[Footnote 2: Life of Galileo, Library of Useful Knowledge, p. 1.] [Footnote 3: De Insidentibus in Fluido.] [Footnote 4: Opere di Galileo. Milano, 1810, vol. IV. p. 248.] [Footnote 5: Life of Galileo, in Library of Useful Knowledge, p. 9.] [Footnote 6: Systema Cosmicum, Dial. II. p. 121.] [Footnote 7: The authenticity of this work has been doubted. It was printed at Rome, in 1656, from a MS. in the library of Somasohi, at Venice. See Opere di Galileo, tom. VII. p. 427.] [Footnote 8: Incredibili animi jucunditate.--_Sid._] [Footnote 9: Nescio quo fato ductus.] [Footnote 10: Berlin Ephemeris, 1788.] [Footnote 11: Edin. Phil. Journ. vol. VI. p. 313.] [Footnote 12: Life and Correspondence of Dr. Bradley. Oxford, 1832, p. 523.] [Footnote 13: See page 22.] [Footnote 14: Edin. Phil. Journ. 1822, vol. VI. p. 317.] [Footnote 15: Joh. Fabricii Phrysii de Maculis in Sole observatis, et apparente earum cum Sole conversione, Narratio. Wittemb. 1611.] [Footnote 16: It does not appear from the history of solar observations, at what time, and by whom, coloured glasses were first introduced for permitting the eye to look at the sun with impunity. Fabricius was obviously quite ignorant of the use of coloured glasses. He observed the sun when he was in the horizon, and when his brilliancy was impaired by the interposition of thin clouds and floating vapours; and he advises those who may repeat his observations, to admit at first to the eye a small portion of the sun's light, till it is gradually accustomed to its full splendour. When the sun's altitude became considerable, Fabricius gave up his observations; which he often continued so long, that he was scarcely able, for two days together, to see objects with their usual distinctness. Scheiner, in his "Apelles post Tabulanti," describes four different ways of viewing the spots: one of which is by the _interposition of blue or green glasses._ His first method was to observe the sun near the horizon; the second was to view him through a transparent cloud; the third was to look at him through his telescope with a blue or a green glass of a proper thickness, and plane on both sides, or to use a thin blue glass when the sun was covered with a thin vapour or cloud; and the fourth method was to begin and observe the sun at his margin, till the eye gradually reached the middle of his disc.] [Footnote 17: See Istoria e Demostrazioni, intorna alle macchie solari. _Roma_, 1613. See Opere di Galileo, vol. V. p. 131-293.] [Footnote 18: Discorso intorno alle cose che stanno in sa l'acqua, o che in quella si muovono. Opere di Galileo, vol. II. pp. 165-311.] [Footnote 19: Opere di Galileo, vol. II. pp. 355-367.] [Footnote 20: Ibid. 367-390.] [Footnote 21: These three treatises occupy the whole of the third volume of the Opere di Galileo.] [Footnote 22: It is said that Galileo was cited to appear at Rome on this occasion; and the opinion is not without foundation.]