Nothing, in fact, proves that sensible variations may not in time be produced in the value of an arc of the meridian, and serious difficulties may arise regarding the probable inequality of the various meridians.
For all these reasons, the idea of finding a natural unit has been gradually abandoned, and we have become resigned to accepting as a fundamental unit an arbitrary and conventional length having a material representation recognised by universal consent; and it was this unit which was consecrated by the following law of the 11th July 1903:-- "The standard prototype of the metrical system is the international metre, which has been sanctioned by the General Conference on Weights and Measures." Sec.3.THE MEASURE OF MASS On the subject of measures of mass, similar remarks to those on measures of length might be made.

The confusion here was perhaps still greater, because, to the uncertainty relating to the fixing of the unit, was added some indecision on the very nature of the magnitude defined.

In law, as in ordinary practice, the notions of weight and of mass were not, in fact, separated with sufficient clearness.
They represent, however, two essentially different things.

Mass is the characteristic of a quantity of matter; it depends neither on the geographical position one occupies nor on the altitude to which one may rise; it remains invariable so long as nothing material is added or taken away.

Weight is the action which gravity has upon the body under consideration; this action does not depend solely on the body, but on the earth as well; and when it is changed from one spot to another, the weight changes, because gravity varies with latitude and altitude.
These elementary notions, to-day understood even by young beginners, appear to have been for a long time indistinctly grasped.