At the meeting of the Naturforscherversammlung at Innsbruck in 1869, he was one of the founders of the German Anthropological Society, of which he became president in the following year; and from 1869 onwards he presided over the Berlin Anthropological Society, also acting as editor of its proceedings in the Zeitschrift fiir Ethnologic. In ethnology he published a volume of essays on the physical anthropology of the Germans, with special reference to the Frisians; and at his instance a census, which yielded remarkable results, was carried out among school children throughout Germany, to determine the relative distribution of blondes and brunettes.
As the captial of the ancient district of Kennemerland between den Helder and Haarlem, Alkmaar frequently suffered in the early wars between the Hollanders and the Frisians, and in 1517 was captured by the united Gelderlanders and Frisians.
Beyond these were found the Frisians, a people of German origin, who gave their name to the territory between the Rhine and the Ems. Of the other tribes the best known are the Caninefates, Chauci, Usipetes, Sicambri, Eburones, Menapii, Morini and Aduatici.
The Frisians struggled against Roman over-lordship somewhat longer, and it was not until A.D.
The strip of coast from the mouth of the Scheldt to that of the Ems remained, however, in the hands of the free Frisians (q.v.), in alliance with whom against the Franks were the Saxons, who, pressing forward from the east, had occupied a portion of the districts known later as Gelderland, Overyssel and Drente.