Last week y’all got the crash course on how to recognise a Newton book, and boy did it pay off! There’s even rumours that more is to come soon. In the mean time yours truly spent an exciting week leafing through all sorts of rare books in the Huntington Library‘s Ahmanson Reading Room. Only on Saturday did one librarian finally dare exclaim: “You, sir, are either the world’s fastest reader, or you are not actually reading all these books…” (I’d swear he said, “You sir, are a madman!” – but that must be my corrupted mind playing tricks). While I did not find any unknown Newton holding, so far I did find lots of those suspicious looking dog-ears that we briefly discussed last week.

When librarians come across dog-ears, their first response is to fold them back. Which is on the one hand fully understandable – because dog-ears can damage a book – but on the other hand rather unfortunate. Just like annotations, dog-ears can tell us much about the reading practices of a book’s previous owner. They tell us how a book was read: the dog-ear often serves to mark a particular passage that the reader found interesting and presumably wanted to return to, or it can simply be a bookmark that told the reader where to continue. It can be quite tricky to discern the exact meaning and purpose of a dog-ear, and the linguist or historian needs to tread with care.

In Newton’s books we come across dog-ears like the ones above: small folds whose meaning or significance is unclear. We also come across folds like these

If we were to fold the tip of the page down, it would touch a particular word, as in the following image, from another of Newton’s books:

As far as we know, this is a quintessentially Newtonian practice: the use of large dog-ears, sometimes more than one per page.

But how do we know that the passages they’re pointing at are indeed relevant? Wasn’t Newton simply folding pages in an arbitrary way? Good question. Fortunately, we have more than just Newton’s library books. We also have an incredible amount of manuscript material, much of which has been carefully transcribed by the Newton Project over the past 17 years, amounting to more than 10 million words in total. A significant amount of these manuscripts consist of notebooks, recording for instance Newton’s infamous bodkin experiment, showing Newton’s experimental side:

As he wrote in a notebook section headed “Of Colours“,

I tooke a bodkin gh & put it betwixt my eye & the bone as neare to the Backside of my eye as I could: & pressing my eye with the end of it (soe as to make the curvature a, bcdef in my eye) there appeared severall white darke & coloured circles r, s, t, &c. Which circles were plainest when I continued to rub my eye with the point of the bodkin, but if I held my eye & the bodkin still, though I continued to presse my eye with it yet the circles would grow faint & often disappeare untill I renewed them by moving my eye or the bodkin.

In these and other notebooks, we find Newton not only recording optical experiments and performing mathematical wizardly – they are also full of notes taken from authors such as Robert Boyle, Robert Hooke, and Rene Descartes. When I inspected Newton’s copy of Robert Boyle’s Essays of the Strange Subtlety, Determinate Nature, & Great Efficacy of Effluviums, published in 1673, I found two dog-ears on page 26, of which I made a note. Lo and behold, in that same notebook about colours, we find an entry which reads:

Mr Boyle mentions one that by sickness became so tender sighted as in the dark night to see & distinguish plainly the colours of ribband (& other objects) on purpose pinned on the inside of his curtains against he awaked. Of the determinate nature of Effluviums p 26, And of another that by a feaver became of so tender hearing as to hear plainly soft whispers at a distance which others could not at all perceive, but when he grew well his hearing became but like that of other men. Ibid.

And indeed, the passages that Newton mentions here are exactly the ones that the dog-ears point at. So with Newton these dog-ears are not merely bookmarks, but they reflect his interests. Maybe this is also an example of Newton’s typical economy. He could have used a pen or pencil to underline or annotate the passage, but in order to find it back he’d have to make a dog-ear anyway. So why not simply combine both into one? This is obviously conjecture, but it might be closer to the truth than we think.

Now, before we all start refolding dog-ears: let’s not do that. We don’t want to loose our dear librarian friends. They are vital in providing us access to these wonderful volumes. What we need is a way to reconstruct folded back dog-ears, and in order to do this all we need is a proper image and some elementary geometry, like this:

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