‘Historians of alchemy’, wrote Herbert Butterfield in 1949, ‘seem to become tinctured with the kind of lunacy they set out to describe.’ Seventy years on, readers may believe that this gloriously rude assessment needs no updating. But what, then, are we to make of the fact that the greatest scientific hero of them all, that model of geometric rationality, Isaac Newton, devoted a great proportion of his life to the pursuit of transmutation? This was the problem that faced another titan of his discipline, the economist John Maynard Keynes, when in 1936 he acquired at auction a large number of Newton’s papers dealing with alchemy. Newton, Keynes was forced to declare, ‘was not the first of the age of reason’ but rather ‘the last of the magicians’.

The discovery of Newton’s alchemical manuscripts – containing no fewer than a million words, some of the pages mutilated by the acids used during his quest for the philosopher’s stone – led to a flurry of scholarly activity. This culminated in the 1980s in the work of Richard Westfall, still Newton’s greatest biographer, and Betty Jo Teeter Dobbs. In a spectacular rejection of Butterfield’s dismissiveness, they argued that alchemy underpinned Newton’s whole world-view. Newton’s belief in transmutation, Dobbs claimed, was akin to a religious quest, with the ‘philosophic mercury’, believed to be ableto break down metals into their constituent parts, acting as a spirit mediating between the physical and divine realms. Westfall suggested that it was assumptions born in Newton’s alchemical researches about invisible forces acting at a distance that allowed him to develop his greatest theory: that of universal gravitation, which he announced to the world in his Principia of 1687.

In half a century, scholars had gone from treating Newton’s alchemy as something to be embarrassed about to suggesting that it be seen as the very foundation of all his endeavours. Such wild oscillations of the interpretative pendulum are rarely healthy. Butterfield, Keynes, Dobbs and Westfall disagreed about how important alchemy was to Newton and to the development of modern science, but they all shared the assumption that it was part of an ‘occult’ tradition, to be categorised alongside astrology and magic. In the last twenty years or so, we have learned to think very differently. In what has been perhaps the most spectacular revision of our understanding of the so-called Scientific Revolution, we have come to appreciate that alchemy was not simply a deviant activity conducted by magi driven semi-mad by mercury fumes and the unfortunates whom they managed to dupe. Rather, it was a central part of the early modern study of nature, not to be separated from what later became chemistry.

Historians now use the contemporary term ‘chymistry’ to describe a set of practices that includes the production of chemical medicines, various types of experimental manipulation of ores, salts and acids, and also the attempt to transmute metals into gold. Such activities involved some of the most pioneering modes of experimentation. Consequently, they aroused the interest of many of the leading scientific minds, including not only Newton, but also Robert Boyle, John Locke and Gottfried Leibniz, to name a few.

At the forefront of this historiographical revolution has been William Newman. In a set of seminal books and articles, he has shown how alchemical ideas and experiments first developed by medieval Arabic scholars gradually penetrated Western thought and practice and contributed to the early modern transformation of beliefs about nature, not least towards the development of an atomic theory of matter. (After all, who more than an alchemist wants the world to be made up of small bits that can be put together in different ways?) And now, after fifteen years of hard labour, he has given us a depiction of Newton’s alchemical ambitions that is very far from both the dismissiveness of Butterfield and the overstatements of Dobbs.

And what hard labour it has been! Early modern alchemical prose is often as impenetrable as that of modern poststructural theorists. Indeed, the motivations were sometimes the same: to disguise what are in fact trivial points under a veneer of obfuscatory jargon, in the hope that someone would pay to have the ‘secrets’ revealed. But, as Newman shows, the alchemists also deployed their repertoire of mythological codewords and symbols out of a sense of social responsibility, for they truly believed that if they did not conceal their results it would lead to the collapse of the social order, as gold lost its value.

But that leaves the historian with a huge problem, namely how to understand (never mind interpret) statements on Newton’s part such as this one:

That this solar 🜍 & ⊖ may be digested wth ye mercuriall spt of ♁ to an Elixir. Which intimates that that spt is substantially ☿ because substituted in liew of ye ☿ of ☉.

Newman’s solution is threefold. First, in collaboration with several others, he has systematically organised, read, dated and compared Newton’s alchemical manuscripts in a way previously undreamed of (curious readers can see the results for themselves at www.chymistry.org). Second, he has done what any good historian of ideas should do: he has tried to read everything that his subject read. This reveals how heavily influenced Newton was by European alchemists, above all the Pole Michael Sendivogius (who, the story goes, had convinced Holy Roman Emperor Rudolf II of his ability to perform transmutation). Drawing on their experiments, Newton in the 1670s developed an all-encompassing geochemical theory of nature, according to which the earth functions, in his words, as a ‘great animall or rather inanimate vegetable’, circulating a nitrous component of the air between its core and the outer reaches of the atmosphere. In Newton’s view, this process explained gravitation (among many other things), although he would abandon this idea when he came to write the Principia .

Third, and perhaps most remarkably, Newman has deciphered many of the puzzles of the manuscripts by repeating Newton’s own experiments. The results are sometimes spectacular, with many of Newton’s laboratory practices revealed for the first time. We learn that he continued his alchemical experimentation even when he moved to London in 1696 to become warden of the Royal Mint, collaborating with locals of much lower social status (and generating the delicious image of an alchemist in charge of the coin of the realm). We discover how Newton integrated his reading and decoding of earlier alchemical texts with his own experimental practice. And we come to realise that Newton’s alchemical activities had nothing to do with his heterodox religion, with any other ‘occult’ pursuits or with his final explanation of universal gravitation. Rather, they formed a separate part of his attempt to improve knowledge of the natural world.

What is equally impressive is that alongside Newman’s interpretative energy and inventiveness, he displays judicious caution, admitting when he has been unable to decode a Newtonian experiment and always refusing to posit alchemy as a master key to Newton’s mind. Only once do I think he may have overplayed his hand, when he suggests that Newton’s famous discovery that white light is composed of a mixture of variously refrangible coloured rays was influenced by ‘chymical’ ideas about the composition of mixed substances.

As I read through this long, brilliantly detailed book, I sometimes found myself wondering whether we really need yet another ten pages on how Newton tried and failed to find the internal principle of metallic activity that would allow him to make gold, usually through a new use of ‘vitriol of Venus’ (a crystalline copper compound that is volatile at low temperatures). But then I would correct myself: of course we do. This is Newton, and these are the activities that formed the mind of the man who perhaps did more to transform Western thinking about the natural world than anyone else in history. A reader who wants to understand this but is daunted by the detail of Newman’s work would do well to begin with Niccolò Guicciardini’s Isaac Newton and Natural Philosophy, published last year, which incorporates some of Newman’s previously published findings into a wonderfully clear account of Newton’s scientific thought as a whole.

Newman’s patient research has produced a masterpiece of scientific history. It is to his great credit that he has avoided the kind of master-narrative that the Newton industry so regularly churns out. Such books promise us gold but usually end up dissolving into the ether. Newman, on the other hand, has concocted a book of genuine substance that will still be read in a century.