It was 1695, and England was in crisis. Again.

Not that everything was bad: King William III, aka William of Orange, was winning the Nine Years War against the hated French, and all he had to do was keep it up for another two years (although he didn’t exactly know that at the time). The trouble was, he’d need to maintain his record-breaking army of about 100,000 soldiers, who were currently standing in Belgian fields waiting to be paid. But the king had no money to pay them.

That was because the money he should have had was worth more when it was melted down and sold on the continent, meaning the Thames was literally flowing with silver.

On top of that, coin clippers were shaving metal off the old, wonky, hand-pressed currency, cutting shillings, pennies and groats down to as little as half their proper weight. And counterfeiters were rising to fill the demand for money: more than one in ten coins were fake.

It wasn’t only the king’s campaign that suffered from the cash shortage. Workers couldn’t receive their wages, shopkeepers and landlords couldn’t be paid, and the people rioted when they couldn’t pay their taxes.

The problem had been building for years, but the government was lost for ideas. Pretty much the only idea they had left was to ask someone smarter. Fortunately, just down the road in Cambridge lived the smartest man in Europe.

This man himself was a bit lost for direction at the time, spending his life, as he put it, sleeping too often by his fire. It was about a decade since he’d completed his greatest work, revealing the invisible forces that turn the spheres in the heavens, and unpicking the strands of the rainbow. His mathematics had penetrated the infinitesimal to reach the infinity of space, and his writings were the talk of the western world. And only a couple of years prior, he’d believed he’d actually found the alchemist’s dream, the Philosopher’s Stone.

But then came the collapse of possibly the closest relationship he ever had, in his life of emotional hardness and spiritual purity. His affectionate correspondence with the flighty Swiss mathematician Nicholas Fatio de Duillier broke down, and he broke with it. What use then the mere ability to turn base metal into gold?

It was to this wounded, but slowly mending man that a letter finally came, and with it the beginnings of his new mission to help save the kingdom.

And that’s how the legendary Isaac Newton became Warden of the Royal Mint.

This new role meant moving to London, which at the end of the seventeenth century was not a pleasant place. The Great Fire of 1666 seemed to have burned away the bubonic plague, but the city was rebuilt much the way it was, except in stone instead of wood.

The streets were still paved with garbage and sewage, the air was thick with fumes from faeces and fires, and drinking the water wasn’t an option; the half-million or so residents had to survive on gin and ale.

In the thick of it all was that old fortress, the Tower of London, where in narrow, smoky, sweaty rooms along its outer wall, the furnaces, mills and presses of the Royal Mint strove and failed to keep up with the demand for cash. The Tower was also to be Newton’s new home, in a small house next to his workplace.

His first idea was to staunch the tide of precious metal by reducing the silver content of each shilling, thus reducing the exchange rate. But the concept that money could be an abstract expression of value and not a specific unit of metal was far too radical and his proposal was rejected.

So if the silver content couldn’t be altered, Newton reasoned, then coin clipping had to be stopped. The only way to do this was to recall all the shabby old coins in the land and issue completely new ones, machine-pressed with a pattern that couldn’t be shaved.

This was a risky move, considering England was already short on cash. And with the Mint’s machines designed to produce a maximum 15,000 pounds per week, recoining the entire kingdom would take nearly nine years.

But to Newton this was just another maths problem. He observed the process closely, identifying where capacity could be increased and where there were bottlenecks. Once he’d established the quickest time in which coins could be pressed—without the loss of too many fingers—he established a rhythm that drove the entire production line. Soon the Mint was doing the impossible, turning out 50,000 pounds and eventually 100,000 pounds per week.

With cash supplies starting to rebuild in a matter of months, Newton turned to the problem of counterfeiting. This was not really by choice: in his role of Warden he was also the Mint’s magistrate. Enforcing currency laws in and around London was his responsibility alone.

So counterfeiters were added to the long list of people Newton didn’t like, but with particularly good reason. Like twisted alchemists, they could also turn base metals into gold or silver. Except that, instead of the Philosopher’s Stone, they used cast moulds or die stamps they carved themselves—or pinched from the Mint—to make copies gilded with a thin skin of the real stuff.

Also, Newton had conducted his alchemical experiments with the lofty goal of understanding and honouring the works of God, whereas the coiners were mocking the authority of the king, divinely appointed as he was—at least according to Protestants like Newton.

As a result, counterfeiters were considered to be committing high treason, and were to be hanged, drawn and quartered.

