Science Secrets Page 7

  He [Milton] took from that ridiculous Trifle the first Hint of the noblest Work, which human Imagination hath ever attempted, and which he executed more than twenty Years after.

  In the like manner, Pythagoras ow'd the Invention of Musick to the Noise of the Hammer of a Blacksmith. And thus in our Days, Sir Isaac Newton walking in his Gardens, had the first Thought of his System of Gravitation, upon seeing an Apple falling from a Tree.

  If the Difference of Genius between Nation and Nation, ever appear'd in its full Light, ‘tis in Milton's Paradise Lost.

  The French answer with a scornful Smile, when they are told there is in England an Epick Poem, the Subject whereof is the Devil fighting against God, and Adam and Eve eating an Apple at the Persuasion of a Snake.13

  Thus the story about Newton and the apple appeared in print, layered between Milton, Pythagoras, the Devil, God, Adam, Eve, and the snake. One could hardly wish for a more wonderful public birth for this scientific tale! A few years later, without writing about Adam or Eve, Voltaire elaborated his account of Newton's creative moment:

  He retreated in 1666, because of the plague, to the countryside near Cambridge, one day he was walking in his garden, & he saw fruits fall from a tree, he let himself go into a deep meditation about such Gravity about which all the philosophers have sought the cause for so long a time in vain, & in which the common people do not even sense the mystery; he said to himself, from any height in our hemisphere that these bodies fall, their descent will certainly be at the rate discovered by Galilei; & the spaces covered by them will be as the squares of the time. This power which makes heavy bodies descend, is it the same without any sensible diminution to any depth that one be in the Earth, & atop the highest mountain; why might not that power extend right up to the Moon? And if it is true that it reaches that far, is there no great likelihood that this power holds her in orbit & determines her motion?14

  Here, Voltaire just wrote about “fruits,” rather than specifying an apple. He noted that he had learned of this event from Newton's niece, Catherine Barton, wife of John Conduitt (the couple lived with Newton in his house in London, until he died).15

  One more report is worth mentioning. Henry Pemberton had interviewed Newton about the thoughts that led him to his theory of gravity. And Pemberton too reported:

  As he sat alone in the garden, he fell into a speculation on the power of gravity: that, as this power is not found sensibly diminished at the remotest distance from the center of the earth, to which we can rise, neither at the tops of the loftiest buildings, nor even on the summits of the highest mountains; it appeared to him reasonable to conclude, that this power must extend much farther then was usually thought; why not as high as the moon, said he to himself? And if so, her motion must be influenced by it; perhaps she is retained in her orbit thereby.16

  Pemberton did not mention an apple, but he reported that Newton had inspirational thoughts while alone in the garden.

  An important aspect of the apple story is that, over time, in contrast to other questionable stories, evidence for it has increased. In 1831, David Brewster published a biography of Newton, and he noted, “The anecdote of the falling apple is mentioned neither by Dr Stukely nor by Mr Conduit, and, as I have not been able to find any authority for it whatever, I did not feel myself at liberty to use it.”17 Later, Brewster did find one account by Conduitt; and others later found Stukeley's detailed, handwritten account.

  Henry Pemberton, William Stukeley, John Conduitt, Catherine Barton, and Martin Folkes all apparently claimed that Newton said that he was inspired at the garden in 1665 or 1666, and apparently four of them referred to a fruit or apple. If we had a document by Newton himself, we would regard it as a firsthand account; hence, two of our sources are at least secondhand (Stukeley and Conduitt), and two others (Voltaire and Greene) are at best thirdhand accounts. Still, the nine manuscripts and published accounts converge on one conclusion: the story came from Newton.

  It might seem as if I just asserted that really Newton was inspired by a falling apple in the year of the plague, 1666. But note that I did not actually claim that. We have no good reason to assume that Voltaire and others accurately described the sequence of thoughts, the chain of reasoning, that apparently was triggered by an apple, sixty years earlier. Instead, there are plenty of manuscripts that historians have used to fairly trace Newton's gradual progress. And in any case, it took Newton many years of work to formulate his mathematical theory of universal gravitation.

