Name: Ian L. M.
Several references have stated that the decrease in the
earth's rotation has been determined from eclipse records. Can you
suggest a reference that briefly describes how this is (was) done?
The cause of this small effect is primarily due to tidal friction caused
by the moon-earth-sun gravitational interaction. I do not recall the exact
web site but if you search terms like: "tidal forces" or "gravitational
effects" or "tidal friction" I think you will find out there are a lot of
small but measurable effects on the earth-moon-sun system.