Newton's letter to Oldenburg, 1676: full text and summary

On 26 April 1676 Isaac Newton wrote from Cambridge to Henry Oldenburg, Secretary of the Royal Society, about an experiment of Robert Boyle's: a mercury that, mixed with gold, grew hot by itself. In the letter Newton doubts that such a mercury is of much use, but asks that Boyle keep “high silence” about how it is prepared, because, if the Hermetic writers tell any truth, it might be an inlet to something not to be communicated “without immense damage to the world”. And it ends: “pray keep this letter private to yourself.”¹ The previous article told of Newton's alchemy through what others saw; this is one of the few times we hear it in Newton's own voice, in a letter.

The text of the letter is in the public domain: Newton died in 1727, and I read it in an edition of 1841, from the images of the pages. The summary, notes and piece in this article are ours and may be freely copied, including for commercial purposes, provided the source is credited (CC BY 4.0 licence).

The letter in five points

1. Thanks. Newton thanks Oldenburg for publishing his last letter in the Philosophical Transactions and for proposing to have “the experiment in controversy” tried before the Royal Society, so that “Mr. Linus's friends” will acquiesce. (Linus was a Jesuit of Liège who criticised Newton's experiments and had died in 1675.)²
2. Boyle's mercury. Newton has just read Boyle's paper on the “incalescence” of gold and mercury, and believes “the fingers of many will itch” to know how it is prepared. Boyle is prudent, Newton thinks, not to reveal it.
3. A mechanical explanation. Newton does not think such a mercury worth much in medicine or chemistry, and compares it with aqua fortis: the metallic particles dissolved in it would be grosser than those of mercury and, mixing with the gold, would “shake” it and heat it.
4. “High silence”. Even so, since others who knew the method have concealed it, it might be “an inlet to something more noble”, not to be communicated without immense damage to the world “if there should be any verity in the Hermetic writers”. So Boyle should keep silent until judged by “a true Hermetic philosopher”, “if there be any such”.
5. Secrecy. Newton gives an opinion because Boyle seemed to want others' views, and asks Oldenburg to keep the letter private.

What Boyle had published

In the Philosophical Transactions of February 1676 there appeared, signed only with the initials “B. R.”, a paper in English and Latin titled “Of the incalescence of quicksilver with gold”. Boyle said that many alchemists denied such a mercury existed, and that those he had questioned confessed, each separately, “that they never actually saw any Incalescent Mercury, though they sometimes heard it boasted of by Alchymists”; one honest chemist had even been sold a pretended one, which was brought to Boyle and, on trial, did not grow hot. Boyle said he had had his own since about 1652, and that Oldenburg himself had made the experiment with his own hands, successfully. Boyle did not claim it was the alchemists' “Philosophick Mercury”, and explained why the method was withheld: the fear of queries and requests, a hand too weak to write, and the unsuitability of dictating “such a subject” to an amanuensis.³

Newton read the paper and wrote the letter the next day: “Yesterday I, reading the two last Philosophical Transactions…”.¹

The full text of the letter

Cambridge, April 26, 1676.

Sir,

I am now to return you thanks on a double account, the one for publishing my letter in your last Transactions, the other for motioning to get the experiment in controversy tried before the Royal Society. I could be very desirous, not to say ambitious, to have such a thing done, did I not fear I should be troublesome; and therefore I shall esteem it a great favour, if you please to get it done, being apt to think that Mr. Linus's friends will not otherwise acquiesce.

