At the suggestion of Professor P. G. Tait, I undertook the further investigation of an experiment, an account of which he communicated to this Society on Monday, the 15th of April 1878.

In this experiment a platinum plate of moderate thickness is inserted between the electrodes of an electrolytic cell, so as to completely fill the cross-section. This platinum plate thus becomes the common electrode of two cells, and on perforating it it is found that a comparatively small hole at once changes its functions to that of an obstacle in one cell.