  Another problem is that in order to gauge Newton's honesty, we need to question his originality. It is inspiring to imagine that the young lad, sitting alone in his garden, was the first person to imagine that the force of gravity extends all the way up to the moon. But actually, such arguments were relatively common in astronomy at the time. For example, in 1609, Kepler published a work in which he explained gravity and the tides as follows:

  If the Earth should cease to attract its waters to itself, all the sea waters would be raised, and would gush up to the body of the Moon…. The sphere of influence of the attractive virtue in the Moon extends out onto the Earth, and it lifts up the waters in the torrid zone…. Therefore, if the Moon's attractive virtue extends as far as the Earth, it follows with greater reason that the Earth's attractive virtue extends to the Moon, and far beyond; and thus, nothing that consists of earthly material whichever, though lifted up to any height, can ever escape the powerful action of this attractive virtue.18

  There it was, already—the idea that gravity extends beyond the height of mountains, up to the moon, and that there is a mutual attraction between Earth and the moon. Following William Gilbert, Kepler had tried to explain gravity as caused by a magnetic power within bodies. Kepler's work was one of the most widely circulated texts in astronomy. Kepler did not claim that the planets attract one another, only kindred bodies such as Earth and the Moon. Kepler did not have a notion of universal gravity, but Newton's reportedly initial reflections about the apple were quite consonant with previous astronomers' works.19

  Another problem is that Newton was secretive, paranoid, and quite capable of making up stories to backdate his discoveries and to claim priority over someone else. For example, his law of gravity was so impressive that there were debates and speculations about its origins.

  Independently of Newton's work, Robert Hooke guessed that the force of gravity decreases inversely as the square of the distance.20 He inferred and complained, wrongly, that Newton had plagiarized his account.21 Deeply annoyed, Newton proceeded to delete his previous acknowledgments to Hooke from his Principia and look instead for an older, more prestigious pedigree for his discovery. To Newton, the inverse square law seemed reminiscent of the brilliant accomplishments of the ancient philosophers. He surmised that Thales and Pythagoras knew well that some bodies exhibit magnetism, electricity, and gravity—acting at a distance upon one another—because they are all infused by the animating soul of God.22

  Newton began to associate his notion of universal gravity with Pythagorean legends. Tradition claimed that the Pythagoreans had found that the same tension on a string half as long acts four times as powerfully. Newton conjectured that the Pythagoreans had hidden their knowledge about gravity and the solar system in such statements.23 Newton knew of the old claim that Pythagoras experimented with intestines of sheep and sinews of oxen stretched by hanging weights, and conjectured that Pythagoras had discovered a musical proportion which Pythagoras: “applied to the heavens and consequently by comparing those weights with the weights of the Planets and the lengths of the strings with the distances of the Planets, he [Pythagoras] understood by means of the harmony of the heavens that the weights of the Planets towards Sun were reciprocally as the squares of their distances from the Sun.”24 Newton based his conjectures on claims by Macrobius: that “Pythagoras was the first of all the Greeks” to grasp that the rotations of the heavenly spheres emit harmonious sounds, and, that Pythagoras discovered “the great secret” of the numerical
ratios of the fundamental musical concords by experimenting with hammers, stringed instruments, and intestines and sinews stretched by weights.25

  It is merely fiction that Pythagoras knew the law of gravity. The accounts of how he allegedly discovered the musical ratios are also false because, contrary to the claims by ancient writers, replications of the described experiments do not reveal the effects sought. For example, the vibrations of strings are not proportional to the number of units of weight on the strings, but to the square roots of the units of weight. (Accordingly, Newton improved his version of what Pythagoras allegedly found in music.) Likewise, hammers of different weights do not necessarily produce a different tone or pitch. For example, it is difficult to distinguish the sound of a one-pound hammer striking iron on an anvil in contrast to a two-pound hammer.

