Page:Tycho brahe.djvu/369

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SCIENTIFIC ACHIEVEMENTS.

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an equation of 1° 14′ 45″ (evection), not differing much from Ptolemy's values, though somewhat more accurate.^[1]

So far Tycho had not made much advance, but the discovery of the third and fourth inequalities was a very great step in advance. He probably thought that there were epicycles enough in his theory, and therefore he did not attempt to account for the variation by adding another. He merely let the centre of the first epicycle oscillate (librate) backwards and forwards on the deferent to the extent of 40′.5 on each side of its mean position, the latter moving along the deferent with the moon's mean motion in anomaly, and the centre of the epicycle being in its mean position at the syzygies and quadratures, and farthest from it at the octants, the period of a complete libration being half a synodical revelation.^[2] At the same time Tycho's observations showed

↑ We have mentioned (p. 272) that Tycho had got part of the appendix on the lunar theory printed at Hamburg, but did not make use of the sheets thus printed, giving as reason that the printer had done his work badly. Tengnagel had given a copy to Magini, who in 1600 pointed out some discrepancies, the two first inequalities being stated to amount at most to 7° 41′ 15″, while the dimensions of the circles, so far as Magini could make out, gave 11′ or 14′ less. Tycho replied that the whole had been recast, partly at Wittenberg, partly in Bohemia, and that new tables had been calculated (Carteggio, pp. 232 and 238). In his Astronomia Danica, 2nd edit., Amstel., 1640, p. 242, Longomontanus talks of the lunar hypothesis described above as one "quam anno Salvatoris nostri 1600 apud Nobilissimum et omnium præstantissimum astronomum Dn. Tychonem Brahe invenimus."
↑ I shall not here enter into a discussion of the well-nigh thrashed out question whether Abul Wefa's mohadzat is the lunar variation or not, but only point out the utter absurdity of the suggestion of L. A. Sédillot Matériaux, i. p. 216) that Tycho might possibly have seen a translation of the Almegist from the Arabian, in which some abstract from Abul Wefa's book might have been given. If so, why has nobody else known this book until the present century? Tycho's discovery was not, as Sédillot believed, found among his papers and published by Kepler in 1610; it is distinctly announced in his Mechanica (fol. G. 2 verso), published in 1598, as a new inequality: "Nam & aliam quandam habet ea inæqualitatis insinuationem secundum Longitudinem, quam ab iis animadversum est." Kepler in many places mentions Tycho as the discoverer of the variation, and the insinuation that Tycho himself did not claim the discovery, but merely called his lunar theory "hypothesis redintegrata," is groundless, as Tycho used the same expression of his planetary system, which he most assuredly did claim as his own (e.g., in a letter to Mästlin, Kepleri Opera, i. p. 45).

[1] We have mentioned (p. 272) that Tycho had got part of the appendix on the lunar theory printed at Hamburg, but did not make use of the sheets thus printed, giving as reason that the printer had done his work badly. Tengnagel had given a copy to Magini, who in 1600 pointed out some discrepancies, the two first inequalities being stated to amount at most to 7° 41′ 15″, while the dimensions of the circles, so far as Magini could make out, gave 11′ or 14′ less. Tycho replied that the whole had been recast, partly at Wittenberg, partly in Bohemia, and that new tables had been calculated (Carteggio, pp. 232 and 238). In his Astronomia Danica, 2nd edit., Amstel., 1640, p. 242, Longomontanus talks of the lunar hypothesis described above as one "quam anno Salvatoris nostri 1600 apud Nobilissimum et omnium præstantissimum astronomum Dn. Tychonem Brahe invenimus."

[2] I shall not here enter into a discussion of the well-nigh thrashed out question whether Abul Wefa's mohadzat is the lunar variation or not, but only point out the utter absurdity of the suggestion of L. A. Sédillot Matériaux, i. p. 216) that Tycho might possibly have seen a translation of the Almegist from the Arabian, in which some abstract from Abul Wefa's book might have been given. If so, why has nobody else known this book until the present century? Tycho's discovery was not, as Sédillot believed, found among his papers and published by Kepler in 1610; it is distinctly announced in his Mechanica (fol. G. 2 verso), published in 1598, as a new inequality: "Nam & aliam quandam habet ea inæqualitatis insinuationem secundum Longitudinem, quam ab iis animadversum est." Kepler in many places mentions Tycho as the discoverer of the variation, and the insinuation that Tycho himself did not claim the discovery, but merely called his lunar theory "hypothesis redintegrata," is groundless, as Tycho used the same expression of his planetary system, which he most assuredly did claim as his own (e.g., in a letter to Mästlin, Kepleri Opera, i. p. 45).

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