"Newton was a decidedly odd figure--brilliant beyond measure, but solitary, joyless, prickly to the point of paranoia, famously distracted (upon swinging his feet out of bed in the morning he would reportedly sometimes sit for hours, immobilized by the sudden rush of thoughts to his head), and capable of the most riveting strangeness. He built his own laboratory, the first at Cambridge, but then engaged in the most bizarre experiments. Once he inserted a bodkin--a long needle of the sort used for sewing leather--into his eye socket and rubbed it around 'betwixt my eye and the bone near to the backside of my eye as I could' just to see what would happen. What happened, miraculously, was nothing--at least nothing lasting. On another occasion, he stared at the sun for as long as he could bear, to determine what effect it would have upon his vision. Again he escaped lasting damage, though he had to spend some days in a darkened room before his eyes forgave him.
"Set atop these ... quirky traits, however, was the mind of a supreme genius. ... [As recounted by] Newton confidant, Abraham DeMoivre, 'In 1684 Dr. Edmond Halley [of Halley's comet fame] came to visit at Cambridge and after they had some time together the Doctor asked [Newton] what he thought the curve would be that would be described by the planets supposing the force of attraction toward the sun to be reciprocal to the square of their distance from it.' This was a reference to a piece of mathematics known as the inverse square law, which Halley was convinced lay at the heart of the explanation, though he wasn't sure exactly how. 'Sir Isaac replied immediately that it would be an ellipse. The Doctor, struck with joy and amazement, asked him how he knew it. 'Why,' saith he, 'I have calculated it,' whereupon Dr. Halley asked him for his calculation without further delay, Sir Isaac looked among his papers but could not find it.'
"This was astounding--like someone saying that he had found a cure for cancer but couldn't remember where he had put the formula. Pressed by Halley, Newton agreed to redo the calculations and produce a paper. He did as promised, but then did much more. He retired for two years of intensive reflection and scribbling, and at length produced his masterwork: the Philosophiae Naturalis Principia Mathematica or Mathematical Principles of Natural Philosophy, better known as the Principia."
Bill Bryson, A Short History of Nearly Everything, Broadway Books, Copyright 2003 by Bill Bryson, pp. 46-48.