FW: Time zone: the next generation

[Clive D.W. Feather]

Olson, Arthur David (NIH/NCI) said:
>     - Prior to the Julian conversion, different locales had different
>       rules for when the number of the year changed.  In and before
>       1752 in Great Britain, for instance, the number of the year changed
>       on 25 March; 1-24 March belonged to the previous year!  With
>       the adoption of the Gregorian calendar, the change was
>       universally 1 January.

It's not even that simple:
- England and Wales used the March 25th rule, but Scotland used January 1st.
- Some uses even in E&W followed the January 1st rule anyway (e.g. leap
  year determination).
- The change wasn't synchronised with the Gregorian change, but happened
  a little earlier: 1751 began on Mar 24th but 1752 began on 1st January
  (thus, while 1752 lost 11 days, 1751 lost 83).

> (For this reason, you'll sometimes see
>       eighteenth-century dates as O.S. ("Old Style") or N.S. ("New Style")
>       when the year would otherwise be ambiguous.

And the day, actually.

>     - As you correctly observe, leap years were observed irregularly
>       in Rome in Republican and early Imperial times.  In fact, they were
>       so irregularly observed that it was occasionally necessary to
>       intercalate entire months.

You're confusing the pre-Julian calendar (which used intercalary months)
with the Julian one (which used leap days). It wasn't so much "irregular"
as "erroneous" - leap days were inserted every *three* years in the period
starting 46 BCE; when the mistake was spotted, several leaps had to be
omitted. I *believe* that 45, 45, ... 9 BCE were all leap years, then there
were 15 common years in a row, with 8 CE being the next leap year.

>     - I use a message catalog (the same catalog in which I hold localised
>       month names) to hold a locale's Julian conversion date, and then
>       select the catalog according to LC_TIME.  Tcl's ordinary
>       message catalog functionality can be used to change the date.

There may be more than one conversion date: Sweden converted twice
(including a year which had a February 30th in it).

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Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:    +44 20 8495 6138
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