[Lex Computer & Tech Group/LCTG] An interesting bit of history of the metre

Wed Jun 8 12:21:37 PDT 2022

All,

Based on today's very interesting talk about measurement and Michelson -- I
thought that the interesting history of the first standard [the
"almighty metre"] might be of interest

The following is from the Wikipedia article
https://en.wikipedia.org/wiki/Metre

A couple of highlights relevant to recent talks:
Wavelength definition[edit
<https://en.wikipedia.org/w/index.php?title=Metre&action=edit&section=7>]

In 1873, James Clerk Maxwell
<https://en.wikipedia.org/wiki/James_Clerk_Maxwell> suggested that light
emitted by an element be used as the standard both for the metre and for
the second. These two quantities could then be used to define the unit of
mass.[100] <https://en.wikipedia.org/wiki/Metre#cite_note-100>

In 1893, the standard metre was first measured with an interferometer
<https://en.wikipedia.org/wiki/Interferometer> by Albert A. Michelson
<https://en.wikipedia.org/wiki/Albert_Abraham_Michelson>, the inventor of
the device and an advocate of using some particular wavelength
<https://en.wikipedia.org/wiki/Wavelength> of light
<https://en.wikipedia.org/wiki/Light> as a standard of length. By 1925,
interferometry <https://en.wikipedia.org/wiki/Interferometry> was in
regular use at the BIPM. However, the International Prototype Metre
remained the standard until 1960, when the eleventh CGPM defined the metre
in the new International System of Units
<https://en.wikipedia.org/wiki/International_System_of_Units> (SI) as equal
to 1650763.73 wavelengths <https://en.wikipedia.org/wiki/Wavelength> of the
orange <https://en.wikipedia.org/wiki/Orange_(colour)>-red
<https://en.wikipedia.org/wiki/Red> emission line
<https://en.wikipedia.org/wiki/Emission_line> in the electromagnetic
spectrum <https://en.wikipedia.org/wiki/Electromagnetic_spectrum> of the
krypton-86 <https://en.wikipedia.org/wiki/Krypton-86> atom
<https://en.wikipedia.org/wiki/Atom> in a vacuum
<https://en.wikipedia.org/wiki/Vacuum>.[101]
<https://en.wikipedia.org/wiki/Metre#cite_note-Marion-101>

Timeline[edit
<https://en.wikipedia.org/w/index.php?title=Metre&action=edit&section=9>]
DateDeciding bodyDecision
8 May 1790 French National Assembly
<https://en.wikipedia.org/wiki/National_Assembly_(French_Revolution)> The
length of the new metre to be equal to the length of a pendulum
<https://en.wikipedia.org/wiki/Pendulum> with a half-period
<https://en.wikipedia.org/wiki/Period_(physics)> of one second
<https://en.wikipedia.org/wiki/Second>.[36]
<https://en.wikipedia.org/wiki/Metre#cite_note-Larousse-36>
30 Mar 1791 French National Assembly Accepts the proposal by the French
Academy of Sciences
<https://en.wikipedia.org/wiki/French_Academy_of_Sciences> that the new
definition for the metre be equal to one ten-millionth of the length of a
great circle quadrant <https://en.wikipedia.org/wiki/Circular_sector> along
the Earth's meridian
<https://en.wikipedia.org/wiki/Meridian_(geography)> through
Paris, that is the distance from the equator to the north pole along that
quadrant.[117]
<https://en.wikipedia.org/wiki/Metre#cite_note-FOOTNOTEBigourdan190120%E2%80%9321-117>
1795 Provisional metre bar made of brass and based on Paris meridan
<https://en.wikipedia.org/wiki/Paris_meridian> arc (French: *Méridienne de
France*) measured by Nicolas-Louis de Lacaillle
<https://en.wikipedia.org/wiki/Nicolas-Louis_de_Lacaille> and Cesar-François
Cassini de Thury
<https://en.wikipedia.org/wiki/C%C3%A9sar-Fran%C3%A7ois_Cassini_de_Thury>,
legally equal to 443.44 lines <https://en.wikipedia.org/wiki/Line_(unit)> of
the *toise du Pérou* (a standard French unit of length
<https://en.wikipedia.org/wiki/Units_of_measurement_in_France_before_the_French_Revolution#Length>
from
1766).[36] <https://en.wikipedia.org/wiki/Metre#cite_note-Larousse-36>[37]
<https://en.wikipedia.org/wiki/Metre#cite_note-Levallois-37>[82]
<https://en.wikipedia.org/wiki/Metre#cite_note-Wolf-82>[99]
<https://en.wikipedia.org/wiki/Metre#cite_note-entreprises-99> [The line
was 1/864 of a *toise*.]
10 Dec 1799 French National Assembly Specifies the platinum metre bar,
presented on 22 June 1799 and deposited in the National Archives
<https://en.wikipedia.org/wiki/National_Archives_of_France>, as the final
standard. Legally equal to 443.296 lines on the *toise du Pérou*.[99]
<https://en.wikipedia.org/wiki/Metre#cite_note-entreprises-99>
24–28 Sept 1889 1st General Conference on Weights and Measures
<https://en.wikipedia.org/wiki/General_Conference_on_Weights_and_Measures>
 (CGPM) Defines the metre as the distance between two lines on a standard
bar of an alloy of platinum <https://en.wikipedia.org/wiki/Platinum> with
10% iridium <https://en.wikipedia.org/wiki/Iridium>, measured at the
melting point of ice.[99]
<https://en.wikipedia.org/wiki/Metre#cite_note-entreprises-99>[118]
<https://en.wikipedia.org/wiki/Metre#cite_note-118>
27 Sept – 6 Oct 1927 7th CGPM Redefines the metre as the distance, at 0 °C
<https://en.wikipedia.org/wiki/Celsius> (273 K
<https://en.wikipedia.org/wiki/Kelvin>), between the axes of the two
central lines marked on the prototype bar of platinum-iridium, this bar
being subject to one standard atmosphere of pressure
<https://en.wikipedia.org/wiki/Atmospheric_pressure> and supported on two
cylinders of at least 10 mm (1 cm) diameter, symmetrically placed in the
same horizontal plane at a distance of 571 mm (57.1 cm) from each other.
[119] <https://en.wikipedia.org/wiki/Metre#cite_note-119>
14 Oct 1960 11th CGPM Defines the metre as 1650763.73 wavelengths
<https://en.wikipedia.org/wiki/Wavelength> in a vacuum
<https://en.wikipedia.org/wiki/Vacuum> of the radiation
<https://en.wikipedia.org/wiki/Electromagnetic_radiation> corresponding to
the transition between the 2p10 and 5d5 quantum levels of the krypton
<https://en.wikipedia.org/wiki/Krypton>-86 atom
<https://en.wikipedia.org/wiki/Atom>.[120]
<https://en.wikipedia.org/wiki/Metre#cite_note-FOOTNOTEJudson1976-120>
21 Oct 1983 17th CGPM Defines the metre as the length of the path travelled
by light <https://en.wikipedia.org/wiki/Light> in a vacuum during a time
interval of 1/299 792 458 of a second <https://en.wikipedia.org/wiki/Second>
.[121] <https://en.wikipedia.org/wiki/Metre#cite_note-121>[122]
<https://en.wikipedia.org/wiki/Metre#cite_note-122>
2002 International Committee for Weights and Measures
<https://en.wikipedia.org/wiki/International_Committee_for_Weights_and_Measures>
 (CIPM) Considers the metre to be a unit of proper length
<https://en.wikipedia.org/wiki/Proper_length> and thus recommends this
definition be restricted to "lengths ℓ which are sufficiently short for the
effects predicted by general relativity
<https://en.wikipedia.org/wiki/General_relativity> to be negligible with
respect to the uncertainties of realisation".[123]
<https://en.wikipedia.org/wiki/Metre#cite_note-taylor2008a77-123>

