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HISTORICAL VIEW OF THE

In the theory of the moon, some important discoverieswere also made by this indefatigable and skilful ob-server. Two inequalities we have noticed as known toI’tolemy. Tycho discovered a third, called the “ Va-riation.” He also showed that there is a small period-ical change in the inclination of the moon’s orbit: andagain, that a periodical change takes place in the motionof its nodes.

Tycho argued ably, from observations on the cometof 1577, against the received Aristotelian doctrine,that comets are only meteors formed in our atmosphere.He determined the horizontal parallax of the comet inquestion, which was such as to prove that it movedbeyond the orbit of the moon. It hence followed thatthe celestial spaces could not be occupied by solid crys-talline spheres. He was violently attacked on this pointby the adherents of the school doctrine ; and his adver-saries completely exposed the weakness of their causeby having recourse to invective, and even personalcalumny. The real nature of the cometary motions,however, remained undiscovered ; though both Tychoand Msestlin proposed theories involving epicycles.

The objections which Tycho unhappily entertainedagainst the Copernican system were built partly onphysical and partly on theological grounds. He, how-ever, speaks of Copernicus in the highest terms ofadmiration ; and even joins in the refutation of theobjections urged against the diurnal motion of theearth by Ptolemy . The argument by which he himselfwas satisfied of the fallacy of the diurnal rotation wasthis ; that if a stone be suffered to fall from the top of ahigh tower, it ought to reach the ground far behind thefoot of the tower, which it does not. To this Rothmannreplied, that a stone is a part of the whole mass, andtherefore partakes in the earth’s motion.

Against the earth’s annual motion, Tycho urged theold and thrice refuted objection of parallax ; for thecomplete answer to which he might have been referredback to Aristarchus . Another argument was derived