, of the German Reich. In 1872 he was sent as one of the representatives of Germany to the international committee for the worldwide uniform introduction of the metric system , from which the Meter Convention 1875 emerged. Thanks to his negotiating skills, he saved the negotiations of the Meter Convention in 1875 from failure. From 1891 to 1920 he was President of the International Committee for Weights and Measures.

The Venus expeditions in 1874 and 1882 were largely thanks to him.

He was a member and most influential personality of the permanent commission of the "International Earth Measurement".

Foerster was a co-founder of the Astronomical Society, the Astronomical Central Office, the quarterly journal of the Astronomical Society, the Astronomical Computing Institute and editor of the Berlin Astronomical Yearbooks 1867-81.

Foerster also aimed to introduce a world calendar alongside the existing calendar systems and to redefine Easter.

He wrote: "The need for a" world calendar "common to all peoples, countries and languages ​​is certainly present in the arithmetical field of science and global business life, and here the uniformity of the setting of the common starting epochs and day numbers in connection with tables is sufficient, which facilitate and secure the transition from the dates of the various national and religious calendars still in use to the world calendar. "

The Vatican recognized the "advantages in civil life" of Foerster's proposal, submitted in 1897, regarding the postponement of Easter, but rejected it because it was not only contrary to tradition, but also deepened the division with the Eastern churches .

Popular science engagement: Lectures - science journalism - URANIA and friends of astronomy

Foundation of the Berlin company "URANIA"

It was Alexander von Humboldt (1769–1859) who inspired Foerster to become involved in popular science. Humboldt had already given public lectures on scientific subjects in the Berlin Singakademie in 1827/28 , proposed the construction of the Berlin observatory and obliged it "that it had to serve the audience on about two evenings every month for instruction and inspiration."

In 1844 he played a decisive role in founding the Scientific Association , which held a popular science lecture every Saturday in the Singing Academy . Foerster was introduced to the association's group of speakers by Humboldt and chaired it until 1880.

Together with Werner von Siemens (1816-1892) and Max Wilhelm Meyer (1853-1910), Foerster founded the astronomical society Urania in 1888 .

Foerster's social position and his relationships as well as his organizational power played a major role. He won important industrialists and bankers as sponsors, with the science journalist Harro Hess (1935–2011) pointing out that there was also an interest in industry in popularizing the latest technical developments and products.

The name of the new company URANIA goes back to Förster and the creation of the modernly equipped observatory with dome as the main part of the new URANIA building is due to his influence.

Förster was chairman of the supervisory board of URANIA and was involved with lectures and articles in the journal of the Society Heaven and Earth .

The society reached a high level through popular science lectures by important scientists.

Association of the Friends of Astronomy and Cosmic Physics

Foerster was the founder and chairman of the Association of Friends of Astronomy and Cosmic Physics , which endeavored to spread astronomical knowledge widely and stimulated amateur astronomical activities. The association was founded in 1891.

Foerster also founded the popular science monthly magazine Die Himmelswelt , the association's magazine , in 1891 and published it until 1905. It was published until 1949.

Science journalism

Foerster also contributed to the dissemination of scientific knowledge through his publications.

Foerster's lectures appeared both individually and in several collections.

He also published other popular scientific works, for example one on the calendar system. In the introduction he explains how, as a professional, he adapts to the general public:

According to the intention of the editors, this little book is not intended to be a textbook on chronology, including the past and the future of its development. Rather, without the apparatus of complete documentary evidence and technical discussions, it is essentially intended to serve the interests of a generally scientifically educated public, but in particular the representatives and administrators of state, social and economic interests in the field of calendar institutions for understanding and communication. However, this also requires certain astronomical considerations and certain retrospectives into the historical developments of culture. In the meantime it should be tried to keep to measure as far as possible and not to give in too much to the inclination of the expert, as the author may consider himself in these matters, in the sense of monographic teaching.

Social-ethical and pacifist aspirations

“Wilhelm Julius Foerster ... represented an ethically founded pacifism that had been taught to him in childhood. His intellectual and ethical development was shaped by a Germany committed to enlightenment, humanity and supranational ties ... Art, science and knowledge of nature were not an end in themselves for Foerster, but were seen as a contribution to moral perfection ", wrote the journalist and publisher Helmut Donat (* 1947) in the Lexicon The Peace Movement .