Yesterday I, reading the two last Philosophical Transactions, had the opportunity to consider Mr. Boyle's uncommon experiment about the incalescence of gold and mercury. I believe the fingers of many will itch to be at the knowledge of the preparation of such a mercury, and for that end some will not be wanting to move for the publishing of it, by urging the good it may do in the world; but in my simple judgment the noble author, since he has thought fit to reveal himself so far, does prudently in being reserved in the rest. Not that I think any great excellence in such a mercury, either for medical or chemical operations: for it seems to me that the metalline particles, with which that mercury is impregnated, may be grosser than the particles of the mercury, and be disposed to mix more readily with the gold, upon some other account than their subtilty, and then in so mixing their grossness may enable them to give the parts of the gold the greater shock, and so put them into a brisker motion than smaller particles could do: much after the manner that the saline particles, wherewith corrosive liquors are impregnated, heat many things, which they are put to dissolve, whilst the finer parts of common water scarce heat any thing dissolved therein, be the dissolution never so quick, and if they do heat any thing, (as quick lime,) one may suspect that heat is produced by some saline particles lying hid in the body, which the water sets on work upon the body, which they could not act on, whilst in a dry form. I would compare, therefore, this impregnated mercury to some corrosive liquor, (as aqua fortis,) the mercurial part of the one to the watery or phlegmatic part of the other, and the metallic particles, with which the one is impregnated, to the saline particles, with which the other is impregnated; both which I suppose may be of a middle nature between the liquor, which they impregnate, and the bodies they dissolve, and so enter those bodies more freely, and by their grossness shake the dissolved particles more strongly than a subtiler agent would do. If this analogy of these two kinds of liquors may be allowed, one may guess at the little use of the one by the indisposition of the other, either to medicine or vegetation. But yet because the way, by which mercury may be so impregnated, has been thought fit to be concealed by others that have known it, and therefore may possibly be an inlet to something more noble, not to be communicated without immense damage to the world, if there should be any verity in the Hermetic writers, therefore I question not but that the great wisdom of the noble author will sway him to high silence till he shall be resolved of what consequence the thing may be, either by his own experience, or the judgment of some other, that thoroughly understands what he speaks about, that is, of a true Hermetic philosopher, whose judgment (if there be any such) would be more to be regarded in this point than that of all the world beside to the contrary, there being other things beside the transmutation of metals, (if those great pretenders brag not,) which none but they understand. Sir, because the author seems desirous of the sense of others in this point, I have been so free as to shoot my bolt; but pray keep this letter private to yourself.

Your servant, Is. Newton.¹

This piece goes through the letter sentence by sentence, with a note on each:

What it says and what it does not

What stands out on reading it whole is how much Newton hedges. The call for silence is made conditional three times: “if there should be any verity in the Hermetic writers”, “if there be any such” true philosophers, and “if those great pretenders brag not”. And before that comes an explanation in terms of gross and fine particles, with nothing secret about it, and the view that such a mercury is of little use. The letter does not say that Boyle had the philosopher's stone, nor that Newton believed it near. It says that, just in case, silence was better.

There is also an irony. Newton asked for the letter to be kept private, and in 1841 Stephen Peter Rigaud published it, with others, from the originals in the collection of the Earl of Macclesfield.¹ Today anyone can read it, and that is what makes it possible to discuss it.

How to copy and cite this summary

The summary in five points, the notes and the piece in this article may be copied, translated and reused in any medium, including for commercial purposes, with credit. One way to do it: “Summary of Isaac Newton's letter to Henry Oldenburg of 26 April 1676, by Anima Mundis (animamundis.tech), CC BY 4.0.” The English text of the letter is in the public domain and needs nobody's permission.

What I could not read

I did not read the original manuscript of the letter, nor the modern edition of Newton's correspondence (H. W. Turnbull and others, from 1959), which is in copyright and annotates the letter in more detail. I used Rigaud's edition of 1841, which prints the letter in that edition's spelling, not Newton's. Of Boyle's paper I read the English part in the digitised text, which has recognition errors; I did not check it against the page images. Linus and Oldenburg come from Wikipedia.²

What we do with this

Newton asked for secrecy and today the letter belongs to everyone. That is a good reason for what we write about it to belong to everyone too: knowledge of a letter from 1676 should not stay locked inside a copyrighted edition. At the Observatory we count voices in the open for the same reason.