"This is the Fizeau apparatus."
"..."
"I made it in my dream a while back and brought it here."
"Fizeau."
"Heard of the name, at least?"
"Nope."
"It's that thing that measures the speed of light using a cogwheel and a mirror, I think..."
"You pass a beam of light through the notches and reflect it back from afar..."
"Then, you calculate the speed of light using how fast the cogwheel was rotating when the reflected light got eclipsed by the cog tooth next in line..."
"Yeah, that."
Mirror
Cogwheel
Light Source
50/50 beam splitter
"Don't talk smart to me!"
"Why...?"
Note that Sis said Fizeau in katakana, but Majime said it in hiragana.