Re: Métres carrés et Le Monde

["Jean Fontaine" <jfontain@xxxxxxxxxxx>]

Jacques André, écrit :

> Puis, de toutes façons L c'est aussi lumen...

Le symbole de lumen est lm et non L, qui est bien une variante de l (litre),
variante tolérée mais non encouragée par le SI.

La définition et le statut du litre (et de son symbole) ont une histoire
assez compliquée, bien résumée dans cet extrait d'un dico en ligne :

liter or litre (L or l)
the common metric unit of volume. The liter was originally defined to be the
volume occupied by a kilogram of water, and the gram as the mass of a cubic
centimeter of water. This would make the liter equal to exactly one cubic
decimeter, that is, to the volume of a cube 0.1 meter (or 10 centimeters) on
a side. Unfortunately, the physical objects constructed to represent the
meter and kilogram disagreed slightly. As measured by the standard meter and
standard kilogram, the standard liter turned out to be about 1.000 028 cubic
decimeters. This discrepancy plagued the metric system for a long time. In
1901 an international congress accepted the discrepancy and formally defined
the liter to be exactly 1.000 028 dm3. No one was particularly happy with
such an awkward definition, so in 1964 the CGPM repealed the definition. In
the SI, volumes are to be measured in cubic meters or power-of-ten multiples
thereof, not in liters. However, the SI states that the liter "may be
employed as a special name for the cubic decimeter." Throughout this
dictionary, the liter is used as a name for exactly 1 cubic decimeter, 1000
cubic centimeters, or 0.001 cubic meter. In its new guise as the cubic
decimeter, the liter is approximately 61.023 744 cubic inches. Compared to
the customary volume units, the liter is a little more than a U. S. liquid
quart (1.056 688 qt) but a little less than a U. S. dry quart (0.908 08 qt)
or a British imperial quart (0.879 89 qt). Its name comes from a French
volume unit, the litron, which was in turn derived from the Latin litra.
Both the lower case letter l and the upper case L are accepted as symbols
for the liter, but the U.S. Department of Commerce specifies that L be used,
at least by businesses, to avoid confusion with the numeral 1. The unit is
spelled liter in the U.S. and litre in Britain; there are many other
spellings in various languages (see Spelling of Metric Units).

source : http://www.unc.edu/~rowlett/units/index.html


Jean Fontaine