Moreover, in Oct 1975 Scientific American, (pp 120), C.L. Strong questioned the constancy of of the speed of light "as science has failed to get a consistently accurate value."
Historical measurements of the speed of light have converged inexorably on the modern value. They were sometimes lower, often higher, but the modern value has always been well within the error bars of the measurements.
At first, Setterfield drew an inverse-exponential curve through selected measurements and announced the speed of light had followed the curve. Denounced for rejecting all the points that don't fit, he drew a squiggly line through all the measurements and announced that he sees a damped oscillation, the inverse-exponential decline having bottomed just before historical measurements began.
Yeah! Right!