Dear Frank et al, I note that the letters 'PI' (as well as PII and PW) appear as one of the centres of Oughtred's Horizontal Instrument. They are actually engraved on the instrument made by Elias Allen. Perhaps this is another red herring..... Regards, John D ---------------
"Frans W. Maes" <[EMAIL PROTECTED]> wrote: Dear Frank & all, On the meaning of "PI Long": Waugh uses the symbol P in his computational treatment of the declining dial on p. 80. The P values for each hour line in table 10.2 are "what Holwell (in Clavis Horologiae, London 1712) calls the polar angles". The polar angle for noon equals the so-called difference in longitude DL. Converted to time, this is the time of the sub-style line. So here is at least a link between P and Long.
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