Talk:History of the metric system/Archive 2

Archive 1

Archive 2

Metre and Kilogram des archives & The first metric system: France, 1799

These sections are wordy, wordy, wordy, even though I've whittled them down to just relevant material. Only two things happened here: prototypes were fashioned and entered into the archives, and a law was passed making the metric system the official system of France. 5 dates in 1799 appear in the sections; maybe we don't need them at all, since the section head tells us the year. Other details appear or should appear in prior sections, so they're superfluous here. I think two sentences, one section of one short paragraph, is more than enough here. How about:

In June of 1799, platinum prototypes were fabricated according to the measured quantities, the metre des archives defined to be a length of 443.296 lignes, and the kilogramme des archives defined to be a weight of 18827.15 grains, and entered into the French National Archives. In December of that year, the metric system based on them became by law the sole system of weights and measures in France from 1801 until 1812.

Sometimes details of history matter, and there's a place for them. Scientific details (like the broad-brush statement that the metric system is a <this>, <that>, and <next thing>) might be more properly placed in the companion article Metric system about the science. Sometimes history is just about the end result; we only say what we need to say.

Sbalfour (talk) 21:00, 15 January 2018 (UTC)

Done. Sbalfour (talk) 03:26, 16 January 2018 (UTC)

Electrical units

Answer these two questions, based only on what you read here: 1) why did the ampere unify the EMU/ESU/Gaussian/International systems of units? 2) what is the dimensional manifestation of electricity?

The mechanical dimensions have intuitive notions: length because things have size; mass because they are heavy; time passes as events happen, we age, clocks tick, etc. Why isn't it good enough to define the ohm as meters/second? As long as we stay within the system (EMU), things actually work rather well. The Kelvin and candela are both definable in terms of the MKSA system. Why do they remain base units? It's intuitive that we have a base unit of one spacial dimension; it's just as useful and intuitive to have a base unit of two spacial dimensions, i.e. area, and one of three spacial dimensions, i.e. volume (litre). Why don't we? None of these questions can be answered in the article, and probably some of them shouldn't be. But we spend a lot of column space on fragmented electrical systems of units, and then don't provide any closure. Some science is needed. There is absolutely a defined dimensional manifestation of electricity, and it is necessary. The original editors didn't have a fundamental grasp of that, so they wrote a whole lot of stuff and said nothing. It doesn't matter that we know it was called an abohm (actually, it wasn't called that until much later), or that it was named for Georg Ohm. That's worth a footnote. Those hairy equations are utterly inaccessible in an article about history. I think we need to start over here. Sbalfour (talk) 04:10, 16 January 2018 (UTC)

Defining the ohm as meters/second would have the drawback of reintroducing fractional exponents in units. If [R]=m/s, and P=I²R, then [I]= kg^1/2 m^1/2 s^-1. Ceinturion (talk) 17:52, 16 January 2018 (UTC)

The units of weight and length

The section 'The units of weight and length' contains a nonchronological sentence that should probably be removed: While Méchain and Delambre were completing their survey, the commission had ordered a series of platinum bars to be made based on the provisional metre. When the final result was known, the bar whose length was closest to the meridianal definition of the metre would be selected. These two sentences are unclear and they do not seem to make much sense. They can be removed because a later section, 'The French metric system', already says what needs to be said: 'In June of 1799, platinum prototypes were fabricated '. Ceinturion (talk) 19:54, 18 January 2018 (UTC)

Yeh, I know. Bzzzzt. I haven't read anywhere what must've happened, but it's pretty clear: a number of prototypes were made around the established value of 443.44 lignes, probably varying by only a few hundredths of a lignes. When the surveyed value came in well more than a tenth of a lignes shorter, they had to discard the prototypes and make a new one exactly 443.296 lignes. I've since combined the sentences to make sense of them. Sbalfour (talk) 05:31, 19 January 2018 (UTC)

I think the French description by Delambre is somewhat like: in 1795, the provisional metre was calculated to be 0,513243 toise, and they tried to create a prototype with an accuracy of 10^-6 toise. The length of objects could be measured on a subdivided toise scale with Lenoir's 'comparator', presumably a kind of vernier calipers. Lengths of up to 4 meters could be measured, with an accuracy of 10^-5 toise. Four approximate metre bars were made, from brass (not platinum). By measuring the bars together, in different combinations, the accuracy of each bar improved. The bar closest to 0,513243 toise was chosen as the prototype provisional metre.

