Talk:Prime meridian (Greenwich)

Requested move

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: page moved per sources and ngram -- JHunterJ (talk) 18:17, 14 April 2012 (UTC)

---

Greenwich Meridian → Greenwich meridian – There is no basis for the capitalization. This term is usually lowercase in sources. Dicklyon (talk) 02:41, 31 March 2012 (UTC)

• Support as nom. Dicklyon (talk) 04:11, 10 April 2012 (UTC)

• Support - Five separate Greenwich meridians are recognized, those of Flamsteed, Halley, Bradley, Airy and the IRM. This article should include at least the first four that were represented by transit circles, so "meridian" should not be capitalized. Bradley's meridian is still in use as the zero meridian of the Ordnance Survey. — Joe Kress (talk) 04:35, 31 March 2012 (UTC)

• Comment there are several related meridian requests, see Talk:Greenwich_Meridian, Talk:Paris Meridian, talk:Washington meridian, talk:Warsaw meridian. 70.24.244.198 (talk) 04:39, 31 March 2012 (UTC)
  • Comment also Talk:Prime Meridian. 70.24.244.198 (talk) 04:08, 1 April 2012 (UTC)

• Oppose. Greenwich Mean Time, Greenwich Peninsula, Greenwich Peninsula Ecology Park, Greenwich Hospital, Greenwich District. Greenwich Meridian. If there are 5 people called Joe, they would still be written Joe and not joe? Would they? So what does it matter that there are four or five? This is backed by sources Ngram HTML2011 (talk) 05:31, 31 March 2012 (UTC)

Huh? Your n-gram links shows a distinct minority capitalization of "meridian" in that context. What are you claiming? I agree the argument about number is meaningless, but look at MOS:CAPS. Dicklyon (talk) 05:41, 31 March 2012 (UTC)

• Oppose. This is the proper name for the Greenwich Meridian (of which there is only one), not just a Greenwich meridian. Bazonka (talk) 17:03, 1 April 2012 (UTC)

MOS:CAPS says we decide about proper names by consulting sources. Sources don't capitalize the Greenwich meridian, as the n-gram links show. Dicklyon (talk) 23:53, 2 April 2012 (UTC)

• Support. It looks to me like it is usually not capitalized, and we can follow the sources in this regard. Good Ol’factory ^(talk) 03:36, 4 April 2012 (UTC)
• Support—go with the sources (not to mention our house style). Tony (talk) 02:50, 10 April 2012 (UTC)
• Support— per Joe Kress. --Ohconfucius ^¡digame! 04:20, 10 April 2012 (UTC)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

What is that? The supporters outvote logic? People base moves on dubious Ngrams? What is "per Joe Kress" - Joe Kress said there are several Greenwich meridians, but then the article should be named Meridians in Greenwich or Greenwich meridians. Tony says "go with the sources" - which sources? The Royal Observatory which says Greenwich Meridian at this page? HTML2011 (talk) 03:36, 17 April 2012 (UTC)

Look at the ext link named "sources" in the original proposed move. Dicklyon (talk) 22:45, 18 April 2012 (UTC)

GPS anomaly

I am interested in the commentary on one of the photographs:"A GPS receiver at the prime meridian. This does not indicate a longitude of zero because the GPS reference meridian is about 100 metres to the east." I can't see any reference to this in the main body of the text nor, for that matter, in the article on GPS. Is this worth referencing within the main article, and explaining why this has occured? Perhaps naively, I would have thought that the Greenwich Meridian would be the demarcation of East and West. KPOK (talk) 17:28, 2 January 2013 (UTC)

This is explained at Prime meridian#IERS Reference Meridian. In my view, this article in its present state adds so little to what is in the "Prime meridian" that it hardly deserves to exist.

Another issue with the picture is that recreation-grade GPS receivers can be off by 100 metres, so we can't say how much of the reading displayed is to a difference between the Greenwich and IERS meridian, and how much is due to error in the GPS measurement. Jc3s5h (talk) 17:47, 2 January 2013 (UTC)

Actually, the GPS is almost spot on as its position puts the meridian line 5.4 seconds of arc west of the practical meridian. It is in fact 5.3101 seconds of arc west of the meridian, so the GPS is off by about 1.5 metres. Not bad! I B Wright (talk) 17:13, 17 August 2015 (UTC)

The ecliptic and the prime meridian

Am I mistaken, or does the ecliptic intersect the equator exactly on the prime meridian? And did this play a role in the decision?

http://en.wikipedia.org/wiki/Ecliptic_coordinate_system#mediaviewer/File:Ecliptic_vs_equator_small.gif

Werner — Preceding unsigned comment added by 178.203.185.52 (talk) 12:19, 3 October 2014 (UTC)

