Here is a photo of the Selin Device.

At the extreme left is the 20-amp Variac that provides adjustable AC power to the motor. The motor -- on the top of the machine -- is a 3 1/4 HP router motor designed to run at 21,000 rpm. The top and bottom plates of the main assembly are 1/4 inch steel. They are separated by three pieces of 3"X12" C-channel -- painted black. The space between the vertical supports is four inches -- intended to capture the rotor which is 6 inches in diameter. The rotor is painted blue and black with two white squares. To the right of the rotor, mounted on a vertical piece seen edge on, is an optical tachometer. The tachometer looks through a hole in the vertical support and counts the white squares as the rotor spins. This tachometer is designed for use with model airplane engines and is expecting to see a two-blade propeller -- so two white squares are required to get the proper rpm indication. At the bottom of the rotor, mounted horizontally between the vertical supports is a thin aluminum shield. This shield separates the spinning rotor from the stationary test mass. The bottom of the rotor has a cavity machined up into it. The bottom shaft of the rotor comes down from this cavity to the bottom bearings -- held by an aluminum housing. The aluminum shield encloses the bottom shaft, goes up inside the cavity at the bottom of the rotor, and extends out to the three vertical supports. The test mass (the point of this whole thing!) is held up inside the cavity (below the shield) by a long wooden arm. At the right end the arm is held by a knife-edge free pivot point. In the middle the arm rests on another knife edge, sitting on a scale platform. Thus the scale displays a number which is directly proportional to the weight of the test mass.

The point of the experiment is to spin the rotor very fast and see if the weight of the test mass decreases.

Here are some more pictures.