Isaac Newton - James Gleick (2004)

Chapter 8. In the Midst of a Whirlwind

WHEN HE OBSERVED the world it was as if he had an extra sense organ for peering into the frame or skeleton or wheels hidden beneath the surface of things. He sensed the understructure. His sight was enhanced, that is, by the geometry and calculus he had internalized. He made associations between seemingly disparate physical phenomena and across vast differences in scale. When he saw a tennis ball veer across the court at Cambridge, he also glimpsed invisible eddies in the air and linked them to eddies he had watched as a child in the rock-filled stream at Woolsthorpe. When one day he observed an air-pump at Christ’s College, creating a near vacuum in a jar of glass, he also saw what could not be seen, an invisible negative: that the reflection on the inside of the glass did not appear to change in any way. No one’s eyes are that sharp. Lonely and dissocial as his world was, it was not altogether uninhabited; he communed night and day with forms, forces, and spirits, some real and some imagined.

In 1675 Newton journeyed to London and finally appeared at the Royal Society. He met in person these men who had till then been friends and antagonists twice removed, their spirits channeled through Oldenburg’s mail. Among the virtuosi made flesh was Robert Boyle, fifteen years his senior and a mentor of Hooke’s. Boyle was a fervent corpuscularian; in his great polemic The Sceptical Chymist he had developed a theory of fundamental particles as the constituents of matter. He believed that all the phenomena of nature could be explained by the combination and organization of these atoms into mixed bodies, some perfect and some imperfect and none more perfect than gold.1 He believed in the alchemists’ greatest dream, the transmutation of baser metals into gold, but he reviled their traditions of secrecy—“their obscure, ambiguous, and almost Ænigmatical Way of expressing what they pretend to Teach.”2

They have no mind to be understood at all, but by the Sons of Art (as they call them) nor to be understood even by these without Difficulty and Hazardous Tryalls.

His experiments with an air-pump were renowned, and his own investigation of color had spurred Hooke and Newton in turn. He greeted Newton warmly.

Over the next months Newton, back in Cambridge, labored over a new manuscript. He set down in passionate words his own corpuscular theory. Here, finally, was his Hypothesis—he embraced the label he had denied so vehemently before. “An Hypothesis,” he titled it, “explaining the Properties of Light discoursed of in my severall Papers.”3 But he spoke of more than light alone; he was taking on the whole substance of nature. His nemesis, Hooke, loomed large. “I have observed the heads of some great virtuoso’s to run much upon Hypotheses,” Newton said, “as if my discourses wanted an Hypothesis to explain them by.” He noted that “some” could not quite take his meaning when he spoke of light and color in the abstract, and perhaps they would understand better with an illustration. Thus—the “Hypothesis.”

He wanted Oldenburg to read this to the assembled Royal Society but not to publish it. And he wanted his listeners to understand a delicate rhetorical point. He did not pretend to mathematical certainty here, even if, for convenience,4 he chose to “speak of it as if I assumed it & propounded it to be beleived.” Let no man “think me oblig’d to answer objections against this script,” he said. “For I desire to decline being involved in such troublesome & insignificant Disputes.”

This sheaf of papers posted to Oldenburg5 blended calculation and faith. It was a work of the imagination. It sought to reveal nothing less than the microstructure of matter. For generations it reached no further than the few men who heard it read and then raptly debated it through all the meetings of the Royal Society from December 1675 to the next February. Newton had peered deeper into the core of matter than could be justified by the power of microscopes. Through a series of experiments and associations he seemed to feel nature’s fundamental particles just beyond the edge of his vision. Indeed, he predicted that instruments magnifying three or four thousand times might bring atoms into view.6

