Back from the Netherlands and now based up at Highgreen for a week surrounded by high moorland, I’m itching to slip out of the watery depths and into the airy light of contour lines proper. The good news is I have permission to use that image from the Royal Society /Royal Greenwich Observatory /Cambridge University!
The story of provenance remains incomplete, but the lovely Adam Perkins from Cambridge University Library has joined me in sleuth and conjecture; it turns out it probably wasn’t Maskelyne’s notebook at all as Adam rightly points out “the subject of the text is geodetic rather than astronomical”, and although notes on the first page are indeed in Maskelyne’s hand, the rest of the notebook was probably that of one of the surveyors bringing the tally to three hands in play:
“Concerning the notebook’s cover , the hand at the very top with the parenthetic note (Dr Maskelyne’s hand-writing) is well known to me and is that of George Airy, the 7th Astronomer Royal.  I would venture that the hand that wrote Observations made at Shiehalline June – 1775 – is the hand of the remainder of the notebook.”
I wish to be out walking now, not writing, but need to finish my notes from the Netherlands or risk losing some of the twists and threads. Neither Bruinsz nor Ancelin were the initial reason for the visit, the ‘main man’ – and connecting line – is still to be introduced, as well as a tribute (tributary?) to an influential Italian with Dutch and Royal Society friend. Hang in there.
With both credit and gratitude due to Cambridge University Library.