Throughout Newton's life, if his working time was spent on science, alchemy, prophecy and economics, he seems to have spent virtually all of his free time getting very wound up about a series of high-profile enmities.

1672 - 1703: Robert Hooke

From the moment that Newton joined the Royal Society, on the basis of his practical and theoretical work on optics, he crossed swords with the Society's Curator of Experiments, Robert Hooke. Initially, this dispute was diffused by the diplomacy of Henry Oldenburg, the secretary of the Royal Society and Newton's original link to the organisation.

Newton was admitted to the Society on the strength of his revolutionary reflecting telescope, plus his promise of a contribution to the Philosophical Transactions (the society journal) on his Theory of Light and Colours. When he published this, Hooke savaged it for Newton's assumption that light was 'corpuscular' (i.e. made from particles), as opposed to Hooke's own wave theory of light. Hooke also claimed that he had himself invented a reflecting telescope previously. This was a blatantly false claim¹. In June 1672, Newton counter-attacked. He delivered to the assembled Society a stinging and comprehensive rebuttal of Hooke's claims. Hooke was publicly humiliated, and issued with an official reprimand from the Society. Newton had won the battle, but war had been declared. Hooke was a significant figure in the Society, and hence in scientific society in general, and he would never forgive Newton for this episode - and neither was Newton inclined to forgive Hooke. Rather, from this time on Newton would have an ingrained distrust of publishing his discoveries; he would come to view it as opening himself to public and personal attacks. Although Hooke can hardly be held innocent here, this intense rivalry - enmity, really - was to become a recurring pattern throughout Newton's life.

In January 1676, Hooke again attacked Newton, albeit this time less publicly. He alleged that Newton had plagiarised Hooke's Micrographia, which contained Hooke's own theory of light. It was during this exchange that Newton famously replied that if he had 'seen further than others, it was by standing on the shoulders of giants.' Although this has gone down in history as a classic piece of modesty, in fact it was almost certainly a spiteful dig at Hooke's own physical deformities - he was a hunchback, and notably shorter than average.

The timing could not have been worse for this feud to flare up again. Isaac Barrow, one of Newton's key supporters, died the next year and a few months later Henry Oldenburg followed him, further isolating Newton - and Hooke succeeded Oldenburg as Secretary of the Royal Society. For now, Hooke was on the ascendant.

In 1679 - just after the death of Newton's mother - Hooke took full advantage of his new social superiority to avenge his earlier humiliation. In private correspondence, Newton had trustingly shared calculations that, he believed, showed that the path of a body falling to Earth would be a spiral. Hooke realised that Newton's argument only held true if the body were precisely on the equator, and in the more general case the path would be an ellipse. Hooke immediately pounced on the error, and expostulated it in public to the Royal Society. Newton was understandably incensed; to have made a slip was a blow enough to his self-image, but to have this publicly expounded upon based on supposedly confidential correspondence was a calculated insult. (Hooke had told Newton in writing that their correspondence would be 'no otherwise further imparted or disposed of than you yourself shall describe'.) From here, there was no going back for Newton's relationship with Hooke.

Newton responded to Hooke briefly, and then basically sulked, writing to no one for a year. He described Hooke (in private) as 'a man who does nothing but pretend & grasp at all things.' From then on, Newton would regard him as a personal enemy. It was probably from this that Newton went on to calculate that an inverse square law of gravity would lead to elliptical orbits - see Isaac Newton: Genius. Hooke, meanwhile, spared Newton no mercy. Having forced Newton to publically accept one error in his work, Hooke now delved further and uncovered yet more (ironically using an incorrect method himself, although coming to the correct conclusion).

When Newton came to publish the Principia in 1687, this feud again reared its head, as Hooke demanded that the inverse square law be attributed to him². Only the diplomatic intervention of Edmund Halley persuaded Newton to allow the publication of the final volume in his trilogy, Halley telling Newton that Hooke was merely making a public fool of himself - and even then Newton spitefully removed every reference to Hooke.

From there, the feud died down. Its public outpourings limited themselves to a spiteful review of the Principia in a French academic publication, almost certainly penned by Hooke. In private the two detested each other, and on at least one occasion Hooke is known to have left meetings of the Royal Society as Newton entered the room. Hooke died in 1703, never reconciled to Newton. It was only once Hooke was dead that Newton finally felt able to fully publish his Opticks, largely based around the work that Hooke had so savaged.

