[tz] 1911 France change from Paris to GMT

Paul Eggert eggert at cs.ucla.edu
Sun Jun 14 02:39:42 UTC 2020

On 6/13/20 4:42 PM, Steve Allen wrote:
> 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.

I have my doubts that this sort of thing was routinely done by hand, because
even back in 1911 it would have been more reliable to do it automatically.
(Though perhaps it was done by hand on the 1911-03-11 transition, as the
salaries could easily have been justified for that special case.)

Although I haven't found sources for what practices were in place at the Eiffel
Tower on March 10/11, 1911, I did find the following abstract on page 265 of
Science Abstracts. Section B - Electrical Engineering. Vol. XIV. 1911. It
suggests that an automatic relay was feasible at the Eiffel Tower in March 1911,
as Norddeich was already doing that in 1910. And this source confirms that the
Eiffel Tower was routinely broadcasting time signals near midnight by 1910.


Duddell W, Howe GWO, Eccles WH. Wireless time signals. Electrician. volume 66.
1910-11-18 (p 222-3), 1910-11-25 (p 263), 1910-12-09 (p 331). A correspondence,
initated by Duddell, on the subject of daily time signals sent out by wireless
stations. Duddell draws attention to the fact that in addition to the Eiffel
Tower signals Norddeich now sends out signals marking noon and midnight
(Greenwich time). The latter are sent automatically by means of a relay actuated
by a special clock at the station, the time-keeping of this clock being
controlled by the Wilhelmshaven Observatory. After preliminary signals lasting
from about 11h. 58m. 0s. till 11h. 58m. 40s., the actual time signals are given.
These consist of six groups of five dots each. The time is taken from the
commencement of each dot. In each group the dots commence at intervals of one
second. The groups commence as follows : 11h. 58m. 46s., 11h. 58m. 56s., 11h.
59m. 6s. ; 11h. 59m. 36s., 11h. 59m. 46s., 11h. 59m. 56s. ; the last dot of the
last group therefore marks midnight. [The signals are repeated at midday.] The
French signals are single dots at midnight, 0h. 2m. and 0h. 4m. Paris time
(i.e., 11h. 50m. 39.1s., &c., Greenwich time). [They are repeated at 11 a.m.
Paris time.] Eccles disagrees with Duddell in regard to the probable error of
observation in each case, and contends that the Eiffel Tower signals are the
best. Howe states that the wave-length of the Norddeich signals, as measured at
the Central Technical College, is 2000 m., the tuning being sharp. In a second
letter Howe gives a comparison of the Norddeich signals with Greenwich time as
shown by the chronometer of the Astrophysical Department of the Imperial
College, which was checked hourly by an electric signaal from Greenwich. The
observations show discrepancies amounting to as much as 1.3 seconds in one case.
It is pointed out that in both cases electrical transmitting gear is used, and
the quesiton of where the error occurs is not fully determined.   J. E.-M.

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