Talk:History of the metre

Proposition to simplification of the article

I propose the article should beginn with the sections which have recently been removed from the article Metre:

Universal measure: the metre linked to the figure of the Earth up to "Charles Sanders Peirce's work promoted the advent of American science at the forefront of global metrology. Alongside his intercomparisons of artifacts of the metre and contributions to gravimetry through improvement of reversible pendulum, Peirce was the first to tie experimentally the metre to the wave length of a spectral line. According to him the standard length might be compared with that of a wave of light identified by a line in the solar spectrum. Albert Michelson soon took up the idea and improved it". Charles Inigo (talk) 05:25, 27 January 2025 (UTC)

Exact location of Méchain's meridional measurement on Montjuïc hill?

Hi, this and a number of related articles currently state that Mechain's meridional measurement took place at a fortress at the top of the Montjuïc hill near Barcelona. The corresponding pictures link to the Castle of Montjuïc, but call it "Fortress Montjuïc". The Montjuïc article, however, states that the hill was the site of several fortifications, of which only the latest (the Castle of Montjuïc), remains today.

Our articles on the metre assume "fortress" and "castle" to be the same, whilst the dedicated article on the castle does not even mention any meridional measurements at all.

In order to verify and improve the information given in the articles, do the historical sources specify the exact location of measurement in better details, f.e. by naming a specific building or place? --Matthiaspaul (talk) 01:12, 21 October 2015 (UTC)

Delambre specified the location as the tower of the fortress of Montjuic ('tour du fort de Montjouy'), in his 1807 report about the measurement of the meridian arc. ('Base du système métrique decimal ..') Ceinturion (talk) 14:24, 21 October 2015 (UTC)

Great, and thanks for looking this up! So, unless there were two towers (unlikely), we are correctly linking to the Castle of Montjuïc and photos showing its tower. --Matthiaspaul (talk) 23:17, 21 October 2015 (UTC)

I also found a photography of a commemorative plaque on this tower:

Charles Inigo (talk) 04:36, 28 September 2023 (UTC)

Incorrect entry in the "history of definitions" table

The first entry of the table is evidently wrong, as it says that the measurement by Delambre and Mechain was complete in 1795. In fact the measurements by Mechain were not finished until 1798.

Definitions of the metre since 1795

Basis of definition	Date	Absolute uncertainty	Relative uncertainty
1⁄10,000,000 part of one half of a meridian, measurement by Delambre and Méchain	1795	0.5–0.1 mm	10−4
First prototype Mètre des Archives platinum bar standard	1799	0.05–0.01 mm	10−5

Cardarelli, which is given as the source for the entire table, is a questionable source because of unclarities.(link) In this "history of definitions" table, it is unclear how the uncertainty was defined, and why the uncertainty changed. When comparing it to data from better sources, it seems that in this table, before 1800, uncertainty represents uncertainty in the meridian measurement, and after 1800 it represents something else: differences between replicas and the primary standard, the Metre des Archives.

The provisional metre was based on the meridian measurement by Lacaille in 1740. In 1793 Borda estimated the uncertainty of that meridian measurement was 0.03 percent, and the same uncertainty applied to the provisional metre.[1] In 1798 the meridian measurement by Delambre and Mechain was completed. The final metre was declared to be equal to 443.296 lignes, implying an uncertainty of 0.0001 %. A few years later Delambre reviewed the errors and concluded the uncertainty was 0.01 %, according to Ken Alder.[2] These uncertainties represented how much the metre deviated from 1⁄10,000,000 part of the quadrant.

In the 19th century replicas were occasionaly compared to the Metre des Archives, by means of a special micrometer screw gauge. In 1806 the difference was less than 2 µm (or 0.0002%), the uncertainty of the micrometer. In 1864 the difference was 3 µm (or 0.0003%). The uncertainty of the improved micrometer was 0.3 µm.[3]

Therefore, the beginning of the table should be replaced by something like this:

Definitions of the metre since 1793

Basis of definition	Date	Absolute uncertainty	Relative uncertainty
Provisional metre, based on meridian arc measurement by Lacaille in 1740	1793	0.1 mm	10−4
Final metre, based on meridian arc measurement by Delambre and Méchain	1798	0.1 mm	10−4
First prototype Mètre des Archives platinum bar standard	1799	2 µm	10−6

