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192 a distance of about 14,000, and the new star at least at 13,000 semidiameters. The apparent diameter of the new star at its first appearance he estimated at 3$1⁄2$′, and its real diameter must therefore have been 7$1⁄8$ times that of the earth, or somewhat greater than that of the sun. He does not think that the diminution of light was caused by the star having moved away from us in a straight line, partly because no celestial body moves in a straight line, partly because it would, when about to disappear, have been at the incredible distance of 300,000 semidiameters of the earth. The star must actually have decreased in size, so that it at the end of the year 1573 was about equal to the earth in size.

This finishes what Tycho has himself found by observation and speculation concerning the star of Cassiopea, and he next devotes the third part of his book, 300 pages, to an examination of the writings of other astronomers or authors about the star. First he discusses in Chapter VIII. the observations of those who could not find any parallax (the last book considered being his own little book of 1573, of which he reprints the greater part, omitting the astrological predictions); next he deals in Chapter IX. with those authors who thought they had found some parallax, but who did not place the star within the lunar orbit; and lastly, he deals with the writers "who have not brought out anything solid or important, and either maintained that the star was not new or that it was a comet or a sublunary meteor." His remarks are often written in a sarcastic style, with puns or play upon words, by which he perhaps meant to relieve the dulness of this far too lengthy part of the book. We have above, in our third chapter, given the reader some idea of these various classes of writers, and need not, therefore, here enter into further details about these chapters of Tycho's book.