Abstract
Ancient philosophers generally offered three lines of thought for conceiving of light. Classical atomism took light to be a material emission of small and swift particles; Plato spoke about light as a phenomenon charged with metaphysical tones; and Aristotle, who surprisingly only spoke of light in two brief passages in his entire corpus, asserted that light was not a substance but a quality of the medium. During the Middle Ages phenomena related to light were studied mathematically by geometrical optics, though it is well known that the mathematical approach was not, strictly speaking, a part of natural philosophy. The nature of light in that period was only studied—with few exceptions—by authors who expressed conceptions of nature that were closer to Neoplatonic cosmologies. In most cases, the study of light was nearer to metaphysics than to natural philosophy.
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- 1.
About the relation of metaphysical and physical arguments in medieval and renaissance philosophies of light, see Lindberg, “The Genesis of Kepler’s Theory of Light.”
- 2.
Properly speaking, few seventeenth-century natural philosophers were strict mechanists, but I think we have to distinguish a proper “mechanical philosophy” in the sense Boyle attributed to it from a set of epistemological values which from the beginnings of the seventeenth century were shaping the mechanical image of the natural world. As Daniel Garber says in his article in this volume (Chap. 1), Galileo was not a strict mechanist, but I believe he really conceived the mechanical explanations as a regulatory principle of his scientific work. In fact, the development of his interpretations of the nature of light shows both his failure to achieve an absolute mechanical explanation and his efforts to achieve it. Besides the aforementioned article of Daniel Garber, which reviews the topic of the mechanical philosophy in the history of science, see Baldini, Zanier et al., Ricerche sull’atomismo del Seicento; Boas Hall, “The Establishment of the Mechanical Philosophy”; Clericuzio, Elements, Principles and Corpuscles; Festa and Gatto (eds.), Atomismo e continuo nel XVII secolo; Festa, Jullien and Torrini (eds.), Géométrie, atomisme et vide; Lüthy, Murdoch and Newman (eds.), Late Medieval and Early Modern Corpuscular Matter Theories; Meinel, “Early 17th-Century Atomism”; Newman, Atoms and Alchemy.
- 3.
See Westfall, The Construction of Modern Science, p. 36.
- 4.
About the different connotations of the concept of atom along the different phases of Galilean work, see Galluzzi, Tra atomi e indivisibili. I wrote this article before Galluzzi published his work, which explains why I have not taken into account some very interesting remarks and interpretations he offers, with which I mostly agree. See also Gómez, “The Mechanization of Light in Galilean Science”; Nonnoi, “Galileo Galilei: quale atomismo?”
- 5.
Festa, “Repères pour une analyse historique des notions de continuum et d’atomisme”; Pyle, Atomism and Its Critics.
- 6.
For an analysis of the relation between Galileo’s theories of matter and motion, see Palmerino, “Una nuova scienza della materia per la scienza nova del moto”; Palmerino, “The Isomorphism of Space, Time and Matter in Seventeenth-Century Natural Philosophy”.
- 7.
Redondi, Galileo eretico.
- 8.
Galileo, Opere, vol. V, p. 301: “substanza spiritosissima, tenuissima e velocissima, la quale, diffondendosi per l’universo, penetra per tutto senza contrasto, riscalda, vivifica e rende feconde tutte le viventi creature.”
- 9.
Light was the original substance, created on the first day and only 4 days later put into that great warehouse the Sun, as Galileo himself wrote: “Di questa luce primogenita e non molto splendida avanti la sua unione e concorso nel corpo solare, ne aviamo attestazione dal Profeta nel Salmo 73, v. 16 Tuus est dies et tua est nox: Tu fabricatus es auroram et Solem; il qual luogo vien interpretato, Iddio aver fatto avanti al sole una luce simile a quella dell’aurora: di più, nel testo ebreo in luogo d’ aurora si legge lume, per insinuarci quella luce che fu creata molto avanti il Sole, assai più debile della medesima ricevuta, fortificata e di nuovo diffusa da esso corpo solare” (Galileo, Opere, vol. V, p. 302). On this, see Lindberg, “The Genesis of Kepler’s Theory of Light”; Hamilton, Three worlds of Light; Maecling, The Doctrine of Light; Puliafito, “Per uno studio della Nova de universis philosophia.”
