Definition:Metric System/Length/Metre
Metre
The metre is the SI base unit of length.
It is defined as the distance travelled by light in vacuum in $\dfrac 1 {299 \ 792 \ 458}$ of a second.
Conversion Factors
| \(\ds \) | \(\) | \(\ds 1\) | metre | |||||||||||
| \(\ds \) | \(=\) | \(\ds 100\) | centimetres | |||||||||||
| \(\ds \) | \(=\) | \(\ds 1000\) | millimetres | |||||||||||
| \(\ds \) | \(=\) | \(\ds 1 \, 000 \, 000\) | micrometres | |||||||||||
| \(\ds \) | \(=\) | \(\ds 39 \cdotp 3708\) | inches | |||||||||||
| \(\ds \) | \(=\) | \(\ds 3 \cdotp 28\) | feet | |||||||||||
| \(\ds \) | \(=\) | \(\ds 1 \cdotp 09\) | yards |
Symbol
- $\mathrm m$
The symbol for the metre is $\mathrm m$.
Its $\LaTeX$ code is \mathrm m .
Square Metre
The square metre is the SI unit of area.
| \(\ds \) | \(\) | \(\ds 1\) | square metre | |||||||||||
| \(\ds \) | \(=\) | \(\ds 10 \, 000\) | square centimetres | |||||||||||
| \(\ds \) | \(=\) | \(\ds 10.76\) | square feet |
Cubic Metre
The cubic metre is the SI unit of volume.
| \(\ds \) | \(\) | \(\ds 1\) | cubic metre | |||||||||||
| \(\ds \) | \(=\) | \(\ds 1000\) | litres | |||||||||||
| \(\ds \) | \(\approx\) | \(\ds 35 \cdotp 32\) | cubic feet |
Historical Note
- 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 Dunkirk 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.
Linguistic Note
The word metre originated with Tito Livio Burattini who pioneered the concept of a universal set of fundamental units.
He used the term metro cattolico from the Greek μέτρον καθολικόν (métron katholikón), that is universal measure.
This word gave rise to the French word mètre which was introduced into the English language in $1797$.
The spelling metre is the one adopted by the International Bureau of Weights and Measures.
Meter is the variant used in standard American English, but can be confused for the word for a general device used to measure something, in particular the standard household electricity meter, water meter and so on.
While $\mathsf{Pr} \infty \mathsf{fWiki}$ attempts in general to standardise on American English, the name of this unit is one place where a deliberate decision has been made to use the international spelling.
Sources
- 1944: Alfred E. Holbrow: Geometrical Drawing (12th ed.) ... (previous) ... (next): Section $\text I$. Introduction
- 1966: Isaac Asimov: Understanding Physics ... (previous) ... (next): $\text {I}$: Motion, Sound and Heat: Chapter $2$: Falling Bodies: Free Fall
- 1969: J.C. Anderson, D.M. Hum, B.G. Neal and J.H. Whitelaw: Data and Formulae for Engineering Students (2nd ed.) ... (previous) ... (next): $1.$ Units and Abbreviations: $1.2$ SI units $(1)$ Basic units
- 1976: Ralph J. Smith: Circuits, Devices and Systems (3rd ed.) ... (previous) ... (next): Chapter $1$: Electrical Quantities: Definitions and Laws: The International System of Units
- 1976: Ralph J. Smith: Circuits, Devices and Systems (3rd ed.) ... (previous) ... (next): Chapter $1$: Electrical Quantities: Definitions and Laws: The International System of Units: Table $1$-$1$ Basic Quantities
- 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
- 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): metre