In 1892 Foerster was a founding member and chairman of the German Society for Ethical Culture (DGfeK, in which personalities such as Ferdinand Tönnies and Albert Einstein were also members) and in the same year a founding member of the German Peace Society (DFG), because he widespread it at the end of the 19th century Rejected ideas of nationalism .

The cultural scientist Horst Groschopp (* 1949) recalls that Wilhelm Foerster gave two presentations at the founding meeting of the DGfeK, the first on "literary and journalistic activity" and the second on "activity against the evils of social and economic conditions" and explains further: “Over time, a practical program grew out of it. Thereafter, the ethical cultural society sought public discussions on moral issues and wanted to devote itself to youth education and adult education. With literary means she undertook an ethical propaganda and in the following period expressed herself in detail on Freemasonry, the women's movement, efforts for peace, abstinence from alcohol and against anti-Semitism . "

Foerster fought under the DGfeK "the three-class franchise , anti-Semitism, social evils like child labor , the housing shortage, the corporal punishment of children, servants and prisoners. He advocated women's suffrage , shortening working hours to eight hours , the right to form coalitions and to strike, and for those convicted of innocence. ”He gave lectures at home and abroad and published numerous articles in the journal of the Society Ethical Culture .

Foerster campaigned for international arbitration and against the arms race . Together with his son Friedrich Wilhelm he strove to found an international ethical academy.

Donat judges: His ability to reveal opposites with diagnostic clarity and his tolerance, which mediates between the various directions of the ethical movement, made him an outstanding figure in the German and international peace movement. "

In October 1912 he headed the V German Peace Congress in Berlin as chairman of the Berlin DFG local group. The greeting on the occasion of the unveiling of the Berlin memorial plaque for Foerster in the Ahornallee in 2009 continued:

“But hardly anyone remembers that Wilhelm Julius Foerster was one of only 16 people who had the courage to sign Berta von Suttner's call for a pacifist peace society. Who knows his "Association for the Defense against Anti-Semitism"? Who initiated the welfare programs for elementary school students? Who knows about his commitment to public libraries - to which the Berlin City Library ultimately goes back? "

Foerster was one of the few German scholars who, as early as 1871, rejected the annexation of Alsace-Lorraine by Germany as a source of future conflicts. In March 1914, Foerster no longer considered a world war possible. He said: “that now in the midst of all the preparations for war we really believe in the realization of the beginning of a common, that means an eminently peaceful administration of the earth, because a war between the great civilized peoples under the current existential and moral conditions is so close to madness would limit that it will hardly have begun and will be over. "

In 1914 he first signed the nationalist appeal to the cultural world , but shortly afterwards, like his son Friedrich Wilhelm, the contrary appeal to the Europeans .

The French writer Romain Rolland counted Wilhelm Foerster in his diary of the war years as the "spirit of the old, legally thinking, humane Germany".

After the world war Foerster advocated Franco-German reconciliation.

Interlinguistics and Esperanto

As Foerster participated in various international endeavors, he also became aware of the world language idea and the developing international Esperanto language community .

The Esperanto founder Ludwig Zamenhof (1859–1917) mentions Foerster as early as 1904 in his contribution Esperanto: Nova Internacia Lingvo (Esperanto - a new international language) as one of those people under whose patronage an Esperanto magazine is published, the "specially scientific Matters is dedicated ".

In 1910, in an article for the Esperanto magazine Germana Esperantisto, the stages of development of the commonality of the auxiliary language , he explains what needs to be done “to meet the undoubted and certainly increasing need for certain adjustments and for certain common means of communication in the human world in the field of language and writing to gradually prepare fulfillment without in any way restricting the healthy and creative character and freedom of the various folk souls. "

He explains: “Obviously one would have to start with the simplest and simplest commonalities of work and communication that are obvious to everyone, that is, with numbers and forms of counting, then with the division of time and the calculation of time and from there into the terminology of the most common technology and pass over to science, with which the national peculiarity of the language has nothing at all to do, but for which uniform understanding is of great social and economic importance. "

Foerster, like many other scientists, including the geophysicist Adolf Schmidt (1860-1944) and the chemist Wilhelm Ostwald (1853-1932), joined the delegation founded in Paris in 1901 for the acceptance of an international language and became its honorary chairman. Under the chairmanship of Ostwald, a committee of the delegation met in Paris in 1908, including Foerster. With the participation of the linguists Jan Baudouin de Courtenay (1845–1929), Otto Jespersen (1860–1943) and Hugo Schuchardt (1842–1927), the committee decided after evaluating various world auxiliary language projects for Esperanto with some changes in the direction of the Louis de Committee Beaufront (1855–1935) presented Reform Esperanto (Ido ), the author of which, as later research showed, was probably Louis Couturat (1868–1914), one of the initiators of the delegation . As Ido was subsequently to be enforced without reaching an agreement with the Esperanto language community, Förster resigned the honorary chairmanship and resigned from the committee, "because," he wrote, "I miss any social wisdom in this process" .