- 10.
On the concept of spiritus in Renaissance natural philosophy, see Garin, “Il termine ‘spiritus’ in alcune discussion fra Quattrocento e Cinquecento.”
- 11.
Aristotle, Metaphysics, VII 3, 1029a20–30.
- 12.
Aristotle, Physics, VI 3, 234a, and VII 6, 337a. See Lindberg, “The Genesis of Kepler’s Theory of Light.”
- 13.
See Lindberg, “The Genesis of Kepler’s Theory of Light”; Thonnard, “La notion de lumière en philosophie augustinienne.”
- 14.
On the metaphysics of light in Ficino and his conception of the Sun, see Rabassini, “La concezione del Sole secondo Marsilio Ficino”; id., “‘Amicus lucis’. Considerazioni sul tema della luce in Marsilio Ficino”; id., Il vincolo dell’universo ; Deitz, “Space, Light, and Soul in Francesco Patrizi’s Nova de universis philosophia (1591).” Note the differences with respect to the interpretations of some eminent Neoplatonic philosophers, such as Al-Kindi or Avicebron, who thought that a medium was necessary for the diffusion of light, which was an impression on the medium, and therefore thought that radiating light was corporeal. In his synthesis of Aristotelianism and Neoplatonism, Grosseteste defended the instantaneity of light, considering it as the prime “corporeal form” because it gives extension to matter. Saint Buenaventura defended very similar ideas. The interpretations of these two later authors were picked up and developed by Roger Bacon, who continued to defend the definition of light as “corporeal form” and asserted its instantaneity, see Lindberg, The Genesis of Kepler’s Theory of Light; id., Theories of Vision from al-Kindi to Kepler; id., Roger Bacon’s Philosophy of Nature; McEvoy, “The Metaphysics of Light in the Middle Ages.”
- 15.
Neoplatonic philosophy admits the existence of spatial forms separated from matter. The best examples of such non-material spatial forms are the geometrical and real entities of the Platonic World of Ideas. The way the Neoplatonic philosophers argued separately about matter and form—in addition to the idea of unity of all universal things—led to a proliferation of “corporeal forms” (corporeal insofar as they were spatial) that penetrate everywhere throughout the universe without being hindered by the resistance caused by the impenetrability of material bodies. Angels were the main protagonists of this proliferation of forms. Furthermore, the independence of spatial forms contributed to the development of a concept of space independent of the bodies that it contains, over and against the Aristotelian identification of space and place, therefore also contributing to the defense of void spaces. These elements were among the principal causes of the intersection between atomism and Neo-Platonism, as, for example, is evident in Patrizi’s philosophy. On this issue, see Henry, “Void Space, Mathematical Realism and Francesco Patrizi da Cherso’s Use of Atomic Arguments.”
- 16.
“la somma velocità del muoversi per immensi spazii, essendo l’emanazione della luce come instantanea,” Galileo, Opere, vol. V, p. 302.
- 17.
Ibid., vol. V, pp. 301f.: “essere qualche cosa di più del lume, poi che ei penetra e si diffonde per tutte le sustanze corporee, ben che densissime, per molte delle quali non così penetra essa luce.”
- 18.
Many years later, in 1637, the questions about the difference between light and heat and opacity will reappear in the letters that Castelli sent to Galileo, known as “La Mattonata” (ibid., vol. XVII, pp. 121–123, 150–155 and 156–169). These letters were published in Castelli, Alcuni opuscoli filosofici di Benedetto Castelli, pp. 57–79. See Campogalliani, “Mattoni al sole”; Gómez López, “Galileo y la naturaleza de la luz.”
- 19.
