by John Gribbin
Publication of the Principia was completed in July 1687, establishing Newton in the eyes of the world as the greatest scientific giant. Michael Cooper has suggested that ‘without Hooke’s hints and goading and Halley’s cash and moderating influence on both men, Newton might not have bothered with it.’ But he did bother, and Hooke would soon be relegated to a footnote of scientific history. The dispute rumbled on, at least from Hooke’s side, for the rest of the century. But in 1687 he was also struck by a more devastating personal blow when Grace died, at the age of only twenty-seven (Hooke was then fifty-two). Richard Waller tells us that ‘the concern for whose Death he hardly ever wore off, being observ’d from that time to grow less active, more Melancholly and Cynical’.fn10 More of Hooke’s declining years shortly, but first we want to spell out the key insights in the Principia, which paved the way for the development of modern physics, and highlight just who deserves credit for what.
First, we have the idea of a universal law of gravitation, the same in heaven as on Earth, showing that the same laws apply throughout the Universe. Definitely Hooke. Then, the fact that gravity is a centripetal attraction. Hooke again.fn11 The proof that an inverse square law is necessary and sufficient to explain planetary motion. Newton, but prompted by Hooke. Newton also spelled out in his book three laws of motion, which formed the foundations of physics. First, every body continues at rest or moving in a straight line unless acted upon by a force. Hooke, of course. Second, the acceleration of an object is proportional to the force acting on it. Newton. Third, when a force is applied to a solid object it responds with an equal and opposite force – action and reaction. Newton. And a more subtle but crucial notion: gravity operates at a distance, without the need for any intervening fluid such as the ether. Hooke.
By our count, that is Hooke four, Newton three, but allowing the importance of the mathematics we might as well call it fifty–fifty. That is, Hooke made a fifty–fifty contribution to Newton’s singular achievement, as well as all the other things he did for the development of science, while Newton made a fifty–fifty contribution to his own singular achievement, and nothing else for the development of science, except to make pretty patterns with prisms.
We exaggerate slightly, but nowhere near as much as the achievements of Newton have been exaggerated, relative to the achievements of Hooke, for more than three centuries.
Remember Hooke’s practical explanation for why the inverse square law should apply to gravity, based on the idea of an influence spreading out over the surface of an expanding sphere. As we explained, it also demonstrates the difference between the mind of a physicist and the mind of a mathematician. The physicist pictures what is going on and makes analogies with similar physical systems. The mathematician plays with equations and finds the ones that match the physical reality of our world. Science progresses when the equations and the physical insight come together in one package, but in the mid-seventeenth century there was no sense that the mathematical approach was more important, let alone pre-eminent. Indeed, ideas were the key component. Hooke was a great scientist, who came up with the first scientific world-view; Newton was a great mathematician, who put Hooke’s world-view on a secure mathematical foundation, and then claimed credit for the whole thing himself.
Although this is not a book about Newton (he has had plenty of books written about him), it would be remiss not to mention what happened to him after the publication of his masterwork, not least because his life took such an unexpected turn.
Postscript: Newton after the Principia
Newton did little of scientific significance after the publication of the Principia, although when Hooke was safely out of the way he did publish his Opticks, based on work he had done decades before and also including, without credit, Hooke’s ideas. A colleague of ours used to joke about a reference he had received in support (?) of an applicant for an academic post. It said ‘he is a man of singular talent’. Our colleague claimed that this meant ‘he only had one good idea in his life’. It might be slightly unkind to apply this epithet to Newton, but it isn’t far from the truth, especially compared with the breadth and depth of Hooke’s contributions. So what did Newton get up to in the forty years from 1687 to 1727?