No, the ecliptic intersects the celestial equator (which is the projection of the terrestrial equator into space) at the equinoxes. The prime meridian is on earth and moves with the surface of the Earth. Longitude is measured on the surface of the Earth from the prime meridian, which is 0°longitude. The celestial meridian passing through the celestial poles and the equinoxes doesn't have a special name that I know of, but obviously it is nearly fixed compared to the stars; it does not move with the surface of the earth. The angle measured eastward along the celestial equator from the vernal equinox to the point of interest is the right ascension. Jc3s5h (talk) 13:24, 3 October 2014 (UTC)

Thanks! You say "the ecliptic intersects the celestial equator (which is the projection of the terrestrial equator into space) at the equinoxes." Doesn't it do so roughly at the same spot each year? I'm just wondering why old geographers included an "ecliptic" on their maps, as if it is not fixed, how was it useful for navigating? Ah, well...

Werner — Preceding unsigned comment added by 178.203.185.52 (talk) 14:27, 3 October 2014 (UTC)

Astronomers often speak of the "fixed stars". These are stars that are so far away that their motion is not detectable; they serve as fixed reference points in the sky. Due to precession of the equinoxes, the location of the equinoxes makes a complete circle around the ecliptic (which is the projection of the plane of the Earth's orbit around the Sun onto the celestial sphere) in about 26,000 years. So the location of an equinox, compared to the fixed stars, is almost fixed. When thinking of the equinoxes as reference points, they exist all the time, not just when the Sun is at the equinox. Jc3s5h (talk) 14:58, 3 October 2014 (UTC)

Upmerge

this article overlaps significantly with the merger target section. Fgnievinski (talk) 03:17, 11 February 2015 (UTC)

In its present state this article seems like a suitable merge candidate. However, it could be expanded considerably by merging in United Kingdom Ordnance Survey Zero Meridian, which really doesn't need to be a separate article. Also, a description of any better measurements between the various meridians that pass through the Royal Observatory, Greenwich, may be found or better measurements may be performed in the future. So I think this article is a good repository for any details we wish to add about these meridians rather than cluttering up the Prime meridian article, which is already fairly long. Jc3s5h (talk) 15:19, 11 February 2015 (UTC)

Consensus for Calculation of observed transits?

Per WP:TPO, closing section initiated in response to editing of IP sockpuppet of banned User:Vote (X) for Change
The following discussion has been closed. Please do not modify it.
A London area IP editor, 86.153.131.100 (talk) * contribs), made the following change [1], [2]: Was: "The times for the observed transits were therefore a little earlier than they should have been causing the measurements to refer to a meridian 102 metres east of the transit circle" To: "The times for the observed transits were therefore 354 milliseconds earlier than they should have been causing the measurements to refer to a meridian 102 metres east of the transit circle" (emphasis added). I reverted as unsourced [3] and explained why on the IP's talk page [4]. The IP restored, with the editsummary "Anyone can calculate this", and a response on their talk page [5] noting "The calculation is 5.3101 seconds of arc divided by 360 degrees of arc multiplied by 24 hours = 0.354+ seconds". I am not going to re-revert, but WP:CALC states "Routine calculations do not count as original research, provided there is consensus among editors that the result of the calculation is obvious, correct, and a meaningful reflection of the sources. Basic arithmetic, such as adding numbers, converting units, or calculating a person's age are some examples of routine calculations. " I don't think this calculation fits the plain meaning of a routine calculation. The elements of the calculation, noted only on the IP's talk page, are not contained in the article nor is the calculation itself obvious. As such, the change provided should be backed up by a reference to a reliable source. What is the consensus of other editors? Thanks, JoeSperrazza (talk) 12:56, 20 August 2015 (UTC) There is some discussion of the extent of the math exception in the thread Wikipedia talk:No original research‎#MEDRS and primary/secondary near the end. (The math question is really a bit off-topic for that thread.) One could argue this is just a unit conversion from arcseconds to seconds of time. If this were a more technical article, where only a person who converted between angles and time in their sleep could hope to understand the article, I would let it go. Since this is a more general-interest article, I would explain the conversion in a footnote. I also noticed the precision of the coordinates for the Airy transit were too precise and came from a self-published source, so I corrected that. Jc3s5h (talk) 13:39, 20 August 2015 (UTC) @JoeSperrazza: The calculation is fairly straightforward, but the result needs qualification. If the real meridian is 5.3101 seconds of arc east of the marked or defined meridian, and the earth takes 23 hours and 56 minutes (a sidereal day) to go through a full revolution (360 degrees), then the calculation is a simple ratio and gives .331424 seconds (or .3456 sidereal seconds if you prefer). I believe our anonymous friend assumed that the earth turns through 360 degrees in 24 hours which put his answer in sidereal seconds. I B Wright (talk) 13:45, 20 August 2015 (UTC) It sounds like the text entered needs clarification or correction and a footnote. Would one of you subject matter experts be able to do that? Thanks, JoeSperrazza (talk) 14:00, 20 August 2015 (UTC) I agree with @I B Wright: except for precision. Since I've edited the article to limit precision of the longitude of the Airy transit to tenths of arcseconds, the precision of the time should be limited to 3 places after the decimal point. Indeed, since Malys et al. don't provide any obvious error bounds on the longitude coordinate, it might be safer to limit the time to 2 places after the decimal point. Jc3s5h (talk) 14:13, 20 August 2015 (UTC) The difference is insignificant. 5.31 seconds or 5.3 seconds gives the same answer to 3 significant figures. Sourcing the true eastern shift is problematic because the Greenwich observatory itself puts the GPS referenced meridian at 5.64 seconds east of the Airy transit circle, though they don't say what type of GPS receiver they used. The measurement should have been made using a surveying type phase carrier receiver whose error is around 20 centimetres if 12 satellites are visible overhead. The best a standard recreational one can do is about 10 metres though this can be substantially improved upon if measurements are taken over a long period of time. I B Wright (talk) 14:27, 20 August 2015 (UTC) Checking on Google maps, 5.3" misses the Airy transit circle by about 7 metres. 5.31" is better but still misses by a metre or two. I B Wright (talk) 14:39, 20 August 2015 (UTC) Go to the SAO/NASA Astrophysics Data System and search for articles by the authors of the Malys et al. paper. You will see the authors of that paper are deeply involved in the fundamentals of astronomical and terrestrial coordinate systems. A web page by a museum (which is what the Royal Observatory, Greenwich is now) or a Google map cannot compare to those authors in terms of reliability. Also, Google does not seem to make any statement about how accurate their maps are. I certainly wouldn't trust them to better than 30 metres unless I identified some nearby reference marks that had been measured by a reliable organizaiton, such as the National Geodetic Survey, and compared the measured vs. Google values. Jc3s5h (talk) 15:10, 20 August 2015 (UTC) I put my hands up. You are right, I did use 24 regular hours. 86.153.131.100 (talk) 15:39, 20 August 2015 (UTC)

