Problem 5.224

In the Fizeau experiment on measurement of the velocity of light the distance between the gear wheel and the mirror is $l$ $=7.0 \mathrm{~km},$ the number of teeth is $z=720 .$ Two successive disappear- ances of light are observed at the following rotation velocities of the wheel: $n_{1}=283$ rps and $n_{2}=313$ rps. Find the velocity of light.