The dramatic change in Newton’s life began before the publication of the Principia, and was a result of the death of Charles II in 1685 and the accession of his brother, James II. Charles had been happy to be at least nominally Protestant; James, however, was not only openly Catholic, but was foolish enough to attempt to impose his Catholicism on British institutions, including the University of Cambridge. On 9 February 1687, he ordered the University to admit a Benedictine monk, Alban Francis, to the degree of Master of Arts. This kind of thing was not uncommon – rather like the modern practice of honorary degrees. But it was clear that Francis, if he was admitted, would exercise his right as an MA to participate in the affairs of the University, and that James intended to make further appointments of this kind, packing the administration of the University with Catholics. The University resisted, and one of the leaders of the resistance was Newton, who suddenly came out of his shell and became actively involved in politics. The reason was simple. He was a closet Arian who did not accept key doctrines of the Church. By keeping quiet and, among other things, not taking Holy Orders (very unusual for a University Fellow), he had been able to get by as nobody had asked him any awkward questions. But if the University were to be taken over by Catholics, those awkward questions would surely be asked, and at the very least he would lose his position, as would indeed later happen to William Whiston. Attack being the best form of defence, Newton now devoted himself to the attack, speaking out against James’s interference in University affairs. This took some courage: Newton was one of nine Cambridge Fellows summoned before the notorious Judge Jefferies, then Lord Chancellor, to explain himself. But James’s position was increasingly shaky, and he was in no position to enforce his wishes. There was considerable Catholic sympathy in the country at large, but there was also an overwhelming wish not to get involved in any re-run of the turmoil of the middle part of the seventeenth century.
Something had to give, and the something turned out to be James. At the end of 1688, England was invaded by an army under the Dutch Prince William of Orange, who had been encouraged by a large section of the English Parliament to take the throne. William was the son of Charles II’s sister, and his wife Mary was the daughter of James II, which lent some semblance of legitimacy to the invasion, which was afterwards referred to by seventeenth-century spin doctors as ‘the Glorious Revolution’. But don’t be fooled by the spin: this, not the events of 1066, was the last successful invasion of British soil. James was allowed to leave quietly for exile on the continent.
In order to legitimise the takeover, a Convention Parliament was called in 1689 to establish William and Mary as joint monarchs, and the Church of England as, well, as the Church of England. The University of Cambridge was entitled to send three of its Fellows as Members of Parliament (nothing so sordid as a public election was involved), and Newton, wreathed in the glory of his public stand against James, was one of them. He said nothing and voted the party line during the year and a month that the Parliament sat, but suffered one disappointment. When the Parliament passed an Act to give more tolerance to religious dissenters, it specifically excluded ‘any person that shall deny in his Preaching or Writeing the Doctrine of the Blessed Trinity.’ But the disappointment must have been tempered by a development in Newton’s personal life.
Christiaan Huygens had a brother, Constantijn, who was a secretary to King William. Naturally, Christiaan visited his brother in London and attended meetings of the Royal, where he met Newton on 12 June 1689. On 9 July Newton visited Christiaan at Hampton Court. On both occasions a young Swiss mathematician, Nicholas Fatio de Duillier (usually referred to as Fatio), was also present, as a member of Huygens’ party. Fatio seems to have hero-worshipped Newton, in the manner of a scientific groupie, and Newton seems
to have become infatuated with Fatio. The intense friendship lasted for about four years. Fatio spent a month with Newton in London in 1690, then just over a year based in the Netherlands, where he acted as a conduit for the exchange of ideas between Newton and Huygens. There were other visits to England, and plans for Fatio to live in Cambridge while working with Newton on a new edition of the Principia. But the close relationship ended in 1693. After Fatio suffered an unspecified illness at the end of 1692, Newton urged him repeatedly to come to Cambridge to recuperate, but Fatio declined and the correspondence petered out, although Fatio remained an extravagantly enthusiastic supporter of Newton, particularly in the dispute with Leibniz about who had invented calculus.
