In 2004 we celebrate the 100th birthday of a great scientist and a leading proponent of our geophysical disciplines, Hans Ertel, who was formerly professor of geophysics and theoretical mechanics at Humboldt University in Berlin. He was also director of the (German) Institute of Metorology and Geophysics, and vice-president of the German Academy of Sciences; also in Berlin. Ertel was the founder of the Alexander von Humboldt Commission. Under his leadership, and in cooperation with other German academies, a comprehensive collection of letters from and to von Humboldt has been assembled and edited.