Maxima of the first kind involve streaming that arises from inequalities of the surface tension at different parts of the mercury drop. These inequalities arise from differences in the local interfacial potential and the latter arise from a non-uniform current-distribution.
It is pointed out that the requisite differences in interfacial potential can arise only in the region of the rising part of the polarographic step, and only if the concentration of depolarizer exceeds some particular lower value. Thus, one expects quite narrow streaming maxima: contrary to previous ideas, it is negative maxima that are "normal" and positive ones that are anomalous. Positive maxima cover a wider range of potentials because the flux of depolarizer, induced by the streaming, prevents concentration polarization at the neck of the drop.
Experiments with fine-tipped capillaries, designed to decrease the non-uniform current-distribqtion. have been inconclusive because the measured currents were at least partly controlled by the resistance and not solely by the extent of shielding.