  Nevertheless, Newton credited Pythagoras. Accordingly, his friend Fatio de Duillier noted that Newton believed that Pythagoras, Plato, and others were well aware of the inverse square law of gravity, and had anticipated all of Newton's demonstrations.26 John Conduitt noted in a manuscript that “Sir I. admired Pythagoras [and] thought his Musick was gravity.”27 Another confidant, David Gregory, went even further by attributing the law of gravity to Pythagoras by the same speculative conjectures, without evidence—in a textbook.28

  This example illustrates how the authority of a successful scientist, Newton, enabled his arbitrary historical conjecture infiltrate a science textbook, a common happening in the history of physics. Fortunately in this particular case, other authors did not copy Gregory's account, so Pythagoras did not become the widely acknowledged author of the inverse square law.

  Now, Voltaire mentioned Newton while discussing Paradise Lost. Milton's poem includes science: it refers to Galileo, it ponders whether the sun is the center, whether Earth has three motions, as Copernicus argued. It refers to the sun's magnetic “attractive virtue,” like Kepler. In Milton's Garden of Eden, the serpent claimed to have eaten apples from the tree of knowledge of good and evil.29 It gained speech and reasoned about “things visible in Heav'n or Earth.” Leading curious Eve to the prohibited “root of all woe,” the serpent praised this tree, “Mother of Science,” which gave knowledge of causes. Eating, Eve became inebriated by the “sciential sap.”30 Let's summarize similarities between stories:

  Risking death, young Eve wandered in her Father's garden. She conversed with the serpent by the apple tree. Eve ate an apple and began to think differently about heaven and Earth. She shared this new knowledge; she proceeded to sin. Affected by a natural trifle, Eve ruined the harmony of the world.

  Avoiding the plague, young Isaac retreated to his mother's garden. He sat alone in contemplation, near an apple tree. An apple fell, Isaac began to think differently about heaven and Earth. Keeping this new knowledge secret, he proceeded to science. Affected by a natural trifle, Isaac found the harmony of the world.

  In both stories, a God-fearing youth discovers extraordinary truth about the world thanks to an ordinary thing.

  Shortly before dying, Newton apparently said: “I don't know what I may seem to the world; but as to myself, I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.”31 He seemed to echo Milton:

  Deep versed in books, and shallow in himself,

  Crude or intoxicate, collecting toys

  And trifles for choice matters, with a spunge,

  As children gathering pebbles on the shore.32

  By 1827, an amusing claim arose: “When Newton read ‘Paradise Lost,’ he calmly remarked, ‘It is a fine poem, but what does it prove?’”33

  It is very plausible that Newton saw an apple fall; for there were apple trees in his farm. Regardless of whether the event happened, it effectively has the shape of a myth: the simple start of a great development, a major transformation. It therefore resonated and gained currency. Consider now some traces of how the original account evolved.

  In 1760, the mathematician Leonhard Euler wrote many letters explaining science to the Princess of Anhalt Dessau, niece of the King of Prussia. In one such letter, Euler conveyed a version of this story that later became common:

  This great English philosopher & mathematician, one day was laid down in a garden, under an appletree, an apple fell on his head, & gave him occasion to have several thoughts. He knew well that heaviness had made the apple fall, after it detached from the branch, maybe by the wind or by another cause. This idea seemed very natural, & maybe any peasant would have had the same thought, but the English philosopher went much further…. If Newton had not laid down in a garden under an appletree, & if by chance an apple had not fallen on his head, maybe we would still find ourselves in the same ignorance about the motion of heavenly bodies, & about an infinity of other phenomena that depend on that.34

  Thus by 1760, it seemed that the apple had actually hit Newton on the head! Euler's letters were published and translated into several languages.

  In 1791, a work was published anonymously, titled Curiosities of Literature. The author argued, “Accident has frequently occasioned the most eminent geniuses to display their powers.”35 He claimed that great poets, philosophers, and artists alike are made by sudden incidents:

  It is also well known, that we owe the labours of the immortal Newton to a very trivial accident. “When, in his younger days, he was a student at Cambridge, he had retired during the time of the plague into the country. As he was reading under an appletree, one of the fruit fell, and struck him a smart blow on the head. When he observed the smallness of the apple, he was surprised at the force of the stroke. This led him to consider the accelerating motion of falling bodies; from whence he deduced the principles of gravity, and laid the foundation of his philosophy.”36

  The anonymous author was Isaac D'Israeli, a Doctor in Civil Law at the University of Oxford. As an essayist, he became very popular, and was celebrated by George Byron (later Lord Byron), Sir Walter Scott, and other eminent men. Regarding his comments on Newton, apparently D'Israeli was quoting a prior account; it was not his own invention. Still, his Curiosities became widely reprinted and reissued.

