“I am with you so far,” said Newton, “if all you are saying is that forces other than Gravity act on Dr. Waterhouse’s pen when he is writing something, and that such forces do not appear to motivate rocks or comets.”

“Hooke was fascinated by muscles,” Daniel put in, “and looked at them under his microscope, and labored at making artificial ones, so that he could fly. Those, I predict, could have been described by Mechanical Philosophy; after all, they were naught more than practical applications of the Rarefying Engine, and as such, subject to Boyle’s Law. With more time and better microscopes, Hooke might have found, within muscles, tiny mechanisms, likewise describable by mathematical laws, and thereby put to rest any supposed mysteries-”

But he stopped as both Newton and Leibniz were making the same sort of hand-waving gestures employed to bat away farts. “You miss the point!” said Leibniz. “I have no interest in the physics of muscles! Think, sir, if Hooke had made his flying-machine, driven, in a deterministic fashion, by Rarefying Engines, what more then would he have had to add to this device, to make it flutter to a safe perch atop the cupola of Bedlam, and balance there as ’twas buffeted by divers wind-gusts, and take flight again without o’ersetting and tumbling to the ground like a shot squab? I am trying to draw our attention to what it is that comes down those nerves from the brain: the decisions, or rather, the physical manifestations thereof-the characters, as it were, in which they are writ-and transmitted to the muscles, that they may inform what would otherwise be without form and void.”

“I understand that,” said Daniel, “and I say it is all pistons and cylinders, weights and springs, to the very top. And that’s all I need to explain how I inform ink on a page, and how a bird informs the air with its wings.”

“And I agree with you!” said Leibniz.

This produced a dumbfounded pause. “Have I converted you to the doctrine of Materialism so easily, then?” Daniel inquired.

“By no means,” said Leibniz. “I say only that, though the machine of the body obeys deterministic laws, it does so in accordance with the desires and dictates of the soul, because of the pre-established harmony.”

“Of that, we must needs hear more, for it is very difficult to understand,” said the Princess.

“Chiefly because it is wrong!” said Sir Isaac.

Caroline now had to literally step between the two philosophers. “Then we are all in agreement that further discourse concerning the pre-established harmony is wanted from Baron von Leibniz,” she said. “But first, I would fain hear Sir Isaac address the ph?nomena of which Drs. Waterhouse and Leibniz have just been discoursing. Sir Isaac, we have heard from both of these gentlemen that they are wholly satisfied it is all mechanism to the very top. What of you? Do you require something more?”

Newton said, “If we allow, not only the muscles, but the nerves, and even the brain itself, to be ‘pistons and cylinders, weights and springs’ as you put it, whose machinations might be observed and described by some future Hooke, then we must still explain how those mechanisms are informed by the soul, spirit, or whatever we are going to call it-the thing that has free will, that is not subject to deterministic laws, and that accounts for our being human. This is ultimately the same problem as we discoursed of earlier-the problem you find boring, Daniel-of God’s relationship to the Universe. For the relationship that our souls bear to our bodies, is akin to the relationship that God bears to the entire Universe. If God is to be something more than an Absentee Landlord-something more than the perfect watch-maker, who sets His clock a-run, and walks away from it-then we must account for how He influences the movements of things in the world. This gets us round to that mysterious ph?nomenon called Force. And when we discourse of animal motion we must in the end address a like problem, namely of how the soul that inhabits a body may influence the operation of what is in the end just a big soggy clock.”

“I could not disagree more, by the way,” said Leibniz. “The soul and body influence each other not at all.”

“Then how does my soul know that yonder candle is flickering?” asked Princess Caroline. “For I can only know such a thing through my eyes, which are parts of my body.”

“Because God has put into your soul a principle representative of the candle-flame and everything else in the Universe,” said Leibniz. “But that is most certainly not how God perceives things! He perceives all things, because He continually produces them. And so I reject any such analogies likening God’s relationship to the Universe and ours to our bodies.”

“I do not understand Baron von Leibniz’s hypothesis at all,” Isaac confessed.

“What is your hypothesis, Sir Isaac?”

