On the Origin of Horrocks's Lunar Theory

Horrocks Jeremiah , Opera posthuma (London, 1672), 465–8.

Horrocks Jeremiah , Opera posthuma (London, 1673), 467–72.

Ibid., 336, letter of 12 December 1640: “…in mea Lunae Theoria (quam aestimo ut inventorum meorum quae hactenus assecutus sum potissimum)”.

See Whiteside D. T. , “Newton's lunar theory: From high hope to disenchantment”, Vistas in astronomy, xix (1977), 317–28.

See Mémoires de Berlin, xix (1763), 184–5. Euler gives an early account of the method of varying orbital parameters in an “additamentum” to his Theoria motus lunae of 1752 (Leonhard Euler, Opera omnia, series 2, xxiii, 283ff).

Small Robert , An account of the astronomical discoveries of Kepler (London, 1804), 307.

Horrocks , Opera posthuma (1673 edn), 336.

Gaythorpe S. B. , “Jeremiah Horrocks and his ‘New theory of the Moon’”, Journal of the British Astronomical Association, lxvii (1957), 134–44, p. 135.

Kepler Johannes , Gesammelte Werke (hereinafter KGW), x, 170.

Boulliau Ismael , Astronomia Philolaica (Paris, 1645), 156–7.

Kepler , KGW, xi/1, Nachbericht by Volker Bialas, 520–34.

See Whiteside , op. cit. (ref. 4), 318.

See Kepler , KGW, x, 181, lines 8–11.

The ellipse of Figure 1 can be shown to be produced by the motion of the point C on the small circle BCE of Figure 4, which represents Horrocks's theory.

Kepler , KGW, vii, 350–1.

van Lansberge Philippe , Theoricae motuum caelestium novae (Middelburg, 1632), 5.

Horrocks , Opera posthuma (1673 edn), 249, 251. The library of Trinity College, Cambridge has the copy of Lansberge's Tabulae motuum perpetuae, along with the accompanying Theorica, that was once possessed by Jeremiah Horrocks (the shelf number is T.5.116). The volume contains many pencilled notes in connection with the observations of eclipses that Lansberge reports. At p. 103 of the Theorica Horrocks has written: “Assumitur hic, eadem esse semidiametrum umbrae veram, tam in Apogaeo quam in Perigaeo: Quod falsum est: Quia figura umbrae est conica.” This is one of the Lansbergian errors of which Horrocks complains in his letter to Crabtree of 11 August 1636 (Opera posthuma (1673 edn), 249). As we shall see, prediction of the duration of lunar eclipses as it depends on the semidiameter of the Earth's shadow and on the Moon's distance from the Earth will play an important role in Horrocks's final reformulation of the lunar theory.

Horrocks , Opera posthuma (1673 edn), 260.

Ibid., 262.

Ibid., 287.

Ibid., 287–8.

Ibid., 290.

Ibid., 292.

Ibid., 291–4.

Ibid., 301.

Ibid., 315ff.

Ibid., 316.

Horrocks , Opera posthuma (1672 edn), 465.

Ibid., 466.

Ibid., 465.

Horrocks , Philosophicall exercises, Royal Greenwich Observatory, Flamsteed MSS, lxviii, fol. 83r.

Ibid., fol. 83v.

See for example Horrocks's letter to Crabtree of 29 April 1637, in his Opera posthuma (1673 edn), 277–8.

Horrocks , Philosophicall exercises, Part I, paragraphs 9–10, fols 56v-57v.

See Horrocks , Opera posthuma (1673 edn), 312–14; Philosophicall exercises, Part I, paragraphs 14–25, fols 60r-71v.

Horrocks , Philosophicall exercises, Part I, paragraph 26, fols 71v-73v.

Flamsteed supposes that Horrocks has here returned, if doubtingly, to the magnetic notions of Kepler, and goes on to offer an explanation of his own, hardly more plausible, at p. 495 of Horrocks's Opera posthuma (1673 edn).