The Importance of the Transit of Mercury of 1631

E.g., Grant Robert , History of physical astronomy (London, 1852), 212; Pannekoek Antoni , A history of astronomy (New York, 1961), 284; Woolf Harry , The transits of Venus: A study of eighteenth-century science (Princeton, 1959).

E.g., Woolf , op. cit., 13.

Convenient tables of these distances and sizes, listing the values which astronomers from Antiquity to the middle of the seventeenth century had adopted, can be found in Riccioli Battista Giovanni , Almagestum novum (2 vols, Bologna, 1651), i, 419, 708.

Except perhaps for Tycho Brahe who made the distances to the outer planets considerably smaller and fitted the shell of the fixed stars immediately around the orb of Saturn, giving the distance to the fixed stars as 14,000 Earth-radii; see Astronomiae instauratae progymnasmata (1602), in Tychonis Brahe Dani opera omnia (15 vols, Copenhagen, 1913–29; reprint 1972), ii, 430.

These values are mainly due to the Moslem astronomers Al-Fargānī (ninth century) and Al-Battānī (c. 858–929), who measured the apparent diameters of the planets, and determined the distances by simply assuming that the highest point of one planet (starting with the known distance of the Moon) was equal to the lowest point of the next. The ratio of highest to lowest point for each planet came from Ptolemy's theories for the motions of the planets. See Al-Fargānī , Rudimenta astronomica , ed. de Monteregio Johannes (Nuremberg, 1537), 20v–21r; Al-Battānī sive Albatenii opus astronomicum, ed. Nallino Alphonso Carolo (3 vols, Pubblicazioni del Reale Osservatorio di Brera in Milano, no. 40, 1899–1907), i, 120–124. See also Willy Hartner's discussion of these measurements and calculations in “Medieval Views on Cosmic Dimensions and Ptolemy's Kitālo al-Manshūrāt”, Mélanges Alexandre Koyré (2 vols, Paris, 1964), i, 252–82.

Galileo , Sidereus nuncius (1610), in Le opere di Galileo Galilei (Edizione Nazionale, Florence, 1890–1909; reprint 1930–39), iii, 75–76.

One could, of course, choose to interpret the apparent smallness of the fixed stars to signify not that they were farther away, but rather that they were in fact smaller than had been thought. Galileo and his followers, however, chose to interpret the smallness as an indication of distance. See Alexandre Koyré's discussion of this in From the closed world to the infinite universe (Baltimore, 1957), 94–95. There is, however, good reason to believe that in the case of the planets, whose apparent diameters he found to be much smaller than had been thought, Galileo interpreted the smallness to signify actual smallness, for in his Dialogoq 1632 he used an accepted value for the distance to the Sun of 1208 Earth-radii (Opere, vii, 386).

See Galileo's discussion of this objection in his Dialogo; Opere, vii, 385–7.

Galileo to Sarpi, 12 February 1611; Opere, xi, 49.

Istoria e dimostrazioni intorno alle macchie solari (1613); Opere, v, 197.

Lettera a Francesco Ingoli (1624); Opere, vi, 525.

Scheiner Christoph , Sol ellipticus (Ingolstadt, 1613), 25.

Riccioli , op. cit., i, 708.

Epitome astronomiae copernicanae (1617–21); Johannes Kepler gesammelte Werke (Munich, 1938–), vii, 282.

Adelmi Benedictini, vel secundum alios Ademari Monachi, annales francorum regum Pipini, Karoli Magni, Hludovici Pii, per annos continuos lxxxvii , in Corpus francicae historiae veteris et sincerae (Hanover, 1613), 409. Life of the Emperor Karl the Great, translated from Eginard, by William Glaister (London, 1877), 89. See also Sarton George , “Early Observations of the Sunspots”, Isis, xxxvii (1947), 69–71; Goldstein Bernard R. , “Some Medieval Reports of Venus and Mercury Transits”, Centaurus, xiv (1969), 49–59. For early Chinese observations of sunspots, see Needham Joseph Science and civilization in China (Cambridge, 1961–), iii, 434–6.

