High accuracy of measurement in the electrolytic tank can be achieved by a suitable ratio of impedance as between tank and measuring circuit. With this requirement fulfilled, the axial distribution of the symmetrical lens was explored and found to satisfy a relation Vz=V0+Ae−bz(2), where V0 is the potential of the outers with respect to the middle electrode, `z,' the distance from the center of the lens, while A and b are constants from any one geometry. The effect of varying the separation between the elements was specially investigated. It was found that the maximum value of the gradient between electrodes increases as the separation between them increases, reaches a flat maximum between 0.8 and 0.4 D (D, bore diameter) and then decreases with further increase in spacing. This means that a decrease in separation produces a weaker field and an increased focal length. The potential at the saddle point is very sensitive to changes in separation in the region up to about 0.5 D; it was also found to vary linearly with bore up to 3 D. The relaxation method of field plotting was also applied to map the distribution; the results are compared with those given by the tank.