Who showed that light travels more slowly in water than in air?

Was it Fizeau (sp?) who used rapidly spinning cogwheels to time light beams reflected by mirrors?

Not the right name professor, but keep working on it ...you're not far away.

Sorry, that was my final answer. I'm doing this Jeopardy-style, just blurting out an answer and hoping it's right. You mean I'm supposed to look this stuff up first?

Armand Hippolyte Louis Fizeau is the answer I have, also

Another source credits Foucault in 1850, but Fizeau's experiments took place in 1849.

Fizeau

Foucalt

Further clarification:

Fizeau-Foucault Apparatus

Foucault is my, um, newer final answer.

The first measurement of c on Earth was by Armand Fizeau in 1849. He used a beam of light reflected from a mirror 8 km away. The beam passed through the gaps between teeth of a rapidly rotating wheel. The speed of the wheel was increased until the returning light passed through the next gap and could be seen. Then c was calculated to be 315,000 km/s. Leon Foucault improved on this a year later by using rotating mirrors and got the much more accurate answer of 298,000 km/s. His technique was good enough to confirm that light travels slower in water than in air.

What I always wanted to know was, how did they accurately measure rotational speed (rpm's)?

Thank you to both of you, Foucault is the man I was looking for.