as there was that difference between the polar distances above and below the pole; but his instruments had at that time not reached the degree of accuracy which they did ten years later, and the difference is not surprising. Peucer and Wolfgang Schuler at Wittenberg found a parallax of 19′, which Tycho believed was a consequence of their having used an old wooden quadrant; and, in fact, when he learned that the Landgrave had found little or no parallax, Schuler had a large triquetrum constructed, and also found that the star had no parallax, or at most a very small one.[1] Many observers measured the distance of the new star from the neighbouring ones, but the results found were generally considerably in error. Thus the Bohemian, Thaddæus Hagecius, physician to the Emperor, in an otherwise sensible book,[2] gives a number of observed distances, some of which are 7′ to 12′ (one is even 16′) wrong, and even the English mathematician, Thomas Diggs (or Digges), who had made a special study of the cross staff, and had his instrument furnished with transversal divisions, differed 112′ to 4′ from Tycho,—possibly, as the latter thinks, because he did not allow sufficiently for the error of excentricity.[3] Cornelius Gemma, a son of the well-known astronomer, Gemma Frisius, and professor of medicine at Louvain, had a great
- ↑ The triquetrum had been much in use from the time of Ptolemy. It consisted of two arms of equal length and movable round a hinge, while a third and carefully graduated arm gave the means of measuring the angle between the two former by the aid of a table of chords.
- ↑ "Dialexis de novæ et prius incognitæ Stellæ invsitatæ Magnitudinis et splendissimi Luminis Apparitione et de eiusdem Stellæ vero loco constituendo. Per Thaddæum Hagecium ab Hayck." Francofurti, a. M. 1574. 176 pp. 4to. In an appendix are two papers on the star by Paul Fabricius and Corn. Gemma. Some years after Hagecius sent Tycho a copy with many MS. corrections and additions, which Tycho quotes extensively in his Progymnasmata (p. 505 et seq.). In this corrected copy the most erroneous measures had been improved or struck out, whereby the greatest differences from Tycho's results were reduced to 4′ or 6′.
- ↑ "Alæ seu Scalæ Mathematicæ, quibus visibilium remotissima Cœlorum Theatra conscendi, et Planetarum omnia itinera novis et inauditis methodis explorari . . . Thoma Diggeseo authore." Londini, 1573. 4to.
