Mathematician. He studied in the gymnasium at Meldorf from 1852 till 1856. He then worked as an engineering apprentice at Flensburg. In 1859 he entered the Polytechnicum at Karlsruhe to study mathematics and then continued as a Ph.D. student at Heidelberg in 1862. Henrici then went to Berlin and studied under Weierstrass and Kronecker. After being appointed a dozent at Kiel University he found it impossible to make sufficient money to live on, so he came to England in 1865, where he was barely able to make sufficient money by teaching school level mathematics. In 1869 Henrici was appointed professor of mathematics at Bedford College for Women. He married Helen Stodart Kennedy, the daughter of a Congregational minister, on 15 August 1877. Their son, Ernst Olaf Henrici, became a major in the Royal Engineers but was a fine mathematician who collaborated with his father on a paper in 1912. In 1879 Clifford, who had been professor of applied mathematics and mechanics at University College, died, and Henrici was asked to take over his teaching duties. Clearly the duties of the two chairs were too much for one person so in 1880 he was formally installed as professor of applied mathematics and mechanics and resigned his chair of mathematics. In 1884 he moved from University College to take up the chair of mechanics and mathematics at the new Central Technical College. He was elected a fellow of the Royal Society in 1874 and was a member of its Council during 1882-83. In 1882, in addition to serving on the Council of the Royal Society, he was elected President of the London Mathematical Society, holding this position from 1882 to 1884. He was awarded an honorary degree by the University of St Andrews in 1884.