Johann Friedrich Hennert
Johann Friedrich Hennert (* October 19, 1733 in Berlin, † March 30, 1813 in Utrecht ) was a German mathematician and astronomer in Utrecht.
Life
The son of Privy Councillor at the Supreme Court in Berlin's Friedrichshain Hennert ( † before June 12, 1771 ) grew up in apparently no impotent family and was the older brother of Karl Wilhelm Hennert. He received his first scientific studies at Joachimsthal high school that he frequented under the rectorship of Johann Philipp Heinius ( 1688-1775 ). Although his father would have liked it, that he might attend to the law, but he developed a taste for the mathematical sciences. Here he found from 1747 in Johann Georg Sulzer a teacher who could bring him the mathematical knowledge of his time closer. That it was probably also brought him in contact with Leonard Euler, who worked at the Royal Prussian Academy of Sciences in Berlin. Gladly he remembered this teacher who had a lasting effect on him.
In 1755 he completed a journey that took him through different European locations. This allows, for example, his enrollment on September 11, 1755 to demonstrate at Leiden University. However, his goal was to Paris, where he lived for two years in the house of Joseph -Nicolas Delisle. At that time he also met the professor of mathematical physics Pierre Charles Lemonnier know. To 1757 he moved to The Hague, where he was in the field of philosophical sciences teaching and in 1758 his first work, Traite sur les thermometres published. On November 1, 1759 we find him again at Leiden University, where he worked as Repetent in Leiden and established a mathematical school with the permission of the professors. Since Johann Castillon 1763 had received a call to Berlin, was sought in Utrecht for a suitable successor for this. Therefore Hennert was appointed on January 2, 1764 by the Curators of the University of Utrecht, associate professor of philosophy, mathematics and astronomy.
In order to have the necessary academic qualifications, he had the treatise dissertatione et sportulis presented, after which he was appointed by Johann David Hahn honorary doctor of philosophical sciences on 3 February of the same year. He joined the task entrusted to him on February 6, 1764 of the speech de ingenio Mathematici to, received on 7 October 1765, the appointment as full professor of philosophy, mathematics and astronomy, and took office on 18 November 1765 of the speech De matheseos studio cum solida educatione conjungendeo. In Utrecht he had also participated in the organizational tasks of the university and exercised in the years 1768/69 and 1781/82 the Rector of the Alma Mater. Here, among other things, Jan Hendrik van Swinden was one of his foremost disciples. During that time, he had also received offers in Berlin and at the University of Halle, which he turned down.
When in 1787 the Batavian Republic riots broke out, he placed on the March 6, 1787 resigned his professorship in Utrecht and went to Hanover. After the riots were over, efforts were again about drawing Hennert to Utrecht. Here he took over on August 31, 1788 again from his office and was confirmed by the same on 1 September 1788 by the Curators of the University. After that, he had 1794/95 involved again as rector of the Alma Mater at the organizational tasks of the university. 1802 Hennert suffered an inflammation of the left eye and became blind in consequence. Therefore, he asked for his release from the university service, retired in December 10, 1804 and spent his remaining years in retirement. His successor in the field of mathematical and astronomical sciences in Utrecht was his former student January Frederik van Beeck.
Hennert was in his first marriage with the poet Petronella Johanna de Timmerman ( born February 4, 1724 in Middelburg, † May 1, 1786 in Utrecht) married. He completed his second marriage with Constantia Agneta de Reder.