On 2020-06-09 16:05, Paul Eggert wrote:

... I didn't see anything in the source about time-of-day for the transition, though. In cases like that we simply list the date. So for now I installed the attached proposed patch.

   Yes, I know: in such cases the zic default is taken, so that the time    of day is supposed to jump from 00:00 to 23:43:40.    But this is certainly not the way of how railway times were adjusted.    Railway time was not produced by each station but was disseminated via    time signals sent from a single observatory. These time synchronization    signals were sent frequently (eg, every ten minutes or so) on a telegraph    line to all the stations in order to make sure that they all had the same    time -- and the "same" time at least to the minute is essential for the service.    So the jump in railway time would most likely be realized by the omission    of several time synchronization signals for a short while before the jump    (to alert the service personnel that clocks needed adjustment), followed by    the synchronization signals for the time scale after the jump. In other words,    the jump would be from (some signals before) 00:16:20 to the first    synchronization signal for the new scale, at 00:00 exactly.    In all the cases where I could check the exact time of day of a switch    to time zone time, this turned out to be the case -- except, of course,    for Dublin on 1916-10-01 where British law said that the time had to jump    from 03:00:00 to 02:25:21.1.    I guess I just wanted to say that the default jump produced by zic    is not necessarily a good guess of what really has happened (except    possibly for Britain).    Michael Deckers.

   On 2020-06-09 20:52, Paul Eggert wrote about strange jumps in tzdb time scales:

There are other such cases in tzdb. For example, the 1911-03-11 transition in Paris is from 00:01 Paris Mean Time to 23:51:39 GMT the previous day. If the comments are right this transition came from Ciro Disceopolo but we don't have exact citations.

   Well, that is what tzdb says, but what actually happened was different,    and it was the same in Paris and in Monaco.    Le Gaulois, 1911-03-11, page 1/6, online at [https://www.retronews.fr/societe/echo-de-presse/2018/01/29/1911-change-lheur...]       "Instantanément, toutes les horloges pneumatiques s'arrêtèrent...        Neuf minutes vingt et une seconde plus tard, les aiguilles        reprirent leur marche circulaire."        [ Instantly, all pressure driven clock dials halted...          Nine minues 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",    online at    [https://gallica.bnf.fr/ark:/12148/bpt6k6192911/f1.item.zoom].    Anyway, thanks for your remarks!    Michael Deckers.

Anyway, the bottom line is that the stopped clocks make this an oddball transition that cannot be modeled exactly by tzdb

Unless you're willing to have a slew of one-second-apart transitions with each one differing from its neighbor by one second.-) @dashdashado On Wed, Jun 10, 2020 at 5:25 PM Paul Eggert <eggert@cs.ucla.edu> wrote:

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.

    On 2020-06-10 21:25, Paul Eggert wrote:

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.

    Let us not get carried away and consider this an oddball transition.     It was a transition from a local time to a time zone time that is just     a few minutes slower, as has happened in many locations all over the world.     Legal time in France was never stopped; it just switched from UT + 00:09:21     to UT.     Since 1891-03-16 (sic!), legal time in France was the mean solar     time in Paris, and the law published on 1911-03-10 (online at     [https://gallica.bnf.fr/ark:/12148/bpt6k2022333z/f2]) changed it     to mean solar time in Paris minus 00:09:21; this change took effect     on the day after publication, 1911-03-11. The appended decree     (loc cit) makes it clear that the new definition of legal time     was used with values from 1911-03-11T00:00:00 onwards. There is     no mention in the legal texts of how the change is to be effected     (let alone that legal time would stop for some time).     Hence, the old definition of legal time applied until just before     it took the value 1911-03-11T00:09:21, and the jump in legal time     was from 1911-03-11T00:09:21 to 1911-03-11T00:00:00.     The newspaper reports about some remote-controlled public clocks     ("pendules pneumatiques") shows that these clocks were stopped     when they reached 1911-03-11T00:00; the next minute pulse only     came 10 minutes and 21 seconds later and put them to 1911-03-11T00:01.     That does not imply that legal time had stopped, it just indicates     how these clocks were adjusted. Other clocks (such as clocks on     churches and pocket watches) would certainly have been adjusted     in a less time-consuming manner.     Railway time in France was also adjusted at the same occasion     from UT + 00:04:21 to UT. Here it may be more appropriate to     say that "time was stopped" (at least for the trains not     currently in motion) because railway time is the parameter     used for planning train motions and should be monotone.     Michael Deckers.

