# Caspar Isenkrahe

Mathias Caspar Hubert Isenkrahe (12 May 1844 in Müntz, Rhine Province – 12 August 1921 in Trier) was a German mathematician, physicist and Catholic philosopher of nature.

## Life

Isenkrahe's father died before Caspar's birth. Isenkrahe visited in 1856 the Progymnasium in Jülich, in 1857 the Marzellengymnasium in Cologne and from 1858 to 1863 the Realprogymnasium in Bonn. In 1868 he studied at the University of Bonn where he chose the subjects mathematics, physics, chemistry, mineralogy, botany, zoology, philosophy, Latin and German. On 31 July 1866 he made his PhD with an award-winning work about the anatomy of Helicina titanica, a species of snail. He became a teaching authority as a senior primary school teacher (pro facultate docendi) on 26 February 1869 for his chosen courses.
After a probationary year 1869–1870 at the high school of Bonn, he worked at the high school of Krefeld (at least to 1878) and then at the Realprogymnasium in Bonn. Trying to change to a high school career at the mathematical faculty at the University of Bonn, he sent a habilitation document. The faculty approved his plan but it failed because of the Berlin government for reasons unconnected with the subject. A later attempt to receive a lectureship at the technical University of Braunschweig also failed. From 1893 to 1911 he was working as a high school professor at Trier until his retirement.
Until his death in 1921 he was actively engaged in the fields of mathematics, physics and natural philosophy. He corresponded with well-known mathematicians and physicists, such as Hermann von Helmholtz, Heinrich Hertz, Felix Klein and Philipp Lenard.
Because of his unusual scientific creativity and versatility, the philosophical faculty of the University of Bonn honored him demonstratively on the occasion of his golden doctoral anniversary with the renewal of his doctoral dignity on 31 July 1916. Caspar Isenkrahe died after serious physical sufferings on 12 August 1921.
His legacy is kept safe in Trier (with part in the town archives and the rest in the diocese archives). The partial papers I (size: 0.5 meters) in the town archives of Trier includes correspondences, poems, clay creations, manuscripts as well as different collections from the cultural life around the time of the turn of 19th to the 20th century. The partial papers II (size: 2.50 meters) in the diocese archives includes personal documents, works, a biography as well as additional correspondence.

## Work

Isenkrahe always had a special inclination towards mathematics and produced a row of publications in the field of abstract mathematics. In particular his works around the theory of the prime numbers were appreciated.
The question of infinity fascinated him in the field of the Philosophy of nature.
As a physicist, Isenkrahe criticised the theories of gravitation of his time. Based on a Le Sage type model, which he developed independently, he presented an explanation of the phenomenon of gravity which was noticed by well-known physicists like Paul Drude, Walter Ritz and Arnold Sommerfeld.
As educationalist and religious Roman Catholic he felt obliged to give a proof of the existence of God on a natural philosophical basis. He also considered it to be necessary to examine the paranormal phenomena which were issued by the Roman Catholic Church as a 'miracle'. He dealt increasingly with experimental theology later.
In a book written in 1921 he tried to mediate in the debate around the theory of relativity, which had partly been led by both sides by scientifically inadmissible means.

## Endnotes

* ↑ Isenkrahe, C. (April 6, 1900). "Ueber eine Lösung der Aufgabe, jede Primzahl als Function der vorhergehenden Primzahlen durch einen geschlossenen Ausdruck darzustellen". Mathematische Annalen. 53 (1–2): 42–44. doi:10.1007/bf01456027. S2CID 123474671. Archived from the original on May 25, 2014. Retrieved September 12, 2013.
* ↑ Isenkrahe, C. Das Endliche und das Unendliche. Schärfung beider Begriffe, Erörterung vieler Streitfragen und Beweisführungen, in denen sie Verwendung finden, Münster 1915.
* ↑ Isenkrahe, C. „Isaac Newton und die Gegener seiner Gravitationstheorie unter den modernen Naturphilosophen", Schulnachrichten des Gymnasiums zu Crefeld, Crefeld 1978.
* ↑ Isenkrahe, C. Das Räthsel von der Schwerkraft: Kritik der bisherigen Lösungen des Gravitationsproblems und Versuch einer neuen auf rein mechanischer Grundlage, Braunschweig 1879.
* ↑ Isenkrahe, C. Die Rückführung der Schwere auf Absorption und die daraus abgeleiteten Gesetze, Leipzig 1892.
* ↑ Paul Drude (1897) „Ueber Fernewirkungen“ (Referat gehalten für die 69. Versammlung der deutschen Naturforscher und Aerzte in Braunschweig, 1897; Sektion Physik) Beilage zu den Annalen der Physik und Chemie 62. Neue Folge, Heft 1, I – XLIX; Berichtigung zu Seite XXXIX: Annalen der Physik und Chemie 62, Heft 12, 693, Dezember 1897.
* ↑ Walter Ritz (1909) „Die Gravitation“, Scientia, 1 April 1909.
* ↑ Isenkrahe, C. Zur Elementaranalyse der Relativitätstheorie. Einleitung und Vorstufen, Braunschweig 1921.