Isaac Newton - James Gleick (2004)

Chapter 5. Bodys & Senses

HE WAS LOOKING inward as well as outward. Introspection told him that his imagination could see things as they really were. “Phantasie is helped,” he noted, “by good aire fasting moderate wine.” But it is also “spoiled by drunkenesse, Gluttony, too much study.” He added: from too much study, and from extreme passion, “cometh madnesse.”1

He wished to understand light itself—but did light’s essence lie outside or within the soul of the observer? In all the blooming perplexity of new philosophy, little was as muddled as the boundary between the perceived and the perceiver. Surely the mind, composed of pure thought, must have a point of contact with the body—at the pineal gland, Descartes proposed. The poet Andrew Marvell, graduate of Trinity College and now Member of Parliament for Hull, imagined the body and soul as enslaved, each by the other: “A soul hung up, as ’twere, in chains of nerves and arteries and veins.”2 For Aristotle optics had been first a science not of light but of sight.

Newton, in his Questiones, had pondered the difficulty of understanding the senses, when those very senses were employed as the agents of understanding.

The nature of things is more securely & naturally deduced from their operations out upon another than upon our senses. And when by the former experiments we have found the nature of bodys, by the latter we may more clearely find the nature of our senses. But so long as we are ignorant of the nature of both soul and body we cannot clearly distinguish how far an act of sensation proceeds from the soul and how far from the body.3

With this paradox in mind, Newton, experimental philosopher, slid a bodkin into his eye socket between eyeball and bone. He pressed with the tip until he saw “severall white darke & coloured circles.… Which circles were plainest when I continued to rub my eye with the point of the bodkin.” Yet when he held both eye and bodkin still, the circles would begin to fade.4 Was light a manifestation of pressure, then?

Almost as recklessly, he stared with one eye at the sun, reflected in a looking glass, for as long as he could bear. He sensed that color—perhaps more than any of the other qualities of things—depends on “imagination and fantasy and invention.”5 He looked away at a dark wall and saw circles of color. There was a “motion of spirits” in his eye. These slowly decayed and finally vanished. Were they real or phantasm? Could such colors ever be real, like the colors he had learned to make from crushed berries or sheep’s blood? After looking at the sun, he seemed to perceive light objects as red and dark objects as blue. Strangely, he found that he could reproduce these effects, with practice, by pure, willful thought. “As often as I went into the dark & intended my mind upon them as when a man looks earnestly to see any thing which is difficult to be seen, I could make the phantasm return without looking any more upon the sun.”6 He repeated the experiment until he began to fear permanent damage and shut himself up in a dark room. He remained there for three days; only then did his sight begin to clear.

(illustration credit 5.1)

Experiment—observation—science: these modern words were impressing themselves upon him. He read them in a new book from London, titled Micrographia: “The Science of Nature has been already too long made only a work of the Brain and the Fancy. It is now high time that it should return to the plainness and soundness of Observations on material and obvious things.”7 The author was Robert Hooke, a brilliant and ambitious man seven years Newton’s senior, who wielded the microscope just as Galileo had the telescope. These were the instruments that penetrated the barrier of scale and opened a view into the countries of the very large and the very small. Wonders were revealed there. The old world—the world of ordinary scales—shrank into its place in a continuum, one order among many. Like Galileo, Hooke made meticulous drawings of strange new sights and popularized his instrument as a curiosity for wealthy aristocrats—though, after they bought the device from the lens shop in London where he sometimes worked, they rarely succeeded in seeing anything but vague shadows. Hooke was Newton’s inspiration now (though Newton never acknowledged that). He became Newton’s goad, nemesis, tormentor, and victim.

Hooke had a unique post. He was employed, if seldom actually paid, as Curator of Experiments to a small group of men who formed, in 1662, what they called the Royal Society of London. They meant to be a new sort of institution: a national society dedicated to promoting—and especially “communicating”—what they called “the New Philosophy” or “Experimental Philosophy.”8 Amazing discoveries warranted this banner: comets and new stars; the circulation of the blood; the grinding of glasses for telescopes; the possibility of vacuities (and nature’s abhorrence thereof); the descent of heavy bodies; and diverse other things.9

