Henry VIII, not satisfied with six wives, had maintained any number of mistresses, storing them, when not in use, in a sort of bolt-hole on the top of a hill above Greenwich Palace. His successors had not shared his appetites, and so the royal fuck-house had largely fallen into ruin. The foundations, however, were still sound. Atop them, Wren and Hooke, working in a hurry, and on a tiny budget, had built some apartments, which served as plinth for an octagonal salt-box. Atop that was a turret, an allusion in miniature to the Norman turrets of the Tower of London. The apartments were for Flamsteed to live in. The octagon above was constructed essentially so that the court-fop contingent of the Royal Society would have a place to go and peer learnedly through telescopes. But because it had been built on the foundations of Henry VIII’s hilltop love shack, the whole building was oriented the wrong way. To make real observations, it had been necessary to construct an alienated limestone wall in the garden out back, oriented north-south. This was partly sheltered by a sort of roofless shack. Bolted to it were a pair of Hooke-designed quadrants, one looking north and the other looking south, each equipped with a sighting-tube. Flamsteed’s life, thereafter, consisted of sleeping all day, then going out at night, leaning against this wall, peering through the sighting-tubes at stars swinging past, and noting their positions. Every few years, the work was enlivened by the appearance of a comet.

“What was Newton doing one year ago, Daniel?”

“Sources tell me he was calculating the precise date and hour of the Apocalypse, based upon occult shreds of data from the Bible.”

“We must have the same sources,” Roger said agreeably. “How much do you pay them?”

“I say things to them in return. It is called having conversations, and for some it is payment enough.”

“You must be right, Daniel. For, several months ago, Halley shows up and has a conversation with Newton: ‘Say, old chap, what about comets?’ And Newton drops the Apocalypse and turns to Euclid. Within a few months he’s got De Motu out.”

“He worked out most of it in ’79, during his last feud with Hooke,” Daniel said, “and mislaid it, and had to work it out a second time.”

“What-Doctor Waterhouse-do alchemy, the Apocalypse, and the elliptical orbits of heavenly bodies have in common? Other than that Newton is obsessed with all of them.”

Daniel said nothing.

“Anything? Everything? Nothing?”Roger demanded, and slapped the edge of the table. “Is Newton a billiard ball or a comet?”

“I beg your pardon?”

“Oh, come here, Daniel,” Roger clucked, going into sudden motion. Rather than standing up first, then walking, he lowered his wig, raised his hindquarters, and lunged off into the crowd like a bull, and in spite of bulk, middle age, gout, and drink, forged a path through the coffee-house faster than Daniel could follow. When Daniel next caught sight of Roger, the Marquis was shouldering his way past a fop. The fop was gripping a wooden implement shaped vaguely like a long-handled flour-scoop, and taking aim at a painted wooden sphere at rest on a green baize firmament. “Behold!” Roger exclaimed, and shoved at the ball with his bare hand. It rolled into another ball and stopped; the second ball rolled away. The fop was gripping his stick with both hands and winding up to break it over Roger’s head, when Roger adroitly turned his back on the table, giving the fop a clear view of his face. The stick fell from the fop’s hands. “Excellent shot, m’Lord,” he began, “though not wholly in line with the spirit or the letter of the rules…”

“I am a Natural Philosopher, and my Rules are the God-given Rules of the Universe, not the arbitrary ones of your insipid sport!” Roger thundered. “The ball transfers its vis viva into another ball, the quantity of motion is conserved, all is more or less orderly.” Roger now opened one hand to reveal that he had snatched another ball. “Or, I may toss it into the air thus-” he did so “-and it describes a Galilean trajectory, a parabola.” The ball plonked down squarely into a mug of chocolate, halfway across the room; its owner recovered quickly, raising the mug to Roger’s health. “But comets adhere to no laws, they come from God only knows where, at unpredictable times, and streak through the cosmos on their own unfathomable trajectories. So, I ask you, Daniel: Is Newton like a comet? Or, like a billiard ball, is he following some rational trajectory I have not the wit to understand?”

“I understand your question now,” Daniel said. “Astronomers used to explain the seeming retrograde movements of the planets by imagining a phantastic heavenly axle-tree fitted out with crystalline spheres. Now we know that in fact the planets move in smooth ellipses and that retrograde motion is an illusion created by the fact that we are making our observations from a moving platform.”

“Viz. the Earth.”

“If we could see the planets from some fixed frame of reference, the retrograde motion would disappear. And you, Roger, observing Newton’s wandering trajectory-one year devising new receipts for the Philosophic Mercury, the next hard at work on Conic Sections-are trying to figure out whether there might be some Reference Frame within which all of Isaac’s moves make some kind of damned sense.”

“Spoken like Newton himself,” Roger said.

“You want to know whether his recent work on gravitation is a change of subject, or merely a new point of view-a new way of perceiving the same old Topic.”

“ Nowyou are talking like Leibniz,” Roger said grumpily.

“And with good reason, for Newton and Leibniz are both working on the same problem, and have been since at least ’77,” Daniel said. “It is the problem that Descartes could not solve. It comes down to whether the collisions of those billiard balls can be explained by geometry and arithmetic-or do we need to go beyond pure thought and into Empirical and/or Metaphysical realms?”

“Shut up,” Roger said, “I’m working on a murderous headache as it is. I do not want to hear of metaphysics.” He seemed partly sincere-but he was keeping one eye on someone who was coming up behind Daniel. Daniel turned around and came face to face with-

“Mr. Hooke!” Roger said.

“M’lord.

“You, sir, taught this fellow to make thermometers!”

“So I did, m’lord.”

“I was just explaining to him that I wanted him to go up to Cambridge and gauge the heat of that town.”

“The entire country seems warm to me, m’lord,” said Hooke gravely, “in particular the eastern limb.”

“I hear that the warmth is spreading to the West country.”

“Here is a pretext, ” said the Marquis of Ravenscar, stuffing a sheaf of papers into Daniel’s right hip pocket, “and here is something for you to peruse on your journey-the latest from Leipzig.” He shoved something rather heavier into the left pocket. “Good night, fellow Philosophers!”

“Let us go and walk in the streets of London,” Hooke said to Daniel. He did not need to add: Most of which I laid out personally.

“RAVENSCAR HATED HIS COUSINJohn Comstock, ruined him, bought his house, and tore it down,” Hooke said, as if he’d been backed into a corner and forced to admit it, “but learned from him all the same! Why did John Comstock back the Royal Society in its early days? Because he was curious as to Natural Philosophy? Perhaps. Because Wilkins talked him into it? In part. But it cannot have escaped your notice that most of our experiments in those days-“

“Had something to do with gunpowder. Obviously.”

“ RogerComstock owns no gunpowder-factories. But his interest in the doings of our Society is no less pragmatic. Make no mistake. The French and the Papists are running the country now-are they running Newton?”