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 an fascinating attempt to define the metre using time. The metre 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 metre.