   On 2020-06-12 03:21, Paul Eggert wrote:

Still, it does appear that, at least according to US press accounts, common practice in France was to stop the clocks.

     That "all French clocks stopped" for 00:09:21 is a misreading of      French newspapers; this sort of adjustment applies only to certain      remote-controlled clocks ("pendules pneumatiques", of which there      existed perhaps a dozen in Paris, and which simply could not be      set back remotely), but not to all the clocks in all French towns      and villages. So even contemporary sources may be plain wrong.      For instance, the following story in the "Courrier de Saône-et-Loire"      1911-03-11, page 2, online at [https://www.retronews.fr/societe/echo-de-presse/2018/01/29/1911-change-lheur...]      only works if legal time was stepped back (was not monotone):        "On fait observer que des enfants qui naîtraient à minuit moins 5 et         mourraient à minuit de l'ancienne heure, se trouveront être morts         avant d'être nés, l'heure ayant reculé et supprimé théoriquement         9 minutes et 25[sic] secondes de leur existence, c'est-à-dire         plus qu'ils n'en pouvaient dépenser."         [One can observe that children who had been born at midnight less          5 [minutes] and who had died at midnight of the old time, would          turn out to be dead before being born, time having been set back          and having suppressed 9 minutes and 25 seconds of their existence,          that is, more than they could spend.]      Michael Deckers.

Date: Fri, 12 Jun 2020 14:42:08 -0700 From: Paul Eggert <eggert@cs.ucla.edu> Message-ID: <d4a3820c-7f1c-fb5d-54b8-e5cfec855475@cs.ucla.edu> | But this is curious, as that story also makes sense only if clocks | were set back at 00:00 "old time" Huh? I haven't read the story in question (I don't understand a word of French, well, merde, maybe just one or two) but I don't see how when the clocks were set backwards makes any difference at all. Simply setting clocks backwards means a later event can seem to have happened at an earlier time, so a child could be born at time X, at X+5 the clocks are set backwards 20, at X+10 (original clock time - which is now X-10 shown on the clocks) the child dies, hence lived from X to X-10. What the value of X is is irrelevant. kre

On 6/13/20 2:08 AM, Robert Elz wrote:

I haven't read the story in question (I don't understand a word of French, well, merde, maybe just one or two) but I don't see how when the clocks were set backwards makes any difference at all.

It's because of one specific detail of the story: that the unfortunate lifetime began at 23:55 and ended at 24:00 old time. If the clock is not set back until 00:09:21 the next day, this particular person would not have a nominal death time preceding nominal birth time. You're right that there would still be a problem with a five-minute lifetime beginning at (say) 00:05:00 old time and ending at 00:00:39 new time, but that's not what the story said. You can see Michael's translation of the story here: https://mm.icann.org/pipermail/tz/2020-June/029090.html

On 6/13/20 5:50 AM, Michael H Deckers wrote:

    the common perception of people about the transition     can hardly be determined from a single newspaper report either --

Quite true. It's just one report (and a hypothetical one at that!).

    However, we _do_ have detailed reports on the switch in French     railway time (implying a jump from 00:04:21 to 00:00:00),

The public-facing railway clocks in question didn't jump; they stopped at 00:00:00 for 4 minutes and 21 seconds. The only railway clocks that jumped were the private watches of the stationmasters, implying that the public-facing clocks (which everybody else used) recorded the public railway time used by almost everybody there, with the stationmasters' watches being merely auxiliary devices to help make sure the public clocks were accurate.

    we know that radio signals since 1911-03-11T00:00:00 (not since     1911-03-10T23:50:39) were ordered to be transmitted with the     label "heure nouvelle".

