Societies and Academies

Abstract

LONDON Physical Society, December 13.—Prof. Guthrie, President, in the chair.—The following communications were read:—On the effect of an electrical current on the rate of thinning of a liquid film, by Profs. A. W. Reinold, F.R.S., and A. W. Rücker, F.R.S., read by Prof. Reinold. In 1877 the authors communicated to the Royal Society an account of some experiments upon the electrical resistance of liquid films. The results then obtained showed that there was some disturbing influence present, and the authors now find this to be the action of the current upon the film itself. The films experimented on were, as in the original experiments, cylindrical and vertical, formed upon two coaxial platinum rings which are the electrodes by which an electric current can enter or leave the film. The mode of formation of these films and the precautions necessary to keep them from gaining or losing moisture by condensation or evaporation have been already described before the Royal Society (Phil. Trans., 1881, part 2). When such a film, just formed, is left to itself, it shows a set of colours of different orders arranged in horizontal bands; as it thins under the action of gravity, these bands gradually broaden out, and descend; a black band soon appears at the top, which likewise extends downwards. If a current is now passed downwards through the film, the motion of the colour-bands is accelerated, showing that the effect of the current is to assist gravity in thinning the film; the black band, however, becomes in part or entirely white. This upon examination is found to be due to the following action; the film is not directly dependent upon the upper ring, but is attached to it by a comparatively thick mass of liquid. The action of the current is to transfer liquid in its own direction, thus, like gravity, thinning the film; the mass of liquid, however, on which the film hangs, by this same action is forced down into the black portion, which consequently becomes white. If the current be passed upwards, the reverse effects occur: the downward motion of the bands is retarded, or, with a strong current, reversed. The explanation is precisely the same as before: the liquid is transferred along the film in the direction of the positive current; it sometimes collects in the form of pendent drops attached to the upper ring; these increase in size, and stream down the sides of the film. Prof. Reinold then formed a plane film between two horizontal wires; the film was illuminated by the lime-light, and its image projected upon a screen the motion of the bans of colour in the direction of the current produced by fifty Grove's cells was clearly shown.—In a discussion which followed upon the transference of matter with the current, Prof. Ayrton described some experiments recently made by Prof. Perry and himself, which showed that certain metals were carried through mercury in the direction of the current, Mr. Boys remarked upon the apparent inertia of the film; the current seemed to require time to develop its action, no motion of the colour-rings being visible for some seconds after making the current.—Dr. Stone exhibited a tuning-fork interrupter commutator. This is an instrument for reversing an electric current through a circuit a given number of times per second. From the free end of a spring, kept vibrating in unison with an electrically maintained fork, by an electromagnet in the circuit of the fork acting upon an iron armature attached to the spring, project two small aluminium plates, side by side, but insulated by ebonite from the spring and from each other. These are connected by fine wires, which do not interfere with the vibration of the spring, to screws upon the base of the instrument, to which the poles of a battery are joined. The motion of each plate is arrested upwards and downwards by aluminium-stops, so that there are four such stops arranged at the corners of a rectangle. They are connected in pairs diagonally, and each pair is in communication with one end of the external circuit. Thus, when the spring is up, the current flows to the aluminium plates, and is transmitted through the circuit in one direction; when the spring is down, it flows by the lower stops in the opposite direction. The electromotive force is thus reversed in the circuit twice as many times as the fork vibrates per second.—Mr. Lewis W right exhibited his new oxy hydrogen lantern microscope. Details of this instrument will shortly be published. Geological, medical, and biological specimens were exhibited upon the screen with great distinctness, the definition being singularly perfect under the highest powers.