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220 he refers to the calculation as not having been made accurately enough. It is probable that he used a seriously inaccurate value of the size of the earth, having overlooked the measurements of Snell and Norwood (chapter, § 159); it is known that even at a later stage he was unable

to deal satisfactorily with the difficulty above mentioned, as to whether the earth might for the purposes of the problem be identified with its centre; and he was of course aware that the moon's path differed considerably from a circle. The view, said to have been derived from Newton's conversation many years afterwards, that he was so dissatisfied with his results, as to regard his hypothesis as