In the early 1690s, Newton found life in Cambridge frustrating after his experiences on the broader London stage, and began looking for other employment while devoting himself once again to alchemy. Overwork, frustration at the lack of new opportunities, the break-up of his friendship with Fatio, and the trial of keeping quiet about his sexuality and religious thinking all took their toll, and he suffered a major nervous breakdown in 1693. He gradually recovered, with the support of his colleagues, and in 1696 was offered the post of Warden of the Royal Mint, which he seized on with delight. The appointment was officially dated from 19 March, and by the end of April Newton had shaken the dust of Cambridge from his shoes and was installed in London, where he would remain (except for a few brief visits to Cambridge) for the rest of his life.
The appointment was clearly intended as a sinecure, a reward for past services; the letter of appointment said that it did not ‘require more attendance than you may spare’. The Warden was Number Two at the Mint, which was officially run by the Master. But Newton was incapable of taking things easy, and the Master, Thomas Neale, was happy to let him do all the work if he was so inclined. And there was plenty of work to do. The Mint was about to carry out a complete recoinage, a task that Newton oversaw with his usual single-minded obsessiveness. We also get another insight into his character. One of his tasks was to prosecute counterfeiters, a job he relished so much that he became a magistrate, so that he could not only catch forgers but convict them, usually to be hung. When Neale died in 1699, Newton took over as Master of the Mint, a post he held until he died, although in later years his work was done by a deputy. In 1701, Newton resigned all his posts in Cambridge, having made £3,500 from his post at the Mint that year.
History repeated itself in the early 1700s. Newton became an MP again in 1701, and when William died in 1702 (Mary had predeceased him), Queen Anne, Mary’s sister, succeeded to the throne. During an election campaign in 1705, Anne gave knighthoods to some of her favourites, including Newton, to encourage support for the faction she favoured. The faction Anne favoured did poorly, however, and he was not returned to Parliament that year, or ever again. But the tale is worth telling because many people think Newton was the first person to be knighted for his scientific work. He was not: he was knighted as a party political ploy.
Although Newton would never again serve as an MP, he now had something else to occupy him, apart from his duties at the Mint. In his early sixties in 1703, and with Hooke dead, he was elected as President of the Royal Society, which he ruled with a rod of iron for the next two decades. He also took the opportunity to publish his Opticks in 1704. And somehow, early in Newton’s Presidency when the Royal moved out of Gresham College and into new quarters at Crane Court, the only known portrait of Robert Hooke disappeared. Newton died on 20 March 1727, at the age of eighty-two. Plenty of portraits of him survive. It is worth noting, though, that as late as 1717, in the second English edition of the Principia, Newton, the mystic, was still trying to ‘explain’ gravity in terms of the influence of a medium, the aether, with non-uniform density, through which the planets (‘gross bodies’) moved. His ‘Query 21’ is as confused as any of his writing before the correspondence with Hooke about planetary motion:
And so if any one should suppose that aether (like our air) may contain particles which endeavour to recede from one another (for I do not know what this aether is), and that its particles are exceedingly smaller than those of air, or even than those of light, the exceeding smallness of its particles may contribute to the greatness of the force by which those particles may recede from one another, and thereby make that medium exceedingly more rare and elastick than air, and by consequence exceedingly less able to resist the motions of projectiles, and exceedingly more able to press upon gross bodies, by endeavoring to expand itself.
It seems he never did grasp the significance of Hooke’s concept of a centripetal force which deflects the straight line path of a planet (or, indeed, a comet) into a curve. The irony will become clear in Chapter Eleven, but, as we have hinted, we might well have never had the Principia at all, had it not been for a series of unfortunate events.
CHAPTER EIGHT
HALLEY, NEWTON AND THE COMET
Isaac Newton may never have produced his masterwork if Edmond Halley’s father had not been murdered. Since that murder has been linked with the sordid aftermath of a plot against the King and his brother, it seems that we may not have had the Principia, with all that that implies for the history of science, had it not been for the Catholic leanings of Charles II, and the open Catholicism of James, Duke of York, the heir apparent.
