These researches were summed up in the journal _La Lumière Electrique_ for June 15, 1879. Recently, Mr. Pilleux has addressed to us some new experiments on the same subject, made on the voltaic arc produced by a De Meritens alternating current machine. Naturally, he has found the same phenomena that I had made known; but he thinks that these new researches are worthy of interest by reason of the nature of the arc in which he experimented, and which, according to him, is of a different nature from all those on which, up to the present time, experiments have been made. Such a distinction as this, however, merits a discussion.
With the induction spark, magnets have an action only on the aureola which accompanies the line of fire of the static discharge; and this aureola, being only a sort of sheath of heated air containing many particles of metal derived from the rheophores, represents exactly the voltaic arc.
Moreover, although the induced currents developed in the bobbin are alternately of opposite direction, the galvanometer shows that the currents that traverse the break are of the same direction, and that these are direct ones. The reversed currents are, then, arrested during their passage; and, in order to collect them, it becomes necessary to considerably diminish the gaseous pressure of the aeriform conductor interposed in the discharge; to increase its conductivity; or to open to the current a very resistant metallic derivation. By this latter means, I have succeeded in isolating, one from the other, in two different circuits, the direct induced currents and the reversed induced ones. As only direct currents can, in air at a normal pressure, traverse the break through which the induction spark passes, the aureola that surrounds it may be considered as being exactly in the same conditions as a voltaic arc, and, consequently, as representing an extensible conductor traversed by a current flowing in a definite direction. Such a conductor is consequently susceptible of being influenced by all the external reactions that can be exerted upon a current; only, by reason of its mobility, the conductor may possibly give way to the action exerted upon the current traversing it, and undergo deformations that are in relation with the laws of Ampère. It is in this manner that I have explained the different forms that the aureola of the induction spark assumes when it is submitted to the action of a magnet in the direction of its axial line, or in that of its equatorial line, or perpendicular to these latter, or upon the magnetic poles themselves.
