Dear Dr. Carlson, >Have you considered replacing your analemmic cut-out with a solid of >revolution? It simplifies the manufacturing and operation of the >dial, but it does introduce errors of up to 1 min 30 sec because the >exact analemma is "tilted". This type of dial was apparently invented >by a man named Bernhardt. I independently reinvented it, but that >doesn't count. :(
It is possible to use two half figures of revolution, one for the vernal half of the tropical year, the other for the autumnal. I.e., make two lathe turnings, divide them bilaterally and reassort, pairing the enantiomorphic halves. (You get material for two gnomons, one to use, one to spoil.) You mount this "optical cam" with the division plane declined from the vertical, and offset laterally according to which side's shadow is to be used for reading. Rotate it 180 degrees about the polar direction at each solstice. I don't know who first did this, but I've seen a published description some years ago, perhaps in "SKY & TTELESCOPE." Bill Maddux P.s. I independently reinvented this asymmetric dodge, but I too was anticipated, and my invention doesn't count either. : <