The anti-Catholic plotters intended to murder both Charles and James at Rye House, Hoddesdon, in Hertfordshire, on their way back to London from the races at Newmarket in April 1683; so the misadventure has become known as the Rye House Plot. The plot was betrayed, and several conspirators, including the Earl Russell, Algernon Sidney, and the Earl of Essex, were arrested and imprisoned in the Tower of London awaiting trial for high treason. Russell and Sidney were duly tried, convicted and beheaded. But Essex died in the Tower, without coming to trial, in mysterious circumstances, which is where Edmond Halley senior comes into the story.
As a prominent citizen, the elder Edmond Halley was a Yeoman Warder of the Tower. This was a largely honorary position, with some ceremonial duties, and with the advantage that it excused holders of the post from certain other tedious tasks. Alan Cook, who provides the most complete and up-to-date account of the circumstances surrounding the elder Halley’s death, quotes a pamphlet from 1690 which says ‘This Mr Hawley was very rich, and a warder only to exempt him from parish services but he never waited [at the Tower], unless it were on very solemn occasions’. On 13 July 1683, both the King and the Duke of York visited Essex in the Tower, and Halley senior was among the party, this no doubt being a solemn occasion, if not part of the usual ceremonial duties. Shortly afterwards, Essex died, apparently having cut his own throat. The official story was that he asked for a small knife to trim his fingernails, but that the guard did not have such a knife so lent him a razor. Essex then went into an annexe off his main apartment, where he was later found with his throat slit and covered in blood. Although there were inevitably rumours that he had been murdered, suicide does seem the most likely bet. But the guard seems to have been remarkably careless, and the most plausible explanation of the course of events is that the King, or more probably James, colluded with Essex to allow him to avoid the stigma of conviction and beheading. The Earl’s father had died fighting for Charles I, which might have encouraged leniency, so Essex might have been offered an easy way out, according to the code of the time. Had he been convicted of treason, apart from the stigma there was the practical matter that the family estates would have been forfeited to the Crown. There is also a possibility that Essex was indeed murdered. We shall never know the details, but Edmond Halley senior certainly seems to have known something, which probably cost him his own life.
On 5 March 1684, the elder Halley left home in the morning, telling his wife that he would be back in the evening. He had been having a problem with shoes that pinched his feet, and removed the lining before he left the house. He was never seen alive again. More than a month later, on 12 April, his body was found washed up near Ro
chester, on the Medway. It was badly disfigured, although the exact details of the injuries were never published, and identified by the victim’s unlined shoes. But the inquest concluded that he had not been in the river long, or the body would have been more ‘corrupted’. The verdict was murder by some unknown person or persons, and it seems likely that the corpse was thrown overboard from an outward-bound ship. Speculation at the time, and for years afterwards, was that the elder Halley knew too much about the fate of Essex, had been brooding for months and was now threatening to talk, so he had been silenced. Conspiracy theorists had a field day, with pamphlets being published about the case, but as time passed interest faded, especially after Charles died and James went into exile. We shall never know for sure what happened, but the evidence collected and presented by Cook persuasively makes the case that the elder Halley’s death was not a simple mugging gone wrong.
Whatever the cause of Edmond Halley senior’s death, it changed the younger Halley’s life dramatically, not least because his father had died intestate, and ‘our’ Edmond Halley was not on good terms with his stepmother. Flamsteed wrote to Molyneux in Dublin that:
Mr Halley I suppose may return to live in London, his father having been found drowned [sic] about a fortnight ago in Rochester river. This mishap will cause him a great deal of perplexed business, but nevertheless I hope to see him oftener than I have done of late.
If Flamsteed hoped to carry out joint observations with Halley, those hopes were dashed. After the events of March and April 1684 Halley virtually gave up observing, including his plan to chart the entire lunar cycle, until, eventually, he succeeded Flamsteed as Astronomer Royal.