Each time the arc is broken between A and B the jars are quickly charged and discharged through the primary pp, producing a snapping spark between the knobs KK. Upon the arc forming between A and B the potential falls, and the jars cannot be charged to such high potential as to break through the air gap ab until the arc is again broken by the draught. In this manner sudden impulses, at long intervals, are produced in the primary pp, which in the secondary s give a corresponding number of impulses of great intensity. If the secondary knobs or spheres, KK, are of the proper size, the sparks show much resemblance to those of a Holtz machine. But these two effects, which to the eye appear so very different, are only two of the many discharge phenomena. We only need to change the conditions of the test, and again we make other observations of interest. When, instead of operating the induction coil as in the last two experiments, we operate it from a high frequency alternator, as in the next experiment, a systematic study of the phenomena is rendered much more easy. In such case, in varying the strength and frequency of the currents through the primary, we may observe five distinct forms of discharge, which I have described in my former paper on the subject[A] before the American Institute of Electrical Engineers, May 20, 1891. [Footnote A: See THE ELECTRICAL WORLD, July 11, 1891.] It would take too much time, and it would lead us too far from the subject presented this evening, to reproduce all these forms, but it seems to me desirable to show you one of them. It is a brush discharge, which is interesting in more than one respect. Viewed from a near position it resembles much a jet of gas escaping under great pressure. We know that the phenomenon is due to the agitation of the molecules near the terminal, and we anticipate that some heat must be developed by the impact of the molecules against the terminal or against each other. Indeed, we find that the brush is hot, and only a little thought leads us to the conclusion that, could we but reach sufficiently high frequencies, we could produce a brush which would give intense light and heat, and which would resemble in every particular an ordinary flame, save, perhaps, that both phenomena might not be due to the same agent--save, perhaps, that chemical affinity might not be _electrical_ in its nature.