Foerster publicly advocated the introduction of an international counting system based on Esperanto. When he took over the position of chairman of the Internacia Scienca Asocio Esperanta (ISAE) in October 1912 at the Esperantista Centra Oficejo (central office) in Paris from Hippolyte Sebert (1839-1930) (before he was a member of the advisory board of ISAE), he affirmed that and promoted the projects: creation of a universal calendar and division of the hours according to the decimal system.

At an event of the Esperanto Association Berlin, of which he had been a member since 1908, he also spoke on these topics.

In the Bürgersaal of the Red City Hall in Berlin, where he spoke on June 1, 1912 to celebrate the 25th anniversary of Esperanto about the importance of this international language for all areas of culture. had spoken, congratulated him at the celebratory event on his 80th birthday in December 1912, along with others, Adolf Schmidt, a companion in the commitment to Esperanto, pacifism and science, on behalf of ISAE and the Esperanto Association Berlin. He praised Foerster as a "noble, brave and tireless pioneer of all ethical and scientific-humanistic goals".


The archive of the Berlin-Brandenburg Academy of Sciences in Berlin keeps 1.9 running meters of files from Foerster's estate under the name NL W. Foerster . It contains manuscripts on astronomy, chronometry, standard time, redefinition of Easter and degree measurements; Working materials, calculations, correspondence, newspaper clippings

Förster's letters can also be found in the archives of other scholars, e. B. in the papers of Wilhelm Ostwald and Adolf Schmidt.

This Wilhelm Foerster estate was put together after the archives of the Babelsberg observatory were transferred to the academy archive in 1964. It also contained files from the previous institution, the Berlin observatory, and materials that could be directly assigned to Foerster.

The Berlin State Library (in House 2 on Potsdamer Strasse) has parts of Foerster's estate in the autograph collection of Ludwig Darmstaedter (1846–1927).

The Treptow observatory (today Archenhold observatory Berlin-Treptow) had Foerster correspondence in its manuscript collection, the fate of which is uncertain after 1936.

Most of it ended up in the Berlin State Library (Darmstädter Collection), while a part came in 1941 through the art historian and writer Karl von Hohenlocher (1891 -?). This part (1200 letters from 25 Foerster correspondents, documented in 1971, is in the State Library (House 1).

Another part of this Archenhold collection was owned by the manuscript department of the University Library in Bonn, most of which was lost in the war. The research library in Gotha has another part of the Archenhold collection in a bundle of astronomer manuscripts.

Letters from the collection are also held by the Dortmund City and State Library, the Schleswig-Holstein State Library in Kiel, the Göttingen University Library, the Bavarian State Library in Munich, the University and State Library in Münster and the Berlin State Archive.

In 1994, the Berlin State Library received from Eva Foerster, Karl Förster's widow, parts of the estate that had remained with the family in Bornim; other parts had already been given to archives and societies.

Diedrich Wattenberg , the former director of the Archenhold observatory in Berlin-Treptow , owned parts of Foerster's estate from Bornim . He has documented some of them and published them.


  • Life memories and hopes for life (1832–1910). Printed and published by Georg Reimer, Berlin 1911.
  • Collection of scientific lectures. First to third episode. D. Dümmler and G. Reimer (2nd episode), 1876–1890., Berlin, 1876
  • Collection of popular astronomical messages. Second episode. Ferd. Dümmlers Verlagbuchhandlung, Berlin 1884.
  • About the position of astronomy in science, etc. Speech when taking over the rectorate held in the auditorium of the Royal Friedrich-Wilhelms-Universität zu Berlin on October 15, 1891. Berlin, Buchdruckerei der Königl. Academy of Sciences, 1891.
  • About the goals of popularizing the natural sciences with regard to the journal "Heaven and Earth". In: Himmel und Erde 1, 1889.
  • Calendar and clocks at the end of the century. Verlag Georg Westermann., Braunschweig., 1899.
  • Celestial Science and Prophecy, John Edelheim Verlag, Berlin, 1901.
  • Life questions and life images. Social ethical considerations . VITA German publishing house, Berlin 1902.
  • From the earth's atmosphere to heaven . Berlin Hermann Hillger Verlag, 1906.
  • The stages of development of the commonality of the auxiliary language. In: Germana Esperantisto, 1910, No. 3, pp. 49-50.
  • Address for the 25th anniversary of the URANIA company in Berlin. In: Himmel und Erde (25) 1913, p. 386.
  • Calendar system and calendar reform. Braunschweig, Vieweg collection. Issue 13, 1914.