Telesio, De rerum natura iuxta propria principia, IV, 9–17; see Gómez, “Telesio y el debate sobre la naturaleza de la luz en el Renacimiento italiano”. There are important differences with respect to content and approach between Telesio’s speculation on light and the views of Ficino and Patrizi. While these later authors pointed especially to the metaphysics of light, Telesio instead conceived of his conception of light as part of physics. All of them thought that light and heat are strongly connected, but for Ficino light is the origin of all beings and heat derives from it—that is to say, heat is the result of light’s activity. Telesio, instead, thought that light derives from heat, and that this explains why the sky, the part of the universe where heat dwells, would be the world of light. See also De Franco, “La teoria della luce di Bernardino Telesio.”
- 20.
Concerning this Lincean editorial project, see Redondi, “Fede Lincea e teologia tridentina.” In this essay, Redondi emphasizes the importance of an earlier work by Persio, his Trattato dell’ingegno dell’huomo (1576), where, though not a Copernican, Persio made an ode to the Sun, describing it as the governor of the universe, whose instrument was the light continuously spreading from it. According to Redondi, ideas like this fitted perfectly in the Lincean aim to reconcile the new science with the Bible.
- 21.
See letters from Bartolini to Galileo, 24 February 1612 (Galileo, Opere, vol. XI, p. 278); from Cesi to Galileo, 2 March 1612, where the Prince asked Galileo his opinion about the election of Persio and the publication of his manuscripts (ibid., p. 285). On 19 May 1612, Cesi sent to him “some of Persio’s published things” and some days later Galileo answered that he was attending with great curiosity to the manuscripts in question, ibid., pp. 298 and 301. On 28 December 1612, Cesi sent him “le materie del Persio,” ibid., p. 451.
- 22.
The book, published in 1612, is in vol. IV of Galileo, Opere, with texts connected with the debates around it in the period. On this polemic see De Ceglia, De natantibus.
- 23.
Castelli to Galileo, in Galileo, Opere, vol. XI, pp. 294f. On the polemic about sunspots, see the Introduction by Reeves and van Helden in Galileo, On Sunspots.
- 24.
Ibid., vol. V, pp. 105f.: “Circa a cotal determinazione, io confesso a V.S non aver sin ora tanto di resoluto appresso di me, ch’io m’assicuri di stabilire ed affermare conclusione alcuna come certa; essendo molto ben sicuro, la sustanza delle macchie poter essere mille cose incognite ed inopinabili a noi, e gli accidenti che in esse scorgiamo, cioè la figura l’opacità ed il movimento, per esser comunissimi, o niuna o poca e molto general cognizione ci possono somministrare.”
- 25.
Ibid., vol. V, pp. 230f. In a note in his second letter to Welser, Galileo had already made reference to the problem of the regeneration of the sun, see ibid., p. 140. But he was very prudent in expressing his suggestions, as shown in the sentence closing the passage just cited: “Io peró non intendo di asserire alcuna di queste cose per certa, nè di obbligarmi a sostenerla, non mi piacendo di mescolar le cose dubbie tra le cose certe e risolute,” ibid., p. 231. Some pages before he had insisted on this attitude when writing: “esser ottima resoluzione il posporre ogni atto specolativo a tutte le altre nostre occupazioni. Perchè, o noi vogliamo specolando tentar di penetrar l’essenza vera ed intrinseca delle sustanze naturali; o noi vogliamo contentarci di venir in notizia d’alcune loro affezzioni. Il tentar l’essenza, l’ho per impresa non meno impossibile e per fatica non men vana nelle prossime sustanze elementari che nelle remotissime e celesti,” ibid., p. 187. The problem of solar regeneration is also present in the letter to Dini of 1615, where Galileo will give an explanation very close to some of the ideas expressed by Ficino in his De vita. There Ficino related the luminous and spiritual radiation from stars to a kind of circular breathing of the universal spirit, a leitmotif of the Hermetic tradition. On the metaphysics of light in Ficino and his conception of the Sun, see Rabassini, “La concezione del Sole secondo Marsilio Ficino”; Vasoli, “Su alcuni temi della filosofia della luce nel Rinascimento.”
