Zur Geschichte des Metermasses

Summary

The history of the normal meter shows distinct steps of development. The meter itself was defined by French scientists as a national unit at the beginning of the great French Revolution and realized in 1799 by a platinum rod. A better reproduction of the unit of length was given in 1889 by a 90% Pt-10% Ir platinum bar of special cross section according to an international convention. Every substantial standard, however, has many disadvantages, besides the possibility of an entire loss by an accident. The red cadmium line was therefore used in 1893 to express the meter by the number of its wave lengths in air and a provisional resolution was adopted in 1927 on this basis. Much more suitable, however, is an orange line emitted at 63°K from the isotope⁸⁶Kr, which can be produced in a thermal diffusion column in the state of highest purity. Since 1960, the vacuum wave length of this element has served as the fundamental unit of length.