Abstract

The current standard edition of the works of Spinoza by Carl Gebhardt ends with two short treatises in Dutch entitled Stelkonstige Reeckening van den Regenboog and Reeckening van Kanssen . Both treatises are also included in the collection of shorter works edited in 1982, which forms volume three of the modern Dutch edition of the Works of Spinoza , still to be completed. The two treatises in question were first published anonymously in 1687 — roughly ten years after Spinoza's death — by Levyn van Dyck, a printer in The Hague. The Algebraical Computation of the Rainbow can be viewed as a mathematical explanation of Descartes' studies of the rainbow-phenomenon, as the treatise calls it ; the Calculation of Probabilities deals with problems raised earlier by Christiaan Huygens and others, which are partly solved here. In about 1860 the Amsterdam antiquary Frederik Muller identified a severed copy of the first treatise as a work by Spinoza and was supported in this view by the Spinoza-expert Johannes van Vloten. Soon after, two other experts, J.P.N. Land and D. Bierens de Haan, attributed the second treatise also to Spinoza, among other things on the grounds that this work had formed part of the same volume in the 1687 edition. The most important argument of Van Vloten and others in attributing the Algebraical Computation of the Rainbow to Spinoza, was the fact that the prefaces to Spinoza's Opera Posthuma and to De Nagelate Schriften van B.d.S. mentioned a treatise on the rainbow by the philosopher which had never been found among his literary remains. Furthermore, both prefaces, the Praefatio composed by Lodewijk Meyer and the Voorreeden by Jarig Jelles, suggest in slightly different terms, that Spinoza probably burnt his rainbow treatise, not excluding, however, the possibility of the existence of this tract in some unknown place. As to the authenticity of the Calculation of Probabilities, this was based on a letter by Spinoza to J. van der Meer, which deals with the calculation of chances, albeit in a much simpler way. Convinced of Spinoza's authorship of the two treatises, scholars, notably R. McKeon and M. J. Petry, have tried to fit them into the pattern of Spinoza's thought; probably premature efforts on all parts. Already J. Freudenthal had refused on good grounds to attribute the Calculation of Probabilities to Spinoza. A through analysis of 17th and 18th-century source material shows that at that time nobody took the two treatises published by Van Dyck for Spinoza's work : neither Johannes Colerus, who communicated with friends of Spinoza's who had read his rainbow treatise, nor the well-informed J. Rieuwertsz, son of the Spinoza printer, nor anyone else. This lack of recognition by near-contemporaries already forms a basis on which to doubt Spinoza's authorship of the two treatises. Moreover, a review-article published in Pieter Rabus's scholarly journal, De Boekzaal van Europe, leads one to conclude that the author of the two treatises was still alive in 1693 and father of a son who had studied in Leyden, whereas Spinoza had died childless some sixteen years previously. On top of that, however, Rabus's journal offers indications as to a more probable author of both treatises : namely one of the learned acquaintances of Christiaan Huygens, Salomon Dierquens. One must therefore fear that the 19th century attributions of the Algebraical Computation of the Rainbow and of the Calculation of Probabilities were founded on sand. Until there is better evidence both treatises had better be left out of all considerations and studies of Spinoza's thought