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have not the same effects as violent ones; the lattertending to dissolution, the former, to conservation.This was at least talking to them in their own language :but he adds, much more reasonably, that if Ptolemy ’sargument be worth any thing, it ought to apply withmuch greater force against the motion of the celestialspheres, which must be so infinitely more rapid. Heputs in a very forcible manner the illustration of theapparent motion of bodies, when the real motion is un-perceived in ourselves, as in a ship ; and objects to theAristotelian notion of the earth’s centre being thecentre of gravity of the universe, representing gravityas nothing else than the tendency of parts to draw to-gether and coalesce in the form of a globe; andobserves, that it is probable that such a tendency existsin the sun and moon, and other heavenly bodies ; butthat this does not hinder them from describing their re-spective orbits. He then explains the solar system atlength, pointing out the way in which it simply andsatisfactorily accounts for all the apparent motions ofthe planets, especially their stationary points and retro-gradations, as seen from the earth, itself in motion.

The belief in the perfectly circular form of the celes-tial orbits was an essential point in the peripateticsystem. Copernicus in this particular does not appearto have been superior to his predecessors, but held it asa necessary truth; he therefore was obliged to adoptthe epicycles so far as to account for the obvious devia-tions of the orbits from perfect circles : this, however,occasioned a very slight complexity, compared with thatarising from their introduction to explain all the retro-gradations and apparent irregularities.

His system again was unnecessarily complicated, by afanciful hypothesis he made to explain the cause of theprecession of equinoxes: nor did he discard the tre-pidation.

With all these defects, however, the Copernicansystem will always be esteemed, as giving, at least in itsgeneral outline, a correct and elevated conception of thek 4