Sure, but that does not imply that the radiotelegraph transition was at 00:09:21 old time. On the contrary, the citation you mentioned <https://gallica.bnf.fr/ark:/12148/bpt6k2022333z/f2> suggests that the transition was at 00:00 old time. The cited law says this: “Art. 2. - Pendant la période s’étendant de la nuit du 10 mars au 11 mars (minuit), à la nuit du 30 juin au 1er juillet 1911 (minuit), l’indication de l’heure transmise aux navires en mer, par les stations côtiéres radiotélègraphiques ouveries au service public, sera suivie de la mention : « Heure de l’Europe occidentale ».” which Google Translate renders as: “[Art. 2. - During the period from the night of March 10 to March 11 (midnight), to the night of June 30 to July 1, 1911 (midnight), the indication of the time transmitted to ships at sea, by coastal radio and telegraph stations open to the public service, will be followed by the words: "Western European Time".]” As there were at least two legal timestamps equal to “the night of March 10 to March 11 (midnight)”, this part of the law is arguably ambiguous as to exactly when radio transmissions started being labeled “Western European Time”. The intent is clear: they wanted the after-midnight timestamps labeled "Western European Time" rather than "Paris Mean Time"; but which midnight did they mean? We have more detail to help us resolve this ambiguity, in the next page of the cited source, which says “Jusqu’a la nuit du 30 juin 1911 exclusivement, aucune modification ne sera faite à l’instant de l’envoi des signaux horaires par l’Observatoire de Paris. [Until the night of June 30, 1911 exclusively, no modification will be made at the time of the sending of time signals by the Paris Observatory.]” That is, through June radio time signals were still sent at the same time intervals as before, with the labels altered to be new time. In particular, signals were sent daily “La nuit à minuit 0 m. 0 s., minuit 2 m. 0 s., minuit 4 m. 0 s. de temps moyen de Paris [At 00:00:00, 00:02:00, 00:04:00 Paris Mean Time]” with labels “11 h. 50 m. 39 s., 11 h. 52 m. 39 s., 11 h. 54 m. 39 s. [23:50:59, 23:52:39, 23:54:39]”. We want to know what happened during the change around 1911-03-11 00:00. For example, were the radio signals sent at 1911-03-11 00:04 old time labeled “00:04:00 Paris Mean Time” or were they labeled “23:54:39 Western European Time”? The 1911-03-11 change was supposed to occur from “de la nuit du 10 mars au 11 mars (minuit)”, which suggests that it was intended to affect the broadcasts of 00:02 and 00:04 old time as they occurred after midnight old time. And it would have been odd for the broadcast of 00:00 old time to have been treated differently from the other two. So this suggests that for the radiotelegraph, the transition occurred at 00:00 old time. Of course this is just my reading of the law, and I suppose the law could be read differently. Had I been running the radiotelegraph I would have said something like “The time is now 00:00:00 Paris Mean Time, 23:50:39 Western European Time” for the timestamp sent at midnight old time. This would have complied with the regulations no matter how they were interpreted, and would have lessened confusion among receivers of the broadcast.

On 6/13/20 2:37 PM, Steve Allen wrote:

because no station was broadcasting continuously, there was no ambiguity about whether they were broadcasting before or after the 1911 March 10/11 boundary.