Ceinturion (talk) 13:41, 22 October 2016 (UTC)

References

Some matters of form and composition

As a matter of form, the first sentence of the lead for an article titled foo should say, "A foo is a bar, baz, quux...". Hence: "The history of the metre is the history of <some events> over <some time period>." Now we know what we're going to write about, and the reader knows what he's going to read about. Then the second sentence should probably tell the reader what a metre is in everyday terms. It does say it's a unit of length. But if the article were titled "History of the toise", it too is a unit of length, very familiar (at least in France), but we'd scratch our heads because we don't know what it is. This is an encyclopedia, and it is supposed to be a careful description of what things are. If readers already knew what things are, they wouldn't need us to tell them. A grade schooler in the U.S. probably doesn't know what a metre is. So the second sentence should be something like, "A metre is the metric system unit of length, approximately the height of an average adult man's hip line." We could use any everyday object for comparison, but body proportions are familiar to everyone, even a child. The rest of the sentences in that paragraph also have a defined structure and composition-defined content.

The article should begin with text, not a table. The direct predecessor of the metre was the toise defined in the Carolingian system as a body measure. The metre was originally defined in terms of the toise. Pendulums are irrelevant, so the section Universal measures is toast. The very first provisional metre in 1794-5 was defined according to a survey of earth's meridian by Lacaille in 1740. The metre was never defined as 1/10,000,000 of the meridian. The definition of the metre in French law in 1795 was exactly 443.44 lignes; in French law in 1799, the metre was defined as 443.296 lignes. Both figures represented lengths of fabricated platinum bars, and both were known at the time (or very soon afterward) to be in error as fractions of the meridian, though they didn't know by how much.

The section International prototype meter is a little long but ok. We don't need to know about any organizations or their meetings in order to understand this object. Getting rid of those would shorten it quite a bit. This is an article about history, not administration.

The sections Krypton standard and Speed of light standard are pretty hard science, and this is an article about history (did I say that before?). It is about one of the most familiar everyday items, like a baseball, so the article should be toned in everyday language and terms. I don't think I should need to understand things like "zero nuclear spin" and "laser interferometry" to read an article on baseball. A degree in physics is necessary to substantively understand these sections. The average adult probably doesn't have a good idea of what cadmium and krypton are, certainly not why they're suited to the purpose here. They're wikilinked, but as long as the text stays with the bounds of the article topic, we shouldn't need to keep jumping outside the article. Footnotes describing these two is probably a better way to go. Something like, "krypton is an inert gas similar to neon that occurs in trace amounts naturally, and is used in certain kinds of fluorescent tubes". Even so, spectral analysis is something most adults won't know anything about. History is a kind of narrative and these two sections are "bumpy". I think they can be rewritten to make them shorter and more accessible. Technical terms should be replaced with vernacular. Any "hard" science should be moved to sideboxes or footnotes so the text is readable.

Sbalfour (talk) 22:57, 19 January 2018 (UTC)

Duplication of text and content

The existence of this article is quixotic, and duplicative.

The section Universal measures is about pendulums, which are irrelevant.

The sections Meridional definition and Metre des archives were largely cut-and-pasted from other articles, esp. an earlier rendition of History of the metric system. Parts of other sections while not cut-and-pasted, duplicate facts and content in other articles. What content here wouldn't be a welcome addition to History of the metric system? There are also large history sections in International system of units and Metric system articles. They're all one and the same. I estimate by count of paragraphs, sentences and phrases/facts found in other articles, that over 2/3 of this article is duplication.

I suppose there'll be, or someone will deign to create it, History of the Kilogram, and History of the second, etc. It's hubris, a snake eating its own tail. It's a kind of internal copyvio, because editors will go to existing articles to cut-and-paste for the new one. That should tell them straight away that the article should not be created, and whatever effort they wish to pursue should go into an existing article. The history of the meter is an integral and inseparable part of history of the metric system. So I propose the following:

There are 7 structuring level 2 sections here:

1 History of definition

2 Universal measure

3 Meridional definition

4 Mètre des Archives

5 International prototype metre

6 Krypton standard

7 Speed of light standard

The first "section" is just a table, not really a section at all. It could actually appear in an article just about anywhere and is probably better placed as a kind of appendix rather than introduction. Universal measure is about pendulums, which never became any part of any measurement system. That section can simply be deleted. Meridional definition and Metre des archives are wholly duplicate, and can be deleted. The first two paragraphs of International prototype metre are also cut-and-pasted with a little fudge in the last sentence or two; what's left of it can be merged into History of the metric system.