Nullius in verba was the Royal Society’s motto. Don’t take anyone’s word for it.10 These gentlemen had begged for and received the king’s patronage, but patronage meant good will only; the society collected from its members a shilling at a time and strained to find meeting places. Among the founders was John Wilkins, author of The Discovery of a New World a generation before. If one man was their muse, he was the late Francis Bacon, who had written:

We must … completely resolve and separate Nature, not by fire, certainly, but by the mind, which is a kind of divine fire.… There will remain, all volatile opinions vanishing into smoke, the affirmative form, solid, true and well-defined. Now this is quickly said, but it is only reached after many twists and turns.11

The twists and turns became the responsibility of the Curator of Experiments, Hooke, technician and impresario. He demonstrated experiments with air-pumps. At one meeting he cut open the thorax and belly of a living dog, observed its beating heart, and used a bellows to inflate its lungs in an experiment on respiration, which he later felt reluctant to repeat “because of the torture of the creature.”12 Another meeting dazzled and confused the Duchess of Newcastle with colors, magnets, microscopes, roasted mutton, and blood.13 This was all science, a new spirit and almost a method: persuasion from practical experience, and formalized recording of data. Hooke lacked mathematics but not ingenuity. He invented or improved barometers, thermometers, and wind gauges, and he tracked London weather obsessively.14

In Micrographia he displayed the “new visible world” to be seen through the instrument he described as an artificial organ. “By the help of Microscopes, there is nothing so small, as to escape our inquiry,” he declared.15 As a geometer begins with a mathematical point, he examined the point of a needle—perfectly sharp, yet under the microscope, blunt and irregular. By analogy he suggested that the earth itself, seen from a great enough distance, would shrink to a scarcely visible speck. More specks were to be found in printed books: he proceeded to study and draw the mark of a full stop, the punctuation mark—again surprisingly rough and irregular, “like a great splatch of London dirt.” 16 He found wonderment in the edge of a razor and the weft of fine linen. He discovered shifting, iridescent colors in thin flakes of glass. He knew that Descartes had seen a rainbow of colors in light passed through a prism or a water drop, and he compared microscopic rainbows.

And here he made his book something more than a registry and gazetteer for his new world. He notified readers that he offered a theory—a complete and methodical explanation of light and color. Aristotle had thought of color as a commingling of black and white. His followers considered colors fundamental qualities of matter, carried by light into the eye. Descartes had speculated that color came from globules of light changing speed when refracted by glass or water. Hooke disputed this and, grandly invoking the shade of Bacon, turned to experiment: an “Experimentum Crucis, serving as Guide or Land-mark.”17 True, Hooke observed, a prism produces colors when refracting light. But he asserted that refraction was not necessary. His landmark was the production of color in transparent substances:18 “for we find, that the Light in the open Air, either in or out of the Sun-beams, and within a Room, either from one or many Windows, produces much the same effect.”

Light is born of motion, he argued. “That all kind of fiery burning Bodies have their parts in motion, I think will be very easily granted me.” Sensing more than he could truly see, he asserted that all luminous bodies are in motion, perhaps vibrating: sparks, rotting wood, and fish. Further, he observed, or thought he observed, that two colors were fundamental: blue and red. They were caused by “an impression on the retina of an oblique and confus’d pulse of light.”19 Where red and blue “meet and cross each other,” the imperfection generated “all kinds of greens.” And here his theory ended. “It would be somewhat too long a work for this place zetetically to examine, and positively to prove, what particular kind of motion it is.… It would be too long, I say, here to insert the discursive progress by which I inquir’d after the properties of the motion of Light.…”20

Yet all in all he claimed to have explained everything; to have given—“newly” given—the causes

capable of explicating all the Phenomena of colours, not onely of those appearing in the Prisme, Water-drop, or Rainbow … but of all that are in the world, whether they be fluid or solid bodies, whether in thick or thin, whether transparent, or seemingly opacous.”21

Newton absorbed this bold claim.22 He had no microscope and no chance of obtaining one. For that matter, he had no room with more than one window. He did have a prism. He darkened his study and made a hole in the window shutter to let in a sunbeam, white light, the purest light, light with no intrinsic color, philosophers still thought. He performed his own experiments—even, he felt, an experimentum crucis. He noted the results and told no one.

Bacon had also warned: “God forbid that we should give out a dream of our own imagination for a pattern of the world.”23

The plague abating, Newton returned to Cambridge, where among those he did not tell of his experiments was the professor of mathematics, Isaac Barrow.