The orbital period we know-it is the lunar month, corrected for the motion of the Earth around the Sun, which also affects the length of time between one 'new moon' and the next. If it was the same force, then a connection would exist between the way objects fell and the motion of the Moon around Earth, that is, its distance and orbital period. ( Keesing, R.G., The History of Newton's apple tree, Contemporary Physics, 39, 377-91, 1998) Why not as high as the Moon thought he to himself & that if so, that must influence her motion & perhaps retain her in her orbit, whereupon he fell a-calculating what would be the effect of that superposition. to his mother in Lincolnshire & while he was musing in a garden it came into his thought that the power of gravity (which brought an apple from a tree to the ground) was not limited to a certain distance from earth, but that this power must extend much further than was usually thought. In the year 1666 he retired again from Cambridge. John Conduitt, Newton's assistant at the royal mint and husband of Newton's niece, had this to say about the event when he wrote about Newton's life: Supposedly, the above question occured to Newton when he saw an apple falling from a tree. Was that the same force which pulled all falling objects downward? To keep the Moon moving in that circle-rather than wandering off-the Earth must exert a pull on the Moon, and Newton named that pulling force gravity. Since its size does not appear to change, its distance stays about the same, and hence its orbit must be close to a circle. (20) Newton's theory of 'Universal Gravitation' Index

Isaac newton gravity