Newton’s apple: The real story
We’ve all heard the story. A young Isaac Newton is sitting beneath an apple tree contemplating the mysterious universe. Suddenly – boink! -an apple hits him on the head. “Aha!” he shouts, or perhaps, “Eureka!” In a flash he understands that the very same force that brought the apple crashing toward the ground also keeps the moon falling toward the Earth and the Earth falling toward the sun: gravity.
Or something like that. The apocryphal story is one of the most famous in the history of science and now you can see for yourself what Newton actually said. Squirreled away in the archives of London’s Royal Society was a manuscript containing the truth about the apple.
It is the manuscript for what would become a biography of Newton entitled Memoirs of Sir Isaac Newton’s Lifewritten by William Stukeley, an archaeologist and one of Newton’s first biographers, and published in 1752. Newton told the apple story to Stukeley, who relayed it as such:
“After dinner, the weather being warm, we went into the garden and drank thea, under the shade of some apple trees…he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. It was occasion’d by the fall of an apple, as he sat in contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to himself…”
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The Royal Society has made the manuscript available today for the first time in a fully interactive digital form on their website at royalsociety.org/turning-the-pages. The digital release is occurring on the same day as the publication of Seeing Further (HarperPress, £25), an illustrated history of the Royal Society edited by Bill Bryson, which marks the Royal Society’s 350th anniversary this year.
So it turns out the apple story is true – for the most part. The apple may not have hit Newton in the head, but I’ll still picture it that way. Meanwhile, three and a half centuries and an Albert Einstein later, physicists still don’t really understand gravity. We’re gonna need a bigger apple.
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Newton sitting under the apple tree
Newton’s home at Woolsthorpe Manor and the probable apple tree in question
In grade school you probably learned Newton’s apple story around the time you learned that George Washington chopped down a cherry tree, that people in Columbus’ time thought that the world was flat, or that the Pilgrims celebrated the first Thanksgiving in America and invited the Native Americans to join them. Since literally none of the latter three stories here are true (follow the preceding links for full details), you probably have your doubts about whether Newton actually sat under an apple tree and had something of a “eureka” moment concerning gravity.
It might surprise you to learn, then, that your teachers got one of these stories (partially) correct. Newton was indeed sitting under an apple tree when he had his so-called “eureka” moment on how gravity worked.
Although, it took him over two decades more to develop the fully-fledged theory of “universal gravitation”, first published in his Philosophiæ Naturalis Principia Mathematica on July 5, 1687. He also didn’t complete it without some ideas others had already come up with, such as Christopher Wren, Robert Hooke, and Edmond Halley (who Halley’s comet is named after); though Newton claims particularly Hooke, who corresponded heavily with Newton on gravity, and his ideas had little real bearing on his work, other than simply to inspire him to continue working on the problem.
As Newton stated when Hooke accused Newton of plagiarizing his work:
Yet am I not beholden to him for any light into that business but only for the diversion he gave me from my other studies to think on these things & for his dogmaticalness in writing as if he had found the motion in the Ellipsis, which inclined me to try it…
So perhaps “eureka” conveys much too strong of a leap. From accounts, he was more just put on the correct path while musing under the tree.
Further, it would seem that the apple didn’t fall directly on his head- at least there is no documented evidence of this. But if you discount the notion that he near instantly fleshed out his universal theory and the “fell on his head” bit, the common story is pretty accurate.
One of the best sources we have for the “apple falling on Newton’s head” anecdote is a manuscript written by Newton’s friend William Stukeley. He published Memoirs of Sir Isaac Newton’s Life in 1752, becoming one of Newton’s first biographers. Many of the incidences described in the book were recorded much earlier than 1752, including the “apple” story which was first documented in 1726, the year Newton died, and then again a year later by Voltaire in his Epic Poetry.
Stukeley’s account is as follows:
John Conduitt, Newton’s assistant and the husband of his niece, told pretty much the same story. Newton lived with the pair in his later years and doted upon their daughter. When writing about Newton, Conduitt said:
In the year he retired again from Cambridge on account of the plague to his mother in Lincolnshire & whilst he was musing in a garden it came into his thought that the same power of gravity (which made an apple fall from the tree to the ground) was not limited to a certain distance from the earth but must extend much farther than was usually thought – Why not as high as the Moon said he to himself & if so that must influence her motion & perhaps retain her in her orbit, whereupon he fell a calculating what would be the effect of that supposition but being absent from books & taking the common estimate in use among Geographers & our sea men before Norwood had measured the earth, that 60 English miles were contained in one degree of latitude his computation did not agree with his Theory & inclined him then to entertain a notion that together with the power of gravity there might be a mixture of that force which the moon would have if it was carried along in a vortex, but when the Tract of Picard of the measure of the earth came out shewing that a degree was about 69.12 English miles He began his calculation a new & found it perfectly agreeable to his Theory.