In 1798 Delambre and Mechain concluded that final metre was 0,5130740740 toise. Twelve approximate metre bars from iron were made. By measuring the twelve iron bars together, in different combinations, the accuracy of each bar improved. The iron bar closest to 0,5130740740 toise was used as reference for making two bars from platinum. One became primary standard, and was called "mètre des Archives". The other one became a secondary standard, and was called "mètre de l'Observatoire". Delambre, Base du système métrique

So I would think the two sentences should be something like: After Méchain and Delambre had completed their survey, the commission ordered a series of bars to be made based on the final metre. The bar whose length was closest to the final metre would be selected. Ceinturion (talk) 02:17, 20 January 2018 (UTC)

GA status

I am checking on Good Articles with cleanup tags and have just arrived at this. I see there is a lot of talk page activity aimed at improving the article, which is excellent. Hopefully you can get the article cleaned up and resolve any outstanding tags. Let me know if you need any help regarding GA criteria or anything else. AIRcorn (talk) 02:58, 27 March 2018 (UTC)

Still plenty of tags. Will probably look to take this through WP:GAR soon. AIRcorn (talk) 09:53, 20 January 2020 (UTC)

One ten millionth?

The description original definition of the length of the metre is incorrect; it currently reads "one ten millionth". It is actually "one ten thousandth". While changing, I would recommend using a wording that is even less susceptible to misinterpretation "one tenth of a thousandth". PhysicistQuery (talk) 01:20, 14 September 2019 (UTC)

Actually, "one ten millionth" is correct. The original definition was: "one ten millionth of the distance between the North Pole and the Equator". That distance is 10,000 km = 10,000,000 m. Maybe you accidentally confused km with m? Ceinturion (talk) 09:05, 14 September 2019 (UTC)

coulomb and the Daniell_cell

I wrote in Talk:2019_redefinition_of_the_SI_base_units:

I have wondered for some time how it is that the electrical units, especially the volt and amp, have convenient size. Note, for example, that a common flashlight battery supplies 1.5V at about 1A. Since these are derived from the coulomb, it must be that it was appropriately defined. It is not so hard to get factors of 2, 3, or pi into unit definitions, in addition to an appropriate power of 10. The first reference to this actually being done, that I know of, is Daniell_cell. It seems that at the time, this cell was believe to be about 1V, where now it is closer to 1.1V. Less convenient definitions might have changed this by factors of 10, 100, or 1000. (About 300 for the statvolt.) More details on how this was done would seem useful.

I was then told about this article. Yet this article seems to have almost nothing on where the volt came from. Gah4 (talk) 00:49, 6 June 2020 (UTC)

A lovely account of the history and how the electromagnetic units were chosen may be found in: Authur E. Kennelly (1935), I.E.C. Adopts MKS System of Units (PDF), retrieved 2020-06-06 —Quondum 14:11, 6 June 2020 (UTC)

Yes that is what I wanted. (Except that it is 1935 instead of 1953.) Now all we need is to get it into the article. It seems that the Daniell_cell accidentally happened to be close to a power of 10 of the desired volt. That is the part that I didn't know before. By the way, if you want to read about how to accurately measure voltage, without measuring current: THE KELVIN ABSOLUTE VOLTMETER and the speed of light is pretty neat. (Besides that my father use to work for its author.) Gah4 (talk) 21:16, 6 June 2020 (UTC)

Thanks – I've fixed my 1935/1953 typo above to avoid it propagating. Anyone who has the inclination can start the inclusion of material from the source. Even adding only the reference to a suitable section would be a good start. —Quondum 22:31, 6 June 2020 (UTC)

It may be interesting to consider Latimer Clark's article, written in 1861 when the committee of the B. A. started. He proposed a set of coherent practical electrical units, and he described for which voltage range and which resistance range the units were needed. His unit of emf corresponded to 1 volt (because of the Daniell cell), and his unit of resistance corresponded to 10^8 ohm. This surprisingly high unit of resistance was derived from Clark's tentative unit of capacitance, 10 nF, a parallel plate capacitor composed of 1 m2 plates at a 1 mm gap, and [R] = [t] / [C]. Clark described that the unit of e.m.f. was needed for measurements between 1 V and 1 MV (1 volt for batteries, 10 kV for sparks across small air gaps, and 1 MV for electrostatic experiments). The unit of resistance was needed for measurements bewteen 1 Ω and 1 GΩ (10 Ω for the copper conductor of 1 mile of telegraphic cable, 1 GΩ for the insulating cover of 1 mile of submarine cable. In the same article, Clark introduced the names volt and ohma (although he used volt for resistance, and ohma for e.m.f., which makes it hard to read), and he defined coherent units of current, charge, and capacitance, and he proposed prefixes for 10^6 and 10^9. (link) Ceinturion (talk) 18:36, 7 June 2020 (UTC)

Gah4, here on p. 138 is a clear, direct statement of what I think you were looking for: "In more modern language, they chose 10⁸ CGS electromagnetic units of electromotive force as the practical unit because it was approximately equal to that of the Daniell cell, and suggested the name volt for it. They chose 10⁹ CGS electromagnetic units of resistance with the name ohm as the practical unit because it was approximately equal to the Siemens Unit defined by a column of mercury 1 m long and of 1 sq mm cross section." The rôle of the Daniell cell in this choice is also mentioned the the 1935 reference that I gave above (p. 1374), but the wording is not quite as clear. —Quondum 01:20, 3 July 2020 (UTC)

