Note:  Do not rely on this information. It is very old.

Foucault Currents

Foucault Currents, in Electricity, are eddy currents set up in the iron cores of armatures, etc., which are useless in increasing the available current for the external circuit, and which may damage the insulation of the parts of the structure by heating up the metal. They may be reduced by making the iron core in thin segments or discs, that shall not offer continuous mass of metal in the direction in which the eddy tends to flow, and yet shall be continuous in the direction of the lines of force that require to be conducted through the core. [Dynamo.]