- 26.
Le Soleil à la renaissance.
- 27.
Galileo, Opere, vol. V, p. 30: “un piccol parto, bisognoso d’esser ridotto a miglior forma, lambendolo e ripulendolo con affezione e pazienza, essendo solamente abbozzato e di membra capaci sì di figura assai proporzionata, ma per ora incomposte e rozze: se averò possibilità, l’anderò riducendo a miglior simmetria.”
- 28.
Nonnoi, “Galileo Galilei: quale atomismo?” finds an example of Galileo’s attitude in this sentence of Castelli in his defence of Galileo (in the Errori di Giorgio Coresio): “gli atomi sono così detti non perchè siano non quanti, ma perchè, sendo i minimi corpuscoli, non se ne danno altri minori da i quali possano essere divisi,” Galileo, Opere, vol. IV, p. 281. See also Redondi, “Atomi, indivisibili e dogma.”
- 29.
Galileo, Opere, vol. VI, pp. 351f.: “con quella proporzione d’eccellenza qual è tra il finito e l’infinito, tra ‘l temporaneo e l’istantaneo, tra ‘l quanto e l’indivisibile, tra la luce e le tenebre.” I think that it is erroneous to attribute to Galileo an atomistic conception of the secondary qualities. When he speaks about tactile sensations, odors or flavors, it should be noted that he does not use the word “atom,” but expressions like minimi sottillissimi, minimi ignicoli, minimi del fuoco, all of which refer to extended particles with specific figures and motions. Nothing is said about their indivisible nature. The extension of these corpuscles implies a defense of a classical atomistic theory of qualities and sense perception only if Galileo had conceived them (as he did in the Discorso when speaking about atoms of fire) as the smallest division of matter. But Galileo did not do so in Il Saggiatore. Therefore, it would be better to speak of a corpuscularian rather than atomistic explication of sense perception and secondary qualities.
- 30.
Ibid., vol. VI, p. 352, trans. in Discoveries and Opinions of Galileo, p. 278: “E forse mentre l’assottigliamento e attrizione resta e si contiene dentro a i minimi quanti, il moto loro è temporaneo, e la lor operazione calorifica solamente; che poi arrivando al’ultima ed altissima risoluzione in atomi realmente indivisibili, si crea la luce, di moto o vogliamo dire espansione o diffusione instantanea, o potente per la sua, non so s’io debba dire sottilità, rarità, immaterialità, o pure altra condizion diversa da tutte queste ed innominata, potente, dico, ad ingombrare spazii immensi.”
- 31.
Ibid., vol. VIII, p. 201.
- 32.
Ibid., vol. VI, p. 352, trans in Discoveries and Opinions of Galileo, p. 279, italics are mine: “Io non vorrei, Illustrissimo Signore, inavvertentemente ingolfarmi in un océano infinito, onde io non potessi poi ridurmi in porto; nè vorrei, mentre procuro di rimuovere una dubitazione, dar causa al nascerne cento, sì come temo che anco in parte possa essere occorso per questo poco che mi sono scostato da riva: però voglio riserbarmi ad altra ocasion più oportuna.”
- 33.
Ibid., vol. VIII, p. 89, trans. in Two New Sciences, p. 51: “Ma in quai pelaghi ci andiamo noi inavvertentemente pian piano ingolfando? tra i vacui, tra gl’infiniti, tra gli indivisibili, tra i movimenti instantanei, per non poter mai, dopo mille discorsi, giugnere a riva?”
- 34.
Giudice, Luce e visione.
- 35.
See the letter from van Helmont to Mersenne, 15 January 1631, in Correspondance, vol. III, pp 34f. About the semi-corporeal nature of light defended by some Paracelsians and Helmontians, see Clericuzio, Elements, Principles and Corpuscles, pp. 61f., 90–92, 180f.
- 36.
