There is a large period literature on ³dialing² which not only included sundials, but all sorts of ways to measure time from celestial objects using angles. Discussions of trigonometry, surveying, navigation, and ³dyaling² in relationship were also quite common during the period. These could be found in popular books, and sometimes in almanacs (some of which had huge circulations).
The use of building features to reckon sidereal time is quite old. In the 6th century, Gregory of Tours wrote DE CURSU STELLARUM about sidereal timekeeping, and the techniques were later simplified to use buildings within a monastery in HOROLOGIUM STELLARE MONASTICUM. The secondary sources on these two medieval works are: Constable, Giles. 1975. Horologium Stellare Monasticum. Corpus Consuetudinum Monasticarum, volume 6, pages 1-18. McCluskey, Stephen. 1990. Gregory of Tours, Monastic Timekeeping and Early Christian Attitudes to Astronomy. Isis, volume 81, pages 8-22. Sobel gives the false impression that such knowledge was held by only a few and that Harrison was a bit of a country bumpkin, but in fact, when one considers that the inventor of the deadbeat escapement was from Carlisle, and that gear-cutting machines for clocks were improved by Hindley in York, this suggests that there was widespread interest in clock-making in addition to the widespread interest in astronomy in the North of England, and a look at all the books and pamplets published on the topic suggests that the interest extended into Ireland and Scotland, as well. Basically, the sort of expertise to do what Harrison did using his window and a neighbor¹s chimney was extremely widespread, and the literature giving instructions is overwhelming in its size. I did a quick search on astronomy and dialing in one of my go-to databases (18th Century Collections online) and got 383 hits. If you know French, you can go to gallica at https://gallica.bnf.fr/accueil/en/content/accueil-en?mode=desktop and search for works on astronomy and dialing, and find similar sources, although my impression always has been that the English were more obsessed with the topic in the 17th and 18th century than the French. Best, Kevin -- Kevin K. Birth, Professor Department of Anthropology Queens College, City University of New York 65-30 Kissena Boulevard Flushing, NY 11367 telephone: 718/997-5518 "Tempus est mundi instabilis motus, rerumque labentium cursus." --Hrabanus Maurus "We may live longer but we may be subject to peculiar contagion and spiritual torpor or illiteracies of the imagination" --Wilson Harris On 3/26/19, 10:48 PM, "time-nuts on behalf of Tom Van Baak" <time-nuts-boun...@lists.febo.com on behalf of t...@leapsecond.com> wrote: >EXTERNAL EMAIL: please report suspicious content to the ITS Help Desk. > > >BobH wrote: >>> This would be an excellent project for time-nuts to verify. First, a >>> better explanation of John Harrison¹s method is in order. A vertical >>> window edge is not sufficient - a second vertical reference at a >>> distance is required - Harrison used a chimney on a neighbor's house. > >Agreed! The project is the perfect intersection of amateur astronomy and >amateur timekeeping. Surely, a couple of people on the list could 1) >attempt to verify the Harrison method, and 2) determine what the limits >of its accuracy are, say, with little effort vs. with hard work vs. with >extreme dedication. > >JimL wrote: >> To get 1 second accuracy, you need 360/86400 = 0.004 degree >> measurements. That's 0.073 milliradian - 1 cm at 140 meter distance. >> >> I'm not sure an "edge" is sharp enough (diffraction, etc.), although >> your eye is pretty good at "deconvolving" the linear equivalent of an >> Airy disk/rings. > >Keep in mind too that one can take more than one star reading per night. >Any identifiable star that crosses your edge is a recordable timing event >that evening. So, in theory, if you measure N stars you get sqrt(N) >improvement in accuracy per day. > >I want to encourage anyone to study the problem and help solve the >riddle, either by uncovering existing professional or amateur literature >or by actually trying this at home. It boils down to how accurately can >you measure earth rotation using the Harrison method. > >To put this in time nuts context, precision timekeeping prior to the >middle of the 20th century was always a form of "Earth Disciplined >Oscillator". Not unlike a GPSDO, your observatory's pendulum clock kept >accurate time short-term and star tracking (earth rotation) kept accurate >time long-term. The ADEV's crossed just like a GPSDO. > >The short-term ADEV of a really good pendulum clock is here: > >http://leapsecond.com/pend/shortt/ > >The long-term ADEV of earth rotation is here: > >http://leapsecond.com/museum/earth/ > >So the performance of a DIY earth disciplined oscillator would be a >combination of the two. > >/tvb > > >_______________________________________________ >time-nuts mailing list -- time-nuts@lists.febo.com >To unsubscribe, go to >http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.