1672 - 1673: Christiaan Huygens

Christiaan Huygens was next in line to cross swords with Newton. Huygens also queried Newton's theory of gravity, echoing many of the points that Hooke made. This time, Huygens can hardly be held at fault. He questioned Newton politely and, more importantly, in private correspondence. Nevertheless, Newton took affront, probably still over-sensitive due to the treatment he had received from Hooke, and even threatened to resign from the Royal Society. Clearly, Newton did not like to be questioned under any circumstances, and even at this early stage in his public career there was something of the prima donna about him.

This was one of the few professional disagreements that Newton had that seems to have been resolved amicably. Newton's initial reaction faded away, and there is no question of Huygens feeling any personal animosity towards the Englishman.

1680 - 1719: John Flamsteed

When Newton needed observations on the 'double' comet of 1680, he turned to the Astronomer Royal, John Flamsteed. Ironically, it was Flamsteed who first proposed that the two comets were one, an idea that Newton initially rejected. Instead, Newton sought a purpose for comets in God's great plan for the universe - they might refuel the sun and stars, or perhaps the tail 'replenished life on Earth'. It was clear that Flamsteed could not keep up with Newton's theoretical leaps, writing 'I cannot conceive of any impression made by the one planet... can disturb the motion of the other. It seems unlikely such small bodies as they are compared to the Sun... should have any influence upon each other at so great a distance.' But his practical observations were essential to Newton. Within five years, Newton was clearly thinking of a more general - indeed, a universal - gravitation, while Flamsteed was still hung up on the counterargument that magnetism, a much stronger force than gravity, was undetectable even 100 yards away.

Flamsteed's background was not dissimilar to Newton's. The son of a tradesman, his mother had died when Flamsteed was three years old. The position of Astronomical Observer - later Astronomer Royal - was created for him in recognition of his talents. Even before he fell out with Newton, he had feuded with Edmund Halley after the latter had the temerity to correct some errors in a table of tides that Flamsteed had compiled. Like Newton, Flamsteed was rather puritanical, with a somewhat spartan lifestyle.

The major break with Newton came as a consequence of some small errors in the data Flamsteed sent to Newton. Flamsteed attempted to make amends by carrying out some of the calculations that Newton needed for himself - but Newton caustically informed Flamsteed that he needed his observations, not his calculations. Flamsteed could hardly help but feel mistreated, and he threatened to withhold his data.

Newton needed these calculations for a new section he was planning for the second edition of the Principia, around 1703, on a 'Theory of the Moon'. So he used his courtly influence to persuade Queen Anne's husband, George, to commission a royal star catalogue, to be printed by the Royal Society. It was a clever gambit. Flamsteed could hardly refuse this commission from his direct employer; and yet the moment he handed his draft data over to the Royal Society, it was certain to go straight to Newton, who now dominated there. Flamsteed did the only thing he could; he stalled. He published data as slowly as possible; when he had to publish something, he made certain it was not the data that Newton needed. He quibbled over an error in Newton's measurement of the size of stars in Opticks. In response, Newton deliberately excluded Flamsteed from the discussions about the publication of his catalogue. Flamsteed's personal salary of £100pa had to cover staff and equipment, and his request for a £2,000 grant to purchase a new telescope was rejected under Newton's influence. Finally, Flamsteed's tenacity paid off; in 1708, Prince George died, and the star catalogue project died with him. Without a sponsor, it simply dried up. Newton took what revenge he could; when Flamsteed's membership of the Royal Society lapsed in 1709, Newton refused to renew it, effectively expelling Flamsteed.

But Newton was never one to let an old grudge die, and besides he was desperate for the data he needed for his study of the Moon. By 1711, he had persuaded Queen Anne to take up the mantle of sponsor of her late husband's project. He also now began to exert more direct pressure on Flamsteed. A rather snitty note of 1711 threatened that '[If you] make any excuses or unnecessary delays it will be taken for an indirect refusal to comply with Her Majesty's order.' In Newton's eyes, failure to comply with his every whim was becoming little short of treason.

