<P> In 1886, Hertz married Elisabeth Doll, the daughter of Dr. Max Doll, a lecturer in geometry at Karlsruhe . They had two daughters: Johanna, born on 20 October 1887 and Mathilde, born on 14 January 1891, who went on to become a notable biologist . During this time Hertz conducted his landmark research into electromagnetic waves . </P> <P> Hertz took a position of Professor of Physics and Director of the Physics Institute in Bonn on 3 April 1889, a position he held until January 1894 . During this time he worked on theoretical mechanics with his work published in the book Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt (The Principles of Mechanics Presented in a New Form), published posthumously in 1894 . </P> <P> In 1892, Hertz was diagnosed with an infection (after a bout of severe migraines) and underwent operations to treat the illness . He died of granulomatosis with polyangiitis at the age of 36 in Bonn, Germany in 1894, and was buried in the Ohlsdorf Cemetery in Hamburg . </P> <P> Hertz's wife, Elisabeth Hertz née Doll (1864--1941), did not remarry . Hertz left two daughters, Johanna (1887--1967) and Mathilde (1891--1975). Hertz's daughters never married and he has no descendants . </P>

What is the contribution of hertz in electromagnetic wave