“That most of the animal body is a determined machine, I’ll grant. That it is controlled from the brain, has been proved, by Willis and others. It follows, simply, that, by laws of God’s choosing, the soul has the power to operate upon the brain, and thereby to influence animal movements.”

“This is just Descartes and the pineal gland all over again!” Leibniz scoffed.

“He was wrong about the pineal gland,” Newton said, “but I’ll grant a certain formal resemblance between his way of thinking about it, and mine.”

“In each case,” Daniel translated, “there is some sense in which a free, non-corporeal, non-mechanical spirit can effect physical changes in the workings of the machinery of the brain.”

“I think that much is obvious; as is the fact that God-Who is likewise a non-corporeal Spirit-has power to effect physical changes-that is, to exert Force-upon any thing whatsoever in this Universe.”

“And is it the case that when you study the causes and seats of Force in your Praxis work, you seek to understand Forces of that type as well?”

“I do not think that any account of Force that failed to address this topic could be deemed complete.”

“When Sir Isaac was working on the Principia,” said Daniel, “I paid him a visit up at Trinity. He had requested what seemed to me to be an odd lot of information: tables of the tides, data on a certain comet, astronomical observations of Jupiter and Saturn. Well, it was a long ride, and by the time I had reached Cambridge I’d managed to work out that there was a common thread running through all of these: gravity. Gravity causes the tides and determines the orbits of comets and planets alike. To us it is obvious now; but back then it was by no means agreed that a comet, let us say, might be bound by the same force that kept the Earth in its gyre. Isaac’s triumph was to perceive that all of these ph?nomena were attributable to the same cause, working everywhere in the same way. Now, I have long been nonplussed by Isaac’s Alchemical research, but as years have gone by I have perceived that he would achieve a similar triumph by finding a single common underlying explanation for ph?nomena that we think of as diverse, and unrelated: free will, God’s presence in the Universe, miracles, and the transmutation of chymical elements. Couched in the willfully obscure jargon of the Alchemists, this cause, or principle, or whatever one wants to call it, is known as the Philosopher’s Stone, or other terms such as the Philosophic Mercury, the Vital Agent, the Latent or Subtile Spirit, the Secret Fire, the Material Soul of Matter, the Invisible Inhabitant, the Body of Light, the Seed, the Seminal Virtue.”

“You are confusing a number of different ideas,” said Isaac, “but this does at least prove that you perused my notes before burning them.”

At this Caroline was taken aback for a moment; then curiosity got the better of her. “What is this Agent or Spirit? Have you seen it, Sir Isaac?”

“I see it now, in the emotions and thoughts flickering across your face, highness. I see its effect everywhere,” was the somewhat evasive response of Newton. “In Nature I perceive two categories of actions: mechanical and vegetable. By mechanical I mean, of course, just the sort of thing that Drs. Waterhouse and Leibniz discoursed of earlier: in a word, clock-work. By vegetable I do not mean turnips. That is a new and vulgar meaning of the word. I use it in its ancient sense of something animate, living, growing. It describes generative and creative processes. Clocks, even good ones, run down and wear out. The mechanical world decays. Counterpoised against this tendency to decline must be some creative principle: the active seed-the Subtile Spirit. An unimaginably tiny quantity of this, acting upon a vastly larger bulk of insipid, dead, inactive matter, wreaks immense, even miraculous transformations, to which I give the general name vegetation. Just as the general principle of Gravity manifests itself in diverse specific ways, such as tides, the orbits of comets, and the trajectories of bullets, so the vegetative principle may be perceived, by those who know how to look for it, in diverse places. Just to mention one example, which we discoursed of earlier: a flying-machine, constructed of artificial muscles, would be a mechanical device, whose fate, I believe, would be to crash to the ground, like the corpse of a bird that has died on the wing. If that machine were to take flight-which would mean sensing every fluctuation of the air, and responding in the correct way-I should ascribe that, ultimately, to the workings of some sort of vegetative principle. But Daniel is correct in thinking that it is also related to such matters as souls, miracles, and certain of the more profound and astonishing chymical transformations.”