Definitions of the metre since 1795[124]
<https://en.wikipedia.org/wiki/Metre#cite_note-FOOTNOTECardarelli2003-124>
Basis of definitionDateAbsolute
uncertaintyRelative
uncertainty
1/10 000 000 part of the quadrant
<https://en.wikipedia.org/wiki/Circular_sector> along the meridian
<https://en.wikipedia.org/wiki/Meridian_(geography)>, measurement by
Delambre <https://en.wikipedia.org/wiki/Jean_Baptiste_Joseph_Delambre> and
Méchain <https://en.wikipedia.org/wiki/Pierre_M%C3%A9chain> (443.296 lines)
1795 500–100 μm 10−4
First prototype *Mètre des Archives
<https://en.wikipedia.org/wiki/History_of_the_metre#M%C3%A8tre_des_Archives>*
platinum
bar standard 1799 50–10 μm 10−5
Platinum-iridium bar at melting point of ice (1st CGPM
<https://en.wikipedia.org/wiki/CGPM>) 1889 0.2–0.1 μm (200–100 nm) 10−7
Platinum-iridium bar at melting point of ice, atmospheric pressure,
supported by two rollers (7th CGPM) 1927 n.a. n.a.
Hyperfine <https://en.wikipedia.org/wiki/Hyperfine_structure> atomic
transition; 1650763.73 wavelengths of light from a specified transition in
krypton-86 <https://en.wikipedia.org/wiki/Krypton-86> (11th CGPM) 1960 4 nm
4×10−9[125] <https://en.wikipedia.org/wiki/Metre#cite_note-125>
Length of the path travelled by light in a vacuum in 1/299 792 458 second
(17th CGPM) 1983 0.1 nm 10−10

and to further the obfuscation of the old standards with the new --

The kilogram is defined by taking the fixed numerical value of the Planck
constant, ℎ, to be 6.626 070 15 × 10-34 when expressed in the unit J s,
which is equal to kg m2 s−1, where the metre and the second are defined in
terms of the speed of light, 𝒸, and the hyperfine transition frequency of
the caesium-133 atom, ∆ν, respectively.

 herewith a NIST publication all about the new Kg definition in terms of
Planck's constant, the speed of light, and the hyperfine transition
frequency for Cs133

https://www.nist.gov/system/files/documents/2019/09/05/si_k_trifold_brochure_web.pdf

Ted
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