SCIENCE FILE: An exploration of issues and trends affecting science, medicine and the environment. : I Didn’t Know That...
Q: How was the length of the meter originally determined?
A: The first common unit of measurement was the foot, which was probably defined in prehistoric times as the actual length of a ruler’s foot. Different countries had different rulers, however, and different feet, which was very confusing. To overcome this problem, 18th-century French researchers defined the meter as one 10-millionth of the distance from the equator to the North Pole.
Because of the difficulty of measuring such a meter, however, the official meter was for decades defined as the distance between two fine scratches on a platinum bar kept in a vault in France. More recently, to improve accuracy and to make a standard of measurement more widely available, the meter has been officially defined as the distance light travels in 1/299,792,458 of a second. That number was chosen because the speed of light was determined as 299,792,458 meters per second. (A second is defined as the time required for 9,192,631,770 vibrations of the cesium-133 atom.)
