>From c9da9f27c53b0b77289e51848f723339d9bc4ca4 Mon Sep 17 00:00:00 2001
From: Paul Eggert
Date: Mon, 4 Dec 2017 10:26:43 -0800
Subject: [PROPOSED 2/3] Improve documentation of Dublin/Dunsink time
* europe: Clarify Dublin vs Dunsink time, and mention the
1896 change in the Nautical Almanac for the Dunsink offset.
* theory.html (Time zone abbreviations): DMT also stands
for Dunsink Mean Time.
---
europe | 29 ++++++++++++++++++++++-------
theory.html | 4 ++--
2 files changed, 24 insertions(+), 9 deletions(-)
diff --git a/europe b/europe
index 1f54767..6420b8a 100644
--- a/europe
+++ b/europe
@@ -278,16 +278,31 @@
# The following claim by Shanks & Pottenger is possible though doubtful;
# we'll ignore it for now.
# * Dublin's 1971-10-31 switch was at 02:00, even though London's was 03:00.
+
+# From Paul Eggert (2017-12-04):
#
-#
-# Whitman says Dublin Mean Time was -0:25:21, which is more precise than
-# Shanks & Pottenger.
-# Perhaps this was Dunsink Observatory Time, as Dunsink Observatory
-# (8 km NW of Dublin's center) seemingly was to Dublin as Greenwich was
-# to London. For example:
+# Dunsink Observatory (8 km NW of Dublin's center) was to Dublin as
+# Greenwich was to London. For example:
#
# "Timeball on the ballast office is down. Dunsink time."
# -- James Joyce, Ulysses
+#
+# The abbreviation DMT stood for "Dublin Mean Time" or "Dunsink Mean Time";
+# this being Ireland, opinions differed.
+#
+# Whitman says Dublin/Dunsink Mean Time was UT-00:25:21, which agrees
+# with measurements of recent visitors to the Meridian Room of Dunsink
+# Observatory; see Malone D. Dunsink and timekeeping. 2017-01-24.
+# . Malone
+# writes that the Nautical Almanac listed UT-00:25:22 until 1896, when
+# it moved to UT-00:25:21.1 (I confirmed that the 1893 edition used
+# the former and the 1896 edition used the latter). Evidently the
+# news of this change propagated slowly, as Milne 1899 still lists
+# UT-00:25:22 and cites the International Telegraph Bureau. As it is
+# not clear that there was any practical significance to the change
+# from UT-00:25:22 to UT-00:25:21.1 in civil timekeeping, omit this
+# transition for now and just use the latter value, omitting its
+# fraction since our format cannot represent fractions.
# "Countess Markievicz ... claimed that the [1916] abolition of Dublin Mean Time
# was among various actions undertaken by the 'English' government that
@@ -478,7 +493,7 @@ Link Europe/London Europe/Isle_of_Man
# Zone NAME GMTOFF RULES FORMAT [UNTIL]
Zone Europe/Dublin -0:25:00 - LMT 1880 Aug 2
- -0:25:21 - DMT 1916 May 21 2:00s # Dublin MT
+ -0:25:21 - DMT 1916 May 21 2:00s
-0:25:21 1:00 IST 1916 Oct 1 2:00s
0:00 GB-Eire %s 1921 Dec 6 # independence
0:00 GB-Eire GMT/IST 1940 Feb 25 2:00s
diff --git a/theory.html b/theory.html
index cc2d3d2..8ea5771 100644
--- a/theory.html
+++ b/theory.html
@@ -362,7 +362,7 @@ cause trouble here, as the numeric strings would exceed the POSIX length limit.
AMT Amsterdam, Asunción, Athens;
BMT Baghdad, Bangkok, Batavia, Bern, Bogotá, Bridgetown, Brussels, Bucharest;
CMT Calamarca, Caracas, Chisinau, Colón, Copenhagen, Córdoba;
-DMT Dublin;
+DMT Dublin/Dunsink;
EMT Easter;
FFMT Fort-de-France;
FMT Funchal;
@@ -390,7 +390,7 @@ WMT Warsaw.
GMT/BST/IST/BDST established for time in the UK. They are:
CMT/BST for Calamarca Mean Time and Bolivian Summer Time
-1890–1932, DMT/IST for Dublin Mean Time and Irish Summer Time
+1890–1932, DMT/IST for Dublin/Dunsink Mean Time and Irish Summer Time
1880–1916, MMT/MST/MDST for Moscow 1880–1919, and RMT/LST
for Riga Mean Time and Latvian Summer time 1880–1926.
An extra-special case is SET for Swedish Time (svensk
--
2.14.3