John Conduitt writes:
Mr Machin told me that telling Sir I. once that he admired very much his fine problems in Geometry, but infinitely more his Theory of the Moon for which he had no rule that was all sagacity – Sir I. smiled & said his head never ached but with his studies on the moon —
Halley told me he often pressed Sir I. to compleat his Theory of the Moon saying no body else euer could, Sir I. told him it had made his head ach & kept him awake so often that he would think of it no more, but Sir I. said afterwards to me that if he lived till Halley had made six years observations he would haue t'other stroke at it.
From "Drafts of portions of John Conduitt's intended Life of Newton", [The Newton Project] (http://www.newtonproject.sussex.ac.uk/view/texts/normalized/THEM00169), accessed 20110901.
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