Sign in

Stephen Johnston

@stephenaj.bsky.social
455 followers 174 following 565 posts

Curator Emeritus at Oxford's History of Science Museum, with interests in instruments and material culture. Current research focus on armillary spheres and astrolabes in medieval Europe. (Disclaimer: focus known to wander.)

PostsRepliesMedia
Stephen Johnston @stephenaj.bsky.social · 12/09/2026
I really wanted to attend but am at a conference so couldn't make it - but I'm hoping that it was recorded for watching later?
110
Stephen Johnston @stephenaj.bsky.social · 01/09/2026
And turns out it's all online: sharedcanvas.be/IIIF/viewer/.... Come for the astrolabe and stay for the nice copy of Sacrobosco's sphere - very useful for a current project!
sharedcanvas.be
B_OB_MS522 - Kalendarium. Tabula Gerlandi. Compotus Balduini. Algorismus. Liber de spera Iohannis de Sacrobosco et Compotus eiusdem. Compositio quadrantis et vsus eius. Theorica planetarum. De motu oc...
172
Stephen Johnston @stephenaj.bsky.social · 31/08/2026
Is that a special conservator-approved type of "blu-tak" to hold the piece in place? (Other colours apparently available....)
100
Stephen Johnston @stephenaj.bsky.social · 17/08/2026
It's part of Peter Heering and Roland Wittje's Objects of Understanding: Historical Perspectives on Material Artefacts and Practices in Science Education - the proceedings of a COVID-delayed conference. (When the rearranged meeting finally happened I couldn't go!) biblioscout.net/en/book/10.2...
biblioscout.net
Objects of Understanding
“Objects of Understanding” brings together studies of artifacts, collections, and practices in science education from the early 18th century to co...
000
Stephen Johnston @stephenaj.bsky.social · 17/08/2026
Occasionally (very occasionally) I emerge from medieval astrolabe obsession. Here's a piece from last year, now released from publisher embargo. Inspired by a museum acquisition and C19 in focus: "Object lessons from the asylum: the portable museum of Thomas E. Dexter" ora.ox.ac.uk/objects/uuid...
ora.ox.ac.uk
Object lessons from the asylum: the portable museum of Thomas E. Dexter - ORA - Oxford University Research Archive
120
Stephen Johnston @stephenaj.bsky.social · 13/08/2026
After last-minute spectacle yesterday evening, the sun about to return to normal service this morning - inevitably with hardly a cloud in sight this time round.
020
Stephen Johnston @stephenaj.bsky.social · 13/08/2026
And I like how he's almost at right angles to the philosophers!
020
Stephen Johnston @stephenaj.bsky.social · 12/08/2026
Haha - how wrong I was!
170
Stephen Johnston @stephenaj.bsky.social · 12/08/2026
Setting aside my unspeakable jealousy of Belgian skies, it was actually pretty dramatic suddenly having slivers of sun reappear - a story that kept unfolding. But the sun's now disappeared into the haze towards the horizon and I don't think we'll see any more now...
110
Stephen Johnston @stephenaj.bsky.social · 12/08/2026
Mais il y a du monde sur la montagne - a real occasion for family outings
040
Stephen Johnston @stephenaj.bsky.social · 12/08/2026
Incredible weather in Ghent! In the Pyrénées it's glimpses between the clouds
130
Reposted by Stephen Johnston
DLR-next @dlr-next.bsky.social · 10/08/2026
Weil es so kompliziert ist, hier nochmal eine unserer aufwendigen Visualisierungen, die (natürlich nur stark vereinfacht) den Unterschied zwischen einer partiellen und einer totalen Sonnenfinsternis zeigt.
Mal wieder eines unserer Spaßbilder, das wir hier aus dem Archiv gekramt haben. Wobei es eigentlich zwei Bilder sind, und zwar jeweils mit zwei runden Keksen auf einer Tischplatte. Im linken Bild liegt ein Schokokeks nur teilweise auf einem hellen Keks, sodass davon ein Großteil unbedeckt bleibt. Im rechten Bild liegt der Schokokeks ganz auf dem hellen Keks - na ja, jedenfalls fast.
811906455
Stephen Johnston @stephenaj.bsky.social · 09/08/2026
Thanks. I can't exactly picture it either, but the proto-kaleidoscope descriptor seems fair.
020
Stephen Johnston @stephenaj.bsky.social · 09/08/2026
I'm very curious about the optical chamber: any more details given? (Tho' I also couldn't help looking up purpentine, imagining it would be a term for porpoise - to find this would be a sea porcupine?! And how on earth were dead things adequately preserved in the summer - all by early taxidermy?)
