[tz] Fwd: DST changes in Hungary (full historical revision)
Paul Eggert
eggert at cs.ucla.edu
Wed Jun 10 21:25:05 UTC 2020
Thanks for the heads-up. I also found a contemporaneous English-language source,
the Brooklyn Daily Eagle Almanac (1912).
Unfortunately, we have no good way to model stopped clocks in tzdb, as tzdb
clocks are always running. So we need a transition of some sort, presumably
either one like 2020a (from 00:01:00 local time to 23:51:39 the previous day),
or the other, more-logical one (from 00:09:21 local time to 00:00:00 the same day).
Now that I'm looking into it, the line "0:09:21 - PMT 1911 Mar 11 0:01 # Paris
MT" that's currently in tzdb is surely a typo. It's not what's in Shanks, who
gives a transition time of "0:00". Formerly tzdb had no time for that
transition, which defaulted the time to 00:00. My patch dated 2001-03-13 changed
this to "0:01", but this part of the patch patch was in response to an email
dated 2000-12-20 (or -19) from Ciro Disceopolo
<https://mm.icann.org/pipermail/tz/2000-December/011284.html> which says nothing
about that "0:01". Evidently I mistakenly copied the "0:01" from the previous
line "Zone Europe/Paris 0:09:21 - LMT 1891 Mar 15 0:01", where Shanks does say
"0:01".
Anyway, the bottom line is that the stopped clocks make this an oddball
transition that cannot be modeled exactly by tzdb, and that given the story you
mentioned you are correct that it's better modeled using an ordinary transition
(from 00:09:21 to 00:00:00) than the unusual transition we're currently using. I
installed the attached proposed patch into the development database.
Given the above, we have a new trivia question: when and where could a stopped
clock have been correct *more* than three times in a single day? Answer: a clock
stopped at 00:00 was correct an infinite number of times that day in France.
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From 1c8ce71c30b2acb8453b2b43c67052a6f9db2090 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert at cs.ucla.edu>
Date: Wed, 10 Jun 2020 13:51:29 -0700
Subject: [PROPOSED] =?UTF-8?q?French=20clocks=20stopped=20for=209=E2=80=B2?=
=?UTF-8?q?21=E2=80=B3=20on=201911-03-11?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
(Thanks to Michael Deckers.)
* NEWS, theory.html (Accuracy of the tz database): Mention this.
* europe (Europe/Paris): Model the 1911-03-11 transition as
occurring at 00:09:21, not at 00:01.
---
NEWS | 7 +++++++
europe | 30 +++++++++++++++++++++++++++++-
theory.html | 7 +++++++
3 files changed, 43 insertions(+), 1 deletion(-)
diff --git a/NEWS b/NEWS
index e3ab402..5289d4e 100644
--- a/NEWS
+++ b/NEWS
@@ -16,6 +16,13 @@ Unreleased, experimental changes
(Thanks to Géza Nyáry.) Also, the 1890 transition to standard
time was on 11-01, not 10-01 (thanks to Michael Deckers).
+ The 1911-03-11 French transition from +00:09:21 to +00 is now
+ modeled as occurring at 00:09:21, not at 00:01. Legally, clocks
+ stopped at 00:00 for 9 minutes, 21 seconds but this cannot be
+ represented in tzdb, so tzdb instead represents the common
+ practice of keeping an old clock running until the new clock
+ started up. (Thanks to Michael Deckers.)
+
Changes to code
The undocumented and ineffective tzsetwall function has been
diff --git a/europe b/europe
index f0acb42..4fa7119 100644
--- a/europe
+++ b/europe
@@ -1326,6 +1326,34 @@ Link Europe/Helsinki Europe/Mariehamn
# Françoise Gauquelin, Problèmes de l'heure résolus en astrologie,
# Guy Trédaniel, Paris 1987
+# From Michael Deckers (2020-06-10):
+# Le Gaulois, 1911-03-11, page 1/6, online at
+# https://www.retronews.fr/societe/echo-de-presse/2018/01/29/1911-change-lheure-de-paris
+# ... [ Instantly, all pressure driven clock dials halted... Nine minutes and
+# twenty-one seconds later the hands resumed their circular motion. ]
+# There are also precise reports about how the change was prepared in train
+# stations: all the publicly visible clocks stopped at midnight railway time
+# (or were covered), only the chief of service had a watch, labeled
+# "Heure ancienne", that he kept running until it reached 00:04:21, when
+# he announced "Heure nouvelle". See the "Le Petit Journal 1911-03-11".
+# https://gallica.bnf.fr/ark:/12148/bpt6k6192911/f1.item.zoom
+#
+# From Paul Eggert (2020-06-10):
+# French time in railway stations was legally five minutes behind civil time,
+# which explains why "old time" ran to 00:04:21 instead of to 00:09:21.
+# The Brooklyn Daily Eagle Almanac (1912), page 494, says:
+#
+# ALL CLOCKS STOPPED IN FRANCE.
+# On March 10, 1911, all clocks in the Republic of France were stopped
+# for 9 minutes and 21 seconds. This was in obedience to a measure
+# adopted by the French Senate, which went into effect at midnight....
+# Owing to this change in time a question arose in the French press as
+# to whether or not a child that was born and died within the elapsed
+# time could be said to have legally lived.
+#
+# tzdb has no way to represent stopped clocks. As the railway practice
+# was to keep a watch running on "old time" to decide when to restart
+# the other clocks, model this as a transition for "old time" at 00:09:21.
#
# Shank & Pottenger seem to use '24:00' ambiguously; resolve it with Whitman.
@@ -1395,7 +1423,7 @@ Rule France 1976 only - Sep 26 1:00 0 -
# on PMT-0:09:21 until 1978-08-09, when the time base finally switched to UTC.
# Zone NAME STDOFF RULES FORMAT [UNTIL]
Zone Europe/Paris 0:09:21 - LMT 1891 Mar 15 0:01
- 0:09:21 - PMT 1911 Mar 11 0:01 # Paris MT
+ 0:09:21 - PMT 1911 Mar 11 0:09:21 # Paris MT
# Shanks & Pottenger give 1940 Jun 14 0:00; go with Excoffier and Le Corre.
0:00 France WE%sT 1940 Jun 14 23:00
# Le Corre says Paris stuck with occupied-France time after the liberation;
diff --git a/theory.html b/theory.html
index ffa3b4d..de105f2 100644
--- a/theory.html
+++ b/theory.html
@@ -690,6 +690,13 @@ href="https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanes
often not specified to the accuracy that the
<code><abbr>tz</abbr></code> database requires.
</li>
+ <li>
+ The <code><abbr>tz</abbr></code> database cannot represent stopped clocks.
+ However, on 1911-03-11 at 00:00, French clocks were changed by
+ stopping them for 9 minutes, 21 seconds. This is approximated
+ in <code><abbr>tz</abbr></code> as a transition from 00:09:21 back
+ to 00:00:00 that day.
+ </li>
<li>
Sometimes historical timekeeping was specified more precisely
than what the <code><abbr>tz</abbr></code> code can handle.
--
2.17.1
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