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. For the record, here is my hand-typed transcription of the cited source <https://gallica.bnf.fr/ark:/12148/bpt6k2022333z/f2>, followed by an English rendering by Google Translate. ------ Le Sénat et la Chambre des députés ont adopté. Le Président de la République promulgue la loi dont la teneur suit : Article unique. - L’heure légale en France et en Algérie est l’heure, temps moyen de Paris, retardée de neuf minutes vingt et une secondes. La présente loi, délibérée et adoptée par le Séenat et par la Chabre des députés, sera exécutée comme loi de l’Etat. Fait à Paris, le 9 mars 1911. Le sous-secrétaire d’Etat des postes et des télègraphique, Arrête : Art. 1er. - A partir de la nuit du 10 au 11 mars 1911, à minuit, l’heure de tous les bureaux de poste, télègraphe et télèphone est celle du temps moyen de Paris, retardée de neuf minutes et vingt et une secondes. Art. 2. - Pendant la période s’étendant de la nuit du 10 mars au 11 mars (minuit), à la nuit du 30 juin au 1er juillet 1911 (minuit), l’indication de l’heure transmise aux navires en mer, par les stations côtiéres radiotélègraphiques ouveries au service public, sera suivie de la mention : « Heure de l’Europe occidentale ». Art. 3 - Le prèsent arrête sera déposé au cabinet du sous-secrétariat d’Etat des postes et des télègraphes pure être notifié à que de droit. Mode de transmission de l’heure aux navires en mer. Jusqu’a la nuit du 30 juin 1911 exclusivement, aucune modification ne sera faite à l’instant de l’envoi des signaux horaires par l’Observatoire de Paris. Ces signaux seront envoyés : Le metin à 11 h. 0 m. 0 s., 11 h. 2 m. 0 s., 11 h 4 m. 0 s. de temps moyen do Paris. La nuit à minuit 0 m. 0 s., minuit 2 m. 0 s., minuit 4 m. 0 s. de temps moyen de Paris. Ces instants exprimés en temps légal seront représentés : Le matin par 10 h. 50 m. 39 s., 11 h. 52 m. 39 s., 10 h. 54 m. 39 s. Le soir par 11 h. 50 m. 39 s., 11 h. 52 m. 39 s., 11 h. 54 m. 39 s. A partir de la nuit du 30 juin an 1er juillet inclusivement, les signaux seront envoyes aux heures légales suivantes : Le matin 10 h. 45 m. 0 s., 10 h. 47 m. 0 s., 10 h. 49 m. 0 s. La nuit 11 h. 45 m. 0 s., 11 h. 47 m. 0 s., 11 h. 49 m. 0 s. Dans la période de transition s’étendant du 10 mars au 30 juin, les stations côtiéres radiotélegraphiques ouvertes au service public transmetiront l’heure légale suivie de la mention : « Heure de l’Europe occidentale ». ------ The Senate and the Chamber of Deputies adopted. The President of the Republic promulgates the law whose content follows: Single item. - The legal time in France and Algeria is the time, average time of Paris, delayed by nine minutes twenty-one seconds. This law, deliberated and adopted by the Senate and by the Chamber of Deputies, will be executed as state law. Done in Paris, March 9, 1911. The Undersecretary of State for Posts and Telegraph, Stopped : Art. 1st. - From the night of March 10 to 11, 1911, at midnight, the time of all post offices, telegraph and telephone is that of Paris average time, delayed by nine minutes and twenty-one seconds. Art. 2. - During the period from the night of March 10 to March 11 (midnight), to the night of June 30 to July 1, 1911 (midnight), the indication of the time transmitted to ships at sea, by coastal radio and telegraph stations open to the public service, will be followed by the words: "Western European Time". Art. 3 - The present order will be deposited in the office of the Under-Secretary of State for Posts and Telegraphs to be notified to that of right. Mode of transmission of time to ships at sea. Until the night of June 30, 1911 exclusively, no modification will be made at the time of the sending of time signals by the Paris Observatory. These signals will be sent: Morning at 11 a.m. 0 m. 0 sec., 11 a.m. 2 m. 0 sec., 11 h 4 m. 0 sec. of Paris average time. At midnight 0 m. 0 sec., Midnight 2 m. 0 sec., Midnight 4 m. 0 sec. Paris average time. These moments expressed in legal time will be represented: In the morning by 10 a.m. 50 m. 39 s., 11 a.m. 52 m. 39 s., 10 a.m. 54 m. 39 s. In the evening by 11 a.m. 50 m. 39 s., 11 a.m. 52 m. 39 s., 11 a.m. 54 m. 39 s.