He saw a vast range of phenomena to explain, and the cool certainties of geometry had reached the limit of their usefulness here. There were all kinds of chemical activity, processes like vegetation, fluids that interacted with more or less “sociableness.” He closed his eyes to no problem because it was too mysterious or intractable. He confounded the distant members of the society with a vivid description of an experiment revealing electricity, a power certain bodies gained when excited: he rubbed a glass disk with cloth and then waved it over bits of paper. They sprang to life:

Sometimes leaping up to the Glass & resting there a while, then leaping downe & resting there, then leaping up & perhaps downe & up again … sometimes in lines perpendicular to the Table, Sometimes in oblique ones … & turn often about very nimbly as if … in the midst of a whirlwind.7

Irregular motions, he emphasized—and he saw no way to explain them mechanically, purely in terms of matter pressing on matter. It was no static world, no orderly world he sought to understand now. Too much to explain at once: a world in flux; a world of change and even chaos. He gave out poetry:

For nature is a perpetuall circulatory worker, generating fluids out of solids, and solids out of fluids, fixed things out of volatile, & volatile out of fixed, subtile out of gross, & gross out of subtile, Some things to ascend & make the upper terrestriall juices, Rivers and the Atmosphere; and by consequence others to descend.…8

The ancients had often supposed the existence of ether, a substance beyond the elements, purer than air or fire. Newton offered the ether as a hypothesis now, describing it as a “Medium much of the same constitution with the air, but far rarer, subtiler & more strongly Elastic.” As sound is a vibration of the air, perhaps there are vibrations of the ether—these would be swifter and finer. He estimated the scale of sound waves at a foot or half-foot, vibrations of ether at less than a hundred thousandth of an inch.

This ether was a philosophical hedge, a way of salvaging a mechanical style of explanation for processes that seemed not altogether mechanical: iron filings near a magnet arrange themselves into curved lines, revealing “magnetic effluvia”; chemical change occurs in metals even after they have been sealed in glass; a pendulum swings far longer in a glass emptied of air, but ceases eventually nonetheless, proving that “there remains in the glass something much more subtle which damps the motion of the bob.”9 The mechanists were laboring to banish occult influences—mysterious action without contact. The ether, more subtle than air, yet still substantial, might convey forces and spirits, vapors and exhalations and condensations. Perhaps an ethereal wind blew those fluttering bits of paper. Perhaps the brain and nerve transmitted ethereal spirit—the soul inspiring muscle by impelling it through the nerves.10Perhaps fire and smoke and putrefaction and animal motion stemmed from the ether’s excitation and swelling and shrinking. Perhaps this ether served as the sun’s fuel; the sun might imbibe the ethereal spirit “to conserve his Shining, & keep the Planets from recedeing further from him.”11 (The apple had dropped long since, but universal gravitation remained remote.)

Hooke, listening to Oldenburg read Newton’s words aloud, kept hearing his name. “Mr Hook, you may remember, was speaking of an odd straying of light … near the edge of a Rasor.…” Indeed, earlier in 1675 Hooke had put forward his new discovery of the phenomenon later known as diffraction: the bending of light at a sharp edge. One way to explain diffraction—the only way, until quantum mechanics—was in terms of the interference of waves. Did this spreading of light rays mean that they could curve after all, as sound waves apparently do around corners? Newton said he was unsure: “I took it to be onely a new kind of refraction, caused perhaps by the externall æthers beginning to grow rarer a little before it come at the Opake body.…” He recalled, though, that Hooke had been

pleased to answer that though it should be but a new kind of refraction, yet it was a new one. What to make of this unexpected reply, I knew not, haveing no other thoughts but that a new kind of refraction might be as noble an Invention as any thing els about light.

A noble invention, Newton agreed. But he remembered having read about this experiment before Hooke’s account. He was obliged to mention that the French Jesuit Honoré Fabri had described it; and Fabri in turn had got it from a Bolognese mathematician, Francesco Maria Grimaldi.12 It was not Hooke’s discovery.

