It is known from his notebooks that Newton was grappling in the late 1660s with the idea that terrestrial gravity extends, in an inverse square proportion, to the Moon, however it took him two decades to develop the full fledged theory. The question was not whether gravity existed, but whether it extended so far from Earth that it could also be the force holding the Moon to its orbit. Newton showed that if the force decreased as the inverse square of the distance, one could indeed calculate the Moons orbital period, and get good agreement. He guessed the same force was responsible for other orbital motions, and hence named it universal gravitation.Various trees are claimed to be the apple tree which Newton describes. The Kings School, Grantham, claims that the tree was purchased by the school, uprooted and transported to the headmasters garden some years later. The staff of the [now] National Trust owned Woolsthorpe Manor dispute this, and claim that a tree present in their gardens is the one described by Newton. A descendant of the original tree can be seen growing outside the main gate of Trinity College, Cambridge, below the room Newton lived in when he studied there. The National Fruit Collection at Brogdale can supply grafts from their tree, which appears identical to Flower of Kent, a coarse fleshed cooking variety.