  Afterward, the poet Baron Byron composed several lines about Newton and the apple. The lines are part of his poem Don Juan, published in 1823. A beautiful thing about these lines, in hindsight, is that they foretell of journeys in spaceships to the moon:

  When Newton saw an apple fall, he found

  In that slight startle from his contemplation—

  ’Tis said (for I'll not answer above ground

  For any sage's creed or calculation—)

  A mode of proving that the earth turned round

  In a most natural whirl, called “Gravitation;”

  And this is the sole mortal who could grapple,

  Since Adam, with a fall, or with an apple.

  Man fell with apples, and with apples rose,

  If this be true; for we must deem the mode

  In which Sir Isaac Newton could disclose

  Through the then unpaved stars the turnpike road,

  A thing to counterbalance human woes:

  For ever since immortal man hath glowed

  With all kinds of mechanics, and full soon

  Steam-engines will conduct him to the Moon.37

  Meanwhile, a few writers became annoyed by D'Israeli's account of Newton and of other historical figures. One writer suggested that D'Israeli should write about “the Inconsistencies of authors” and include himself as an example.38 Another, the literary critic Bolton Corney, sought to refute D'Israeli's distortions of many topics. Corney had first read Curiosities at a young age and had greatly enjoyed it, but he was perplexed by its many errors when he again read it in its ninth edition of 1834. To rebut D'Israeli's account of Newton, Corney quoted the writings of Conduitt, Voltaire, Pemberton, and a few later writers. Corney complained against men who accept, va
lue, and echo hearsay of hearsay. He said that it's important to correct the errors of popular works and that “it may also be expedient to unveil the deception and conceit of its author.” He estimated the propagation of errors in this particular book's many editions: “we must conclude that D'Israeli, in this instance alone, had misled more than twenty thousand of his readers!”39

  Instead of simply admitting his mistakes, the famous D'Israeli defended himself in a pamphlet.40 He belittled Corney as incompetent without giving any evidence to ground his old claims. Corney replied: “I am not apt to be reckless when the truth is at stake; nor was I reckless on this occasion…. If I may now be permitted to hint to the man of ideas, that ideas unsupported by facts are mere day-dreams…. I have built my sixth-rate bark of the best materials within reach; have equipped her to the best of my humble skill for the service required; and she shall float on the stream of time in spite of the broad-sides of the write-with-ease school.”41 In this seemingly trivial and irrelevant corner of knowledge, someone fought seriously for a little bit of truth. In short, the famous man had argued by authority, and just shrugged off the critique. But Corney was right, his humble vessel has remained afloat, even in relative darkness, while D'Israeli's account is now known as mere fiction.42

  The mathematician Augustus De Morgan also commented fairly about the apple story, and he too criticized D'Israeli: “I cannot imagine whence D'Israeli got the rap on the head, I mean got it for Newton: this is very unlike his usual accounts of things. The story is pleasant and possible: its only defect is that various writings, well known to Newton, a very learned mathematician, had given more suggestion than a whole sack of apples could have done, if they had tumbled on that mighty head all at once.”43 Some writers viewed Newton's insight as caused by the accident; others denied that great discoveries are triggered by accidents, and instead insisted, like De Morgan, that Newton's discoveries stemmed from his extraordinary studies; and still other writers attributed such breakthroughs to the innate quality of men. One anonymous writer argued: “these discoveries are not due to the accident of this or that occurrence taking place at this or that time, but almost entirely to their taking place before the eyes of some fit observer—some one of those spirits which are ever looking from the watch-towers of science into the dark fields of the unknown before them—that a Newton was in the garden when the apple fell—applies with great force.”44 At the time, many people were interested in the would-be science of phrenology, the study of how the shape of a person's head is correlated to intelligence and behavior. Phrenologists generally disagreed with D'Israeli's account: it was not that the apple had hit Newton's head and caused his mental development; it was that his innate mental features enabled him to extract knowledge from the falling apple.