The “year [Newton] retired again from Cambridge” was 1666, which means Stukeley’s recording of the event took place some 60 years after it happened. However, both Stukeley and Conduitt, among others, appear to have independently heard the story directly from Newton himself, making it reasonable to believe a falling apple was, indeed, the source of Newton’s first significant musings over how gravity works.
There are many different places which claim to be the home of the apple tree that inspired Newton’s theory, but the most likely one—given the accounts—is located at his family home of Woolsthorpe Manor near Grantham, UK.
And, yes, there is an apple tree there today that is thought to be the apple tree in question, though it has re-rooted in the interim after being knocked over in a storm in 1890. Now around 400 years old, the tree and the property are protected by the National Trust.
If you’re curious, the tree is a Flower of Kent, which doesn’t produce very good apples for eating by today’s standards, though they are considered good cooking apples. Further, the apples in question are green, not red as is often depicted in Isaac Newton/apple images.
You’ll note, of course, that Stukeley above stated there was more than one apple tree there at the time; so whether this remaining one is “the” apple tree is a question can’t be definitively answered until someone invents a machine that can take us back in time to observe the event. That being said, Dr Richard Keesing from the Department of Physics at the University of York makes a pretty good case for why it probably is the correct tree.
Despite this uncertainty, there are a many trees that have been started as grafts from the Woolsthorpe tree, including one at Trinity College in Cambridge which sits beneath the window of the room Newton used when studying there.
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Legend has it that a young Isaac Newton was sitting under an apple tree when he was bonked on the head by a falling piece of fruit, a 17th-century “aha moment” that prompted him to suddenly come up with his law of gravity. In reality, things didn’t go down quite like that. Newton, the son of a farmer, was born in 1642 near Grantham, England, and entered Cambridge University in 1661. Four years later, following an outbreak of the bubonic plague, the school temporarily closed, forcing Newton to move back to his childhood home, Woolsthorpe Manor. It was during this period at Woolsthorpe (Newton returned to Cambridge in 1667) that he was in the orchard there and witnessed an apple drop from a tree. There’s no evidence to suggest the fruit actually landed on his head, but Newton’s observation caused him to ponder why apples always fall straight to the ground (rather than sideways or upward) and helped inspired him to eventually develop his law of universal gravitation. In 1687, Newton first published this principle, which states that every body in the universe is attracted to every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them, in his landmark work the “Principia,” which also features his three laws of motion.
In 1726, Newton shared the apple anecdote with William Stukeley, who included it in a biography, “Memoirs of Sir Isaac Newton’s Life,” published in 1752. According to Stukeley, “After dinner, the weather being warm, we went into the garden, & drank thea under the shade of some apple trees… he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind…. occasion’d by the fall of an apple, as he sat in a contemplative mood.”
The esteemed mathematician and physicist died in 1727 and was buried at Westminster Abbey. His famous apple tree continues to grow at Woolsthorpe Manor.
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Do Sit Under the Apple Tree
By Owen Gingerich
By James Gleick.
Illustrated. 272 pp. New York:
Pantheon Books. $22.95.
OF all the heroes of the scientific revolution of the 16th and 17th centuries, when the old geocentric worldview was overthrown, Galileo has been the top target of biographers. A feisty figure who in Victorian times began to be seen as a »martyr of science» in consequence of his run-in with the Inquisition, Galileo led a public life well adapted to novels, drama, opera and a panoply of biographies. In contrast, the scientifically far more important but very private Isaac Newton has run a distant second. The comparative lack of personal detail and the complexity of his thought have thwarted potential biographers: Richard Westfall, who in 1982 produced what comes closest to being called the »standard» scientific account of Newton, wrote that »the more I have studied him, the more Newton has receded from me.»
