Discoverer of the effect of relative speed on the observed frequency of waves (7)
I believe the answer is:
doppler
(Other definitions for doppler that I've seen before include "Change focus rapidly" , "--- shift, frequency change with speed" , "Physicist associated with frequency shifts" , "Light, sound frequency shift physicist" , "Austrian physicist, d. 1853 famous for his discovery of the effect of movement on perceived wavelengths" .)