this would be admissible if (as Gellius had told him) Tycho had found Mars in opposition to be nearer than the sun. He begged Tycho particularly to observe Mars, as he suspected its excentricity to be variable and periodical, so that an equation to this effect should be introduced in the theory.[1] In reply, Tycho remarked that he had found this well-known difficulty not only in the theory of Mars, but in a lesser degree also in the theories of the other planets, and he wanted to observe the oppositions of Mars all round the zodiac. He also gave a short account of the reasons why he found it necessary to devise a new system. He would have sent Magini a copy of his star-catalogue, but the distance was so great, and the difficulties of transit so considerable, that it might fall into wrong hands and somebody might publish it as his own.[2] In conclusion, Tycho remarks that he had read in Magini's Tabulæ Secundi Mobilis that geographical latitudes, since the days of Ptolemy, had increased more than a degree, but he does not believe it, as the latitude of Rome, according to Pliny, was 41° 54′, while Regiomontanus found 42° 7′ and 42° 0′; likewise Pliny says that at Venice the gnomon and its shadow were of equal length at the time of equinox, which gives the latitude 45° 16′, agreeing to the minute with Pitati's result; also Pliny gave 44° 10′ for Ancona, which was more than the modern value, 43° 20′, instead of less, as had been imagined.[3]
Gellius spent about two years at Padua, where he was matriculated at the University in October 1589. In 1591 Magini had a sextant made from his description, and
- ↑ This letter is printed in Tycho's Astr. inst. Mechanica, fol. H., reprinted in Carteggio, p. 392.
- ↑ In February 1591 Gellius wrote to Magini that Tycho had determined the places of 500 stars to within a minute of arc. Carteggio, p. 2O2.
- ↑ Carteggio, p. 403. It was Domenico Maria Novara (whose lectures Copernicus had attended) who had suggested that the latitudes had increased.