That leaves the last two sections, 1/3 of whose content is duplicate, so in aggregate they will shrink substantially when properly merged. Both sections are highly technical, and will need to be rewritten for accessibility as noted above. Speed of light standard is mostly current science, and will merge into Speed of light, a science article. The Krypton standard is more history, so will merge into History of the metric system. If it's not rewritten, it will fit better in a science article, Metric system#Realization of units section.

Sbalfour (talk) 22:57, 19 January 2018 (UTC)

@Sbalfour: Please see related discussion at Talk:Metre#History de-duplication. fgnievinski (talk) 18:26, 26 January 2025 (UTC)

Split portions from Meridional definition

It has been proposed that the section 3 Meridional definition be split out into another article titled Meridian arc of Delambre and Méchain. So why not merge the sections Meridional definition and Mètre des Archives into a new section titled "The metre linked to the figure of the Earth". Charles Inigo (talk) 04:47, 28 September 2023 (UTC)

I'd agree with splitting Meridional definition of the metre (and closely related content, about the figure of Earth). It'd allow a more balanced discussion of the non-meridional definitions. In keeping with summary style, the new article's lead would be excerpted in the present article. fgnievinski (talk) 06:36, 27 January 2025 (UTC)

Told

We are told that the Scientific Revolution started with Copernicus in 1543. Copernicus's system was the same as that of Aristarchus, who was much earlier. — Preceding unsigned comment added by 82.15.21.214 (talk) 12:19, 1 March 2019 (UTC)

We are told that the history of the meter started in 1543. It was not mentioned for some time after that. — Preceding unsigned comment added by 82.15.21.214 (talk) 12:24, 1 March 2019 (UTC)

It is implied that the decimal system was introduced after 1543. It was used earlier. — Preceding unsigned comment added by 82.15.21.214 (talk) 12:30, 1 March 2019 (UTC)

It is implied that royal decree or physical prototypes are inferior to the meter. Actually, many definitions of the meter use much the same things. A platinum bar could seen as a physical prototype. — Preceding unsigned comment added by 82.15.21.214 (talk) 12:55, 1 March 2019 (UTC)

The decree of the General Conference is not much different to a royal decree. — Preceding unsigned comment added by 82.15.21.214 (talk) 13:12, 1 March 2019 (UTC)

The sentence "The history of the metre starts with the scientific revolution that began with Nicolaus Copernicus's work in 1543" could be change to "The history of the metre starts with the scientific revolution, which started in the 16th century". The reader can follow the link to scientific revolution to find the exact who and when details. It was the scientific revolution which made the first systematic attempt to base things on unchanging facts rather than vague beliefs or imprecise things like somebody's foot/arm/thumb. It was still a decree but at least it was a lot more precise and didn't change according to who measured it and didn't change according to which person's body part it was measured from. Ie, it was meant to be objective.

The article doesn't claim that the metre itself started in 1543 - only that the process which led to the metre started circa 1543.

The article doesn't claim that decimals were invented after 1543 - only that the proposed unit of length would use the (already existing) decimal system.  Stepho  talk  19:27, 1 March 2019 (UTC)

Recent edits on "seconds pendulum"

I think these are trying to say that a seconds pendulum of 993.934 millimetres replaced the physical International prototype metre - but that doesn't seem to be the case. Hence my revert. — Preceding unsigned comment added by Snori (talk • contribs) 11:19, 17 June 2019 (UTC)

That paragraph and two similar paragraphs which replaced it were placed at the end of the wrong section. I moved them to the end of the Mètre des Archives section where gravimetry, the figure of the Earth, and de Ibero himself are already extensively discussed. — Joe Kress (talk) 23:19, 17 June 2019 (UTC)