The matter came to a head with the eclipse of 4 July, 1711. Observations on this would be invaluable to Newton's calculations. Flamsteed flagrantly refused a direct order to observe it. He was ordered to explain himself before a panel of the Royal Society. This was playing on Newton's home turf now, and at last the hounds seemed to have the fox at bay. The council that was to stand judgement over Flamsteed was selected by the President of the Royal Society - one Sir Isaac Newton - and consisted of Newton and two of his most loyal supporters. It was no surprise when the council ordered the immediate publication of all Flamsteed's hard-won data.

Flamsteed's masterwork, Historia Coelestis, was finally published in 1712, against Flamsteed's wishes and without his involvement. Flamsteed was distinctly underwhelmed with the result, describing it as 'corrupted and spoiled'. The following year, Newton issued the second edition of his Principia, compete with a lunar theory based on Flamsteed's data.

Newton's victory seemed complete, but over the following years, Flamsteed did manage some small measure of revenge. Following the deaths of Queen Anne in 1714 and Lord Halifax, Newton's court sponsor, in 1715, Newton lost influence at court and Flamsteed gained it. Flamsteed was able to have all the copies of the Historia (around 300) purchased and burned. After Flamsteed's own death in 1719, a revised version was published, in line with Flamsteed's intentions. It was all Newton could do to suppress Flamsteed's intended introduction:

Sly Newton... was ready at coining new excuses and pretences to cover his disingenuous and malicious practices... For, honest Sir Isaac Newton (to use his own words) would have all things in his own power, to spoil or sink them; that he might force me to second his designs and applaud him, which no honest man would do or could do; and, God be thanked, I lay under no necessity of doing.

1684 - 1716: Leibniz

Perhaps Newton's most celebrated feud was that with Gottfried Wilhelm Leibniz. Again, there were parallels between the two men, including the strict religious upbringing (Leibniz was a Lutheran), the early death of a father and the rise to scientific acclaim.

Leibniz had the unusual distinction of having been rejected for a doctorate and then having refused a professorship. The University of Leipzig had refused to present him his doctorate because, at 20, he was too young. Then Nuremberg University granted him not only a doctorate - in law - but also offered him a professorship, which he declined in order to spend more time with science. He became a member of the Royal Society in 1673, and over the next two years, in Paris, developed the mathematics of calculus. It was this that was to lead him into conflict with Newton.

Leibniz used John Collins as a publisher and as his contact with the Royal Society, and it is clear that Collins kept Leibniz appraised of Newton's progress. Eventually, Leibniz would receive full details of Newton's discovery of the 'method of fluxions' - calculus - but it is clear that this happened only after Leibniz had perfected his own version. Perhaps due to his ongoing dispute with Hooke over optics, Newton was slow to publish his findings (which dated back to his anni mirabili - see Isaac Newton: Genius). Sensing trouble brewing, mutual friends persuaded Newton to contact Leibniz; Newton penned two lengthy letters in which he attempted to demonstrate that he had invented calculus many years previously, but without actually giving away the 'secret'. Instead, he used a cypher, writing:

I have preferred to conceal it thus: 6accdae13eff7i319n404qrr4s8t12vx.³

In October 1684, Leibniz published a paper on the calculus. Three years later, in the Principia, Newton publicised his own claim.

Perhaps like no other of Newton's feuds, Newton managed to put himself clearly in the wrong here, and yet enjoyed almost universal support, at least in Britain. Even Fatio returned briefly from obscurity to back up Newton (perhaps still smarting from Leibniz' rejection of Fatio's attempt at a calculus) in such blunt terms that even Newton seems to have been embarrassed: 'Neither the silence of the more modest Newton, nor the remitting exertions of Leibniz to claim on every occasion the invention of the calculus for himself, will deceive anyone...'. Leibniz and Newton traded poisonous reviews of each other's work for decades, with Leibniz penning an anonymous review of Opticks that accused Newton fairly directly of plagiarism. Eventually this was brought to a head by a paper written by the Oxford mathematician (and firm Newtonian) John Keill. Although avoiding direct accusations of wrongdoing against Leibniz, he made some clear and bold claims: 'the now highly celebrated arithmetic of fluxions which Mr Newton, without any doubt, first invented [...] under a different name and method of notation, was afterwards, published by Mr Leibniz...'

