The Wolsey/Kratzer dial is discussed in Peter Drinkwater's booklet "The Sundials of Nicholas Kratzer". Although he doesn't analyse the hourlines, it is clear that Drinkwater is no admirer of Kratzer's dialling abilities - he accuses him of all sorts of muddles and mistakes.
The "6" marking on the sub-style line sounds like an attempt at using Italian hours, measured from sunset. But that couldn't be correct. Can you tell from the picture whether the dial is read from the shadow of the tip of the gnomon (as was common on Kratzer's dials) or from its whole length?
Obviously there is a need to look at the dial closely in April!
Regards,
John
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[EMAIL PROTECTED] wrote:
[EMAIL PROTECTED] wrote:
On 25th Jan I posted the following query:
What hour lines should be inscribed, and in what places, on an inferior polar dial for latitude 52N? The centrally-placed gnomon is 13 units high, the overall plate width (east-west) is 37 units and the north-south plate height is 26 units.
Thank you for the various replies sent in (4).
I clarified the term 'inferior' later on that day thus:
"Inferior"..........Think first of a 'normal' polar dial, parallel to the polar axis, aligned E-W but face open to the south i.e. that part of the celestial equator above the horizon. Now consider the underneath of this polar dial, face open to the north, facing that part of the celestial equator which is (mostly) below the northern horizon. You've now got an 'inferior' polar dial. Th! e term is used in a document I came across recently (on the internet). I suppose that an equivalent description would be 'a polar dial facing north' or a direct north dial inclining at an angle to the horizon equal to the latitude of the place (52 deg in this case). Yes - it will be latitude independent, but I included that detail so that it would pin down the discussion a bit.
The BSS Glossary also defines 'inferior' as "refers to an event on the celestial sphere below the horizon. Opposite of superior."
Let me now tell you the reason for my enquiry:
I was looking at the website of the Museum of the History of Science, Oxford (epact.mhs.ox.ac.uk/catalogue), and brought up the details of Nicolaus Kratzer's portable polyhedral dial (1525) made of gilt brass which he presented to Cardinal Wolsey (Inventory No. 54054). It appears to have been made for latitude 52 deg. N
There are dials on nine faces. One is described as an 'inferior polar dial, with lines marked 4,6,! 8. This puzzled me - what is the sense of only hours 4,6,8 on any dial?
The illustration given on the museum's web page is not clear enough to get any detail other than to see that the north face is not visible. However, a postcard I bought at the museum some years ago does show the north face and knowing the overall height of the dial (100mm) I estimate that the height of the gnomon on the inferior polar dial is 13 mm. It seems that the lines for 4 am ( to the west and 8 pm to the east) are wrongly positioned - they should be about 22.5 mm away from the centre of the dial, and are nowhere near this distance.
A further puzzle - why did Kratzer mark the line on which the gnomon lies with a 6? It should be 12 (midnight!) if it's going to be anything - or was it because 6 comes exactly between 8 and 4? A blunder, perhaps?
More measurement pending..........
David Brown
Somerton, Somerset, UK
Dr J R Davis
! Flowton Dials
N52d 08m: E1d 05m)
