Just found this while browsing an all-about-science book in the sale rack at Borders:
The generally accepted value for tidal slowing is that the day lengthens about 2 milliseconds per century. I'm not even certain what that last sentence is talking about, but it appears to be off by a factor of one hundred thousand.Is it true that the rotation speed of the Earth Varies?
The rotation speed is at its maximum in late July and early August and at its minimum in April; the difference in the length of day is about 0.0012 second. Since about 1900 the Earth's rotation has been slowing at a rate of approximately 1.7 seconds per year.