SM016     Delezenne’s circle     circa 1950     Magnetism

Faraday discovered that terrestrial magnetism could develop induced currents in moving conductors.

Delezenne’s circle serves well to demonstrate this clearly.   The coil, consisting of a great length of wire can be rotated at varying inclinations with respect to the earth’s field.   The induced e.m.f. is converted into a direct current by means of a commutator and is sufficient to deflect a sensitive galvanometer such as an astatic needle when the coil is rotated steadily with the cranked handle.

By noting the maximum deflection on a sensitive galvanometer with the axes of the coil orientated so as to cut the earth’s field in a horizontal and a vertical plane, the angle of dip can be determined from the inverse tangent of the ratio of the results.