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History of the metre
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During the French Revolution, the traditional units of measure were to be replaced by consistent measures based on natural phenomena. As a base unit of length, scientists had favoured the seconds pend
Replicas of historical metric standards, including an iron copy of the mètre des Archives.
Replicas of historical metric standards, including an iron copy of the mètre des Archives.
A copy of the "provisional" metre located in the wall of a building, 15 rue de Vaugirard, Paris.
A copy of the "provisional" metre located in the wall of a building, 15 rue de Vaugirard, Paris.
Closeup of National Prototype Metre Bar No. 27, made in 1889 by the International Bureau of Weights and Measures (BIPM) in collaboration with Johnson
Closeup of National Prototype Metre Bar No. 27, made in 1889 by the International Bureau of Weights and Measures (BIPM) in collaboration with Johnson Mattey and given to the United States, which served as the standard for American cartography from 1890 replacing the Committee Meter, an authentic copy of the Mètre des Archives produced in 1799 in Paris, which Ferdinand Rudolph Hassler had brought to the United States in 1805.
A Krypton-86 lamp used to define the metre between 1960 and 1983
A Krypton-86 lamp used to define the metre between 1960 and 1983
Iridium
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Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group is considered the second-densest naturally occur
History of the metre
…on the neutral plane of the standard. The construction was at the limits of technology. The bars were made of a special alloy, 90% platinum and 10% iridium, significantly harder than pure platinum, and have a special X-shaped cross section (a "Tresca section", named after French engineer Henri Tresca) to…
Iridium
Iridium
One troy ounce (31.1035 grams) of arc-melted iridium
One troy ounce (31.1035 grams) of arc-melted iridium
Hydrated iridium trichloride, a common salt of iridium.
Hydrated iridium trichloride, a common salt of iridium.
The Greek goddess Iris, after whom iridium was named.
The Greek goddess Iris, after whom iridium was named.