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.) In November 1679, Robert Hooke (after his appointment to manage the Royal Society's correspondence) began an exchange of letters with Newton: he wished to hear from members about their researches, or their views about the researches of others. The correspondence later led to controversy. Hooke and Newton disagreed about the form of the path of a body falling from a height, taking the motion of the Earth around its axis into consideration. Newton later acknowledged that the exchanges of 1679-80 had reawakened his dormant interest in astronomy. This led Newton to revert to his former conjectures on the Moon. The estimate Newton had used for the radius of the Earth, which had been accepted by geographers and navigators, was based on the very rough estimate that the length of a degree of latitude of the Earth's surface measured along a meridian was 60 nautical miles. At a meeting of the Royal Society on 11 January 1672, Oldenburg, the secretary, read a letter from Paris describing the procedure followed by Jean Picard in measuring a degree, and specifically stating the precise length that he calculated it to be. It is probable that Newton had become acquainted with this measurement of Picard's, and that he was therefore led to make use of it when his thoughts were redirected to the subject. This estimate of the Earth's magnitude, giving 691 miles (1112 km) to 10°, made the two results, the discrepancy between which Newton had regarded as a disproof of his conjecture, to agree so exactly that he now regarded his conjecture as fully established. In January 1684, Sir Christopher Wren, Halley and Hooke were led to discuss the law of gravity, and although they probably all agreed on the truth of the inverse square law, yet this truth was not looked upon as established. It appears that Hooke professed to have a solution of the problem of the path of a body moving around a centre of force attracting as the inverse square of the distance, but Halley declared after a delay of some months that Hooke "had not been so good as his word" in showing his