The Metre and Time
The development of measuring systems is a great human accomplishment. The early Egyptians created a unit of length, the cubit, based on the human forearm. The English and others used the human foot and grains of barleycorn to measure length. The metric system started with a fascinating attempt to define the meter using time. The meter evolved through a number of incarnations many involving distances taken from the planet. Today the meter is defined using the speed of light. This definition relies on a reliable means for measuring time. Time and space have been joined in our current definition of the meter.