Hooke grew irate. In evenings that followed he met with friends in coffee-houses and told them that Newton had commandeered his pulse theory. After all, Newton was talking about color in terms of “vibrations of unequal bignesses.” Large vibrations are red—or, as he said more carefully, cause the sensation of red. Short vibrations produce violet. The only difference between colors was this: a slight, quantifiable divergence in the magnitude of vibration. Newton did not speak of waves. Nor for that matter had Hooke: waves were still a phenomenon of the sea. A lack of vocabulary hindered both men; but what Newton had seen was just what Hooke had sought.

This was insupportable. At the end of the second meeting devoted to the Newton “Hypothesis,” Hooke rose to declare that the bulk of it had come from his Micrographia, “which Mr Newton had only carried farther in some particulars.”13 Oldenburg lost no time in reporting this claim back to Cambridge.

Cambridge fired back. “As for Mr Hook’s insinuation,” Newton wrote Oldenburg, “I need not be much concerned at the liberty he takes.”14 He wished to avoid “the savour of having done any thing unjustifiable or unhansome towards Mr Hook.” So he analyzed the chain of logic and priority. First, what is actually Hooke’s? We must “cast out what he has borrowed from Des Cartes or others”:

That there is an ether. That light is the action of this ether. That the ether penetrates solid bodies in varying degrees. That light is at first uniform. That colors come from a modification of light rays—accelerated to make red and retarded to make blue, all other colors coming from some mixture of red and blue.

All Hooke did was change Descartes’s idea of a pressing motion in the ether to a vibrating one. Globules for Descartes, pulses for Hooke. “In all this,” Newton concluded,

I have nothing common with him but the supposition that æther is a Medium susceptible of vibrations of which supposition I make a very different use: he supposing it light it self which I suppose it not.

For the rest—refraction and reflection and the production of colors—Newton said he explained it all so differently from Hooke as to “destroy all he has said.” He added sarcastically, “I suppose he will allow me to make use of what I tooke the pains to find out.”

Hooke was poking at a soft spot in Newton’s understanding of light. Was it particle or wave? Newton was vacillating on this matter now, as humanity would continue to vacillate until twentieth-century physicists vanquished the paradox by accepting it. Newton both exposed his uncertainty and concealed it. He played a delicate game, ringing changes on the word hypothesis, trying to distinguish between what he knew and what he was forced to suppose. He supposed the existence of an ether—mysterious and even spiritual—because he could not dispense with such a thing, for now.

Oldenburg—no friend to Hooke15—chose to surprise him with a public reading of Newton’s rejoinder at the next Royal Society meeting. Finally, after years of jousting by proxy, Hooke decided to take pen in hand and address his adversary personally.16 He adopted a meek and philosophical tone. He said he suspected Newton was being misinformed; he had experience with such “sinister practices.” He did not wish to contend or feud or be “drawn to such kind of warr.” We are “two hard-to-yield contenders,” he proclaimed. “Your Designes and myne I suppose aim both at the same thing which is the Discovery of truth and I suppose we can both endure to hear objections.”

Newton’s famous reply came a fortnight later.17 If the weapons of this duel were to be insincere politesse and exaggerated deference, he could wield them as well. He called Hooke a “true Philosophical spirit.” He gladly embraced the proposal of a private correspondence. “What’s done before many witnesses is seldome without some further concern than that for truth: but what passes between friends in private usually deserves the name of consultation rather than contest, & so I hope it will prove between you & me.” And then, for the matter of their dispute, he put on record a finely calibrated piece of faint praise and lofty sentiment:

What Des-Cartes did was a good step. You have added much several ways, & especially in taking the colours of thin plates into philosophical consideration. If I have seen further it is by standing on the sholders of Giants.18

The private philosophical dialogue between Newton and Hooke never took place. Almost two years passed before they communicated again at all. By then Oldenburg had died, Hooke had succeeded him as Secretary of the Royal Society, and Newton had withdrawn ever more deeply into the seclusion of his Trinity chambers.