  • Lalande Prize 1860 with Otto Lesser for the discovery of the minor planet Erato.
  • The Wilhelm Foerster observatory on the Insulaner in Berlin-Schjöneberg was named in memory of Wilhelm Foerster. It was opened in 1963. The Wilhelm Foerster Institute had already been founded in 1947 in the Berlin-Süd observatory, General-Pape-Straße 2, and in 1953 the Wilhelm-Foerster-Sternwarte e. V.
  • The asteroid (6771) Foerster was named after him.
  • A Berlin memorial plaque was unveiled on June 4, 2009 at the house at Ahornallee 32 in Berlin-Westend , where Foerster lived from 1904 to 1911 .
  • The Wilhelm Foerster Prize of URANIA Potsdam has been awarded annually since 1993 to scientists, scholars and cultural workers who have contributed to the popularization of new knowledge and intellectual education in Brandenburg.


  • Peter Aufgebauer : Wilhelm Foerster (1832–1921) chronological work. In: The Stars. 50, 1974, ISSN  0039-1255 , pp. 51-59.
  • Johannes Graf: Wilhelm Foerster, father of time distribution in the German Empire. In: PTB-Mitteilungen. 119th volume, issue 3/2009 ( online ; PDF; 3.6 MB), pp. 209–215
  • Mathias Iven (Ed.): 3x Foerster. Contributions to the life and work of Wilhelm Foerster, Friedrich Wilhelm Foerster and Karl Foerster. Schibri-Verlag Milow 1995, ISBN 3-928878-29-8 .
  • Wilfried Schröder: Development phases of the research into the glowing night clouds. Akademie-Verlag, Berlin 1975, ( Academy of Sciences of the GDR, publications of the research area Geo- and Cosmos Sciences 5, ISSN  0138-4600 ).
  • Wilfried Schröder: Wilhelm Foerster and the geophysical observations after the Krakatoa. In: Acta Geodaetica et Geophysica Hungarica. 43, 2008, 4, ISSN  1217-8977 , pp. 473-476.
  • Bruno Wille: Memories of a Star Seer. In: Reclam's Universe: Modern Illustrated Weekly. 27.2, 1911, pp. 972-975.
  • Willy Jahn:  Foerster, Wilhelm Julius. In: New German Biography (NDB). Volume 5, Duncker & Humblot, Berlin 1961, ISBN 3-428-00186-9 , pp. 275 f. ( Digitized version ).
  • J. Bauschinger : Wilhelm Foerster †. In: Astronomical News. Volume 212, 1921, p. 489, bibcode : 1921AN .... 212..489B .
  • NN: Wilhelm Foerster. In: Monthly Notices of the Royal Astronomical Society. Volume 82, 1922, p. 263, bibcode : 1922MNRAS..82..263. (Obituary, English).
  • Harro Hess: From the history of the Berlin society URANIA (1888-1927). Lectures and Papers No. 58, Archenhold-Sternwarte Berlin-Treptow 1979.
  • Helmut Donat: Wilhelm Julius Foerster. In: Helmut Donat and Karl Holl (eds.): The peace movement. Organized pacifism in Germany, Austria and Switzerland. Hermes-Handlexikon, ECON Taschenbuch Verlag, Düsseldorf 1983, pp. 120–123.
  • Friedrich-Wilhelm Foerster: My father. A reminder and a peace program . In: The time of January 5, 1930.