From the night of June 30 to July 1 inclusive, signals will be sent at the following legal times:

In the morning 10 a.m. 45 m. 0 sec., 10 a.m. 47 m. 0 sec., 10 a.m. 49 m. 0 sec. At night 11 a.m. 45 m. 0 sec., 11 a.m. 47 m. 0 sec., 11 a.m. 49 m. 0 sec. In the transitional period from 10 March to 30 June, coast radiotelegraph stations open to the public service will transmit the legal time followed by the words: "Western European time".

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.

On Sat 2020-06-13T19:39:42-0700 Paul Eggert hath writ:

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.

Bulletin Horaire has an answer vol 3 no 46 is a history of timekeeping page 257 says The time signals, inaugurated on May 23, 1910, were given only at night, at 0h0m t. m. civil of Paris. From the following November 21, they were also given in daytime, at 11h.0m. The law of March 9, 1911 having adopted, for the legal time in France, that of the Greenwich meridian, the hours of emission were brought forward to 10h45m and 23h45m, from July 1, 1911 So Tour Eiffel may have broadcast one last set of midnight pulses on old Paris Mean Time at the June 30/July 1 boundary, or they may have omitted those pulses and waited until new 10:45 the next morning. -- Steve Allen <sla@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

Fixing a few typos, and adding titles, etc. ---- LOI portant modification de l'heure légale française, pour la mettre en concordance avec le système universel des fuseaux horaires. Le Sénat et la Chambre des députés ont adopté, Le Président de la République promulgue la loi dont la teneur suit : Article unique. — L’heure légale en France et en Algérie est l’heure, temps moyen de Paris, retardée de neuf minutes vingt et une secondes. La présente loi, délibérée et adoptée par le Sénat et par la Chambre des députés, sera exécutée comme loi de l’Etat. Fait à Paris, le 9 mars 1911. A. FALLIÈRES. Par le Président de la République : Le ministre des travaux publics, des postes et des télégraphes, CHARLES DUMONT. Le sous-secrétaire d’Etat des postes et des télégraphes, Sur la proposition du directeur de l'exploitation télégraphique, Arrête : Art. 1er. — A partir de la nuit du 10 au 11 mars 1911, à minuit, l’heure de tous les bureaux de poste, télégraphe et téléphone est celle du temps moyen de Paris, retardée de neuf minutes et vingt et une secondes. Art. 2. - Pendant la période s’étendant de la nuit du 10 mars au 11 mars (minuit) à la nuit du 30 juin au 1er juillet 1911 (minuit), l’indication de l’heure transmise aux navires en mer, par les stations côtières radiotélégraphiques ouvertes au service public, sera suivie de la mention : « Heure de l’Europe occidentale ». Art. 3 - Le présent arrêté sera déposé au cabinet du sous-secrétariat d’Etat des postes et des télégraphes pour être notifié à qui de droit. Fait à Paris, le 9 mars 1911. CHARLES CHAUMET. Mode de transmission de l’heure aux navires en mer. Jusqu’à la nuit du 30 juin 1911 exclusivement, aucune modification ne sera faite à l’instant de l’envoi des signaux horaires par l’Observatoire de Paris. Ces signaux seront envoyés : Le matin à 11 h. 0 m. 0 s., 11 h. 2 m. 0 s., 11 h 4 m. 0 s. de temps moyen de Paris. La nuit à minuit 0 m. 0 s., minuit 2 m. 0 s., minuit 4 m. 0 s. de temps moyen de Paris. Ces instants exprimés en temps légal seront représentés : Le matin par 10 h. 50 m. 39 s., 11 h. 52 m. 39 s., 10 h. 54 m. 39 s. Le soir par 11 h. 50 m. 39 s., 11 h. 52 m. 39 s., 11 h. 54 m. 39 s. A partir de la nuit du 30 juin an 1er juillet inclusivement, les signaux seront envoyés aux heures légales suivantes : Le matin 10 h. 45 m. 0 s., 10 h. 47 m. 0 s., 10 h. 49 m. 0 s. La nuit 11 h. 45 m. 0 s., 11 h. 47 m. 0 s., 11 h. 49 m. 0 s. Dans la période de transition s’étendant du 10 mars au 30 juin, les stations côtières radiotélégraphiques ouvertes au service public transmettront l’heure légale suivie de la mention : « Heure de l’Europe occidentale ». --- Eric. On 6/13/2020 3:39 PM, Paul Eggert wrote:

