(b. Milan, Italy, 15 October 1586; d. Salzburg, Austria, 29 July 1661)
At the age of two, Magni was taken by his parents, Constantino and Ottavia Magni, from Italy to Prague; he was to spend much of the rest of his life in central Europe. Magni entered the Capuchin order on 25 March 1602, adopting the name Valeriano in place of his original Christian name, Maximilian. After he had gained a reputation as a preacher and instructor at Prague, Linz, and Vienna, he was appointed in 1613 to a chair of philosophy in the Austrian Capital. Three years later Magni helped to establish the Franciscan order in Poland at the request of Sigismund III; the king later tried to obtain a cardinal’s had for Magni. During the 1620’s Magni was active in various roles: as Hapsburg envoy to Paris (1622–1623); novice-master at Linz; professor of philosophy at Prague; Franciscan provincial of Bohema (1624); and Hapsburg emissary to Italy (1625). Following the death of his patron, Sigismund III, Magin played a decisive part in the selection of a successor (1632), and later worked in Poland to consolidate the position of the Catholic church. In 1642–1643, and again in 1645, Magni was in Italy, then in Poland (1646–1648), and subsequently in Vienna and Cologne. In 1655 the combative Magni’s long-standing feud with the Jesuits (he had incited Urban VIII, a close friend, against them in 1631) led to his being accused of heresy; while trying to reconcile Protestants to the Catholic church, he had admitted the supremacy of the pope to be founded on tradition. Pleading that he was too ill to obey a summons to Rome, Magni was arrested in Vienna at the end of 1655. The emperor’s intervention, however, secured his release the following February, whereupon he was sent to Salzburg. There he remained for the rest of his life.
In philosophy Magni was a vehement anti-Aristotelian and an admirer of Galileo and Descartes. In his fight with the Aristotelians, Magni made great use of an experiment designed to demonstrate the existence of the vacuum. Although this was practically identical with the barometric experiment described by Torricelli in 1643–1644, Magni claimed that this idea was conceived independently after reading of Galileo’s work on siphons. There is no firm reason for doubting Magni’s word on this, although at the time his claim aroused great controversy.
In mid-1647 Magni demonstrated his experiment at Warsaw in the presence of Wenceslas VII, and in July of that year he published an account of it (Demonstratio ocularis) which made much of the fact that light could traverse a vacuum, so proving, against Aristotle, that motion was possible in a void. News of the experiment was communicated by a French eyewitness, Des Noyers, to Mersenne at Paris in a letter dated 24 July 1647. Unfortunately for Magni, the French were then pursuing research on the vacuum, and Roberval, who replied on Mersenne’s behalf to Des Noyers’s letter, implicitly accused Magni of plagiarism. In his reply of 20 September 1647 (apparently printed in Paris in the same year) Roberval stated that the Torricelli experiment had been performed years before and that Magni, who was in Italy in 1645, must have heard of it there; in any case, the experiment had been repeated by Petit and Pascal at Rouen in 1646.
Magni quickly wrote a defense of his work, the “Narratio apologetica,” dated 5 November 1647. This he had printed in a collection entitled Admirando de vacuo, which also contained reprints of the Demonstratio ocularis and of Roberval’s letter to Des Noyers. Magni conceded that Torricelli now had the priority, but he strongly denied having heard anything of the Torricelli experiment before the arrival of Roberval’s letter. Torricelli’s work, he said, was not known to any of his (Magni’s) friends at Rome. Rather, it was Galileo’s writings that had stimulated him to devise the experiment.
Magni’s forthright publication of the damaging letter of Roberval suggests strongly that he was telling the truth. In any event, the Demonstratio ocularis of Magni is certainly important as the first printed account of the barometric experiment, Torricelli having left his description in manuscript. Although it was printed at Warsaw, Magni’s treatise became quite well known following its reprinting at Paris in 1647 as part of an edition that also included Petit’s account of the Rouen vacuum experiments. Interestingly, it was Magni who acquainted Guericke with the Torricellian barometric experiment when the two men met at Regensburg in 1654. The several editions of Magni’s writings, and the controversy that surrounded them, undoubtedly helped to disseminate widely the news of the barometric experiment.
I. Original Works. Magni’s main work on the vacuum is Demonstratio ocularis; loci sine locato; corporis successive moti in vacuo; luminis nulli corpori inhaerentis (Warsaw, 1647); repr. by M. Dominicy as Observation touchant le vuide faite pour la première fois en France, contenue en une lettre ėcrite … par Monsieur Petit … le 10 Novembre 1646. Avec le discours qui en a esté imprimé en Pologne sur le mesme sujet, en Ieuillet 1647 (Paris, 1647). This work is also in Admirando de vacuo (Warsaw, 1647), which contains the critical letter of Roberval to Des Noyers as well as the “Narratio apologetica.” The treatise also was published in Bologna (1648) and Venice (1649). Magni published a further treatise entitled Vacuum pleno supletum (Venice, 1650). His Principia et specimen philosophiae (Cologne, 1642) contains the opuscula on the vacuum.
Magni’s main philosophical work is the Opus philosophicum: I. Synopsis philosophiae Aristotelis. II. Philosophia Valeriani (Lithomifflii, 1660). His main attack on the Jesuits is the Apologia … contra imposturas Jesuitarum (n.d. [1655?], n.p.).
Some of the vacuum materials are reprinted in Pascal, Oeuvres, Leon Brunschvicg, ed., II (Paris, 1908–1914), including Des Noyers’s letter to Mersenne (15–18); Roberval’s critique (21–35); and Magni’s defense (503–506).
II. Secondary Literature. German Abgottspon, P.Valerianus Magni, Kapuziner (Olten, 1939), deals mainly with Magni’s political and religious life. Documents and an account of Magni as a scientist are given in Cornelis De Waard, L’expérience barométrique, ses antécédents et ses explications (Thouars, 1936); also see W. E. K. Middleton, The History of the Barometer (Baltimore, 1964), ch. 3. For the bibliography of Magni’s writings on the vacuum see G. Hellmann, “Beiträge zur Erfindungsgeschichte meteorologischer Instrumente,” in Abhandlungen der Preussischen Akademie der Wissenschaften, Phys.-Math.Kl., no. 1 (1920), 33–34.
An Aristotelian reply to Magni is Jacobus Pierius, Ad experientiam nuper circa vacuum R. P. Valeriani Magni demonstrationem ocularem … responsio ex peripateticae philosophiae principiis desumpta (Paris, 1648).
Contemporary references to Magni and the experiment are in Otto von Guericke, Experimenta nova … Magdeburgica de vacuo spatio(Amsterdam, 1672), 117–118; Honoré Fabri, Dialogi physici … (Lyons, 1665), 182–183; and Jakub Dobrzenski, Nova et amaenior … fontium … philosophia (Ferrara, 1659), 27–28. Other references are cited in Lynn Thorndike, A History of Magic and Experimental Science, VII (New York, 1923–1958), 654, 659.
Paul Lawrence Rose