The following research was commenced with the hope of being able to make an exact measuring instrument of a modified form which I had devised (see page 37) of the “Capillary Electroscope,” and to employ it for the determination of the different degrees of electromotive force of different metals in forming tables of electro-chemical series, with different electrolytic solutions. With this object in view, I constructed and tried a considerable number of forms of the instrument; and employed a number of liquids, acid, neutral, and alkaline, as conducting media between the mercurial electrodes. In every case, however, an obstacle to uniform and accurate measurement sooner or later arose, viz., unequal adhesion of the mercury to different parts of the capillary tube. It has been noticed by other investigators that the motion of the slender column of mercury in Lippmann’s “Capillary Electrometer” suddenly stops whilst under the electric influence, and this has been supposed to increase the value of the instrument by rendering its indications sensibly instantaneous. According to Lippmann also when the circuit was closed by a metallic conductor, “all irregularities at once disappeared” (“Phil. Mag.,” April, 1874, p. 284). This sudden stoppage of the mercury, however, whilst under the influence of the current is, I believe, in every case due to a sudden increase of mechanical resistance, usually caused by unequal adhesion of the mercury to different parts of the tube, but sometimes by a minute trace of solid substance in the tube. With a very feeble current this adhesion shows itself in several ways, usually by a more or less sudden retardation or stoppage of the motion of the mercurial column, by a delay in its commencement of motion, or by its non-movement. The current I have employed has, in nearly all cases, been a very feeble one, obtained from two wires, one of copper, and the other of platinum, each about 1 millim. diameter, immersed about 2 or 3 millims. deep in common drinking water. With a very sensitive instrument, and a capillary tube as free from obstruction as could be obtained, this power has been sufficient to move the meniscus 10 or 20 millims.