Thanks. I think the most interesting things is that it came out so close such that only the appropriate power of 10 was needed. I suspect that they went for the rationalized units for that reason. If the unrationalized ones came closer, they would have used those. (That isn't WP:OR because I didn't even do any OR.) You can probably throw in a 2 or so, too. This seems especially interesting, as the units are supposed to be based on force between currents. Gah4 (talk) 06:03, 3 July 2020 (UTC)

I think you are reading too much into a coincidence. I very strongly doubt whether convenience or unit size had anything to do with the rationalization debate. Had they used a lithium cell instead at 3.1 V, I expect they'd have made exactly the same choice. —Quondum 12:49, 3 July 2020 (UTC)

Jean-André Deluc measured the density anomaly of water

The article currently contains a statement "The fact that the density of liquid water has a local maximum as a function of temperature was actually first discovered in the course of these experiments" [by Lefévre-Gineau, after 1795]. This is incorrect. In 1804, Thomas Charles Hope wrote an overview article, in Nicholson's Journal, on the contraction of water by heat. He wrote that the phenomenon was known in the 17th century, and that Jean-André Deluc published accurate measurements in 1772 [1]: "Having devoted his attention to the examination and improvement of the thermometer, [Deluc] was naturally led to the investigation, while engaged in ascertaining the phenomena of the expansion and contraction of different fluids by heat and cold. He employed in his experiments thermometer glasses; and the included water, at or near the term of liquefaction, descended in the stem, and appeared to him to suffer a diminution of bulk by every increase of temperature, till it arrived at the 41st degree. From this point its volume increased with its temperature, and it ascended in the tube. This fluid, when heated and allowed to cool, seemed to him to contract in the ordinary way, till its temperature sunk to the 41°F, but to expand and increase in volume, as the temperature fell to the freezing point. The density of water, he thence inferred, is at its maximum at 41°F." (41°F = 5°C) Jean-André Deluc published his observations in his work "Recherches sur les modifications de l'atmosphère" (1772).[2]

However, Blagden noticed that Deluc had neglected to make a correction for the thermal expansion of the glass. He applied this correction and fixed the maximum of density at 39 °F = 3,9 °C.

Lefevre-Gineau measured that water reaches its maximum density "at the fourth centigrade degree" (4 °C), and concluded this was in agreement with Deluc's result (after Blagden's correction). Ceinturion (talk) 22:48, 5 July 2020 (UTC)

I am going to edit that statement in the article now. Ceinturion (talk) 20:33, 6 July 2020 (UTC)

Thanks, that is an improvement. —Quondum 22:01, 6 July 2020 (UTC)

US use of metric system

@DeFacto: I have two sources (1, 2) saying the US use the imperial system. What is your grief against the data shown on the map? Veverve (talk) 18:25, 13 November 2020 (UTC)

The US uses United States customary units, not Imperial units. The British gallon, for example, is larger than the US gallon. Many general sources are sloppy about paying attention to this. StarryGrandma (talk) 19:13, 13 November 2020 (UTC)

Veverve, those sources are clearly mistaken as the US use US Customary and have never used the imperial system. By the time the UK introduced the imperial system, the US had gained their independence and did not adopt it. Instead, they developed US Customary. Both systems were based on the historic English units, but had diverged in their definitions of some units. -- DeFacto (talk). 19:16, 13 November 2020 (UTC)

Do you have secondary sources to back up those claims? Veverve (talk) 19:43, 13 November 2020 (UTC)

Before Canada went metric, they used the imperial system. Gasoline was sold in imperial gallons, which are 5/4 US gallons. (Or 5 US quarts.) Other than gasoline, I don't remember it being much of a question. In any case, the US didn't, and doesn't, use the imperial system. It might be that some units are the same, and that some people have been confused by the difference. Not to mention that all the US units are defined based on metric units. Gah4 (talk) 03:44, 14 November 2020 (UTC)

Sources to show that some people mistake the US units for imperial units? I suppose that there are some of those, but there are plenty of sources showing the sizes of the different units. Gah4 (talk) 03:47, 14 November 2020 (UTC)

Sources saying the US cannot be said to use imperial units, yes. Veverve (talk) 09:29, 14 November 2020 (UTC)

Much is described here: Imperial_and_US_customary_measurement_systems#Comparison_of_imperial_and_US_customary_systems. Gah4 (talk) 11:43, 14 November 2020 (UTC)

Veverve, "... the US retains, for the most part, its own standardized system, often, and erroneously, referred to as the Imperial system."[3] -- DeFacto (talk). 13:38, 14 November 2020 (UTC)

It occurs to me that such a diagram misses the incomplete conversion that sometimes happens. As well as I know, some places are mostly metric, but some previous units stay in common use. I am told that some otherwise metric countries use stones for weight, for example. There are probably more examples that I don't know about. Gah4 (talk) 06:46, 23 November 2020 (UTC)