References

Edit by I B Wright

I must take issue with this edit by User:I B Wright. What I view as an incorrect approach begins with the sentence "In each case, the transit instrument was installed to be perpendicular to the the reference elipsoid...." Transit circles, even today, are installed so that the axis about which the telescope turns is parallel to local level, as indicated by a spirit level or pool of mercury. This is equivalent to the axis of the telescope, when the telescope is pointed straight up, being parallel to a plumb line. Any correction for the deflection of the vertical would have been corrected mathematically after the observations were taken. One would have to find a source from the late 19th century to determine whether a correction for deflection of the vertical was made. The people who built the observatory, and later chose the Airy transit as the prime meridian, did exactly what they intended to; the current offset is due to new discoveries and refinements since that time. Jc3s5h (talk) 14:02, 20 August 2015 (UTC)

I fail to see your point. If you are saying that transit circles today are installed perpendicular to the local level using a spirit level or pool of mercury (the later unlikely now) and that it is equavalent to using a plumb line, where is the contention? The Airy transit circle was installed just prior to 1851 which would seem to predate any measurements of deflection of the vertical (or if they had started, would appear to be not very advanced if they were still ongoing at the time of the international conference). I would also point out that part was copy editing your contributions, so if you believe I have misinterpreted them, correct them. This is the encyclopedia anybody can edit. I B Wright (talk) 14:12, 20 August 2015 (UTC)

The edit claims the transit circle was installed perpendicular to the reference ellipsoid. In fact, it was installed perpendicular to local level. These are different. Reference ellipsoids are found by making geodesic surveys over a large area and choosing an ellipsoid that is a good compromise for all the stations surveyed. See Earth ellipsoid. Jc3s5h (talk) 14:21, 20 August 2015 (UTC)

Fair enough. I B Wright (talk) 14:29, 20 August 2015 (UTC)

I though that I had understood the History section as rewritten, but this discussion has changed that. If I have got this right (and I confess that this is not my area of expertise), the transit circle was installed to be perpendicular by using a plumb line. You are saying here that by this means that it would be perpendicular to the local level (or as the article puts it, it points toward the centre of gravity of the earth). If I understand this: the local level is a plane at right angles to the line of the plumb line. What the article [currently] is saying is that the transit circle does not point to the celestial meridian (the imaginary line in the sky directly above the terrestrial meridian on which the transit circle sits) but to an alternative and unintended meridian slightly east of it. The article says, and you seem to have taken issue with it, is that it is perpendicular to the surface of some geometric structure, this ellipsoid thingy, that represents the shape of the planet, presumably ignoring geological variations. The Earth ellipsoid article would appear to support my understanding. So the question is: for the transit circle to point toward the intended celestial meridian, what does it have to be perpendicular to and how should it have been constructed?

