the French Revolution, many
people in France realized that their numerous local measures and weights systems of measurement were archaic,
needed to be changed and - ideally - unified. That's exactly what
Charles Maurice de Talleyrand wanted to implement: a radical change
in regard to the way units were to be measured. In 1790, he proposed
to the French National Assembly the development of a new
system. Other nations were also asked to co-operate. Great Britain
did not want anything to do with the creation of a new system of
📏 In 1791, the French Academy of
Sciences decided to set up a commission and one of its
implementations was the standardized definition of length based on
the size of the Earth. Length would now be defined via the metre,
which would be equal to 1/10 000 000 of the length of the meridian
arc from the equator to the north pole.
📏 The metric system follows a pattern that is
decimal: units can easily be divided or multiplied by an integer
power of ten. For example, 1/10 of a metre is a decimetre (0.1
metre), 1/100 of a metre is a centimetre (0.01 metre / cent
in French means hundred) and 1/1000 of a metre is a millimetre
(0.001 metre / mille in French means thousand). The
hectometre is 100 metres and the kilometer is 1000 metres.
📏 The International System of Units (SI) now includes seven
base units or, if you prefer, physical constants. The metre
(length), the kilogram (mass), the ampere (electric current), the
mole (amount of substance), kelvin (temperature), candela (light
intensity) and the second (time). SI is always adapting to new
technologies and the need to be as precise as possible.
📏 Hence, in the SI, the metre is defined as 1 / 299 792 458 of the
distance light can travel in one second. As for the kilogram,
initially defined as the mass of one cubic decimetre of water at 4
degrees Celsius, it is now defined by SI via the Planck constant.
📏 In 1975, the United States' Metric Conversion Act
did declare that the metric system was the preferable system for
weights and measures but it did not suspend the use of other units
in the country. As of today, the United States does not use the
metric system on a wide scale.