speed of light measurement While searching for different methods of speed of light measurement, i came across one of the method of fizeau discussed below which i cannot fully understand.

In short,in Fizeau’s apparatus, a
beam of light was shone between the teeth of
a rapidly rotating toothed wheel, so the
“lantern” was constantly being covered
and uncovered. Fizeau had a
mirror, reflecting the beam back, where
it passed a second time between the
teeth of the wheel. 

I do understand the idea i.e. to measure the time during the course of light "from the wheel to mirror and then back to the mirror".But where are the mirror,lantern and wheel  located? What kind of wheel is that? Does light pass through the holes (or teeth) in the wheel or light gets refracted through the wheel? Finally if a group of light particles goes through one of the hole (or teeth),then how do we know that the same group of light particles came back through which hole (or teeth) after its journey,since there are soo many light particles leaving and entering different holes (or teeth)?
Here is a diagram of his setup:

See the Wikipedia page for a discription.