Re: large sundial

[Chris Lusby Taylor]

John Carmichael wrote: <snip> Have you ever tried to squeeze one minute timelines onto an eight inch dial face?  It's almost impossible. <snip> If I remember correctly, Tony said that his fine photoetching process could just barely do this on an eight inch (20 cm) bronze face. But with my carved stone sundials, I must have at least a 40 inch (100) cm face for one minute lines because if carve lines too close together, it weakens the stone. (and doesn't look good) <snip> An alternative approach doesn't require thin or closely spaced lines. This is to use a nonius (after its inventor Pedro Nunes) which uses diagonal lines at an oblique angle to the radial hour lines. The position where the shadow crosses the diagonal line indicates the exact minute. This is seen on old quadrants and some sundials such as the Tompion dial at Hampton Court (and the replica in Kew). I'm sure I have a book (Cousins, perhaps?) that illustrates a slate dial with minute gradations using a nonius. It cannot be more than 8 inches or so across, I think. There are illustrations of nonii on Epact. Go to <http://www.mhs.ox.ac.uk/epact/> and search for nonius, or seach for 'minute' in 'Horizontal Dials', or find catalog number 308 or 451. Hope this helps Regards to all Chris Newbury, England 51.4N, 1.3W