Web links

Wikisource: Wilhelm Foerster  - Sources and full texts
Commons : Wilhelm Julius Foerster  - Collection of images, videos and audio files

Individual evidence

  1. ^ Friedrich Wilhelm Foerster: My parents. In: Friedrich Wilhelm Foerster: Erlebte Weltgeschichte. 1869–1953, Glock and Lutz, Nürnberg 1953, pp. 40–47. Reprinted in: Eva Foerster and Gerhard Rostin (eds.): A garden of memory. Seven chapters by and about Karl Foerster. Buchverlag Union, Berlin 1992, 3rd revised and redesigned edition, pp. 35–47.
  2. ^ Karl Foerster: Parental home in the observatory. In: Holidays from the Ach. Union-Verlag, Berlin1990, 10th supplementary edition, pp. 5–26.
  3. ^ Wilhelm Foerster: Memories and hopes of life (1832-1910). Printed and published by Georg Reimer, Berlin 1911. Quoted in: Eva Foerster and Gerhard Rostin (eds.): A garden of remembrance. Seven chapters by and about Karl Foerster. Buchverlag Union, Berlin 1992, 3rd revised and redesigned edition, p. 48.
  4. ^ Wilhelm Foerster: The student and politics. Lecture given at the 1st discussion evening of the Berlin Finkenschaft. Academic Association for Social Sciences Dr. John Edelheim, Berlin-Bern 1901.
  5. ^ Johannes Graf: Wilhelm Foerster, father of the time distribution in the German Empire. In: PTB-Mitteilungen 119 (2009), Heft 3, pp. 211–212. (PTB - Physikalisch-Technische Bundesanstalt)
  6. ^ Johannes Graf: Wilhelm Foerster, father of the time distribution in the German Empire. In: PTB-Mitteilungen 119 (2009), Heft 3, pp. 212-213.
  7. ^ Marita Baumgarten: Professors and Universities in the 19th Century (= Critical Studies on History ) Volume 121.
  8. ^ Willy Jahn: Foerster, Wilhelm. In: Neue Deutsche Biographie 5 (1961), pp. 275-276 [online version];
  9. ^ Hans-Joachim Felber: Wilhelm Fierster fight for the Easter reform. German Academy of Sciences in Berlin, publications of the Babelsberg observatory, Volume XV, Issue 2, Akademie-Verlag Berlin 1965.
  10. ^ Wilhelm Förster: Calendars and Calendar Reform , Vieweg Collection, Springer-Verlag, 2013, ISBN 978-3-663-19636-5 , p. 48.
  11. The modern endeavors to establish Easter and to reform the calendar. In:  Salzburger Chronik für Stadt und Land / Salzburger Chronik / Salzburger Chronik. Tagblatt with the illustrated supplement “Die Woche im Bild” / Die Woche im Bild. Illustrated entertainment supplement to the “Salzburger Chronik” / Salzburger Chronik. Daily newspaper with the illustrated supplement “Oesterreichische / Österreichische Woche” / Österreichische Woche / Salzburger Zeitung. Tagblatt with the illustrated supplement “Austrian Week” / Salzburger Zeitung , October 22, 1919, p. 2 (online at ANNO ).Template: ANNO / Maintenance / sch
  12. ^ Wilhelm Foerster: Address for the 25th anniversary of the URANIA company in Berlin. In: Himmel und Erde (25) 1913, p. 386.
  13. Harro Hess: From the history of the Berlin society URANIA (1888-1927). Lectures and Papers No. 58, Archenhold-Sternwarte Berlin-Treptow 1979, p. 5.
  14. Harro Hess: From the history of the Berlin society URANIA (1888-1927). Lectures and Writings No. 58, Archenhold-Sternwarte Berlin-Treptow 1979, pp. 7-12, 24.
  15. Wilhelm Foerster: About the goals of popularizing the natural sciences with regard to the magazine "Himmel und Erde". In: Heaven and Earth 1, 1889.
  16. K.-H. Tiemann: Wilhelm Julius Foerster and the "Association of Friends of Astronomy and Cosmic Physics" (1891 to 1914). In: 3 × Foerster, 1995, pp. 66-87.
  17. Die Himmelswelt: Communications of the Association of Friends of Astronomy and Cosmic Physics, Volume 13, Ferd. Dümmler, Bonn and Berlin 1903.
