Dear Gianni, Thanks very much for the hint regarding dialing resources on "Google Books"!
Quite a few of the full view, downloadable, books in pdf format have at least chapters on dialing. In the mid 1800's it appears that many colleges and universities included dialing as a subject within their mathematics curriculum. There are mathematics books by a Ferguson, for instance, that include dialing from around the 1850's. Could this be the Ferguson that some of you have been searching for? The idea of making a dial point whatever which way in order to either include a fixed set of hours, or to be fully visible from a particular location ( Like the bell ringer or the administration offices. ) sounds really cool! Thanks again, Edley McKnight > Dear Frank (Evans), > I don't agree completely on your conclusions :-) > > In http://books.google.com it is possible to download the book > <John Good - The Art of Shadows, etc. - London 1731> > The PDF version downloaded is 7.0 Mb long and has 222 pages. > > In this book the author always uses the quantity "Planes difference of > Longitude" or "Plane's Longitude" to calculate a declining sundial. > > In the pages 87-88 (of the PDF version) in the "Canon for the > calculation" we find the calculation done with the Logarithms . The > used formula (p. 88 - the last 5 lines) is Tan(Plane's Long.) = > Tan(Decl)/Sin(Lat) > > This is the formula that gives the difference in Longitude within the > place where the sundial is and the place in which the plane of the > dial is tangent to the Earth´s surface (that I have called > Equivalent Point) This quantity is used for finding the angles of the > hour lines (pag. 89- hard to read) > > I have not found where John Good defines or explains what this Plane's > Long is : from the text it seems however that this quantity was well > known and used, at least in 1731. > > Therefore I think that the writing <PI Long> must be read <Pl Long> or > Plane's Longitude. > > I leave the search on other ancient texts (for me very difficult for > availability and for language) to the English friends :- ) > > Gianni Ferrari > >
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