Eggert mods

SCCS-file: Theory
SCCS-SID: 7.7

Theory

@@ -6,6 +6,7 @@
 	Time and date functions
 	Names of time zone regions
 	Time zone abbreviations
+	Calendrical issues
 
 
 ----- Time and date functions -----
@@ -283,3 +284,156 @@ in practice: e.g. `EST' has a different meaning in Australia than
 it does in the United States.  In new applications, it's often better
 to use numeric UTC offsets like `-0500' instead of time zone
 abbreviations like `EST'; this avoids the ambiguity.
+
+
+----- Calendrical issues -----
+
+Calendrical issues are a bit out of scope for a time zone database,
+but they indicate the sort of problems that we would run into if we
+extended the time zone database further into the past.  An excellent
+resource in this area is Nachum Dershowitz and Edward M. Reingold,
+<a href="http://emr.cs.uiuc.edu/home/reingold/calendar-book/index.shtml">
+Calendrical Calculations
+</a>, Cambridge University Press (1997).  Other information and
+sources are given below.  They sometimes disagree.
+
+
+France
+
+Gregorian calendar adopted 1582-12-20.
+French Revolutionary calendar used 1793-11-24 through 1805-12-31,
+and (in Paris only) 1871-05-06 through 1871-05-23.
+
+
+Russia
+
+From Chris Carrier <72157.3334@CompuServe.COM> (1996-12-02):
+On 1929-10-01 the Soviet Union instituted an ``Eternal Calendar''
+with 30-day months plus 5 holidays, with a 5-day week.
+On 1931-12-01 it changed to a 6-day week; in 1934 it reverted to the
+Gregorian calendar while retaining the 6-day week; on 1940-06-27 it
+reverted to the 7-day week.  With the 6-day week the usual days
+off were the 6th, 12th, 18th, 24th and 30th of the month.
+(Source: Evitiar Zerubavel, _The Seven Day Circle_)
+
+
+Sweden (and Finland)
+
+From: msb@sq.com (Mark Brader)
+<a href="news:1996Jul6.012937.29190@sq.com">
+Subject: Re: Gregorian reform -- a part of locale?
+</a>
+Date: 1996-07-06
+
+In 1700, Denmark made the transition from Julian to Gregorian.  Sweden
+decided to *start* a transition in 1700 as well, but rather than have one of
+those unsightly calendar gaps :-), they simply decreed that the next leap
+year after 1696 would be in 1744 -- putting the whole country on a calendar
+different from both Julian and Gregorian for a period of 40 years.
+
+However, in 1704 something went wrong and the plan was not carried through;
+they did, after all, have a leap year that year.  And one in 1708.  In 1712
+they gave it up and went back to Julian, putting 30 days in February that
+year!...
+
+Then in 1753, Sweden made the transition to Gregorian in the usual manner,
+getting there only 13 years behind the original schedule.
+
+(A previous posting of this story was challenged, and Swedish readers
+produced the following references to support it: "Tiderakning och historia"
+by Natanael Beckman (1924) and "Tid, en bok om tiderakning och
+kalendervasen" by Lars-Olof Lode'n (no date was given).)
+
+
+Grotefend's data
+
+From: "Michael Palmer" <mpalmer@netcom.com>
+Subject: Re: Gregorian Calendar (was Re: Another FHC related question
+Newsgroups: soc.genealogy.german
+Date: Tue, 9 Feb 1999 02:32:48 -800
+Message-ID: <199902091032.CAA09644@netcom10.netcom.com>
+
+The following is a(n incomplete) listing, arranged chronologically, of 
+European states, with the date they converted from the Julian to the 
+Gregorian calendar:
+
+04/15 Oct 1582 - Italy (with exceptions), Spain, Portugal, Poland (Roman
+                 Catholics and Danzig only)
+09/20 Dec 1582 - France, Lorraine
+
+21 Dec 1582/
+   01 Jan 1583 - Holland, Brabant, Flanders, Hennegau
+10/21 Feb 1583 - bishopric of Liege (L"uttich)
+13/24 Feb 1583 - bishopric of Augsburg
+04/15 Oct 1583 - electorate of Trier
+05/16 Oct 1583 - Bavaria, bishoprics of Freising, Eichstedt, Regensburg,
+                 Salzburg, Brixen
+13/24 Oct 1583 - Austrian Oberelsass and Breisgau
+20/31 Oct 1583 - bishopric of Basel
+02/13 Nov 1583 - duchy of J"ulich-Berg
+02/13 Nov 1583 - electorate and city of K"oln
+04/15 Nov 1583 - bishopric of W"urzburg
+11/22 Nov 1583 - electorate of Mainz
+16/27 Nov 1583 - bishopric of Strassburg and the margraviate of Baden
+17/28 Nov 1583 - bishopric of M"unster and duchy of Cleve
+14/25 Dec 1583 - Steiermark
+
+06/17 Jan 1584 - Austria and Bohemia
+11/22 Jan 1584 - Luzern, Uri, Schwyz, Zug, Freiburg, Solothurn
+12/23 Jan 1584 - Silesia and the Lausitz
+22 Jan/
+   02 Feb 1584 - Hungary (legally on 21 Oct 1587)
+      Jun 1584 - Unterwalden
+01/12 Jul 1584 - duchy of Westfalen
+
+16/27 Jun 1585 - bishopric of Paderborn
+
+14/25 Dec 1590 - Transylvania
+
+22 Aug/
+   02 Sep 1612 - duchy of Prussia
+
+13/24 Dec 1514 - Pfalz-Neuburg
+
+          1617 - duchy of Kurland (reverted to the Julian calendar in
+                 1796)
+
+          1624 - bishopric of Osnabr"uck
+
+          1630 - bishopric of Minden
+
+15/26 Mar 1631 - bishopric of Hildesheim
+
+          1655 - Kanton Wallis
+
+05/16 Feb 1682 - city of Strassburg
+
+18 Feb/
+   01 Mar 1700 - Protestant Germany (including Swedish possessions in
+                 Germany), Denmark, Norway
+30 Jun/
+   12 Jul 1700 - Gelderland, Zutphen
+10 Nov/
+   12 Dec 1700 - Utrecht, Overijssel
+
+31 Dec 1700/
+   12 Jan 1701 - Friesland, Groningen, Z"urich, Bern, Basel, Geneva,
+                 Turgau, and Schaffhausen
+
+          1724 - Glarus, Appenzell, and the city of St. Gallen
+
+01 Jan 1750    - Pisa and Florence
+
+02/14 Sep 1752 - Great Britain
+
+17 Feb/
+   01 Mar 1753 - Sweden
+
+1760-1812      - Graub"unden
+
+The Russian empire (including Finland and the Baltic states) did not 
+convert to the Gregorian calendar until the Soviet revolution of 1917.
+
+Source:  H. Grotefend, _Taschenbuch der Zeitrechnung des deutschen 
+Mittelalters und der Neuzeit_, herausgegeben von Dr. O. Grotefend 
+(Hannover:  Hahnsche Buchhandlung, 1941), pp. 26-28.