In 1960, as lasers had become available, the 11th [General Conference on Weights and Measures]? changed the definition of metre to be the length of 1,650,763.73 wavelengths in vacuum of the orange-red emission line in the spectrum? of krypton-86. In 1983 the General Conference on Weights and Measures defined the metre as the distance traveled by light in a vacuum in 1/299,792,458 of a second (that is, the speed of light in a vacuum was defined to be 299,792,458 metres per second). Since the speed of light is believed to be constant everywhere, a definition based on light is easier to maintain and more consistent than a measurement based on the circumference of the Earth or the length of a specific metal bar. Thus, should either object be destroyed or lost, the standard meter can still be easily recreated in any laboratory. |

In 1960, as lasers had become available, the 11th [General Conference on Weights and Measures]? changed the definition of metre to be the length of 1,650,763.73 wavelengths in vacuum of the orange-red emission line in the spectrum? of krypton-86. In 1983 the General Conference on Weights and Measures defined the metre as the distance traveled by light in a vacuum in 1/299,792,458 of a second (that is, the speed of light in a vacuum was defined to be 299,792,458 metres per second). Since the speed of light is believed to be constant everywhere, a definition based on light is easier to maintain and more consistent than a measurement based on the circumference of the Earth or the length of a specific metal bar. Thus, should the bar be destroyed or lost, the standard meter can still be easily recreated in any laboratory. |

Metre is a term used in the scansion of poetry, usually indicated by the kind of feet and the number of them: for instance, "iambic pentameter", "dactylic tetrameter", etc. |

Metre is a term used in the scansion of poetry, usually indicated by the kind of feet and the number of them: for instance, "iambic pentameter", "dactylic tetrameter", etc. See meter in poetry. |