How the Meter Came To Be
One can know where one is in the world by the systems of
measurement that specific place uses. There is the English
system used by the United States, which uses pounds and feet for
measurement, and then there is the metric system which is more
accepted in other parts of the so-called civilized world.
While there are three types of systems of units of use today,
the most popular one by far is the International System of Units
(or the SI Systeme International d'Unites).
A measurement in this particular system with regards to length
is in meter/metre. Variations in the meter are prefixes such as
kilometer and millimeter. The word has Greek roots, its origin
being metron, which means "a measure".
The meter follows a timeline dating back to the eighteenth
century, when two approaches to the definition of the standard
unit of length were broached.
The first approach defined the meter as the length of a pendulum
with a half-period of one second. The other approach suggested
that the meter was one-fourth the polar circumference of the
earth.
On May 8, 1790, the French National Assembly approved of the
first approach: its length would be equal to the length of a
pendulum with a half-period of one second.
Barely a year later, in March 30, 1791, has this same assembly
accepted the new proposal of the French Academy of Sciences
which adhered to the second approach: that the new definition of
the meter would be equal to one-fourth the polar circumference
of the world.
It must be noted that the circumference of the Earth, if
measured through the poles, is about forty million meters.
In December 10, 1799, the French National Assembly then
specified that the final standards would be according to the
platinum meter bar constructed on June 23rd 1799 and currently
deposited in the National Archives.
In the 1870's a series of international conferences were held to
devise new metric standards. It was the Meter Convention of 1875
that mandated the establishment of an enduring International
Bureau of Weights and Measures (or BIPM, for Bureau
International des Poids et Mesures) to be based in France.
It was this organization that was tasked to uphold the new
prototype kilogram and meter when it would be constructed. It
would also retain comparisons between the distributed metric
prototypes and the non-metric measurement standards.
Almost a decade later, in September 28, 1889 the CGPM defined
the length as the exact distance between two lines on a standard
bar of an alloy of platinum with ten percent iridium. This
distance was to be measured at the melting point of ice.
This definition would be adjusted over the years. It was in 1893
when Albert A. Michelson, the inventor of the interferometer,
measured the standard meter using his device. It won't be until
1925 when interferometry would be in regular use at the BIPM.
On October 21st, 1983 the seventeenth CGPM definition of a meter
equaled the length traveled by light in vacuum during 1/299,
2972, 458 of a second.
Scientists agree that if a definition is based on the physical
properties of light, then it is infinitely more precise and
reproducible. This is because the properties associated with
light are considered to be universally constant.