Hello Patrick: >Message text written by John Carmichael > >>Now, what if instead of placing the nodus on the style, I use a tall >vertical pointed rod at the dial center for the nodus?< > >That would be fine - indeed it would be better since the weight of the >nodus will not cause the string gnomon to sag.
A little ball nodus would be less than 1/4" in diameter on my dials and would probably weigh less than 1 gram. Since the counterweight weighs about 5 lbs. I think cable sag would be undetectible. Incidentally the nodus >doesn't have to be at the dial's centre - its position should be chosen to >get the solstice lines nicely balanced on the plate Yes, I even thought about placing a vertical nodus south of center, but abandoned the idea because the bolt which attaches the cable to the center would get in the way of the meridian line, summer solstice line and part of the analemma. A nicely balanced solstice line separation can also be achieved by changing the height of the vertical nodus at the center. > >The analemma is simply the time for one particular hour corrected for EoT >(or for EoT combined with the longitude offset) plotted for all dates using >as a scale the date line as determined by the vertical nodus. If you >plotted it that way you could choose an EoT scale equivalent to the middle >of a leap year cycle and then it would probably be a tad more accurate >than one drawn by formula. Mayall p 197-9 describes the graphical method. But Patrick, isn't the graphical method described by Mayall used to project the analemma onto a PERPENDICULAR surface and not a horizontal surface??? Is this correct? John >
