It consists of a celluloid sphere (diameter 6.2 cm) free to rotate around a vertical axis of tapered steel that goes through it from bottom to top through the centre and ends on the inside with a brass cap at the top of the sphere.
Of the two hemispheres into which it is divided by a plane passing through the rotation axis, one is red and the other is white.
Two horizontal brass branches, approximately 90 degrees apart, protrude from the end of the glass insulating staff holding the axis and the celluloid sphere. These branches hold two vertical glass insulating columns. To these are fixed, by means of rotating hubs, two small cylindrical electrodes that terminate with two small brass spheres.
The two electrodes are pointed in the same direction, almost tangent to the equatorial circumference of the celluloid sphere, so that the small balls almost touch it.
The glass staff is fixed to the centre of a circular wooden base painted black (diameter 7.1 cm); the overall height of the instrument is 27.5 cm.