Phaenomenon singulare seu mercurius in sole (1609); Gesammelte werke, iv, 83.

Ibid. Maestlin challenged Kepler's explanation in Disputatio de multivariis motuum planetarum in coelo apparentibus irregularitatibus, seu regularibus inaequalitatibus, earumque causis astronomicis. Quam praeside Michaele Mästlino … defendere conabitur die 21. et 22. Februarii … M. Samuel Hafenreffer (Tuebingen, 1606), thesis 98. See also Gesammelte werke, iv, 489, and Rosen Edward , Kepler's somnium (Madison, 1967), 141–2, n. 385.

Kepler to Samuel Hafenreffer, 16 November 1606; Gesammelte Werke , xv, 359–62, and Phaenomenon singulare; Gesammelte werke, iv, 83–87.

Gesammelte werke, iv, 83–87, 92–95.

In his ephemerides for 1617–20 ( Frisch C. , Joannis Kepleri astronomi opera omnia (Frankfurt, 1858–70), ii, 109–11).

Johannis Keppleri … admonitio ad astronomos, rerumque coelestium studiosos, de raris mirisque anni 1631 phaenomenis, Veneris puta et Mercurii in Solem incursa: Excerpta ex ephemeride anni 1631, & certo authoris consilio huic praemissa, iterumque edita a Jacobo Bartschio (Frankfurt, 1630).

Ibid., 13–14.

Gassendi Pierre , Mercurius in sole visus et Venus invisa Parisiis mdcxxxi. Pro voto & admonitio Kepleri. Epistolae duae cum observatis quibusdam aliis (Paris, 1632), in Opera omnia (6 vols, Lyons, 1658), iv, 499–510, p. 500.

Ibid. Woolf Harry (op. cit., 10–11) states that Gassendi admitted the light into the room through a small opening in the window. This is false. Gassendi wrote: “… I set up for myself the same [apparatus] under a dark roof which I use for observing both spots and eclipses of the Sun. The white circle, when I caught the Sun's rays on this side of the telescope, had a diameter of two-thirds of a Paris foot.” Besides the fact that Gassendi specifically mentions the use of a telescope, it is inconceivable that Gassendi could have obtained an eight-inch diameter image of the Sun in the space of a room, using a simple camera obscura.

Ibid.

Ibid.

Admonitio, 12.

Gassendi , op. cit., 500.

Ibid., 500–1.

Ibid., 501.

Ibid., 501.

Ibid., 502.

Nicholas Claude Fabri de Peiresc to Gassendi, 22 December 1631, published in Humbert P. , “A propos du passage de Mercure 1631”, Revue d'histoire des sciences et de leurs applications, iii (1950), 27–31, p. 31.

W. Schickardi pars responsi ad epistolas P. Gassendi insignis philosophi Galli de Mercurio sub Sole viso, & alijs novitatibus uranicis (Tuebingen, 1632), 4.

Ibid., 9.

Ibid., 11–14.

Ibid., 14.

Martini Hortensi Delfensis dissertatio de Mercurio in Sole viso et Venere invisa (Leiden, 1633), 5–6.

Ibid., 7.

Ibid., 7–9.

Ibid., 23–29.

In his letter to Galileo of 26 January 1637, Hortensius complained that in the Netherlands one could not buy telescopes which would show Jupiter and the Medicean stars clearly (Opere, xvii, 19).

Hortensius , Dissertatio, 51–52.

Ibid., 53.

Ibid., 55–60, 61.

Gassendi to Hortensius, 16 August 1633; Galileo, Opere, xviii, 431–2.

Galileo , Opere, vii, 387–9.

Humbert P. , L'oeuvre astronomique de Gassendi (Paris, 1936), 21.

Gassendi , Institutio astronomica (Paris, 1647) in Opera omnia, iv, 39, 61. See also the second edition (London, 1653), 107, 165.

Riccioli , op. cit., i, 708. Except in the case of Venus whose apparent diameter at perigee was given by Riccioli as 4'8”. Hortensius's values were also reported by Pierre Hérigone in his Cursus mathematicus (2nd edn, 6 vols, Paris, 1644), iv, 62; v, 619.