In short, we have here a transparent box (impermeable to photogenic rays) into which electricity may be led by means of four conductors that are arranged two by two in a line with each other, or in perpendicular positions, and that may be made to approach or recede from one another by maneuvering them from the exterior. This very simple arrangement answers every requirement, and, upon placing a sensitized plate in the vicinity of the conductors, permits of photographing the electric discharge directly and, so to speak, before the eyes of the operator. As a source of electricity, use is made of a bichromate of potash battery of 6 elements, capable of giving 10 volts and 15 amperes. The current from this battery is converted into a current of high tension by means of a strong induction coil capable of giving sparks more than eight inches in length. The discharge shown in Fig. 4 was obtained by means of a Holtz machine. Each experiment lasted less than a second. [Illustration: FIG. 3.] Figs. 2 and 3 represent the efflux that occurred under; the following conditions: The disk, P, was of metal, and was connected with the negative pole of the induction coil; and upon it was laid the photographic plate with the sensitized film downward, and consequently touching the disk. This is what produced the opaque circle in the center. Then the photographic plate was entirely covered with a thin ebonite plate, above which there was a second one supported by small wedges, so as to allow air to circulate between them. Finally, upon this second ebonite plate there was placed another photographic plate, with its sensitized film upward and directly in contact with an upper metallic disk, and connected with the positive pole of the coil by the conductor, L. An inspection of Figs. 2 and 3 shows that the, efflux does not possess the same form at the two poles. We remark at the positive pole a quite wide opaque circle surrounded by a sort of aureola composed of an infinite number of very delicate rays, while at the negative pole the aureola seems not to have been able to spread. We see, moreover, the same phenomenon in examining Fig. 4 (which represents the efflux obtained by means of a Holtz machine), but this time in a horizontal direction. The photographic plate was here placed upon the non-conducting disk, P. As the sensitized film was upward, it was put in contact with the balls at the extremity of the conductors, H and N. [Illustration: FIG. 4.] It will be seen here again that the efflux spreads out widely at the positive pole, while it is contracted at the other. The conducting balls were spaced 0.04 inch apart. A spark leaped from one to the other at the moment the current was being interrupted.