Now the conversation-if it could be called that-was interrupted by a mighty throat-clearing from the opposite end of the room, gallons of air shifting dollops of phlegm out of the main channel. “Speaking of Positions,” said a husky Dutch voice, “would you and your gentleman friend please find a different one? For since you’ve made sleep quite impossible I should like to eat. ”

“With pleasure, meinheer, I would, but your lodger has a poniard at my eye,” said Bob.

“You are much cooler in dealing with men than with women,” Eliza observed, sotto voce.

“A woman such as you has never seen a man in a cool condition, unless you were spying on him through a knot-hole,” Bob returned.

More throat-clearing from the owner: a hearty, grizzled man in his middle fifties, with all that that implied in the way of eyebrows. He had hoisted one of them like a furry banner and was peering out from under it at Eliza; typically for an astronomer who did his best seeing through a single eye. “The Doctor warned me to expect odd callers… but not business transactions. ”

“Some would call me a whore, and some shall, ” Eliza admitted, giving Bob a sharp look, “but in this case you are assuming too much, Monsieur Huygens. The transaction we are discussing is not related to the act we have performed…”

“Then why do both at the same time? Are you in such a hurry? Is this how it is done in Amsterdam?”

“I am trying to clear this fellow’s mind so that he can think straighter,” said Eliza, straightening up herself as she said it, for her back was getting tired and her bodice was griping her stomach.

Bob knocked her dagger-hand aside and sat up violently, throwing her into a backward somersault. She’d have landed on her head except that he caught her upper arms in his hands and spun her over-or something rather complicated and dangerous-all she knew was that, when it was over, she was dizzy, and her heart had skipped a few beats, her hair was in her face and her dagger-hand was empty. Bob was behind her, using her as a screen while he pulled his breeches up with one hand. His other hand had a grip on her laces, which he was exploiting as a sort of bridle. “You should never have straightened your arm,” he explained quietly, “It tells the opponent that you are unable to make a thrust.”

Eliza thanked him for the fencing-lesson by pirouetting in a direction calculated to bend his fingers backwards. He cursed, let go of her laces, and yanked his breeches up finally.

“Mr. Huygens, Bob Shaftoe of the King’s Own Black Torrent Guards. Bob, meet Christiaan Huygens, the world’s foremost Natural Philosopher.”

“Hooke would bite you for saying so… Leibniz is brighter than I… Newton, though confused, is said to be talented. So let us say only that I am the foremost Natural Philosopher in this room, ” Huygens said, taking a quick census of the occupants: himself, Bob, Eliza, and a skeleton hanging in the corner.

Bob had not noticed the skeleton before, and its sudden inclusion in the conversation made him uneasy. “I beg your pardon, sir, ’twas disgraceful-”

“Oh, stop!” Eliza hissed, “he is a Philosopher, he cares not.”

“Descartes used to come up here when I was a young man, and sit at that very table, and drink too much and discourse of the Mind-Body Problem,” Huygens mused.

“Problem? What’s the problem? I don’t see any problem,” Bob muttered parenthetically, until Eliza crowded back against him and planted a heel on his instep.

“So Eliza’s attempt to clarify your mental processes by purging you of imbalancing humours could not have been carried out in a more appropriate location,” Huygens continued.

“Speaking of humours, what am I to do with this?” Bob muttered, dangling a narrow bulging sac from one finger.

“Put it in a box and post it to Upnor as a down payment,” Eliza said.

The sun had broken through as they spoke, and golden light suddenly shone into the room from off the Plein. It was a sight to gladden most any Dutch heart; but Huygens reacted to it strangely, as if he had been put in mind of some tiresome obligation. He conducted a poll of his clocks and watches. “I have a quarter of an hour in which to break my fast,” he remarked, “and then Eliza and I have work to do on the roof. You are welcome to stay, Sergeant Shaftoe, though-”

“You have already been more than hospitable enough,” Bob said.

HUYGENS’S WORK CONSISTED OF STANDINGvery still on his roof as the clock-towers of the Hague bonged noon all around him, and squinting into an Instrument. Eliza was told to stay out of his way, and jot down notes in a waste-book, and hand him small necessaries from time to time.

“You wish to know where the sun is at noon-?”

“You have it precisely backwards. Noon is when the sun is in a particular place. Noon has no meaning otherwise.”

“So, you wish to know when noon is.”

“It is now!” Huygens said, and glanced quickly at his watch.

“Then all of the clocks in the Hague are wrong.”

“Yes, including all of mine. Even a well-made clock drifts, and must be re-set from time to time. I do it here whenever the sun shines. Flamsteed will be doing it in a few minutes on top of a hill in Greenwich.”

“It is unfortunate that a person may not be calibrated so easily,” Eliza said.

Huygens looked at her, no less intensely than he had been peering at his instrument a moment earlier. “Obviously you have some specific person in mind,” he said. “Of persons I will say this: it is difficult to tell when they are running aright but easy to see when something has gone awry.”

“Obviously you have someone in mind, Monsieur Huygens,” Eliza said, “and I fear it is I.”

“You were referred to me by Leibniz,” Huygens said. “A shrewd judge of intellects. Perhaps a bit less shrewd about character, for he always wants to think the best of everyone. I made some inquiries around the Hague. I was assured by persons of the very best quality that you would not be a political liability. From this I presumed that you would know how to behave.”

Suddenly feeling very high and exposed, she took a step back, and reached out with a hand to steady herself against a heavy telescope-tripod. “I am sorry,” she said. “It was stupid, what I did down there. I know it was, for I do know how to behave. Yet I was not always a courtier. I came to this place in my life by a roundabout path, which shaped me in ways that are not always comely. Perhaps I should be ashamed. But I am more inclined to be defiant.”

“I understand you better than you suppose,” Huygens said. “I was raised and groomed to be a diplomat. But when I was thirteen years old, I built myself a lathe.”

“Pardon me, a what?”

“A lathe. Down below, in this very house. Imagine my parents’ consternation. They had taught me Latin, Greek, French, and other languages. They had taught me the lute, the viol, and the harpsichord. Of literature and history I had learned everything that was in their power to teach me. Mathematics and philosophy I learned from Descartes himself. But I built myself a lathe. Later I taught myself how to grind lenses. My parents feared that they had spawned a tradesman.”

“No one is more pleased than I that matters turned out so well for you,” Eliza said, “but I am too thick to understand how your story is applicable to my case.”

“It is all right for a clock to run fast or slow at times, so long as it is calibrated against the sun, and set right. The sun may come out only once in a fortnight. It is enough. A few minutes’ light around noon is all that you need to discover the error, and re-set the clock-provided that you bother to go up and make the observation. My parents somehow knew this, and did not become overly concerned at my strange enthusiasms. For they had confidence that they had taught me how to know when I was running awry, and to calibrate my behavior.”