the sort of table Drake would’ve owned, and he was dressed in a long scarlet dressing-gown over a good linen shirt. His face had not changed all that much, though it had got heavier, and he still had the long white hair. But his hairline had jumped back, making it seem as if his brain were trying to force its way up out the top of his head. His skin had been white when Daniel had walked in, but by the time he had made it to the end of the room to proffer his hand, Isaac had gone red in the face, as if stealing the color from his robe.
“There is nothing in my life quite so irritating as to be riddled and teased with inane conundrums, meant to prove my wit, and to try my senility,” he answered. “Bernoulli—Leibniz’s pawn—sent me—”
“The brachistochrone problem, I recall it,” Daniel said, “and you solved it in hours. It took me rather longer.”
“But you did solve it,” Isaac commanded. “Because it was a problem of the calculus, meant to try whether I understood the calculus or not! Can you fathom the impertinence of it!? I was the first man who could ever have solved it, Daniel, and you the second, because you had the calculus from me first-hand. To be hectored thus, by the Baron’s lackeys, three decades after I had invented it—”
“In truth my riddle is another sort of thing altogether,” Daniel said. “I really am quite sorry to have wrong-footed you.”
Isaac blinked and heaved a sigh. He seemed inordinately relieved. Perhaps he had feared that Daniel would dispute what he had just said: You had the calculus from me first-hand. That was the key. In Daniel, Isaac saw a witness who could testify to Isaac’s priority in the discovery of the calculus. Whatever other annoying and inconvenient qualities Daniel might have, vanished when placed beside that. Daniel felt the muscles of his scalp and neck easing, felt his lungs filling with air. He was going to be all right. He’d make it out of the room whole, even if he said things that made Isaac a little angry. To Isaac, Daniel was more than a pawn; he was a rook, kept sequestered in the corner of the board until the end-game, then brought out at last to sweep inexorably down the board, driving the foe back to the last rank and forcing surrender. Isaac would put up with a lot, from a rook.
He wondered whether Isaac had, through some machinations, caused Daniel to be brought back to London. Perhaps he had exerted some action at a distance upon Princess Caroline in Hanover.
“What is your riddle, Daniel?”
“Earlier today, I was with a man who knows a good deal more than I do about money. This fellow was trying to judge the value of a guinea.”
“Of a coin that purported to be a guinea,” Isaac corrected him.
“Indeed—I say ‘guinea’ because that is what, in the end, it turned out to be.”
“He should have weighed it.”
“That is just what he did. And he could say nothing against the weight of the coin. Which would seem to settle the matter. But then he did something that to me was very odd. He put the coin in his mouth and he bit down on it.”
Isaac made no answer, but Daniel thought he pinkened again, slightly. Certainly he was interested in the story. He clasped his hands together on the table in front of him, composing himself, rather like a cat.
“Now,” Daniel said. “Even I know that coiners frequently make their counterfeits by joining two faces stamped from gold foil, and filling the void between them with solder. The solder is both lighter and softer than gold. This provides two means of detection: one may weigh the coin, or bite it. Either should suffice. In particular, if a coin has passed the test of weighing, its value should be confirmed beyond doubt! For nothing is heavier than gold. Any adulteration should be betrayed by a want of gravity. The weighing test ought to be infallible. And yet this chap—who really is extremely knowledgeable concerning coins—felt it necessary to make the additional test of biting. Is there any reason for it? Or was he being foolish?”
“He was not being foolish,” Isaac said, and stared at Daniel expectantly. His eyes were great luminous ice-balls hanging in space, like comets.
“Do you mean to say that I was, Isaac?”
“To associate with such a man? Foolish, or naïve,” Isaac returned. “As