Compton generator

Constraction of Compton generator.

A Compton generator is a circular hollow glass ring tube shaped like a doughnut, the inside of which is filled with water.[1] If the ring lies flat on the table, the water in the ring is stationary, and it is then turned over by rotating itself 180 degree around a diameter, such that it again lies flat on the table surface, which is horizontal. The result of the experiment is that the water moves with a certain constant drift velocity around the tube after the doughnut has been rotated. If there were no friction with the walls, the water would continue to circulate indefinitely.[1]

The ring used in the initial experiment was made of one inch brass tubing bent into a circle eighteen inches in diameter, where the windows were placed the tube was constricted to a diameter of about three eights of an inch.[5]

Compton used small droplets of coal oil mixed in the water to measure the drift velocity under a microscope.[6]

Assume the diameter of the glass tube is much smaller than the diameter of the ring, and ${\displaystyle R}$ is the radius of the ring, ${\displaystyle \omega }$ is the Earth rotation rate and ${\displaystyle \lambda }$ is the latitude.

Initially the ring is horizontal and the water is stationary. Second the ring is then quickly rotated by 180° around its East-West diameter and stopped, such that it again lies flat on the table surface, which is horizontal. At this time, the velocity ${\displaystyle v_{th}}$ of the water in the tube is given by
     ${\displaystyle v_{th}=2\omega R\sin \lambda }$

Note that a rotation from the vertical to the vertical position produces the velocity ${\displaystyle v_{tv}}$ of the water in the tube is given by
     ${\displaystyle v_{tv}=2\omega R\cos \lambda }$

Compton used this measured drift velocity to determine his latitude to within 3% accuracy.[6]