Also, the second paragraph tells of the 18th century builders of transit circles using a plumb line to erect a structure perpendicular to the surface of this ellipsoid. Was that really their intent or were they intent on building it perpendicular to a level plane - after all, they would not have been aware that there was any difference between them at this time? I can safely assume this, because if they had been aware, they might have built it right. –LiveRail < Talk > 13:08, 21 August 2015 (UTC)

Then and now, transit circles and other ground-based instruments are aligned to local vertical, which is a plane perpendicular to a plumb line. If the plumb line were extended downward toward the center of mass of the Earth, it would miss, because the Earth's crust is not homogeneous, and areas of greater or lesser density, or mountains, near an observation station deflect the direction of the plumb line. So there was never any intent to allign any transit circle to the normal to the ellipsoid.

At the time of the conference, there was the beginning of geodetic surveying that would allow calculations of deflection of vertical for some ellipsoid that was a good fit for the part of the world where the survey was conducted. But until satellites were invented, it wasn't possible to extend these surveys across oceans and choose an ellipsoid that was a good fit for the whole world. I think the people involved in the conference, being representatives of many countries, and being primarily interested in nautical navigation, would not have been interested in whatever ellipsoid applied to Britain. Also, the Malys et al. paper only discusses the astronomical latitude and longitude (with respect to local level) of the Airy transit and the modern WGS-84 and International Terrestrial Reference Frame (ITRF); there is no mention of any 19th century ellipsoids.

You ask "what does it have to be perpendicular to and how should it have been constructed?" It should have been constructed exactly as it was constructed. Observations from similar instruments operating today are mathematically corrected to allow for the WGS-84 and ITRF. Indeed, new implementations of these reference frames (which include an ellipsoid) are constantly being released, so even old observations can be re-corrected when a new version of a reference frame comes out Jc3s5h (talk) 13:50, 21 August 2015 (UTC)

Numbers not quite right (and a typo)

The current text reads: "As a result of this, any measurements of transit time across the view of the transit telescope occured 0.331 seconds (or 0.345 sidereal seconds) before the transit across the intended meridian."

Should that not be (assuming a longitude offset of 5.3"): "As a result of this, any measurements of transit time across the view of the transit telescope occurred 0.352 seconds (or 0.353 sidereal seconds) before the transit across the intended meridian."?

The current numbers assume a solar/sidereal day ratio of 0.345/0.331 = 1.042 while the actual ratio is 1.00274. AstroLynx (talk) 11:01, 23 August 2015 (UTC)

In Urban & Seidelmann's Explanatory Supplement to the Astronomical Almanac p. 78 the number of SI seconds in a sidereal day is given as 86,164 (rounding to nearest second). 5.3"/360° = 4.0895×10⁻⁶. The product of these is 0.352 SI seconds. It takes more sidereal seconds than SI seconds to describe the same interval by the ratio 86,400/86,164 = 1.00274, as AstroLynx says, so 0.352 SI seconds = 0.353 sidereal seconds, just as AstroLynx says. Jc3s5h (talk) 12:21, 23 August 2015 (UTC)

Misunderstanding in the text

The text says "This in turn meant that the Airy transit circle points very slightly to the east of the modern celestial meridian (the line in the sky directly above the prime meridian). As a result of this, any measurements of transit time across the view of the transit telescope occurs 0.352 seconds (or 0.353 sidereal seconds) before the transit across the intended meridian." This is wrong - the local vertical at the Airy transit circle is parallel to the geodetic vertical 102m west (to within the errors) according to Malys et al. (referenced in the next paragraph). This mean an astronomical transit measured at the ITRF zero meridian will be 0.352s seconds (or 0.353 sidereal seconds) before the transit across the intended meridian, it will occur at the correct time at the transit telescope. Similarly, it is the modern geodetic meridian that is very slightly to the east of the Airy transit circle. This appears to have been misunderstood. Robminchin (talk) 15:48, 14 August 2016 (UTC)

Correct. This whole article was written by someone who has completely missed the point: the Greenwich meridian is not a location, it's a direction in space. And the plane of the meridian contains both the direction of the plumbline at the transit circle and of the ellipsoidal normal at the point 102 m west of it (and BTW even without deflections of the vertical, the Greenwich plumbline passes many kilometres south of the geocentre, due to the flattening of the Earth) 130.233.139.251 (talk) 12:25, 19 September 2016 (UTC)

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Capacity versus Meridian

Does anyone know why tonnage is associate with a meridian? Tonnage has to do with ship capacity and not ship location. Therefore, the idea of a location based upon a reference point (meridian) makes sense, but capacity based upon the same reference point does not. - --KitchM (talk) 21:53, 25 April 2019 (UTC)

Tonnage was a deciding point in selecting Greenwich to be the International Meridian because it was used by most ships by far just before the International Meridian Conference in 1884. In its Proceedings is a table of the tonnage of ships using each of 12 meridians (including Greenwich, Paris, Cadiz, and Miscellaneous). Greenwich's tonnage was 14,600,972 tons out of a total of all tonnage of 20,312,093 tons, or 72%. — Joe Kress (talk) 00:11, 26 April 2019 (UTC)

The resolution of the tenth session of the seventh geodesic conference: citations needed.