When he finally saw this paper, in 1710, Leibniz was incensed, and made a major tactical error. He wrote a letter of complaint to the Royal Society, publisher of the journal in which the letter appeared. Keill sent a letter of apology which was no apology at all, but rather a more detailed restatement of how Leibniz could have had access to Newton's calculations via Collins. An even more irate letter from Leibniz to the Royal Society opened the gate for Newton. A full, independent committee of 11 would be set up by the RS. (Of course, at least six would be paid-up, card-carrying Newtonians, and in his capacity as President, Newton would oversee every stage of the committee - but he would have no official involvement.) This was essentially the tactic that Newton would re-use in a few months' time to dispense 'justice' to Flamsteed.

The committee was a sham, taking six weeks to report (and not even fully staffed for the first five of those), anonymous and loaded from the start. Newton would later lie outright in 1719 when he denied any involvement in the preparation of the report itself - draft versions still exist in Newton's own handwriting. Leibniz again responded with an anonymous tract, published throughout Europe, and gained some support on the continent, while Newton continued to obsessively revise his attacks on the German in his personal notes, never to be published. Shortly before Leibniz' death, the squabble reached the closest it would get to a resolution when the former Elector of Hannover, Leibniz' patron and now George I of England, demanded a reconciliation between the London celebrity and the Berlin-based has-been. An exchange of scarcely civil letters followed.

The bad feeling between the two dragged on until Leibniz' death in 1716, thirty years later. Despite Leibniz' version being by far the more efficient of the two, British mathematicians out of blind loyalty to the 'infallible' Newton persevered with his method for the next half-century, before finally dropping his notation in favour of that now used worldwide.

As ever, Newton used his own reputation to further diminish that of his opponent. In 1726, Leibniz' name was deleted entirely from the third edition of the Principia at Newton's direction. Even when in the right - he really did discover calculus earlier - Newton felt the need to use every underhand and personal trick he could find.

1696 - 1699: William Chaloner

One of Newton's final feuds was with someone he would not recognise as his social equal; the ballad of the genius and the forger William Chaloner has been covered in some detail elsewhere⁴.

Chaloner was a small-time crook who had started out as a nail-maker in Warwickshire, then risen through the London underworld to become a major player in the lucrative counterfeiting operations that were endemic at the time. Newton, on the other hand, had retired from science and was now Warden of the Royal Mint (see Isaac Newton: Economist and Saviour of the Nation), and responsible for apprehending men such as Chaloner who threatened the integrity of the English currency.

Chaloner's rise was assisted when a paper he had written in 1694 on how to combat the threat of coining⁵ came to the attention of Charles Mordaunt, Earl of Monmouth. Mordaunt was a political rival of Newton's sponsor Montagu, and although there was no obvious use to which he could put the nouveau riche criminal as yet, he began to keep an eye on his progress. Mordaunt intervened in a claim Chaloner had made for reward money for turning in Jacobite pamphleteers, ensuring that Chaloner received a substantial payout; in return, he procured a tool with which to attack Newton, and through him Montagu.

Newton and Chaloner first met face-to-face in 1696, when Newton interrogated Chaloner about the theft of a set of dies from the Mint. At the time, this was a major scandal; the theft of the equipment to make undetectable forgeries from right under the nose of the Warden of the Mint. Fully half of Newton's working time was dedicated to it, despite this being the height of the recoinage. Newton never tracked the dies down; it seems certain that Chaloner was responsible for the theft, but equally certain that he never got the chance to recover them from wherever he stashed them afterwards.

Whatever the truth of the theft, Chaloner felt he had outwitted the new Warden when he was released without charge, and he seems to have begun to deliberately taunt Newton. The next year, in 1697, he publically alleged (correctly) that there was corruption within the Mint and that its coins were using sub-standard quality metal. He offered his own method of marking the edges of coins - grooving them, rather than milling them - but Newton refused even to see it demonstrated.

At the height of his political influence, Chaloner was even backed for the post of Master of the Mint by Mordaunt; when this failed, Chaloner was forced to move to Egham to continue his coining operations on an unprecedented scale whilst taking great care to do everything via accomplices and never to be directly involved in any criminal activity himself.

