HE WISHED H OOKE WERE HERE. A Natural Philosopher could not but be enthralled by all that was laid out for view by such a rare low tide. The sun had sunk low in the west and, behind London’s dome of smoke, shone the color of a horseshoe when the farrier beats it out on the anvil. That light was skidding across the tidal flats all round, making them seem not so flat at all. The surface of the muck was rippled, as if it were a pond that had been disturbed by a chill wind, then frozen. But more remarkable to Daniel was the shape of Foulness Sand, a few miles to the north, across the mouth of the Thames. This country of muck, larger than some German principalities, lay concealed beneath the water most of the time. It was devoid of any features such as rocks or vegetation. Yet when the tide drew off, the great quantity of water that had been stranded in the dells of all those frozen ripples drained away, not as a streaming sheet, and not by quiet seepage into the earth, but by finding its way to the low places. One hand-sized puddle would erupt in upon its neighbor, and those two would join forces and go looking for a nearby place that lay a hair’s breadth lower, even as every other dollop of water for miles around was pursuing a like strategy. The result, integrated (to use Leibniz’s terminology) over the whole of Foulness Sand, was that entire systems of rivers and tributaries sprang into being. Some of those rivers looked as old as the Thames, and big enough to build cities on; yet in a few hours they’d disappear. Existing in a state of pure alienation, unsoftened by reeds or willows, and not encrusted by the buildings of men, they were pure geometry. Albeit geometry of an irregular and organic cast, repugnant to Euclid or, Daniel suspected, to the silver-haired knight who was standing next to him. But Hooke would have seen beauty and found fascination there, and wrought pictures of it, as he had done with flies and fleas.