Thanks to Charles Inigo, we now have a link to the conference proceedings that resolved in favour of Greenwich:

• Conferenz, Internationale Erdmessung Allgemeine (1884). A.Hirch; Th. v. Oppolzer (eds.). Comptes-rendus des seances de la Septiéme Conférence Géodésique Internationale pour la mesure des degrés en Europe. Reunie a Rome du 15 au 24 Octobre 1863 (in French). G. Reimer. pp. 134-151, 198.

My schoolboy French isn't up to finding the exact page with the resolution. Can anyone else identify it? Annoyingly Google blocks selection copying [to facilitate machine translation] and it doesn't seem to be on archive.org. 𝕁𝕄𝔽 (talk) 14:40, 16 January 2025 (UTC) updated --21:08, 16 January 2025 (UTC)

I should have explained that this source is almost certainly going to resolve the {{cn}} tags I have added to the #History section, so will be worth the effort. --𝕁𝕄𝔽 (talk) 21:08, 16 January 2025 (UTC)

Page 193, Resolution III and IV. I had to pass a French exam in grad school in the old days when one had to be able to read articles in French and German. StarryGrandma (talk) 00:34, 17 January 2025 (UTC)

Excellent, thank you. So using a thief to catch a thief, Google Lens kindly captured the text (which is years out of copyright) and translated it:

Résolutions proposées par la commission

La septième Conférence générale de l'Association géodésique internationale réunie à Rome, à laquelle ont pris part des représentants de la Grande Bretagne, ainsi que les directeurs des principales éphémérides astronomiques et nautiques et un délégué du Coast and geodetic Survey des Etats-Unis, après avoir délibéré sur l'unification des longitudes par l'adoption d'un méridien initial unique, et sur l'unification des heures par l'adoption d'une heure universelle, a pris les résolutions suivantes:

(Adoptée à l'unanimité de la Commission, avec une reserve de M. Faye.)

I. L'unification des longitudes et des heures est désirable, autant dans l'intérêt des sciences que dans celui de la navigation, du commerce et des communications inter- nationales; l'utilité scientifique et pratique de cette réforme dépasse de beaucoup les sacrifices en travail et en accomodation qu'elle entraînerait. Elle doit donc être re- commandée aux gouvernements de tous les Etats intéressés, pour être organisée et con- sacrée par une Convention internationale, afin que désormais un seul et même système de longitudes soit employé dans tous les instituts et bureaux géodésiques et topo- graphiques, pour les cartes géographiques et hydrographiques, ainsi que dans toutes les éphémérides astronomiques et nantiques, à l'exception des données pour lesquelles il convient de conserver un méridien local, comme pour les éphémérides de passage, on de celles qu'il faut indiquer en heure locale, comme les établissements de port, etc.

(Adoptée à l'unanimité.)

II. Malgré les grands avantages que l'introduction générale de la division décimale du quart de cercle, dans les expressions des coordonnées géographiques et géodésiques, et dans les expressions horaires correspondantes, est destinée à réaliser pour les sciences et pour la pratique, il parait justifié, par des considérations essentiellement pratiques, d'en faire abstraction dans la grande mesure d'unification proposée dans la première résolution.

Cependant, pour donner en même temps satisfaction à des considérations scientifiques très-sérienses, la Conférence recommande, à cette occasion, d'étendre, en multipliant et en perfectionant les tables nécessaires, l'application de la division décimale du quart de cercle, du moins pour les grandes opérations de calculs numériques, pour les quelles elle présente des avantages incontestables, même si l'on veut conserver l'ancienne division sexagésimale pour les observations, pour les cartes, la navigation, etc.

(Adoptée par 6 voix contre une.)

III. La Conference propose anx Gouvernements de choisir pour méridien initial celui de Greenwich, défini par le milien des piliers de l'intrument méridien de l'obser- vatoire de Greenwich, parce que ce méridien remplit, comme point de départ des longi- tudes, toutes les conditions voulnes par la science, et que, étant déjà actuellement le plus répandu de tous, il offre le plus de chances d'être accepté généralement.

