On the Heavens is Aristotle's chief cosmological treatise. In it Aristotle argues that the Earth is a sphere by pointing to the evidence of lunar eclipses. Aristotle also provides a detailed explanation of his theory of 'gravity' arguing that things which contain 'earth' fall towards the centre of the Universe because 'earth' is naturally attracted to the centre of the Universe. Aristotle argues that if the planet Earth was moved to the location of the Moon then objects which contain 'eart...