James Gleick, whose book about chaos theory achieved critical acclaim, as did »Genius,» his biography of Richard Feynman, quotes Westfall in this biography of Newton, but undaunted, he accepts the challenge. By any account, even just one of Newton’s several accomplishments would be enough to enroll him among the memorable scientists of all time: the optics of color, the laws of motion, universal gravitation, the general binomial theorem, the differential and the integral calculus. Can a talented but nonspecialist science writer have any hope of contributing a serious, insightful biography of such a monumental man?
In this case Gleick wins the gamble. His »Isaac Newton» is now the biography of choice for the interested layman. Gleick copes with the complex tapestry of Newton’s interests by teasing them apart into individual chapters, assembled into a smooth chronological flow. For example, if we look at the extent of Newton’s reading list in theology in the same years that led up to the writing of his »Principia Mathematica,» it is hard to imagine that he had time to do any science or mathematics at all. Gleick does not omit the theology, or Newton’s long hours of experimental alchemy, but he partitions them into their own sections, a strategic decision that makes this multifaceted life remarkably accessible.
At least part of Newton’s range of accomplishments came from his ability to shut himself off and, as a recluse, to think with intense concentration on the questions that interested him. Strong and self-motivated as he was, his was nevertheless a fragile personality, unable to abide personal criticism. When Robert Hooke dared to disagree publicly with some of his experimental conclusions on the nature of light and color, Newton withdrew into his Trinity College chambers and sulked. When Hooke suggested, through Edmond Halley, the midwife for the »Principia,» that he should have some credit in the preface for finding the mathematical behavior of gravity, Newton harrumphed that science »is such an impertinently litigious Lady that a man had as good be engaged in Law suits as have to do with her. I found it so formerly & now I no sooner come near her again but she gives me warning.»
These moments of high controversy reveal the public Newton and bring drama to a mostly inscrutable life. Newton wrote to Hooke that if he had seen further, it was by standing on the shoulders of giants. Gleick avoids the cheap shot of pointing out that the misshapen Hooke was anything but a giant; he buries the comment in the bibliographical notes documenting his sources — with some disapproval of those who have given it disproportionate play. In fact, he treats Hooke’s claims to have anticipated Newton in some points with considerable sympathy, but he clearly conveys Hooke’s limitations and the considerable distance between what were Hooke’s conjectures and what Newton was able to accomplish.
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The most public of all of Newton’s controversies concerned the priority dispute with the German polymath Gottfried Wilhelm Leibniz over the invention of the calculus. Yet the public brouhaha concealed a secret underside, as modern investigations of the manuscript legacy reveal. When Newton, as president of the Royal Society, appointed an independent investigating committee to look into the matter, the 18th-century public could not know that it was Newton who wrote draft after draft of the committee’s report, and who also wrote the anonymous review of the report that appeared in The Philosophical Transactions, the official organ of the Royal Society. The Newton-Leibniz rivalry was not limited to the invention of the calculus. After the »Principia» appeared, Leibniz wrote to acquaintances saying he had had no idea Newton was working on the problem of motion, and so he published his own, presumably earlier account. When Newton saw it, he opined that Leibniz couldn’t have done it without seeing his own work. Late in the 20th century, when Leibniz’s manuscripts were finally sorted out, his first draft was found to contain frequent page references to the »Principia»!
While Gleick achieves an excellent balance among color, detail and narrative flow, sometimes the trees conceal the forest. If I had to summarize in a sentence Newton’s essential contribution to the scientific revolution, it would not single out gravitation, the laws of motion or the calculus, but rather his unification of the age-old dichotomy between the celestial and the terrestrial. In Aristotle’s vision, the ethereal heavens had their own unending circular motions, totally unworldly and separate from our world of earth, air, fire and water. Newton showed that the same laws of nature apply to earth and sky, to the apple and the moon. It was an upheaval of as great a consequence to human understanding as the heliocentrism of Copernicus 150 years earlier. With the Newtonian synthesis came full appreciation that natural processes, whether above or below, can be subjected to mathematical scrutiny. In the wake of his »Principia» came insight into the cause of tides, the shape of the earth, the return of comets, the intricate path of the moon.
The extraordinary breadth of Newton’s interests is brilliantly delineated by Gleick. Newton the man emerges from the shadows. If the unifier remains somewhat hidden, we can console ourselves with the rest of what Westfall said: »Only another Newton could hope fully to enter into his being, and the economy of the human enterprise is such that a second Newton would not devote himself to the biography of the first.»
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