On Mon, 29 Mar 2010, David Patte wrote:
- I am particularly interested in the meaning and accuracy of the opening entries for each tz zone. Almost every zone starts with an LMT record. For example, For Europe/London, the opening record states:
Zone Europe/London -0:01:15 - LMT 1847 Dec 1 0:00s
Does this mean that the city of London decreed that all clocks in the city of London should follow mean solar time with this pattern?
No, as Paul says, that entry relates to the railways and perhaps also shipping. Legal time in Britain was local mean time until 1880. See http://www.srcf.ucam.org/~jsm28/british-time/
And what was the time-keeping standard before that date?
Hard to determine. For example, I read somewhere (and lost the reference, sorry) that in the 18th century, time in London (or perhaps just at court) was determined by the Kew Observatory, not Greenwich.
Its easy enough to determine a location's apparent solar time, but determining when a place moved from apparent solar time to mean solar time, or then to a regional tz-based mean solar time is not clear to me.
The answer to apparent solar time vs. mean solar time is a question of what was the normal practice for setting clocks, which I can't answer. Tony. -- f.anthony.n.finch <dot@dotat.at> http://dotat.at/ GERMAN BIGHT HUMBER: SOUTHWEST 5 TO 7. MODERATE OR ROUGH. SQUALLY SHOWERS. MODERATE OR GOOD.