(Adoptée par 6 voix contre une.)

IV. Il convient de compter les longitudes à partir du méridien de Greenwich dans la seule direction de l'Ouest à l'Est.

(Adoptée à l'unanimité.)

V. La Conférence reconnait, pour certains besoins scientifiques et pour le service interne des grandes administrations des voies de communication, telles que chemins de fer, lignes de bateaux à vapeur, télégraphes et postes, l'utilité d'adopter une heure uni- verselle, à côté des heures locales on nationales, qui continueront nécessairement à être employsées dans la vie civile.

(Adoptée par 5 voix contre 2.)

VI. La Conférence recommande, comme point de départ de l'heure universelle

et des dates cosmopolites, le midi moyen de Greenwich, qui coïncide avec l'instant de minuit ou avec le commencement du jour civil sous le méridien situé à 12h on à 180° de Greenwich.

(Adoptée à l'unanimité.)

Il convient de compter les heures universelles de 0 à 24h.

(Adoptée par 6 voix contre 1.)

VII. Il est désirable que les Etats qui, pour adhérer à l'unification des longitudes et des heures, doivent changer de méridien, introduisent le nouvean système de longitudes, le plus tôt possible, dans les éphémérides et almanachs officiels, dans leurs travaux géodésiques, topographiques et hydrographiques, et dans les nouvelles cartes. Comme moyen de transition, il couvient, dans les nouvelles éditions des anciennes cartes dont il serait difficile de changer le canevas, d'inscrire au moins, à côté de la numé ration des anciens méridiens, leur expression d'après le nouveau systéme.

Il importe enfin que le nouveau systéme soit introduit sans retard dans l'enseignement.

(Adoptée à l'unanimité.)

VIII. La conférence espère que, si le monde entier s'accorde sar l'unification des longitudes et des heures, en acceptant le méridien de Greenwich comme point de départ, la Grande Bretagne trouvera, dans ce fait, un motif de plus pour faire, de son côté, un nouveau pas en faveur de l'unification des poids et mesures, en adhérant à la Convention du Métre du 20 mai 1875.

(Adoptée à l'unanimité.)

IX. Ces résolutions seront portées à la connaissance des Gouvernements et re- commandées à leur bienveillante considération, en leur exprimant le vœu qu'une conven- tion internationale, consacrant l'unification des longitudes et des heures, soit conclue le plus tôt possible par les soins d'une Conférence spéciale.

M. Faye remercie M. le rapporteur de la reproduction fidèle et complète de son vote, dont il ne lui avait pas remis de rédaction.

MM. Perrier et Loewy présentent, au sujet de quelques passages du rapport, des observations dont il est tenu compte immédiatement.

M. van der Sande Bakhuyzen demande la parole pour lire, en son nom et en celui de son collègue M. Schols, la déclaration suivante:

Les questions soumises à la Conférence géodésique concernant le choix d'un premier méridien et d'une heure commune, ne nous paraissent pas pouvoir être discutées utilement dans cette réunion. Elles intéressent bien plutôt la cartographie, la marine et les administrations des postes, des télégraphes et des chemins de fer, que la géodésie.

Leur solution ne dépend pas des recherches qui sont l'objet de notre association; elle dérivera de considérations d'un ordre different, en grande partie étrangères même à la science.

Toute résolution prise par cette assemblée à l'égard du choix d'un premier méridien on d'une heure commune, manquerait d'effet utile, tant qu'elle ne serait pas conforme à des intérêts dont la protection ne rentre pas dans les attributions de l'Asso- ciation géodésique.

La solution des questions proposées ne peut être obtenue que par une Con- férence internationale des gouvernements, qui représentent l'ensemble des intérêts en cause. Une Conférence diplomatique a été proposée par le Gouvernement des Etats-Unis. Notre gouvernement ayant donné ses instructions au délégué qui le représentera à cette Conférence, il ne nous appartient pas de les faire connaitre, ni de les discuter dans cette assemblée."

M. Hirsch, tout en reconnaissant que la déclaration qu'on vient d'entendre, doit étre consignée dans le Procès-verbal, s'étonne que Messieurs les délégués Néerlandais ne l'aient pas produite dès l'abord, dans la première séance de la Conférence, on la question de l'unification des longitudes et des heures, a été mise à l'ordre du jour et renvoyée à l'étude d'une commission spéciale. Il regrette que ses collègues des Pays-Bas aient era devoir assister à des délibérations dont ils finissent par déclarer se désintéresser complètement. Il tient à constater que les délégués Néerlandais sont seuls à contester la compétence de la Conférence à s'occuper de ce sujet, dont elle a été nantie cepen- dant directement par plusieurs des Etats intéressés. Tous les autres délégués ont été autorisés par leurs Gouvernements à délibérer sur cette matière, et ont même reçu des instructions à cet égard. En tout cas, la déclaration qu'on vient de lire, entraine la conséquence que les commissaires des Pays-Bas, bien qu'ils assistent à la séance, ne peuvent pas être mis en compte dans les votes qui doivent intervenir.

