> When 1975 was rung in last week at Britain's old Royal Greenwich Observatory, which is located on the meridian where the earth's time zones begin, it arrived precisely one second late. For official timekeepers everywhere, including the National Bureau of Standards in the U.S., the delay was significant. The earth's rotation (which forms the basis of time units—hours, minutes, seconds) is gradually slowing down—largely because of tidal friction. For that reason, the timekeepers decided a few years ago to make an occasional correction by inserting a so-called leap second. In that way, the accurate atomic clocks that they rely on...
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