120
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
It's good to be reminded of this paper - the astrolabe I've shown is included in the study, but only briefly in passing as "Related but not part of main group" (in Table 5).
010
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
Whatever my guess, yours is as good as mine.....
010
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
Vega is in the Behenian list, but not Alpheratz - and the symbols are quite different. (Did they go back beyond Agrippa?)
100
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
PS the other faint markings are just irregularities or weaknesses in the metal surface.
000
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
I can see some representations of Lyra have Vega as one corner of a triangle. But even if both had a constellation meaning, why pick out just two? Retes do quite often have construction markings on the reverse, but I've never seen something that could be interpreted as a structural diagram.
100
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
The marks are not adjacent - hopefully they can be spotted here on the back of the rete. Each is placed near a particular star pointer. Could they be associated with the stars ALFERAZ (Alpheratz) and WEGA (Vega)? But why hide them out of sight on the back? Questions, questions.... 4/4
Back of an astrolabe rete, blank apart fom the two engraved characters or symbols.
330
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
The other mark is an engraved triangle. Not any more comprehensible (since it doesn't look like a set of test strokes with the burin/graver), but somehow not as mysterious. 3/4
Engraved triangular mark on metal.
120
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
A couple of marks on the back of the rete had already been recorded. But I wasn't expecting such a clearly defined character as this. It certainly seems purposive and even expressive. Is it a maker's personal mark? If not, what else might it be? 2/4
Microscopic image of an engraved symbol on brass: like a capital letter i with a straight stroke projecting on one side and a curved on the other.
120
Stephen Johnston @stephenaj.bsky.social · 25/07/2026
Anyone up for reading a #medieval symbol (or two)? Here's the rete of an astrolabe at HSM Oxford (hsm.ox.ac.uk/collections-...) - with the circle of zodiac signs for the sun's place in the ecliptic and a selection of star pointers. It's been variously dated to c. 1360 and c. 1400. 1/4
Brass rete of a medieval astrolabe: metal disc cut out to leave a circle for the ecliptic with the names of the zodiac signs and a framework of arcs supporting named star pointers.
32113
Stephen Johnston @stephenaj.bsky.social · 13/07/2026
Sure - happy to meet up. I should generally be around in Oxford, except during the SIC meeting in Neuchâtel.
110
Stephen Johnston @stephenaj.bsky.social · 13/07/2026
As someone else not there in Edinburgh, I took a bit of consolation from realising that, after I'd looked at the programme and found lots of interesting papers, they mostly seemed to be on at the same time as each other!
220
Stephen Johnston @stephenaj.bsky.social · 12/07/2026
That's what I tracked down 6 months ago, just before heading out to Florida (bsky.app/profile/step...). And there have been further twists and turns since then - so that while the SIS article will be about the object, it will also focus on its meaning and use for display in 1950s and '60s Florida.
020
Stephen Johnston @stephenaj.bsky.social · 12/07/2026
If everything goes according to plan, there will be an article in the December issue of the Bulletin of the Scientific Instrument Society. As you'll see, the qualified "newness" of the find isn't just because it's an old object. It was described 70 years ago when sold at a London auction. 1/2
150
Stephen Johnston @stephenaj.bsky.social · 12/07/2026
Just published online: a blog post with the first findings from my January research trip to Jacksonville, Florida. This is the unexpected location of a remarkable "new" astronomical compendium by the 16th-century London maker Humfrey Cole. More to follow.... scientificinstrumentsociety.org/blog/
A cotton-gloved hand holds a silver circular disc, itself part of a larger astronomical compendium. The volvelle disc carries an engraved zodiac-calendar scale and two independently rotating discs, one with a sun pointer underneath a smaller disc with a moon pointer. The centre of the moon disc has an astrological aspectarium and a window to show the phase of the moon. Beyond a hinge, a part of another circular face of the instrument is visible.
2305
Stephen Johnston @stephenaj.bsky.social · 10/07/2026
You'll be well into the production process by now, so this might not be the time to comment. But, when thinking about the extent of "everyone" in the title, have you seen Victor Gysembergh's identification of a Greek translation made before the end of C13? I can send along if this isn't well-known.
100
Stephen Johnston @stephenaj.bsky.social · 09/07/2026
I'm glad you explained it - I couldn't immediately see what was going on, and thought* that the head would automatically refer to the top. Does the actual screw sit on a heavily-worked square base proud of the underside of the head? * actually, I didn't think, I somehow silently assumed
110
Stephen Johnston @stephenaj.bsky.social · 02/07/2026
Haha - that was 2 years ago, no way I'd remember something so distant 😄 - though it could well be true. Working towards a much more operational approach now, rather than high-minded aspiration (at least I hope so)
100
Stephen Johnston @stephenaj.bsky.social · 02/07/2026
Really?! Can't think what that would have been. (Doesn't mean I didn't, but could it have been someone else? And someone who I'd better find out about!)
