style=\"text-decoration:none\" height=\"23px\" valign=\"middle\" face=\"arial\"

1. Rebuttals to theobjections raised by traditional philosophers; for example, the thoughtexperiment on the ship.

2. Observationsthat are incompatible with the Ptolemaic model: thephases of Venus, for instance, which simply couldn’t happen, or theapparent motions of sunspots, which could only be explained in thePtolemaic or Tychonic systems as resulting from an implausibly complicatedprecession of the Sun’s axis of rotation.

3. Argumentsshowing that the elegant unified theory of the Heavens that thephilosophers held, which was believed to prove thatthe Earth was stationary, was incorrect; for instance, themountains of the Moon, the moons of Jupiter, and the very existence of sunspots,none of which was part of the old astronomy (though these are of somewhatdoubtful relevance, as none of these phenomena dealt directly with the questionof the motion of the earth or sun).

4. Direct physicalargument for the Earth’s motion, by means of an explanation oftides.