The law of variation of the electromotive force of polarisation with current-density has been very thoroughly investigated. It is found that it may be represented by an equation of the form

where x is the current-density, and a, b, c are constants. So for very feeble direct currents the reverse polarisation current is proportional to the current-density; but for strong currents it cannot be expressed by an algebraical formula as a function of the current-density in a finite series of terms. The above formula gives the maximum value of the polarisation current. So far as I know, no observations have been made regarding its variation with time from its commencement until the maximum is reached. This question is of interest chiefly from a theoretical point of view. The object of this note is to describe the result of some experiments made on this subject. Platinum electrodes, heated to redness before each experiment, were used.