Did you know that as scientists discovered new information and developed more precise ways of measuring the official length of a meter has changed over time? Early measurements were based on the distance a pendulum would travel in one second. In 1791 a meter was defined as one ten-millionth of the distance between the Earth’s North Pole and the Equator. In 1893, a meter was defined by a certain number of wavelengths of light. Now we use the definition from 1983: a meter is the distance light in a vacuum travels in 1/299,792,458 of a second.
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The word ‘meter’ comes from the Greek word μετρέω (metreo) or μέτρον (metron) which mean ‘to measure’ or ‘measure’.
The system using a pendulum to define the length of a meter fell out of favor because the force of gravity varies around the surface of the Earth, which would change the size of a meter measured.
The system using the meridian arc, or distance between the North Pole and Equator fell out of favor because the Earth is not a perfect sphere. The first bar produced to represent a ‘meter’ using this method was actually 200 micrometers off due to the variance and flattening of the Earth’s shape.
In 1870 another meter bar was created. It was made of 90% platinum and 10% iridium, measured at the melting point of ice.
In 1893, a meter was defined as 1,650,763.73 wavelengths of the orange-red emission line of a krypton-86 atom in a vacuum.