But now Newton seemed to gain the upper hand. Chaloner's operation was simply too large. One of his accomplices, Thomas Holloway, was arrested for an unrelated crime, and in exchange for his pardon offered to 'sing' on Chaloner. Newton investigated meticulously, even planting his informants within Chaloner's organisation. Chaloner was careful to keep himself distant from the actual casting of forged coins, and Newton knew that juries would be reluctant to sentence a man to death purely on the word of a paid informer⁶. And then fate smiled on Newton once more.

Still desperate for cashflow, Chaloner had hit on a scheme to earn fast money. He approached the Lords Justices asking for reward money for turning in a Jacobite conspiracy to unseat the king. On one level, this was a canny idea. Chaloner had earned good money in the past for turning in former confederates, and the nation as a whole was paranoid about invasion by Catholic French-Scottish forces. And since there was little connection between the various law enforcement agencies, Chaloner had little concern that the Lords Justices would know that he was wanted by the Mint. But unfortunately for Chaloner, the day he was in court, so too was Newton, who recognised him and promptly had him arrested.

Chaloner was on the back foot, but by no means out. Once again, he managed to outwit the 'genius' from the Mint. Thomas Holloway and his entire family were spirited out of London; by the time Newton knew they were gone, they were well on their way to Scotland, then still a separate country where Newton's legal powers could not reach. After seven weeks in Newgate Prison, the case against Chaloner collapsed without its star witness. Chaloner pushed his revenge a step further, and tried (unsuccessfully) to have Newton convicted of framing him.

Chaloner seemed to have won both their first two encounters, but he had lost everything financially. The man who six months previously had been carefully avoiding any personal contact with the home counties mansion where his minions operated a major coining operation for him, was now reduced to casting shillings himself in the grate of his rented flat, in constant danger of being interrupted by his landlady.

For Chaloner, the Malt Lottery⁷ was another opportunity - now he could start forging without the expense of metals; he simply needed paper and ink. And, of course, an accomplice with a print shop. Once again, it was his need for others that let Chaloner down. Hardly had he finished his weeks of intricate work carving the presses to print his fake tickets than he was back inside Newgate. Newton knew his man by now, and employed his standard technique of putting into Chaloner's cell a series of cellmates who he knew would talk - the last and most successful of which was one John Ignatius Lawson.

Finally, Newton had his man. Lawson's testimony was everything Newton needed for a conviction on charges of treason, and Chaloner knew it. But Chaloner did not give up. He twisted and turned, first writing letters pleading with Newton to let him go, then feigning madness. Nothing worked, and Chaloner stood trial at the Old Bailey before the Recorder of London, Salathiel Lovell, a notoriously corrupt judge (whom Chaloner lacked the funds to influence), but also a man known to be fond of hanging verdicts.

Perhaps still smarting from his previous humiliations at Chaloner's hands, Newton played every card he could to ensure a conviction and execution. The trial was a sham. Newton presented a series of six witnesses, blackening Chaloner's name with a series of claims, some of them false and none of them directly relevant to the actual charges. Chaloner was warned of only two of them, the other four being a complete surprise to him in court. Chaloner's perfectly legitimate protest that the trial was invalid since he was being tried by a Middlesex court for crimes committed in London was ignored. Chaloner was convicted of High Treason and the next day, 4 March, 1699, was sentenced to death. He was hung, drawn and quartered at Tyburn - though, as a forger, he was granted the 'mercy' of being allowed to die before being disembowelled and having his intestines burned in front of him.

Even by Newton's standards, this was exceptionally merciless. None of his other feuds ended in judicial killings, much less with the other party pleading for mercy. Chaloner wrote to Newton after his trial. His letter, perhaps unwisely forthright in setting out his grievances at the way he had been treated, ends, 'O dear Sr nobody can save me but you O God my God I shall be murderd unless you save me O I hope God wil move yor heart with mercy and pitty to do this thing for me.' (sic throughout)

Had Chaloner known of Newton's squabbles with his social equals in matters of science, perhaps he would have known that in matters of personal insult, 'mercy and pitty' were two virtues that Sir Isaac utterly lacked.