The instrument is composed of a toroidal electromagnet (internal diameter 8.4 cm, external diameter 12.6 cm) with a soft iron nucleus (diameter 1.5 cm) and is fixed to a circular wooden platform with lathed feet; it is protected by a sturdy glass bell (diameter 19 cm, height 13 cm) the edge of which fits into a groove in the wooden platform.
By placing the glass bell in such a way that its circular aperture corresponds to the polar expansions of the electromagnet, it is possible to place small samples of different materials between the poles to discover if they are paramagnetic or diamagnetic.