The notion of a Univeral dial is interesting. My Wenger Sundial has some of the elements of such a dial.
Currently the sphere that I use to represent the earth has a hole in it at the base for introduction of the center piece that is used to establish the subsolor point and thus to determine the time. Conceptually the sphere can be made without the hole and with the center piece introduced in some other way. Then the sphere may be rotated and placed with the users position in the local zenith and the poles aligned and the dial is set for reading the time anywhere on the surface of the earth. BUT, the numbering of the analemmas is time zone dependant. Just leaving off the numbering of the time zones is still not going to do the job since time zones do not always match up with the 15 degree longitude lines. There are zones that use the 7 1/2 + 15 degree longitude lines. Also, although my dial does show standard time and daylight saving time when used, not all countries use daylight saving time, ie. Japan for example. So, even though my design has some of the features of a Universal dial, namely it reads mean time and has the same accuracy no matter where used on the earth, ie. good at all latitudes, it still does not meet the desired goals of a Universal dial. Just some rambling on the subject. I think Sara's comments re taxonomy are excellent and need to be applied consistently. Dan Wenger > I have to agree with Sara Schechner about taxonomy. We really >MUST keep to a standard format for describing all dials. > > I have one question for Sara. In the case of a universal dial, >you say, 'a dial adjustable for multiple latitudes'. I feel that we >should perhaps sub-divide this into 3 (or possibly more) categories. I >look forward to any comments that you may like to make. > >1 A dial that covers all latitudes 90°N to 90°S. This is truly >UNIVERSAL. (We could even apply this to dials that perhaps do not quite >reach the 90° of both poles. Many only cover 80°N-80°S or thereabouts). > >2 A dial that covers just the Northern Hemisphere (or Southern). >This could be called SEMI UNIVERSAL. But then, should we specify which >hemisphere? > >3 A dial with a limited range of useful latitudes, like a >Butterfield, this could be PART UNIVERSAL. (It doesn't sound nice. >There must be a better description.) > > There are also some dials, quite rare that cover 60°N to 10°S. >I think that I would call these PART UNIVERSAL. > > The question therefore is, 'What can we call these various sub- >divisions of UNIVERSAL?' I look forward to your comments. > > As an alternative approach we could get round this by specifying >the angles of universality. e.g., UNIVERSAL 60°N - 10°S. This is a >more scientific way of doing it. Again, I look for your comments. > > > Regards, > Mike. > <[EMAIL PROTECTED]> > Cambridge, UK. Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
