_De Tonitruis ad Herefridum_, and _De Minutione Sanguinis sive Phlebotomia_. Many spurious treatises were attributed to Bede but there are some reasons for believing these genuine, although they are not named by Bede in the list of his writings which he gives in his _Ecclesiastical History_. Giles included them in his edition after some hesitation. Footnote 13: For the predominance of astrology in the mathematics of the 9th, 10th, 11th and 12th centuries, cf. _Histoire Littéraire_, vol. v, p. 183; vi, 9; vii, 137; ix, 197. Footnote 14: _De Naturis Rerum_, bk. ii, ch. 173, and bk. i, ch. 7. Volume xxxiv of _The Chronicles and Memorials of Great Britain_. (The Rolls Series.) Footnote 15: _Ibid._, bk. i, ch. 7. Footnote 16: _De Naturis Rerum_, bk. ii, ch. 63. Footnote 17: _Ibid._, bk. ii, ch. 80. Footnote 18: _Ibid._, bk. ii, ch. 3 _et seq._ Footnote 19: _Ibid._, bk. ii, ch. 88. In chapter 87 he writes: “Chelidonius autem rufus portantes se gratissimos facit; niger vero gestatus optimum finem negotiis imponit, et ad iras potentium sedandas idoneus est.” Footnote 20: _Ibid._, bk. ii, ch. 89. Footnote 21: _Ibid._, bk. ii, ch. 85. “In verbis et herbis et lapidibus multam esse virtutem compertum est a diligentibus naturarum investigatoribus. Certissimum autem experimentum fidem dicto nostro facit.” Footnote 22: Preface, p. xii in vol. xxxiv of the Rolls Series. Footnote 23: My information concerning Michael Scot is mainly derived from his biography (Edinburgh, 1897) by Rev. J. Wood Brown, who has studied the manuscript copies of Scot’s works in various European libraries and has succeeded in dispelling much of the uncertainty which previously existed concerning the events of Scot’s career and even the dates of his life. Of Scot’s works the _Physionomia_ exists in printed form; indeed, eighteen editions of it are said to have been issued between the years 1477 and 1660. Footnote 24: The poem is printed in _Forschungen zur Deutschen Geschichte_, vol. xviii, (1878) p. 486. Footnote 25: The part of the manuscript containing the experiment was written between 1450 and 1500, Brown thinks, but purports to be a copy “from a very ancient work.” If spurious, its fabricator at least shows considerable familiarity with Scot’s life. See Brown, pp. 18–19. The recipe is given in full in the appendix of Brown’s book. Footnote 26: _De Secretis Operibus Artis et Naturae et de Nullitate Magiae_, ch. 7. Contained in the Appendix of vol. xv of the Rolls Series, edited by J. S. Brewer, London, 1859. Footnote 27: _Opus Maius_, vol. ii, pp. 204–221. Edited by J. H. Bridges, Oxford, 1897–1900. On page 210 _et seq._ Bacon gives an elaborate recipe for an _elixir vitae_. Footnote 28: _Opus Minus_, Rolls Series, vol. xv, pp. 373–4. Footnote 29: Bridges, _Opus Maius_, vol. i, pp. 137–139. Footnote 30: