Ernst Hagen

Carl Ernst Bessel Hagen (who published under the name Ernst Hagen; 31 January 1851 – 15 January 1923) was a German applied and experimental physicist. With Heinrich Rubens, he identified the so-called Hagen–Rubens equation.

Life 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. The work undertaken by Hagen and Rubens had the effect of confirming Maxwell's equations, notably with respect to the three-vector elements of a constant, non-frequency dependent conductivity up to the infrared frequency range.

Personal In 1896 Ernst Bessel Hagen married Wilhelmine von Bezold (1870–1939) in Berlin. Her father was the notable meteorologist Wilhelm von Bezold. The marriage produced two recorded sons. )