<P> In Book VII of his De Architectura, the Roman engineer and architect Vitruvius contends that gravity is not dependent on a substance's "weight" but rather on its "nature" (cf . specific gravity). </P> <P> If the quicksilver is poured into a vessel, and a stone weighing one hundred pounds is laid upon it, the stone swims on the surface, and cannot depress the liquid, nor break through, nor separate it . If we remove the hundred pound weight, and put on a scruple of gold, it will not swim, but will sink to the bottom of its own accord . Hence, it is undeniable that the gravity of a substance depends not on the amount of its weight, but on its nature . </P> <P> Aryabhata first identified the force to explain why objects do not fall when the Earth rotates, and developed a geocentric solar system of gravitation, with an eccentric elliptical model of the planets, where the planets spin on their axes and follow elliptical orbits, the Sun and the Moon revolving around the Earth in epicycles . Indian astronomer and mathematician Brahmagupta described gravity as an attractive force and used the term "gurutvākarṣaṇ" for gravity . </P> <P> Al Hamdānī and Al Biruni quote Brahmagupta saying </P>

Who was the first person who discovered gravitational pull