By his writings he maintained his hold on his numerous followers in Holland and Friesland.
In the island of Juist, off the Friesland coast, from three weeks' observations they obtained only 5.2 as the mean.
On the death of this general Descartes quitted the imperial service, and in July 1621 began a peaceful tour through Moravia, the borders of Poland, Pomerania, Brandenburg, Holstein and Friesland, from which he reappeared in February 1622 in Belgium, and betook himself directly to his father's home at Rennes in Brittany.
As early as the beginning of the 9th century Ameland was a lordship of the influential family of Cammingha who held immediately of the emperor, and in recognition of their independence the Amelanders were in 1369 declared to be neutral in the fighting between Holland and Friesland, while Cromwell made the same declaration in 1654 with respect to the war between England and the United Netherlands.
This island is joined to the mainland of Friesland by a stone dike constructed in 1873 for the purpose of promoting the deposit of mud.