Foucault Speed of Light Experiment

[S_Flaherty]

In my class's set up of Foucault's design of the experiment to measure the speed of light, the light beam passes through a beam splitter but there is only one beam spot in the microscope. I'm confused as to why this is. Can someone help explain it to me?

 

[Spinnor]

Isn't that what you want? See figure 1,

http://www.phys.ksu.edu/personal/rprice/SpeedofLight.pdf