For the record, here is my hand-typed transcription of the cited source <https://gallica.bnf.fr/ark:/12148/bpt6k2022333z/f2>, followed by an English rendering by Google Translate.

------

Le Sénat et la Chambre des députés ont adopté.

Le Président de la République promulgue la loi dont la teneur suit :

Article unique. - L’heure légale en France et en Algérie est l’heure, temps moyen de Paris, retardée de neuf minutes vingt et une secondes.

La présente loi, délibérée et adoptée par le Séenat et par la Chabre des députés, sera exécutée comme loi de l’Etat.

Fait à Paris, le 9 mars 1911.

Le sous-secrétaire d’Etat des postes et des télègraphique,

Arrête :

Art. 1er. - A partir de la nuit du 10 au 11 mars 1911, à minuit, l’heure de tous les bureaux de poste, télègraphe et télèphone est celle du temps moyen de Paris, retardée de neuf minutes et vingt et une secondes.

Art. 2. - Pendant la période s’étendant de la nuit du 10 mars au 11 mars (minuit), à la nuit du 30 juin au 1er juillet 1911 (minuit), l’indication de l’heure transmise aux navires en mer, par les stations côtiéres radiotélègraphiques ouveries au service public, sera suivie de la mention : « Heure de l’Europe occidentale ».

Art. 3 - Le prèsent arrête sera déposé au cabinet du sous-secrétariat d’Etat des postes et des télègraphes pure être notifié à que de droit.

Mode de transmission de l’heure aux navires en mer.

Jusqu’a la nuit du 30 juin 1911 exclusivement, aucune modification ne sera faite à l’instant de l’envoi des signaux horaires par l’Observatoire de Paris.

Ces signaux seront envoyés :

Le metin à 11 h. 0 m. 0 s., 11 h. 2 m. 0 s., 11 h 4 m. 0 s. de temps moyen do Paris.

La nuit à minuit 0 m. 0 s., minuit 2 m. 0 s., minuit 4 m. 0 s. de temps moyen de Paris.

Ces instants exprimés en temps légal seront représentés :

Le matin par 10 h. 50 m. 39 s., 11 h. 52 m. 39 s., 10 h. 54 m. 39 s.

Le soir par 11 h. 50 m. 39 s., 11 h. 52 m. 39 s., 11 h. 54 m. 39 s.

A partir de la nuit du 30 juin an 1er juillet inclusivement, les signaux seront envoyes aux heures légales suivantes :

Le matin 10 h. 45 m. 0 s., 10 h. 47 m. 0 s., 10 h. 49 m. 0 s.

La nuit 11 h. 45 m. 0 s., 11 h. 47 m. 0 s., 11 h. 49 m. 0 s.

Dans la période de transition s’étendant du 10 mars au 30 juin, les stations côtiéres radiotélegraphiques ouvertes au service public transmetiront l’heure légale suivie de la mention : « Heure de l’Europe occidentale ».

On 6/14/20 9:08 AM, Michael H Deckers wrote:

Is it really so hard to      understand that this must have happened when UT was 1911-03-11T00:00:00,      and not when UT was 1911-03-10T23:50:39 or 1911-03-10T23:55:39 (or      even at different instants for the two time scales)?