  18. ^ Wilhelm Foerster: Collection of scientific lectures. First to third episode. D. Dümmler and G. Reimer (2nd episode), 1876–1890., Berlin, 1876.
  19. ^ Wilhelm Foerster: Scientific knowledge and moral freedom . Collection of lectures and papers, Volume 4, Verlag F. Dümmler, 1896.
  20. ^ Wilhelm Förster: Calendar system and calendar reform. Braunschweig, Vieweg collection. Issue 13, 1914, p. 1.
  21. ^ Helmut Donat: Wilhelm Julius Foerster. In: Helmut Donat and Karl Holl (eds.): The peace movement. Organized pacifism in Germany, Austria and Switzerland. Hermes-Handlexikon, ECON Taschenbuch Verlag, Düsseldorf 1983, p. 120.
  22. Horst Groschopp: Wilhelm Foerster (February 26, 2019).
  23. ^ Helmut Donat: Wilhelm Julius Foerster. In: Helmut Donat and Karl Holl (eds.): The peace movement. Organized pacifism in Germany, Austria and Switzerland. Hermes-Handlexikon, ECON Taschenbuch Verlag, Düsseldorf 1983, pp. 121–122.
  24. ^ Helmut Donat: Wilhelm Julius Foerster. In: Helmut Donat and Karl Holl (eds.): The peace movement. Organized pacifism in Germany, Austria and Switzerland. Hermes-Handlexikon, ECON Taschenbuch Verlag, Düsseldorf 1983, p. 122.
  25. Greeting for the unveiling of the Berlin memorial plaque in honor of Wilhelm Julius Foerster, June 3rd, 3 p.m., Ahornallee 32, 14050 Berlin.
  26. ^ Wilhelm Foerster: The beginning of common administration of the earth . In: Ethical Culture No. 6 , 1914, p. 41.
  27. ^ Romain Rolland: The Conscience of Europe, Diary of the War Years 1914-1919, Volume I, Rütten & Loening, Berlin 1983, pp. 323-324.
  28. ^ Lazaro Ludoviko Zamenhof: Esperanto: Nova Internacia Lingvo. In: “The Independent”, New York,, vol. LVII, No. 2906, August 11, 1904, pp. 326-330. Reprinted in: Adolf Holzhaus: Doktoro kaj lingvo Esperanto, Fondumo Esperanto, Helsinki 1969, pp. 165–173.
  29. ^ Wilhelm Foerster: The stages of development of the commonality of the auxiliary language. In: Germana Espeantisto, 1910, No. 3, pp. 49-50.
  30. ^ Wilhelm Foerster: Letero de Prof. d-ro Wilhelm Foerster . In: Germana Esperantisto 1908, No. 12, pp. 138-139.
  31. Germana Esperantisto, No. 8, Berlin 1908, p. 95.
  32. Dr. A .: Esperanto and science. In: Germana Esperantisto 1912, No. 12, pp. 188-189.
  33. Germana Espeantisto No. 7.8, Berlin 1912, p. 106.
  34. ^ Wilhelm Foerster . Germana Esperantisto, No. 1B, Berlin 1913, pp. 7-8.
  35. Fritz Wollenberg: The interlinguistic conceptions of Adolf Schmidt and his commitment to the international language Esperanto . In: Adolf Schmidt 1860-1944. On the 50th anniversary of the geophysicist and Esperantist's death on October 17, 1994. GeoForschungsZentrum Potsdam with the participation of the Esperanto League Berlin (publisher), Potsdam 1994, p. 25.
  36. ^ Fritz Wollenberg: Ostwald Schmidt kaj Foerster - Esperanto-Ligo Berlin Konscias pri scienchistoria tradicio. In: Esperanto - Language and Culture in Berlin: Jubilee Book 1903–2003, insight, review, outlook. Esperanto League Berlin (ed.), Mondial, New York, Berlin 2006 (contributions in German and Esperanto).
  37. ^ Fritz Wollenberg: Planned languages ​​in the archive of the Berlin-Brandenburg Academy of Sciences . In: Planned Language Libraries and Archives - Contributions to the 17th Annual Meeting of the Society for Interlinguistics e. V., 23-25. November 2007 in Berlin. Interlinguistische Informations, supplement 15, Detlev Blanke (Ed.), Berlin 2008, pp. 45–56.
  38. Wolfgang R. Dick: About the fate of the estate of Wilhelm Foerster. In: Mathias Iven (Ed.), 3 x Foerster. Contributions to the life and work of Wilhelm Foerster, Friedrich Wilhelm Foerster and Karl Foerster, Schibri-Verlag, Milow 1995, pp. 100–107. Online version
  39. ^ Website of the Urania Potsdam