It suffices here to recall Theodore Deschamps, William Davidson, and some years after, in the 50s, Helmontians as Noah Biggs. See Clericuzio, Elements, Principles and Corpuscles, pp. 53, 61, 91.
- 37.
The book had already been finished in 1635 (then under the title De lumine et coloribus). In November of that year, Boulliaud sent the manuscript to Peiresc, who gave it to Gassendi. It was published in Paris in 1637, and on 30 October of that year, Boulliaud sent it to Galileo. It may be inferred from his answer (dated 1 January 1638) that he did not like it very much, Galileo, Opere, vol. XVII, pp. 207f., 245f. On this issue he agreed with Descartes; see Descartes’ letter to Mersenne, 11 October 1638, in Mersenne, Correspondance, vol. VII, p. 11.
- 38.
Letters from 25 January 1647 and 24 May 1648, in Mersenne, Correspondance, resp. vol. XV, pp. 163–164 and vol. XVI, pp. 329f.
- 39.
While Mersenne’s ideas on light changed over the years, his point of view was never completely clear. At the beginning of his scientific career, in his Quaestiones in Genesim, he defended the scholastic view defining light as a visible quality. He reintroduced the question in the Harmonie Universelle, I, prop. IX, p. 17, and he included the Tractatus opticus of Hobbes in his Universae geometriae mixtaeque mathematicae synopsis. In his Cogitata, he asserted that light was a motion of the ether or subtle matter. See Mersenne, Correspondance, vol. XIV, p. 681, note 2.
- 40.
The main source for the Jesuit view of light is found in the Commentarii Collegii Conimbricensis In quatuor libros de coelo, chap. VII. This text discussed the different conceptions of light and their criticisms, and concluded with a clear reluctance to accept the materiality of light, with the defense of its instantaneity, and with the distinction between a divine light (with a clear symbolic value) that pertains to “glorious bodies” and natural light. It is clear that there are cosmological reasons for maintaining these ideas connected with the defense of the Aristotelian distinction between celestial and terrestrial worlds, stressing the incorruptibility of the heavens. Just one of the central points arguing against the materialistic conception of light is the fact that celestial bodies would become depleted and would be extinguished if their light were a material emission, ibid., p. 381. Among the Jesuits who studied the nature of light from the late 1640s on, we find Zucchi, Optica philosophica experimentis et ratione constituta; Maignan, Cursus philosophicus; id., Perspectiva horaria, sive de horographia, gnomonica libri; Kircher, Magnes, sive de arte magnetica, id., Ars magna lucis et umbrae; Schott, Magiae universalis naturae, & artis. Partem priman opticam, sive thaumaturgum opticum; id., Physicam curiosam, sive mirabilia naturae; [Eschinardi], Microcosmus physico-mathematicus; id., Dialogus opticus; id., Centuria problematum opticorum, seu Dialogi optici; Fabri, Dialogi de lumine; id., Physica, id est scientia corporearum, id., Synopsis optica; Traber, Nervus opticus sive tractatus theoricus, in tres libros opticam, catoptricam, dioptricam distributus. Exceptions to the general trend of Jesuits on this problem are Étienne Noёl, a French Jesuit who in his Physica vetus et nova (1648) defended a materialistic theory of light, and Grimaldi, Physico-mathesis de lumine (1665), who though he did not actually assert the material composition of light, developed his arguments as if it were so, using an analogy with fluids.
- 41.
The bibliography on Gassendi is immense and is updated in Murr (ed.), Gassendi et l’Europe. See also Bloch, La philosophie de Gassendi. On Gassendi’s influence and the differences between his matter theory and strictly mechanistic philosophies, see Clericuzio, Elements, principles and Corpuscles, pp. 63 and ff.
- 42.
The correspondence of Gassendi on this issue is in Galileo, Opere, vol. XVIII.
- 43.
Gassendi, Opera Omnia, lib. VI, chap. 11, vol. I, pp. 422f.
- 44.
Letter to Mersenne, 13 December 1635, in Mersenne, Correspondance, vol. V, pp. 532–537.