This reminds me of the difference between the American way of doing DST transitions (all transitions are at 02:00 local time) versus the EU way (all transitions are at 01:00 UTC). The American way is easier to explain to non-experts, but causes sloppy execution (there are periods where New York is temporarily the same as Chicago, for example). The EU way is more logical and has simpler consequences (Paris is always exactly one hour ahead of London), but is harder to explain to non-experts. Although the method you're suggesting for the 1911-03-11 French transition is more logical and has simpler consequences, that doesn't mean it corresponds to how civil-time clocks behaved or to how people thought they should behave. Perhaps they thought the transition meant "turn the clocks back at midnight" or "stop the clocks at midnight" (either of which is easier to specify to non-experts). At this point we don't really know.

     On 2020-06-10 21:25, Paul Eggert proposed:

# Zone NAME STDOFF RULES FORMAT [UNTIL] Zone Europe/Paris 0:09:21 - LMT 1891 Mar 15 0:01

     While we are at it: the law of 1891 (online at      [https://gallica.bnf.fr/ark:/12148/bpt6k64415343.texteImage])      was published on 1891-03-15, so it could only take force on 1891-03-16;      and it does not say that it applies only 1 min after the start of the day.      All of this applies to Monaco and Algiers.      Hence:         - Zone  Europe/Paris    0:09:21  -  LMT  1891 Mar 15  0:01         + Zone  Europe/Paris    0:09:21  -  LMT  1891 Mar 16  0:00         - Zone  Europe/Monaco   0:29:32  -  LMT  1891 Mar 15         + Zone  Europe/Monaco   0:29:32  -  LMT  1891 Mar 16 0:20:11         -                       0:09:21  -  PMT  1911 Mar 11 # Paris Mean Time         +                       0:09:21  -  PMT  1911 Mar 11 0:09:21 # Paris Mean Time         - Zone  Africa/Algiers  0:12:12  -  LMT  1891 Mar 15  0:01         + Zone  Africa/Algiers  0:12:12  -  LMT  1891 Mar 16 0:02:51         -                       0:09:21  -  PMT  1911 Mar 11 # Paris Mean Time         +                       0:09:21  -  PMT  1911 Mar 11 0:09:21 # Paris Mean Time      Michael Deckers.

  On 2020-06-11 14:04, Michael Deckers wrote without checking:

All of this applies to Monaco

     ..and it turns out to be wrong.      In the "Journal de Monaco" of 1892-05-24, online at [https://journaldemonaco.gouv.mc/var/jdm/storage/original/application/b1c67c1...]      we read:         En vertu d'une Ordonnance Souveraine du 13 mai courant, l'heure légale dans la         Principauté sera, à dater du 1 er juin 1892, réglée, comme en France, sur le méridien de Paris.           [In virtue of a Sovereign Ordinance of the May 13 of the current [year], legal time            in the Principality will be set to, from the date of June 1, 1892 onwards,            to the meridian of Paris, as in France.]      In the "Journal de Monaco" of 1911-03-28, online at [https://journaldemonaco.gouv.mc/var/jdm/storage/original/application/de74ffb...]      we read an ordinance of 1911-03-16:      ARTICLE PREMIER. L'heure légale dans la Principauté sera, à         dater de la promulgation de la présente Ordonnance, réglée sur l'heure légale en France,         telle qu'elle est déterminée par la loi française du 9 mars 1911.         En conséquence, l'heure légale sera retardée de 9 minutes 21 secondes.         [Legal time in the Pricipality will be set, from the date of promulgation          of the present ordinance, to legal time in France. Consequently, legal time          will be retarded by 9 minutes and 21 seconds.]      Hence:           + Zone  Europe/Monaco   0:29:32  -  LMT  1892 Jun  1           +                       0:09:21  -  PMT  1911 Mar 29 0:09:21 # Paris Mean Time      Michael Deckers.