Science: Earth-Pulse

The day is now one-thousandth of a second longer than it was a century ago. Although this change has had no effect on clocks, it is highly significant for astronomers. Just before he died last July, venerable, 71-year-old Professor Ernest William Brown of Yale, who spent half a century studying the passage of time, sent the Smithsonian Institution an original hypothesis on the lengthening of the day.

Last week it appeared in the Institution's annual report.

According to mathematicians, the length of the day is determined by the speed of the earth's rotation on its...