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THE ELECTRIC DISCHARGE AND SPARK PHOTOGRAPHED DIRECTLY WITHOUT AN OBJECTIVE.

The study of the form and color that electric discharges exhibit, according to the different ways in which they are produced, has already enticed a certain number of amateurs and scientists.  Every one knows the remarkable researches of the lamented Th.  Du Moncel on the induction spark, and during the course of which he, in 1853, discovered that phenomenon of the electric efflux which has since been the object of important researches on the part of several physicists and chemists, among whom must be cited Messrs. Thenard, Hautefeuille, and Chapuis.  Twenty years ago, Mr. Bertin, who was then Professor at the Faculty of Strassburg, and who was afterward subdirector of the normal school, was directing his researches upon the electric discharges produced by high tension apparatus, plate machines, and Leyden jars.  He thought, with reason, that, on account of its rapidity and complexity, a portion of the phenomenon must escape the eye of the observer, and so the idea occurred to him to photograph the discharge in order to afterward study its forms more at his leisure.  We have recently had an opportunity of seeing a negative which was obtained by him at that epoch; but the photographic processes then in use probably did not allow him to obtain others that were as satisfactory, and he had given up this kind of study, when, last year, he had an opportunity of speaking of it to the well known manufacturer Mr. F. Ducretet, whom he induced to take it up and employ the new gelatino-bromide process.  Unfortunately, he died before these experiments were begun, and was unable to see the realization of his project.  Mr. Ducretet did not abandon the idea, but constructed the necessary apparatus, and obtained the results that we now place before our readers.

[Illustration:  FIG 1.]

His apparatus, which contains no photographic objective, consists of an oblong case, ABCD, made of red glass and resting upon an ebonite table supported by one leg (Fig. 1).  In the top of the case, as well as in the two sides, AD and BC, are apertures that are closed by ebonite cylinders through which slide, with slight friction, copper rods, HLN.  In the leg of the table there is a copper rack which may be maneuvered from the interior by a pinion, and which communicates electrically with a terminal, E. The upper part of this rack, which enters the glass case, is threaded, so that there may be affixed to it either a metallic or an insulating disk.  The rods, HLN, are likewise threaded, so that there may be affixed to their internal extremities balls, points, combs, and disks of metal or of insulating material at will.

[Illustration:  FIG 2.]

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.