(i.) _Systems of Measures._[1]
118. _Metric System._--The metric system was adopted in France at the
end of the 18th century. The system is decimal throughout. The principal
units of length, weight and volume are the _metre, gramme_ (or _gram_)
and _litre_. Other units are derived from these by multiplication or
division by powers of 10, the names being denoted by prefixes. The
prefixes for multiplication by 10, 10^2, 10^3 and 10^4 are _deca-,
hecto-, kilo-_ and _myria-_, and those for division by 10, 10^2 and 10^3
are _deci-, centi-_ and _milli-_; the former being derived from Greek,
and the latter from Latin. Thus _kilogramme_ means 1000 grammes, and
_centimetre_ means 1/100 of a metre. There are also certain special
units, such as the _hectare_, which is equal to a square hectometre, and
the _micron_, which is 1/1000 of a millimetre.
The metre and the gramme are defined by standard measures preserved at
Paris. The litre is equal to a cubic decimetre. The gramme was intended
to be equal to the weight of a cubic centimetre of pure water at a
certain temperature, but the equality is only approximate.
The metric system is now in use in the greater part of the civilized
world, but some of the measures retain the names of old disused
measures. In Germany, for instance, the _Pfund_ is 1/2 kilogramme, and
is approximately equal to 1(1/10) lb. English.
119. _British Systems._--The British systems have various origins, and
are still subject to variations caused by local usage or by the usage of
particular businesses. The following tables are given as illustrations
of the arrangement adopted elsewhere in this article; the entries in any
column denote multiples or submultiples of the unit stated at the head
of the column, and the entries in any row give the expression of one
unit in term of the other units.