A glass torus oriented vertically filled with a suspension of particles in a liquid. When initial motion has damped out, the torus is rotated 180° about the horizontal axis. Weak clockwise motion starts (since the top particles--slightly faster moving because they are at a larger radius from the Earth's center--are now on bottom), with maximum motion occurring when the vertical plane of the tube is oriented east-west and zero motion when the plane is north-south. In the absence of viscous damping, particles in the tube would circulate with a period of 12 hours. The fact that this is half the Earth's rotation period was originally missed by Compton.
References
Compton, A. H. Science 37, 803-806, 1913.
Compton, A. H. "A Determination of Latitude, Azimuth, and the Length of the Day Independent of Astronomical Observations." Phys. Rev. 5, 109, 1915.
Compton, A. H. Popular Astronomy 23, 199, 1915.
Gardner, M. Ch. 14, Problem 18, in Mathematical Carnival: A New Round-Up of Tantalizers and Puzzles from Scientific American New York: Vintage, 1977.
