Carl Ernst Bessel Hagen was born in
Königsberg (rebuilt and relaunched as
Kaliningrad after the
1945 expulsion), eldest of the three recorded sons of the banker-politician
Adolf Hermann Hagen (1820–1894) by his first marriage, which was to Johanna Louise Amalie Bessel (1826–1856).
Friedrich Bessel (1784 - 1846) was a pioneering
astronomer,
mathematician,
physicist and
geodesist. He graduated
successfully from the (secondary school) in 1871 and went on to study university level maths, physics and chemistry at
Humboldt University of Berlin and
Heidelberg University. In Heidelberg, between 1873 and 1875 he combined his studies with work as an assistant to
Robert Bunsen. It was Bunsen who supervised him for his doctorate, which he received in 1875. Then, for six years between 1878 and 1883, he worked with
Hermann von Helmholtz at Humboldt University of Berlin. It was at Berlin that in 1883 he received his
habilitation for work on the thermal expansion of alkali metals. He followed this up in 1885 with a book which did much to raise his public and academic profile. He found himself frequently called upon by public bodies to share his expertise on the subject. He then returned to the Dresden Polytechnikum where he served as extraordinary professor for applied physics and director at the institution's newly founded Electro-Technology Laboratory between 1884 and 1888. Between 1895 and 1908 he was a part-time member of the
patent office. He was also actively involved in the governance of the
Deutsches Museum in Munich. ==Hagen–Rubens equation==