Newton pursued, caught and convicted dozens of coiners during his years in charge of the Mint. Once he got the hang of it, so to speak, he relished taking to London’s filthy streets and dodgy taverns himself, disguised in attire suitable for meeting informants and arresting suspects, then taking them to the Tower or the irons of Newgate prison for interrogation.

Of the twenty-eight he sent to the gallows, his greatest ever prize was the master-counterfeiter William Chaloner.

Chaloner supposedly started his career selling dildos—hidden in hand-made tin watches—on London’s street corners. He had a gift for fraud, and soon graduated to a role as a quack doctor and a fortune-teller, who specialised in locating stolen goods (the trick was to steal it yourself).

In one particularly lucrative scheme, Chaloner persuaded two printers to publish pamphlets advocating the overthrow of the king, gaining them the noose and himself a reward for turning them in.

But his real expertise was in counterfeiting, building on his talent for metalwork and a skill he acquired in ‘japanning’, an Asian technique for applying a thin coat of lacquer to furniture or fabric. By Newton’s time Chaloner was at the top of London’s criminal underworld, producing the finest quality fake coins that even emulated the engraving on the edge, which ironically read decus et tutamen, or ‘a decoration and a safeguard’.

However, his aim was even higher than that. The riskiest part of counterfeiting was passing the fakes into the market. What better way than to do it through the Mint itself?

To this end, Chaloner generously provided advice on improving the Mint to a parliamentary committee. They endorsed him to introduce his new method for milling a groove on the edge of coins that would, he claimed and the committee believed, make the currency counterfeit-proof.

Newton, irked at implications of incompetence as much as anything, refused Chaloner access on the grounds that he’d sworn an oath not to reveal the Mint’s secrets. Instead, he had his own workers groove a handful of coins, which he tossed before the committee, demonstrating the scheme wouldn’t work.

He’d stood his ground, but Newton could no longer ignore Chaloner’s ‘calumny’ and his labouring ‘to accuse and vilify the Mint’, as he put it in his tiny, cramped handwriting. This former ‘Japanner in cloaths threadbare ragged & daubed with colours’ had earned the ire and full attention of London’s greatest ever scientist-detective.

The over-ambitious scheme had also exhausted Chaloner’s funds. He returned to counterfeiting, but with a twist: this time he copied the new paper money that the government was printing to pay off its still growing war debts.

It was for this last scam that Chaloner was finally arrested, but it was the mountain of testimony from his previous years of coining that Newton used against him.

Typically for those days, the trial was brief and Chaloner’s verdict was certain. Naturally he offered to implicate others in exchange for his freedom, but by this stage everyone was over him and, frankly, there was no higher prize. The jury only took a couple of minutes to return its verdict of guilty of high treason.

With mere weeks left to live, Chaloner pleaded with Newton: ‘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 will move yor heart with mercy and pitty to do this thing for me.’

Apparently He didn’t, because Newton didn’t reply; he didn’t even bother to attend the execution.

Newton’s criminal investigations tapered off after Chaloner’s conviction. But he had plenty to keep him occupied, overseeing the shift to the gold standard, calculating the orbit of the Moon and using the Bible to predict the end of the world (no earlier than 2060, you’ll be glad to know).

However, he seems to have quit alchemy, and he never regained the Philosopher’s Stone. Perhaps creating real money in the Mint was good enough.

Chris Lassig is a theoretical physicist turned science writer, presenter and comic artist. Find out more at the Astrocave or follow him on Twitter.

Sir Isaac Newton . Line engraving by G Bickham, senior, 1787. Wellcome Library, London, image number V0004291. The verse inscribed below this print reads:  See the great Newton, He who first Survey’d/The Plan, by which the Universe was made;/Saw Nature’s Simple, yet Stupendous Laws,/And prov’d the Effects tho’ not explain’d the Cause./ O wond’rous Man! in whom the heav’nly Mind/ Shines forth distinguish’d, and above Mankind: /Whilst here on earth, how humble, nice and good!/In Heav’n a Star of the first Magnitude .

Sir Isaac Newton. Line engraving by G Bickham, senior, 1787. Wellcome Library, London, image number V0004291. The verse inscribed below this print reads: See the great Newton, He who first Survey’d/The Plan, by which the Universe was made;/Saw Nature’s Simple, yet Stupendous Laws,/And prov’d the Effects tho’ not explain’d the Cause./ O wond’rous Man! in whom the heav’nly Mind/ Shines forth distinguish’d, and above Mankind: /Whilst here on earth, how humble, nice and good!/In Heav’n a Star of the first Magnitude.

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