Pendulums and geodesy

Charles Inigo (talk · contribs) recently added a lot of material about pendulums and geodesy. For most readers, this is a mere sideline to the history of the metre. It distracts the reader from the history while he is trying to make sense of the technically detailed pendulum and geodesy information. This would be better served by linking to the appropriate articles instead of trying to push it all into this article.  Stepho  talk  00:53, 13 April 2020 (UTC)

Thank you for your contribution. I took it in account when adding informations on the two first international scientific associations following mention of the use of the metre in Great Britain. Charles Inigo (talk) 08:43, 13 April 2020 (UTC)

Combinations of time and space as measures go back to antiquity, but in modern wikipedia the round offs disquise the system.

When did we begin using twice as many seconds in a century as inches in the circumference of the earth at the equator to set a standard?

We might note that subdivisions go back to the use of body measures wherein a hand is 100 mm and 5 hands make a cubit. In Egypt a foot is 300 mm. Feet and cubits begin to be used to measure a days sail in terms of stadions by the Greeks and Stadiums by the Romans and then 75 Roman miles or miliari to a degree. A Greek stadion measures 185 meters as does a Roman Stadium, and both are counted 8 to a mile and 75 miles to a degree from Britain to China in the Geography.2604:6000:1513:4FFD:D8FF:20A9:7618:15DC (talk) 11:38, 8 August 2020 (UTC)

@Stepho-wrs: it's also duplicated in Seconds_pendulum#Relationship_to_the_figure_of_the_Earth. fgnievinski (talk) 18:33, 26 January 2025 (UTC)

What does this line mean?

What does the line 'and that it could complement meridian arc measurements in determining the figure of the Earth' mean? - Para 2, Lines 3-4 — Preceding unsigned comment added by Dhairya Patel0 (talk • contribs) 14:31, 6 December 2020 (UTC)

Scientific revolution began with Copernicus work. Galileo discovered gravitational acceleration explaining the fall of bodies at the surface of the Earth. He also observed the regularity of the period of swing of the pendulum and that this period depended on the length of the pendulum.

Kepler's laws of planetary motion served both to the discovery of Newton's law of universal gravitation and to the determination of the distance from Earth to the Sun by Giovanni Domenico Cassini. They both also used a determination of the size of the Earth then considered as a sphere by Jean Picard.

Christian Huygens found out the centrifugal force which explained variations of gravitational acceleration depending on latitude. He also discovered that the seconds pendulum length was a mean to measure gravitational acceleration. Earth proved to be an oblate spheroid. According to Alexis Clairaut, variations of gravitational acceleration were a mean to determine the figure of the Earth, whose crucial parameter was the flattening of the Earth. When the length of the metre was defined in 1799, the flattening of the Earth was assumed to be 1/334.

In 1841, Friedrich Wilhelm Bessel using the method of least squares calculated from several arc measurements a new value for the flattening of the Earth, which he determinated as 1/299.15. He also devised a new instrument for measuring gravitational acceleration which was first used in Switzerland since 1864 by Emile Plantamour, director of Geneva Observatory. Charles Sanders Peirce and Isaac-Charles Élisée Cellérier (8.01.1818 – 2.10.1889), a Genevan mathematician soon independently discovered a mathematical formula to correct systematic errors of this device which had been noticed by Plantamour and Adolphe Hirsch, director of Neuchâtel Observatory. This allowed, Friedrich Robert Helmert to determine a remarkably accurate value of 1/298,3 for the flattening of the Earth in 1901 more than 25 years after the metre had been adopted as an international scientific unit for the convenience of continental European geodesists following Guillaume Henri Dufour, Ferdinand Rudolph Hassler and Carlos Ibáñez e Ibáñez de Ibero example. Charles Inigo (talk) 06:37, 28 September 2023 (UTC)

Translation

I identified a problem of translation of the source n°5. I translated the corresponding passage from the Wikipédia article Histoire du mètre in French along side with additional material. I have not yet inserted the sources which can be found in the article in French. Charles Inigo (talk) 09:34, 15 October 2023 (UTC)

Airy points: tagged as dubious

I've tagged the following sentence as dubious:

The support requirements represent the Airy points of the prototype—the points, separated by 4⁄7 of the total length of the bar, at which the bending or droop of the bar is minimised.

