speed of light
According to the theories prevailing at the time, light traveling through a moving medium would be a simple sum of its speed through the medium plus the speed of the medium. Contrary to expectation, Fizeau found that although light appeared to be dragged by the water, the magnitude of the dragging was much lower than expected. If 




u
′

=
c

/

n


{\displaystyle u'=c/n}

 is the speed of light in still water, and 



v


{\displaystyle v}

 is the speed of the water, and 




u

±




{\displaystyle u_{\pm }}

 is the water-borne speed of light in the lab frame with the flow of water adding to or subtracting from the speed of light, then
