Page:Tycho brahe.djvu/159

Rh anxious to learn what observations Tycho had made of the comet of 1585, as it was not a very conspicuous one, and probably would not be observed by many astronomers. With this view the Landgrave wrote a letter to the learned Heinrich Rantzov, governor of Holstein, asking that his compliments might be sent to Tycho, with a hint that he would be glad to hear something of the observations of this comet made at Hveen. Tycho was very happy to renew his acquaintance with the Landgrave, to whom he wrote a long letter on the 1st of March 1586, in which he enclosed an abstract of his observations of the comet. In the letter he suggested an exchange of observations of the star of 1572 and of the recent comets, claimed the instrumental improvements already announced to the Landgrave as his own, and gave an account of various instruments he had designed, such as a bifurcated sextant, to be used by two observers, and the equatorial armillæ. He pointed out the great convenience of the latter instrument, which directly gave the right ascension and declination of an object, from which the longitude and latitude could be found either by calculation, or by a specially prepared table, or by a large globe. Tycho also sent the Landgrave a solar ephemeris for the current year, and asked him to compare his observations with it. This letter and its appendices were sent to Cassel by Tycho's assistant, Flemlöse, who was bound for the book-mart at Frankfurt, and could take Cassel on his way, where Tycho doubtless also wished him carefully to inspect the improved instruments.

To this letter the Landgrave at once replied, and Rothmann also took the opportunity of entering into correspondence with Tycho. During the next six years letters