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Or, somewhat inconveniently, the results gave two values for the speed of light, depending on which point on the krypton line was chosen to define the metre. [Note 4] This ambiguity was resolved in 1975, when the 15th CGPM approved a conventional value of the speed of light as exactly 299 792 458 m s −1. [130]
The international prototype would also be a "line standard", that is the metre was defined as the distance between two lines marked on the bar, so avoiding the wear problems of end standards. The French government gave practical support to the creation of an International Metre Commission, which met in Paris in 1870 and again in 1872 with the ...
By modern standards the transition was poorly managed. Although thousands of pamphlets were distributed, the Agency of Weights and Measures who oversaw the introduction underestimated the work involved. Paris alone needed 500,000 metre sticks, yet one month after the metre became the sole legal unit of measure, they only had 25,000 in store.
[4]: 2 For example, using metre per second is coherent in a system that uses metre for length and second for time, but kilometre per hour is not coherent. The principle of coherence was successfully used to define a number of units of measure based on the CGS, including the erg for energy , the dyne for force , the barye for pressure , the ...
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of 1 / 299 792 458 of a second, where the second is defined by a hyperfine transition frequency of caesium.
The second, metre, and candela have previously been defined by physical constants (the caesium standard (Δν Cs), the speed of light (c), and the luminous efficacy of 540 × 10 12 Hz visible light radiation (K cd)), subject to correction to their present definitions. The new definitions aim to improve the SI without changing the size of any ...
The ligne (pronounced), or line or Paris line, [1] is a historic unit of length used in France and elsewhere prior to the adoption of the metric system in the late 18th century, and used in various sciences after that time. [2] [3] The loi du 19 frimaire an VIII (Law of 10 December 1799) states that one metre is equal to exactly 443.296 French ...
Even though the metre was initially defined to equal one ten-millionth of the length of the meridian through Paris from pole to the equator, the first prototype metre bar was subsequently found to be short by 0.2 millimetres (because researchers miscalculated the flattening of the Earth). Nevertheless, this original reference metre was retained ...