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Rh in the beginning of November, and then rapidly to have decreased; and, as an excuse for this considerable quantity not having been detected, he adds his belief that refraction would counteract the parallax near the horizon where the comet was observed.

The remainder of Tycho's book is devoted to a detailed examination of the writings and observations of other astronomers on the comet. This was the first comet which gave rise to a perfect deluge of pamphlets, in which the supposed significance of the terrible hairy star was set forth, and for more than a century afterwards every comet was followed by a flood of effusions from numberless scribblers. The astrological significance of the comet Tycho does not trouble himself about, though he takes the opportunity of stating that he does not consider astrology a delusive science, when it is kept within bounds and not abused by ignorant people. For the sun, moon, and fixed stars would have sufficed for dividing time and adorning the heavens, and the planets must have been created for some purpose, which is that of forecasting the future. But he goes through the observations or speculations of eighteen of his contemporaries, taking first those who had acknowledged the comet to be beyond the lunar orbit (Wilhelm IV., Moestlin, Cornelius Gemma, and Helisæus Roeslin), and afterwards the great herd of those who believed it to move in the "elementary world." Among these there are no generally known names except those of Hagecius and Scultetus. A theory very like that of Tycho was proposed by Moestlin, who also let the comet move in a circle round the sun outside the orbit of Venus, and accounted for the irregular motion by a small circle of libration perpendicular to the plane of the orbit, along the diameter of which the comet moved to and fro. This idea was borrowed from