"He made up a pack of cards and wrote an element and its atomic weight on each... So began the most memorable card game in the history of science. He called it "chemical solitaire" and began laying out the cards... to see if there was a pattern... [P]reviously chemists had grouped the elements in one of two ways, either by their properties... or by... their atomic weight, which is what Berzelius and Cannizzaro had done. Mendeleev's great genius was to combine those two methods together. ...Little more than half the elements ...had been discovered, so he was playing with an incomplete deck of cards. He stayed up for three days and three nights without... sleep... finally dozed off... [and] had an extraordinary dream. He saw almost all of the 63 known elements... in a grand table which related them together."