- 45.
Besomi and Camerota, Galileo e il Parnaso Tychonico, especially pp. 1–31; Solís, “Los cometas.”
- 46.
Bucciantini, Contro Galileo.
- 47.
Guiducci to Galileo, 18 April 1625, in Galileo, Opere, vol. XIII, p. 265.
- 48.
Redondi, Galileo eretico.
- 49.
This is not the place to give a complete account of the different views on Redondi’s thesis. I refer to two examples: Bucciantini in his Contro Galileo and some passages of Camerota, Galileo, pp. 389 and ff. The discovery of a new document in 1999 in the Archives of the Holy Office has reopened the polemic on this question. See Martínez, “Il manoscritto ACDF”; Artigas, “Un nuovo documento sul caso Galilei”; Mateo-Seco, “Galileo e l’Eucaristia”; Shea, “Galileo e l’atomismo.”
- 50.
The Society of Jesus prohibited the teaching of atomism in their schools in 1632. It is significant that only a year later, the Aristotelian Antonio Rocco in the Esercitazioni filosofiche advanced a criticism of atomism, which Galileo answered in manuscript notes, where he had already defended his concept of bodies composed of infinite non-extensive indivisibles. See Galileo, Opere, vol. VII, pp. 682f., 745f., and Redondi, “Atomi, indivisibili e dogma”; Nonnoi, “Galileo Galilei: quale atomismo?”
- 51.
“La nota del nostro q. comun padre e maestro poteva esser circa la condensazione e rarefazione, come punti da me più tosto stimati difficilissimi che resoluti, non vi havendo in quei tempi altro che difficoltà; ma ben poi circa 18 anni sono, ritrovandomi alla villa con il Salviati del Dialogo, mi cadde nella mente una mattina, mentre eramo a messa, un pensiero, nel quale poi più profondamente internandomi, mi vi son venuto confermando, et a me è parso poi sempre ammirando come per modo stupendo di operar della natura, secondo il qual modo (e credo in nessun altro) si possa distrarre e rarefare una sustanza in immenso senza ammettere in essa veruno spazio vacuo, et all’incontro in immenso condensarla senza alcuna penetrazione di corpi: pensiero, credami, assai peregrino, il quale insieme con moltissime altre novità spero che ella vedrà sparse nelle opere che mi restano da mandar fuora, le quali penso di ridurre al netto in questa vernata per mandarle poi alla P. V., acciò ne faccia il suo volere,” Galileo to Fulgenzio Micanzio, 19 November 1634, in Galileo, Opere, vol. XVI, pp. 162f. In the winter following that letter, Galileo sent Micanzio the draft of the First Day, as can be inferred from a letter of Micanzio. In a missive of 3 February 1635 he wrote: “Ho ricevuti altri tre fogli del Dialogo, in tutto 6; li ho anco letti con l’avidità che non posso esplicare: ho necessità di meditarli a verso per verso. La novità delle cose, le ragioni e demostrationi di problemi non più sentiti, mi mettono in un nuovo mondo. L’intento mio mi portava tutto al punto della rarefattione e condensatione, ma m’accorgo che non ci si può ben arrivare che per li passi precedenti.” And on 10 February 1635, he made clear the relation of that draft to his Postille to the work of A. Rocco, see ibid., vol. XVI, p. 203 and pp. 208f.
- 52.
Aristotle, Physics, IV 9, 216b25–217b30.
- 53.
Ibid., vol. VIII, p. 89, trans. in Two New Sciences, p. 51: “Ma in quai pelaghi ci andiamo noi inavvertentemente pian piano ingolfando? Tra i vacui, tra gl’infiniti, tra gli indivisibili, tra i movimenti instantanei, per non poter mai, dopo mille discorsi, giugnere a riva?”
- 54.
Galileo, Opere, vol. VIII, p. 87, trans. in Two New Sciences, p. 49: “Io non saprei intendere che l’azzione della luce, benché purissima, potesse esser senza moto, ed anco velocissimo.… mostra la esperienza quotidiana, l’espansione del lume esser instantanea.”
