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Rh are worthless compared with Tycho's. The next comet was visible in May 1582, and was observed by Tycho on three nights only, the 12th, 17th, and 18th, after which date the strong twilight prevented further observations; but in Germany it was still seen on the 23rd, and in China it was seen for twenty days after the 20th May. Of greater interest are the observations of the comet of 1585, which appeared at a time when Tycho's collection of instruments was complete, and when he was surrounded by a staff of assistants. The comet was first seen by Tycho on the 18th October after a week of cloudy weather, but at Cassel it had already been seen on the 8th (st. v.). Tycho compares its appearance when it was first seen with the cluster (or nebula, as it was then called) Præsepe Cancri, without any tail. The observations are very numerous, and were made partly with a sextant, partly with the large armillæ at Stjerneborg, with which newly-acquired instrument the declinations of the comet and the difference of right ascension with various bright stars were observed at short intervals on every clear night up to the 12th November. The excellence of the observations and the care with which the instruments were treated are fully demonstrated by the most valuable memoir on this comet by C. A. F. Peters. We have already mentioned that this comet gave rise to the correspondence between Tycho and the Landgrave and Rothmann. The next comet appeared in 1590,