STELKONSTIGE Reeckening Van Den Regenboog, Dienende tot naedere samenknoping der Natuurkunde met de Wiskonsten. ["Stelkonstige Reeckening..." is followed by "Reeckening van Kanssen..."; the two treatises have been written by Christiaan Huygens, friend of Salomon Dierquens; they have often been ascribed to Baruch de Spinoza but without sufficient foundation].