On the other hand, W. H. Eccles (_Electrician_, Vol. XLVII., pp. 682 and 715, 1901) has made experiments with Marconi nickel-silver sensitive tubes, using a liquid potentiometer made with copper sulphate, to apply the potential so that infinitesimal spark contacts might be avoided and the changes in potential made without any abruptness. He states that if the coherer tube is continuously tapped, say at the rate of fifty vibrations per second, whilst at the same time an increasing potential is applied to its terminals and the current passing through it measured on a galvanometer, there is no abrupt change in current at any point. He found that when the current and voltage were plotted against each other, a regular curve was obtained, which after a time becomes linear. A decided change occurs in the conductivity of the mass of metallic filings when treated in this manner at voltages lower than the critical voltage obtained by previous methods. He ascertained that there was a complete correspondence between the sensitiveness of the tubes used as telegraphic instruments and the form of the characteristic curve of current and voltage drawn by the above-described method. In the same manner, K. E. Guthe and A. Trowbridge (_Physical Review_, Vol. II., p. 22, 1900) investigated the action of a simple ball coherer formed of half a dozen steel, lead or phosphor-bronze balls in slight contact. They measured the current _i_ passing through the series under the action of a difference of potential _v_ between the ends, and found a relation which could be expressed in the form v = V(1 - e^{ki}), where V and _k_ are constants. The current through this ball coherer is, therefore, a logarithmic function of the potential difference between its ends, of the form i = log(v - V) and exhibits no discontinuity. The inference was drawn that the "resistance" is due to films of water adhering to the metallic particles through which electrolytic action occurs. A good metallic filings tube for use as a receiver in Hertzian wave telegraphy should exhibit a constancy of action and should cohere and decohere, to use the common terms, sharply, at the smallest possible tap. It should not have a current passed through it by the external cell of more than a fraction of a milliampere, or else it becomes wounded and unsensitive.