Re: Ring dial corrections between latitudes

[fer de vries]

Mike,   Your statement about using a sundial at another place is correct for usual dials to read time and date lines because the type of lines are based on the same coodinate system "hourangle, declination". This won't work for e.g. Babylonian, Italian, antique hours, only for usual hours.   But it won't work for a ring dial that hang by a cord. At the new place the used coordinate system "azimuth, altitude" is different.   Or you should "hang" the dial at a line parallel to the vertical of the original spot. This is rather clumsy for a portable ringdial.   Just replacing the suspension point won't work. It still hangs parallel to the vertical of the new place and not parallel to the vertical of the old spot.     Best wishes, Fer.   Fer J. de Vries   De Zonnewijzerkring mailto:[EMAIL PROTECTED] http://www.de-zonnewijzerkring.nl   Eindhoven, Netherlands lat.  51:30 N      long.  5:30 E ----- Original Message ----- From: Mike Cowham To: Helmut Sonderegger ; Thaddeus Weakley ; Sundial List Sent: Saturday, August 06, 2005 10:39 AM Subject: Re: Ring dial corrections between latitudes Dear Helmut,     What you have written surprises me because any dial can be used at any latitude as long as it is in the same position relative to the Sun.  Therefore a Ring Dial only needs to have its suspension point moved so that it thinks that it is at the same latitude that it was designed for.      For example, you can use a Horizontal Dial made for, say, UK, and move it to New Zealand as long as it is still in the exact position as it was in England.  It may now be inverted but will tell the correct time (UK time, of course) near sunrise and sunset during NZ summer months.  Move it out into space and it will work perfectly all of the time (as long as it orbits in synchronisation with the Earth).   Regards, Mike Cowham Cambridge, UK A ring dial (farmers ring) never works correct in different latitudes. It just cannot be constructed for different latitudes at the same time (except you put on its inner side 2 different scales for different latitudes).