100
Stephen Johnston @stephenaj.bsky.social · 02/07/2026
Oohh, interesting. I'm currently thinking about the (semi-) automated digital measurement of astrolabe plates as a way of accessing both the ethos and practice of workshop precision....
110
Stephen Johnston @stephenaj.bsky.social · 02/07/2026
Is it possible to measure or characterise the threaded sockets into which these screws fit? When seeing the amount of variation between different turns of the thread, I can't help but wonder about the rigidity of the fit. And if it didn't matter too much why not just pin parts together?
230
Stephen Johnston @stephenaj.bsky.social · 30/06/2026
For all those dropping everything to attend this seminar tomorrow, there's now a new, simplified link from @luiscamposribeiro.bsky.social: us02web.zoom.us/j/82936830101 See you there!
032
Stephen Johnston @stephenaj.bsky.social · 30/06/2026
Can you or @luiscamposribeiro.bsky.social post the zoom link as a URL? The QR code is too small for my phone to recognise (and I'd rather watch on my laptop anyway!)
100
Stephen Johnston @stephenaj.bsky.social · 26/06/2026
At the time of his death in 2023, Jim Bennett had begun a study of Elizabethan navigation. Only its introduction was approaching completion; the edited draft has now been published in the online journal of the @hakluytsociety.bsky.social. Direct download from www.hakluyt.com/downloadable...
hakluyt.com
0127
Stephen Johnston @stephenaj.bsky.social · 25/06/2026
Stay to the end and you can hear yours truly almost falling off my chair at the extraordinary armillary sphere images in this C15 Italian Sacrobosco MS - which, thanks to Cary Collection staff, now has a significant role in my chapter for the EIDA project's collective volume (eida.hypotheses.org)
eida.hypotheses.org
Home
EIDA is an ANR PRC project (ANR-22-CE38-0014) that was awarded during the 2022 session. The project aims at developing a new critique of astronomical diagrams of the 8th-18th centuries found in Chines...
031
Stephen Johnston @stephenaj.bsky.social · 25/06/2026
Another edition of the excellent Coffee with a Codex series - this time playing away from home with a new acquisition in upstate New York (www.rit.edu/carycollecti...). The live timing was perfect for a viewing party at GHA 2026 eida.hypotheses.org/seminars-2/2....
151
Stephen Johnston @stephenaj.bsky.social · 20/06/2026
"Growing up with it" is definitely the right term. It is (or was) a staple of British TV scheduling at Christmas, so I absorbed it in bits while recovering from turkey and Xmas pudding, without (I suspect) ever really watching it all in one sitting. But I surely know all the songs!
120
Stephen Johnston @stephenaj.bsky.social · 19/06/2026
Aesthetically pleasing, but also technically pleasing, because it reveals the craft necessary for capturing metal objects photographically
120
Stephen Johnston @stephenaj.bsky.social · 19/06/2026
Beautiful. Cover of the published book of your thesis right there! (Maybe back cover? Especially the first of the two images.)
120
Stephen Johnston @stephenaj.bsky.social · 18/06/2026
The pitch looks reasonably constant while the profile of the thread along the length of the screw seems to vary much more. Though maybe that is down to wear? (I also like that the whole thing makes me think of a gaping fish heading leftwards, with a pretty massive backbone.)
100
Stephen Johnston @stephenaj.bsky.social · 18/06/2026
The variation throughout the thread is incredible!!!
110
Stephen Johnston @stephenaj.bsky.social · 18/06/2026
I'm not sure about awful. The snail looks quite cute, and at least it wasn't actually your breakfast...
010
Stephen Johnston @stephenaj.bsky.social · 18/06/2026
Artful images! And an interesting venue, from the framing of the severe chapel to the colourful pointillist décor. Hope it goes well
210
Stephen Johnston @stephenaj.bsky.social · 13/06/2026
All curators know this feeling!
120
Stephen Johnston @stephenaj.bsky.social · 09/06/2026
Or giant cranberries?!
010
Stephen Johnston @stephenaj.bsky.social · 09/06/2026
Looks great, what's the main ingredients?
210
Stephen Johnston @stephenaj.bsky.social · 07/06/2026
The tympan on the other side of this plate is for the north pole (SVB POLO) - but it nevertheless also has 0 0 on its tab. So there's some uncertainty as to what is really going on.... (and it's definitely not as fun without a mouth).
Two small circles punched on brass.
010