# Definition:Metre/Historical Note

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## Historical Note on Metre

- 1671: Jean Picard measured the length $L$ of a simple pendulum whose period is $1$ second, and proposed a unit of measurement $2 L$, which was to be called the universal toise.

- 1675: Tito Livio Burattini suggested the term
**metre**as the length of this pendulum.

It differs from the modern **metre** by half a centimetre.

It was soon established that as Acceleration Due to Gravity varies considerably according to location, this was not a sustainable definition to maintain a standard.

- 19 March 1791: the French Academy of Sciences suggested that the
**metre**should be defined as $10^{-7}$ the distance from the Earth's equator, through Paris to the North Pole (at sea level).

- 26 March 1791: this proposal was adopted.

- 1805: Ferdinand Rudolph Hassler brought a standard
**metre**made in Paris to the United States. He designed a baseline apparatus which instead of bringing different bars in actual contact during measurements, used only one bar calibrated on the metre and optical contact. Thus the metre became the unit of length for geodesy in the United States.

- 1873: James Clerk Maxwell suggested using light emitted by an element as the standard both for the
**metre**and for the second.

- 1889: The international prototype
**metre**was defined as the distance between two lines on a standard bar composed of an alloy of $90 \%$ platinum and $10 \%$ iridium, measured at the melting point of ice.

- 1960: The
**metre**was defined in the new International System of Units as equal to $1 \, 650 \, 763 \cdotp 73$ wavelengths of the orange-red light emitted by the transition $2 P_{10} - 5 D_5$ in the electromagnetic spectrum of the krypton-$86$ atom in a vacuum.

- 1983: defined as the distance travelled by light in vacuum in $\dfrac 1 {299 \ 792 \ 458}$ of a second.

## Sources

- 1938: A. Geary, H.V. Lowry and H.A. Hayden:
*Mathematics for Technical Students, Part One*... (previous) ... (next): Arithmetic: Chapter $\text I$: Decimals: The Metric System - 1964: Milton Abramowitz and Irene A. Stegun:
*Handbook of Mathematical Functions*... (previous) ... (next): $2$. Physical Constants and Conversion Factors - 1986: David Wells:
*Curious and Interesting Numbers*... (previous) ... (next): $10$ - 1997: David Wells:
*Curious and Interesting Numbers*(2nd ed.) ... (previous) ... (next): $10$ - 1998: David Nelson:
*The Penguin Dictionary of Mathematics*(2nd ed.) ... (previous) ... (next):**metre** - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next):**metre** - 2008: Ian Stewart:
*Taming the Infinite*... (previous) ... (next): Chapter $2$: The Logic of Shape: Problems for the Greeks