BEING LOCKED UP in the Tower of London had changed Henry Oldenburg's priorities all around. Daniel had expected that the Secretary of the Royal Society would jump headfirst into the great sack of foreign mail that Daniel had brought him, but all he cared about was the new lute-strings. He'd grown too fat to move around very effectively and so Daniel fetched necessaries from various parts of the half-moon-shaped room: Oldenburg's lute, extra candles, a tuning-fork, some sheet-music, more wood on the fire. Oldenburg turned the lute over across his knees like a naughty boy for spanking, and tied a piece of gut or two around the instrument's neck to serve as frets (the old ones being worn through), then replaced a couple of broken strings. Half an hour of tuning ensued (the new strings kept stretching) and then, finally, Oldenburg got what he really ached for: he and Daniel, sitting face to face in the middle of the room, sang a two-part song, the parts cleverly written so that their voices occasionally joined in chords that resonated sweetly: the curving wall of the cell acting like the mirror of Newton's telescope to reflect the sound back to them. After a few verses, Daniel had his part memorized, and so when he sang the chorus he sat up straight and raised his chin and sang loudly at those walls, and read the graffiti cut into the stone by prisoners of centuries past. Not your vulgar Newgate Prison graffiti – most of it was in Latin, big and solemn as gravestones, and there were astrological diagrams and runic incantations graven by imprisoned sorcerers.