Newton, by calculating from Kepler's laws, and supposing the orbits of the planets to be circles with the sun at the centre, had already proved that the force of the Sun acting upon the different planets must vary as the inverse square of the distances of the planets from the Sun. He was therefore led to inquire whether if the Earth's attraction extended to the Moon, the force at that distance would be of the exact magnitude necessary to retain the Moon in its orbit. He found that the Moon by its motion in its orbit was deflected from the tangent in every minute through a space of 13 feet (3.96 m). But by observing the distance through which a body would fall in one second at the Earth's surface, and by calculating from that on the supposition of the force diminishing in the ratio of the inverse square of the distance, he found that the Earth's attraction at the distance of the moon would draw a body through 15 ft. (4.57 metres) in one minute. Newton regarded the discrepancy between the results as proof of the inaccuracy of his conjecture, and "laid aside at that time any further thoughts of this matter". (See Newton's cannonball.)