[tz] 1911 France change from Paris to GMT

Steve Allen sla at ucolick.org
Sat Jun 13 23:42:17 UTC 2020

On Sat 2020-06-13T15:39:30-0700 Paul Eggert hath writ:
> Yes, that makes more sense than my interpretation. In that case the cited source
> gives no guidance as to what (if anything) French coastal stations broadcast in
> the 9′21″ window between 00:00 old time and 00:00 new time on 1911-03-11. And my
> question about the coastal stations should be applied instead to the Eiffel
> Tower broadcast: for example, did its last time signal in that window say the
> equivalent of "00:04:00 Paris Mean Time" or "23:54:39 Western European Time"? I
> would guess the latter, but it is just a guess.

I am unconvinced that the detailed wording of the law was cognizant of
the actual practices of the Tour Eiffel broadcasts, and detailed
evidence for 1911 is probably buried in publications of Observatoire
de Paris.

The 3 month transition period for Observatoire de Paris is consistent
with the unspoken maxim "Do not ever mess with the master clocks."  It
gave plenty of opportunity for one of the Paris "pendules directrices"
to be taken out of service due to mechanical problem or for
maintenance, and then restarted reset to GMT, and finally connected to
the Tour Eiffel phone wires as of July 1.

The "automatic" format for radio time signals which was designated at
the 1912 International Time Conference is likely based on what Paris
had been broadcasting before then.  The "American" format (basically
still in use by US transmitters) was in use in the 1920s.  The
"rhythmic" format was in use in Paris by the 1920s and the director
of BIH pushed its international option so fiercely that he was removed
from that post.  Additionally, the references to these radio time
formats are hard to parse because each different format was known by
as many as three different names depending on time and place).
A description of time signal formats through the 1920s starts on
page 276 of

Issues of BIH Bulletin Horaire show no indication that Observatoire de
Paris nor Tour Eiffel ever did a time signal broadcast at midnight.
Someone would have needed to be present at both places.  BIH often had
a radio operator listening to signals from other places at any time of
the day, but no big matter if those failed to be received on some
days.  In contrast, making sure that every aspect of the systems for
the pendule directrice, for sending its signal to the Tower, and for
broadcasting it was a big deal that had to be done right for the sake
of navigators depending on it for life and safety.  All of that needed
skilled folks who whose salaries would have been hard to justify at
midnight.  The BIH was always underfunded, and it is clear that many
of its practices had been inherited from the routine operations
which Observatoire de Paris had always done.

I think that the lawyers were uninformed of the details of the times
and practices of the broadcasts.  So in addition to the coastal
transmitters which were doing nothing at midnight on March 10/11, I
think that no signals were being broadcast from Tour Eiffel at the
time of the June 30/July 1 cutover.  This makes the railway clocks
definitive for tzdb, with footnotes deserved to describe the
three months of difference between coastal and Paris transmitters.

Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
1156 High Street               Voice: +1 831 459 3046         Lng -122.06015
Santa Cruz, CA 95064           https://www.ucolick.org/~sla/  Hgt +250 m

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