The reference provided, Phelps 1966, does not back this up, instead stating "the Airy points are symmetrically spaced and separated by the distance ${\textstyle {\frac {l}{\sqrt {3}}}}$." (Note ${\textstyle {\frac {1}{\sqrt {3}}}\approx 0.577}$.) It also mentions "[Bessel showed that] if two supports were used they should be separated by 0.5594 of the length of the bar if the shortening of the bar due to flexure is to be a minimum." Neither of these statements back up the sentence in question.

Airy_points#Bessel_points notes "[support points separated by 571mm] would be the Bessel points of a beam 1020 mm long", suggesting the International Prototype Metre bar (with markings exactly 1 metre apart) is supported at its Bessel points, and should be 1020 mm long. However, we don't currently have a good source confirming this.

Lastly, the provenance of the 4⁄7 claim is as follows: it was added (as 5⁄9) in 22:58, 17 August 2010, followed by a correction to 4⁄7 in 09:59, 26 September 2014. Neither figure matches the bar length proportions of the Airy or Bessel points. Preimage (talk) 15:55, 26 August 2024 (UTC)

Good catch. It looks as if the whole sentence should go. I looked at the report of the 7th CGPM in the hope of finding a hint as to why 571 mm was chosen, but couldn't see any (but my French is not good). NebY (talk) 16:34, 26 August 2024 (UTC)

Thanks. I can now confirm the bar is 102 cm long and is supported at its Bessel points, as per the following three references:

Direction générale des Entreprises. "Histoire du mètre" [History of the meter]. metrologie.entreprises.gouv.fr (in French). Le prototype du mètre est une règle, dont la section a la forme d'un X à talons, comportant une ligne axiale (fibre neutre) ni tendue ni comprimée (selon la théorie des moments de flexion) quand la règle est légèrement fléchie, et qui conserve la même longueur de 102 centimètres, sur laquelle deux traits transversaux marquent les extrémités de l'unité. [The prototype of the meter is a ruler, whose section has the shape of an X with heels, comprising an axial line (neutral fiber) neither stretched nor compressed (according to the theory of bending moments) when the ruler is slightly bent, and which retains the same length of 102 centimeters, on which two transverse lines mark the ends of the unit.]

"National Bureau of Standards Replica Meter Standard". Smithsonian Institution. This aluminum bar, with an X-shaped cross-section, is a replica of the platinum international meter prototype housed in Paris and used as a standard for the metric system from 1889 to 1960. ... Like an actual meter standard, the bar is 102 centimeters long and there are marks 1 centimeter from each end on this side to show the precise length of a meter.

Page, Chester H.; Vigoureux, Paul, eds. (1975). The International Bureau of Weights and Measures, 1875-1975 : translation of the BIPM centennial volume (PDF). U.S. Dept. of Commerce, National Bureau of Standards. p. 67. The distance specified between the support rollers is chosen to minimize the shortening of the standard by flexure under its own weight.

If we're going to mention how long the bar is, its cross-sectional dimensions may also be of interest to readers: 16 mm x 16 mm, as per the following reference:

Gupta, S. V. (2020). Units of measurement: history, fundamentals and redefining the SI base units (2nd ed). Springer. p. 108.

Preimage (talk) 18:34, 26 August 2024 (UTC)

References

red references

There are a ton of red references. This is due to the recent cut and paste from the metre article.

• Eg: the error about :2 is because the full details of reference :2 are back in the metre article and those full details need to be copied into this article.
• Eg: the error about :3 is because reference :3 already existed in this article but a second, different :3 reference was cut and paste from the metre article. Rename it to something unique. This is also a good example of why numeric refderence name are a bad idea.

I fixed the :5 error (similar to the :3 error but also involved multiple references with the same details written in different ways) but I'm far to lazy to fix the rest.  Stepho  talk  10:22, 27 January 2025 (UTC)

Maybe you should wait an answer to my proposition to copy and paste the sections which were removed from the article Metre (see top of the page) to replace the firsts sections of the article before spending too much time in fixing details about references. Charles Inigo (talk) 14:53, 27 January 2025 (UTC)