- 55.
Galileo followed almost literally the criticism Aristotle made to Zeno’s paradoxes in his Physics, VI, 232b and ff., intending to deny the possibility of motion in an infinitely divisible continuum space. But in this case, he wanted to demonstrate the possibility of motion in a space composed of infinite indivisibles. Aristotle, assuming that “time and space are divided according to the same rules and divisions,” refuted Zeno’s paradoxes against motion, asserting that both time and space are infinitely divisible continuous magnitudes. If Galileo wanted to assert the possibility of motion in a continuous medium composed of infiniti atomi non quanti, he had to do the same with time. He did just that in the Third Day of the Discorsi.
- 56.
This is how Galileo expounded it in the previously mentioned letter to Micanzio in 1634, and repeated it using almost the same words in the Discorsi, just after the passage on light: “il comprender come stia il negozio della rarefazzione e della condensazione, senza incorrer per causa di quella nell’inconveniente di dovere ammettere spazii vacui, e per questa la penetrazione de i corpi: inconvenienti, che amendue mi pare ch’assai destramente vengano schivati con l’ammetter detta composizione d’indivisibili,” Galileo, Opere, vol. VIII, p. 93.
- 57.
“Veramente non l’ho sperimentata, salvo che in lontananza piccola, cioè manco d’un miglio, dal che non ho potuto assicurarmi se veramente la comparsa del lume opposto sia instantanea; ma ben, se non instantanea, velocissima, e direi momentanea, è ella, e per ora l’assimiglierei a quel moto che veggiamo farsi dallo splendore del baleno veduto tra le nugole lontane otto o dieci miglia; del qual lume distinguiamo il principio, e dirò il capo e fonte, in un luogo particolare tra esse nugole, ma bene immediatamente segue la sua espansione amplissima per le altre circostanti; che mi pare argomento, quella farsi con qualche poco di tempo; perché quando l’illuminazione fusse fatta tutta insieme, e non per parti, non par che si potesse distinguer la sua origine, e dirò il suo centro, dalle sue falde e dilatazioni estreme,” ibid., vol. VIII, pp. 89 and 104f.
- 58.
The effort to resolve the problem of condensation and rarefaction without admitting either infinite void spaces or the penetrability of bodies reflected Galileo’s effort to overcome two of the principal criticisms that Aristotelians launched against atomism, because as he himself had said in the Discorsi, he really did not have any problem accepting void spaces and penetrability, ibid., vol. VIII, p. 105. He expressed the same in his correspondence with Baliani, who after reading the Discorsi, wrote to Galileo about his suspicions in view of the subtle strategies Galileo used to elude void spaces and penetrability. Baliani, who was a convinced atomist and did not have any problem accepting the existence of void spaces, and did not see any obstacle in also accepting their penetrability. Galileo replied by saying that he, too, had no problem with them, but he was trying to please the Aristotelians: “Quanto a quello che ella mi dice della opinione sua circa alla condensazione e rarefazione, cioè che ammette la penetrazione dei corpi l’uno con l’altro, già ho io scritto (come ella può vedere) che chiunque tale operazione volesse ammettere, io gli concedo quanto li piace, non havendo io hauto intenzione di scrivere quanto in tal proposito ho scritto se non in grazia di quelli che negano la penetrazione e gli spazii vacui potersi dare in natura,” 1 September 1639, ibid., vol. XVIII, pp. 93–95. See also the letters from Galileo to Baliani of 1 August and from Baliani to Galileo of 19 August 1639, in ibid., vol. XVIII, resp. pp. 75–79 and 86–88.
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Gómez, S. (2013). From a Metaphysical to a Scientific Object: Mechanizing Light in Galilean Science. In: GARBER, D. (eds) The Mechanization of Natural Philosophy. Boston Studies in the Philosophy and History of Science, vol 282. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-4345-8_8
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