Messieurs e. Bakhuyzen et Schols s'en déclarent d'accord et demandent à ne pas figurer dans les scrutins qui auront lieu.

Sur la proposition de M. Hirsch, la Conférence décide qu'on votera d'abord sépa-

rement sur chacun des articles et ensuite, par appel nominal, sur l'ensemble des résolutions.

M. le Président constate la présence de 29 membres ayant droit de voter.

La première résolution est mise en discussion.

M. Perrier reproduit une partie des arguments qu'il a exposés dans la Com- mission, pour prouver que l'emploi d'un méridien initial éloigné, ne se recommande pas pour les cartes topographiques et les relevés à grande échelle, pour lesquels il faudra conserver dans chaque pays le méridien national. Au moins il faudrait recourir à une double gra- duation d'après les méridiens universel et national. Il doute que les instituts géodésiques et les bureaux topographiques se résolvent à l'emploi d'un méridien unique. Il renouvelle la proposition qu'il avait faite dans la commission, de restreindre l'emploi du méridien unique aux cartes générales.

M. Hirsch ne comprend absolument pas les difficultés que M. Perrier prévoit pour la topographie; ni dans les relevés sur le terrain, ni dans les calculs, ni dans le dessin de la carte, l'éloignement plus on moins grand du méridien d'après lequel on graduera finalement la carte, ne peut se faire sentir. Est ce que les cartes topogra- phiques des départements orientaux de France sont plus difficiles à faire que les autres, à cause de leur plus grande distance en longitude du méridien de Paris? et cependant cette distance est plus considérable que l'augmentation, de 2 environ, qui résulterait pour les longitudes Françaises, de l'adoption du méridien de Greenwich. Il serait plus prudent de ne pas parler au nom de tous les instituts géodésiques et bureaux topographiques, parmi lesquels on connaît déjà aujourd'hui un grand nombre qui ne verront ancune difficulté à l'emploi d'un méridien unique.

[débat continue]

according Google Translate, that reads:

Resolutions proposed by the commission

The Seventh General Conference of the International Geodetic Association, meeting in Rome, in which representatives of Great Britain, as well as the directors of the principal astronomical and nautical ephemerides and a delegate of the Coast and Geodetic Survey of the United States, took part, after having deliberated on the unification of longitudes by the adoption of a single initial meridian, and on the unification of hours by the adoption of a universal time, took the following resolutions:

(Adopted unanimously by the Commission, with a reservation by Mr. Faye.)

I. The unification of longitudes and hours is desirable, as much in the interest of science as in that of navigation, commerce and international communications; the scientific and practical utility of this reform far exceeds the sacrifices in work and accommodation which it would entail. It must therefore be recommended to the governments of all interested States, to be organized and consecrated by an international Convention, so that henceforth a single and same system of longitudes be used in all geodesic and topographical institutes and offices, for geographical and hydrographical maps, as well as in all astronomical and national ephemerides, with the exception of data for which it is appropriate to keep a local meridian, such as for transit ephemerides, or those which must be indicated in local time, such as port establishments, etc.

(Adopted unanimously.)

II. Despite the great advantages which the general introduction of the decimal division of the quarter circle, in the expressions of geographical and geodesic coordinates, and in the corresponding time expressions, is intended to achieve for science and for practice, it seems justified, by essentially practical considerations, to disregard it in the great measure of unification proposed in the first resolution.

However, in order to give satisfaction at the same time to very serious scientific considerations, the Conference recommends, on this occasion, to extend, by multiplying and perfecting the necessary tables, the application of the decimal division of the quarter circle, at least for the large operations of numerical calculations, for which it presents undeniable advantages, even if one wishes to retain the old sexagesimal division for observations, for maps, navigation, etc.

(Adopted by 6 votes to 1.)

III. The Conference proposes to the Governments to choose as the initial meridian that of Greenwich, defined by the middle of the pillars of the meridian instrument of the Greenwich Observatory, because this meridian fulfils, as a starting point of longitudes, all the conditions required by science, and because, being already at present the most widespread of all, it offers the best chance of being generally accepted.

(Adopted by 6 votes to 1.)

IV. It is appropriate to count the longitudes from the meridian of Greenwich in the direction of West to East only.

(Adopted unanimously.)

VI. The Conference recommends, as the starting point for universal time and cosmopolitan dates, Greenwich mean noon, which coincides with the instant of midnight or with the beginning of the civil day below the meridian located at 12 o'clock or 180° from Greenwich.

