....for which the words of Arthur Cayley in 1883 are still a beautifully apt description:"It is difficult to give an idea of the vast extent of modern mathematics. The word 'extent' is not the right one: I mean extent crowded with beautiful detail - not an extent of mere uniformity such as an objectless plain, but a tract of beautiful country to be rambled through and studied in every detail of hillside and valley, stream, rock, wood, and flower. But, as for everything else, so for mathematical beauty - beauty can be perceived but not explained."

quoted in The Universal History of Numbers II, The Modern Number-System, Georges Ifrah