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  • Light and Void. The Philosophical Background of Valerian Magni's Vacuum Experiments1
  • Tomáš Nejeschleba

The subject of the article is the interpretation of a series of experiments proving the existence of vacuum. This was performed by the Capuchin Valerian Magni in 1647 and described in the treatise Demonstratio ocularis, which is the first printed text referring to successful experiments with vacuum. The work generated great controversy at the time, not only with opponents of void, but also with French scholars, who accused Magni of plagiarism. The article reconstructs both the situation around the work's publication and the reaction to it, with an aim of presenting the philosophical background behind Magni's experiments. Magni understood the experiments as confirmation of his anti-Aristotelianism, and placed them among his metaphysics and natural philosophy, in which he attributes the key epistemological and ontological function to light.

In July 1647, Valerian Magni, a member of the Capuchin order, ecclesiastical politician and a legate of the congregation for the Propagation of the Faith (Sacra Congregatio de Propaganda Fide),2 published in Warsaw a description of his experiment proving the existence of vacuum. His treatise entitled Demonstratio ocularis loci sine locato, corporis successive moti in vacuo, luminis nulli corpori inhaerentis (Magni 1647a) is interesting with respect [End Page 767] to at least two points. First, the publication generated a huge polemic, not only with the opponents of void but also concerning the authorship of the experiment. The extension of the polemics indicates both the importance the issue of void played in the mid seventeenth century and the role of Valerian Magni within it (Fanton D'Andon 1978; Dear 1995, pp. 187–90).3 Second, one can raise the question of the purpose of Magni's experiment. Since Magni was a keen opponent of Peripatetic philosophy,4 the aim of the experiment could have been to only demonstrate the fallacy of Aristotelian natural philosophy and prove the validity of his Anti-Aristotelianism (Shea 2003, p. 85). It seems, however, that there is an inner connection between the experiment, on the one hand and Magni's philosophical system, on the other. This connection is often neglected, however, in the literature dealing with the history of science. It was only sketched out by several historians of philosophy (Blum 1998, p. 108; Blum 2017; Vasoli 1980). The goal of my article is, therefore, to analyze the philosophical meaning of the experiment which Magni gives to it as concerns its philosophical background and show how it is bound with his metaphysics of light in particular.

In the first part of my study I will briefly sketch the circumstances of Magni's experiment and the polemics around it to demonstrate the importance of Magni's activities in this field. Second, I will move on to Magni's philosophy and question how his experiment proving the existence of void is in accord with his philosophical thought being grounded in the Medieval Platonic tradition.

1. Historical Narration—Facti Historia

Valerian Magni performed his vacuum experiment in Warsaw in the presence of the King and Queen of Poland on 12 July 1647. He published a description of the experiment in the form of a historical narration—facti historia (Dear 1995, pp. 187–90) followed by an explanatory part.5 Magni stated at the beginning of the treatise that he was attracted in his experiments with vacuum by a passage from a certain work of Galileo Galilei where Galileo narrates that it is impossible to move water by means of a mechanical tool, i.e., a pump, at a height of more than 18 cubits (Galileo 1638, p. 63).6 Following this information, Magni concluded in his own words that mercury, [End Page 768] which has a higher density, could not exceed a height of 2 cubits. This experiment, as Magni emphasizes, should solve the most important question which has ever been proposed since the creation of the world (Magni 1649, p. 5).7 With these words Magni intends to underline the importance of the issue with respect to the fatal consequences which the existence of vacuum has for Aristotelian natural philosophy. In the narrative part of the treatise, Magni writes that he filled...