(Adopted unanimously.)

Universal times should be counted from 0 to 24 o'clock.

(Adopted by 6 votes to 1.)

VII. It is desirable that States which, in order to adhere to the unification of longitudes and hours, must change their meridian, should introduce the new system of longitudes as soon as possible in official ephemerides and almanacs, in their geodesic, topographical and hydrographical works, and in new maps. As a means of transition, it is appropriate, in new editions of old maps whose outline would be difficult to change, to include at least, alongside the numbering of the old meridians, their expression according to the new system.

Finally, it is important that the new system be introduced into teaching without delay.

(Adopted unanimously.)

VIII. The Conference hopes that, if the whole world agrees on the unification of longitudes and times, by accepting the Greenwich meridian as the starting point, Great Britain will find, in this fact, a further motive to take, on her part, a new step in favor of the unification of weights and measures, by adhering to the Convention of the Metre of May 20, 1875.

(Adopted unanimously.)

IX. These resolutions will be brought to the attention of the Governments and recommended to their benevolent consideration, expressing to them the wish that an international convention, consecrating the unification of longitudes and times, be concluded as soon as possible by the care of a special Conference.

Mr. Faye thanks the Rapporteur for the faithful and complete reproduction of his vote, of which he had not given him a draft.

MM. Perrier and Loewy present, on the subject of some passages of the report, observations which are immediately taken into account.

Mr. van der Sande Bakhuyzen asks for the floor to read, in his name and that of his colleague Mr. Schols, the following statement:

The questions submitted to the Geodesic Conference concerning the choice of a prime meridian and a common hour, do not seem to us to be able to be usefully discussed in this meeting. They concern cartography, the navy and the administrations of the posts, telegraphs and railways, much more than geodesy.

Their solution does not depend on the research which is the object of our association; it will derive from considerations of a different order, largely foreign even to science.

Any resolution taken by this assembly with regard to the choice of a prime meridian or a common hour would lack useful effect, so long as it was not in conformity with interests the protection of which does not fall within the attributions of the Geodesic Association.

The solution of the questions proposed can only be obtained by an international Conference of governments, which represent all the interests concerned. A diplomatic Conference has been proposed by the Government of the United States. Our government having given its instructions to the delegate who will represent it at this Conference, it is not up to us to make them known, nor to discuss them in this assembly."

Mr. Hirsch, while recognizing that the declaration which has just been hear, must be recorded in the Minutes, is surprised that the Dutch delegates did not produce it from the outset, in the first session of the Conference, on the question of the unification of longitudes and times , was placed on the agenda and referred to a special committee for study. He regrets that his colleagues from the Netherlands have had to attend deliberations in which they end up declaring complete disinterest. He wishes to note that the Dutch delegates are alone in contesting the competence of the Conference to deal with this subject, with which it has however been directly granted by several of the States concerned. All the other delegates have been authorized by their Governments to deliberate on this matter, and have even received instructions in this regard. In any case, the statement just read, entails the consequence that the commissioners of the Netherlands, although they attend the session, cannot be taken into account in the votes that are to take place.

Messrs. e. Bakhuyzen and Schols declare themselves in agreement and ask not to appear in the ballots that will take place.

On the proposal of Mr. Hirsch, the Conference decides that a vote will be taken first separately on each of the articles and then, by roll call, on all the resolutions.

The President noted the presence of 29 members entitled to vote.

The first resolution was put up for discussion.

Mr. Perrier reproduced a part of the arguments he set out in the Commission, to prove that the use of a distant initial meridian is not recommended for topographic maps and large-scale surveys, for which it will be necessary to keep in each country the national meridian. At least it would be necessary to resort to a double graduation according to the universal and national meridians. He doubts that geodetic institutes and topographical offices will resolve to the use of a single meridian. He renews the proposal that he had made in the commission, to restrict the use of the single meridian to general maps.

Mr. Hirsch absolutely does not understand the difficulties that Mr. Perrier foresees for topography; neither in the surveys on the ground, nor in the calculations, nor in the drawing of the map, the greater or lesser distance from the meridian according to which the map will finally be graduated, cannot be felt. Are the topographic maps of the eastern departments of France more difficult to make than the others, because of their greater distance in longitude from the Paris meridian? and yet this distance is more considerable than the increase, of approximately 2, which would result for French longitudes, from the adoption of the Greenwich meridian. It would be more prudent not to speak on behalf of all the geodetic institutes and topographical offices , among whom we already know today a large number who will see no difficulty in the use of a single meridian.

[debate continues]]

Our next task is to pluck the citations we need from that. The trans-quotes will need some adjustment, though I fancy the idea of a "cosmopolitan date" --𝕁𝕄𝔽 (talk) 12:35, 17 January 2025 (UTC)