Paul Eggert via tz said:
In my own code I use 1800 as the transition date between LST and LMT when it's not specified elsewhere.
1800 is surely a bit early, for all but the most technologically-advanced locations. In most of the world, solar time maintained its supremacy over local mean time well after 1800. [...] Part of the problem is that people in the early 19th century didn't much care whether they were using local solar time or local mean time, and many towns actually observed a mean-time approximation to solar time. [...] This state of affairs didn't change until the telegraph made it feasible for timestamps to be communicated more accurately, and railroads needed more-accurate time.
I was wandering round the Fitzwilliam Museum in Cambridge the other day and noticed a Thomas Tompion (1639-1713) clock. It had two hands and a dial with Roman numerals I to XII twice going round it. Outside that, in Arabic numerals, were 5, 10, ..., 60, also twice. At the top it said "EQVAL 60 TIME". Immediately outside that was a ring which could clearly rotate separately. This also had 5, 10, ..., 60 on it twice, with "APPARET 60 TIME" (tilde over the first E) at the near top - it was rotated so that the 60 was aligned with 13.6 on the main dial. (Clearly the staff don't know how to set it correctly, since the equation of time was 3.22 that day.) So 1800 is perhaps a bit late, at least for some places. -- Clive D.W. Feather | If you lie to the compiler, Email: clive@davros.org | it will get its revenge. Web: http://www.davros.org | - Henry Spencer Mobile: +44 7973 377646