By the concurrent action of the principal governments of the world, an International Bureau of Weights and Measures has been established
near Paris. Under the direction of the International Committee, two ingots were cast of pure platinum-iridium in the proportion of 9 parts of the
former to 1 of the latter metal. From one of these a certain number of kilogrammes were prepared, from the other a definite number of metre bars.
These standards of weight and length were intercompared, without preference, and certain ones were selected as International prototype stan-
dards. The others were distributed by lot to the different governments, and are called national prototype standards. Those apportioned to the
United States are in the keeping of this office.
The metric system was legalized in the United States in 1866.

The International Standard Metre is derived from the Metre des Archives, and its length is defined by the distance between two lines at o°
Centigrade, on a platinum-iridium bar deposited at the International Bureau of Weights and Measures.

The International Standard Kilogramme is a mass of platinum-iridium deposited at the same place, and its weight in vacuo is the same as that
of the Kilogramme des Archives.

The litre is equal to a cubic decimetre of water, and it is measured by the quantity of distilled water which, at its maximum density, will
counterpoise the standard kilogramme in a vacuum, the volume of such a quantity of water being, as nearly as has been ascertained, equal to a
cubic decimetre.