The Bakerian lecture. On certain motions produced in fluid conductors when transmitting the electric current

Abstract

In the first paragraphs of this lecture, Mr. Herschel describes the phenomena that result on placing a portion of mercury covered with sulphuric acid between the voltaic poles immersed on opposite sides of the globule of metal, but in contact with the acid only. They consist in active motion of those particles of the acid in contact with the mercury, while the superficial molecules of the metal continually radiate from the point nearest the negative pole, and darting to the positive pole return along the axis. The author particularly notices several singular appearances resulting from this current, and shows them to be independent of any electro-magnetic vortices, to which, at first sight, they present considerable analogy. They are incomparably more forcible, in proportion to the electric powers used, than the motions produced by the action of magnets; hence, they furnish an extremely sensible test of the development of feeble Voltaic powers not easily rendered sensible by other means. The author next describes the appearances observed in cases where other liquids and metals are used, and adverts to the influence of several causes upon the uniformity of the results. Among these, impurity in the mercury is especially noticed, which should not only be carefully distilled, but also well washed with dilute nitric acid. Mercury thus prepared, and placed in the current as before, exhibits phenomena varying with the nature of the liquid;—generally speaking, currents are produced radiating from the point nearest the negative pole, which are most violent in acids, and less in saline solutions, in proportion as the electro-positive energy of the base is greater. In many liquids a counter-current from the positive pole is observed; but if either pole be brought in contact with the mercury, no currents are observed from the point of contact, but strong ones are perceived to radiate from the other. If the negative pole touch it, it amalgamates with the mercury, which remains bright; if the positive, the mercury rapidly oxidizes; and in both cases currents are produced.