He spent some time in the Netherlands, where he was sent by the King Władysław IV Vasa to serve in the army of Duke Frederick Henry of Orange during the war with Spain; he participated in the Siege of Hulst in 1645 [REF].
In late 1648 the newly elected king John II Casimir Vasa, who had no plans for the war with Ottomans, advised him to return to the Netherlands and publish his studies there [REF].