Newton, in a letter to Hooke in 1679, proposed an experiment to demonstrate the rotation of the Earth. He reasoned that a body dropped from the top of a tower would fall to the east as the tangential velocity of the top of the tower, due to the Earth's rotation, is greater than that of the ground. Newton claimed that this deflection could be measured and included a sketch purporting to show the path of the body above the ground and also the trajectory it would follow if it were to continue to fall without resistance into the Earth. The path he drew was a spiral (fig 81) ending at the Earth's centre This spiral orbit was a rare mistake on Newton's part and he was deeply chagrined when Hooke corrected him ( R Westfall, Never at Rest).