3. Note on the Behaviour of Iron Filings, strewn on a vibrating plate, and exposed to the action of a magnetic pole

Extract

While a horizontal plate is in a state of rapid vibration (as in Chladni's experiments), iron filings strewed on the surface, near a point of maximum vibration, are prevented from being scattered to the nodal lines by a magnetic pole held above the plate, but, if the pole be held below, they are speedily dissipated. If too powerful a pole be used, or if the magnet be held too near the plate, the filings nearest to the pole are not dispersed in the latter case.