Data taken by the author during August to December 1988 on eclipses of the first major satellite of Jupiter are compared with data taken by Roemer and Picard 300 years ago. Both sets of data are analyzed by the same method, or as nearly the same as possible, to determine whether the speed of light has changed. The conclusion depends on, and is rather sensitive to, whether or not Io's mean daily motion has changed in the 300 years.
