http://en.wikipedia.org/wiki/History_of_gravitational_theory wrote:
<<The Indian astronomer Brahmagupta, in his Brahmasphuta Siddhanta ("The Opening of the Universe"), recognized gravity as a force of attraction. Brahmagupta followed the heliocentric solar system of gravitation, earlier developed by Aryabhata in 499, and understood that there was a force of attraction between the Sun and the Earth. The 11th century Persian astronomer Abu al-Rayhan al-Biruni, in his Ta'rikh al-Hind, later translated into Latin as Indica, commented on their works and wrote that critics refuting Aryabhata's heliocentric system argued:
"People have tried to refute them by saying that, if such were the case, stones and trees would fall from the earth." —Al-Biruni (1030), Ta'rikh al-Hind (Indica)
According to Biruni, Brahmagupta responded to these criticisms with the following argument:
"On the contrary, if that were the case, the earth would not vie in keeping an even and uniform pace with the minutes of heaven, the pranas of the times." —Brahmagupta, in Al-Biruni (1030), Ta'rikh al-Hind (Indica)
The Sanskrit term Brahmagupta used for gravity, gruhtvaakarshan, had roughly the same meaning as "attraction".
Al-Biruni described the Earth's gravitation as:
"The attraction of all things towards the centre of the earth."
In the 11th century, Ibn al-Haytham (Alhacen), a contemporary of Biruni, discussed the theory of attraction between masses. In 1121, Al-Khazini, in The Book of the Balance of Wisdom, claimed that gravity varies with the distance from the centre of the Earth, though he believed that the weight of heavy bodies increased as they moved farther from the centre of the Earth:
"The weight of any heavy body, of known weight at a particular distance from the centre of the world, varies according to the variation of its distance therefrom; so that, as often as it is removed from the centre, it becomes heavier, and when brought nearer to it, is lighter. On this account, the relation of gravity to gravity is as the relation of distance to distance from the centre."
In the 12th century, Hibat Allah Abu'l-Barakat al-Baghdaadi who "tried to explain the acceleration of falling bodies by the accumulation of successive increments of power with successive increments of velocity." According to Shlomo Pines, his work "seems to anticipate in a vague way the fundamental law of classical mechanics, according to which a continually applied force produces acceleration." Later in the 14th century, Jean Buridan and Albert of Saxony refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus.
During the 17th century, Galileo found that, counter to Aristotle's teachings, all objects accelerated equally when falling.
In the late 17th century, as a result of Robert Hooke's suggestion that there is a gravitational force which depends on the inverse square of the distance, Isaac Newton was able to mathematically derive Kepler's three kinematic laws of planetary motion, including the elliptical orbits for the seven known planets:
"I deduced that the forces which keep the planets in their orbs must be reciprocally as the squares of their distances from the centres about which they revolve, and thereby compared the force requisite to keep the moon in her orb with the force of gravity at the surface of the earth and found them to answer pretty nearly." —Isaac Newton, 1666>>