Wm. S. Maddux wrote: > > 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. : <
Bill: Add me too, to the list of disappointed reinventors. My first design approach was to try to use a solid analemmic gnomon shape, but I couldn't think of an easy way to manufacture it or to support it. My big "AHA!" came when I realized that I could use a rotatable plate with an analemmic cutout. I felt this was easier and cheaper to mass produce, it required much simpler support, and it could easily be labeled and read to also indicate every day of the year. I built my first brass sundial, saw that it actually worked, and decided to do a patent search for any similar sundials. I then came across Samual W. Balch's Jan 19, 1926 U.S. Patent #1,570,029, which claims exactly the solid analemmic shape that you have described. I thought I still had his patent beat for the very reasons I stated above, until Fred Sawyer informed me that a sundial which looked almost exactly identical to (mine?) was invented by Mr. John Ryder Oliver in the UK in the 1890's. Sigh. Thanks. Pete.
