The apparatus includes a clear Petri dish 90mm dia. x 12mm depth. The transparent base (140 x 125mm) allows the pattern to be projected via an overhead projector system. Alongside each terminal is a thumbscrew system which permits fine adjustment of the electrodes. Six electrodes are supplied, 2 'point source', 2 'line source' and 2 circular rings of 35 and 70mm dia. The apparatus requires a safe, low current limited 0-5kV EHT supply