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INVENTIONS OK NIKOLA TESLA.

rents are thought to he due either to a different distributionthrough the body or to the tissues acting as condensers. But inthe case of an induction coil with a great many turns the harmless-ness is principally due to the fact that but little energy is avail-able in the external circuit when the same is closed through theexperimenter’s body, on account of the great impedance of thecoil.

In varying the frequency and strenth of the currents throughthe primary of the coil, the character of the secondary dischargeis greatly varied, and no less than live distincts forms are ob-served :—A weak, sensitive thread discharge, a powerful flamingdischarge, and three forms of brush or streaming discharges.Each of these possesses certain noteworthy features, but the mostinteresting to study are the latter.

Under certain conditions the streams, which are presumablydue to the violent agitation of the air molecides, issue freelyfrom all points of the coil, even through a thick insulation. Ifthere is the smallest air space between the primary and secondary,they will form there and surely injure the coil by slowly warm-ing the insulation. As they form even with ordinary frequencieswhen the potential is excessive, the air-space must be most care-fully avoided. These high frequency streamers differ in aspectand properties from those produced by a static machine. Thewind produced by them is small and should altogether cease ifstill considerably higher frequencies could be obtained. A pe-culiarity is that they issue as freely from surfaces as from points.(hving to this, a metallic vane, mounted in one of the terminals ofthe coil so as to rotate freely, and having one of its sides coveredwith insulation, is spun rapidly around. Such a vane would notrotate with a steady potential, but with a high frequency coil itwill spin, even if it be entirely covered with insulation, providedthe insulation on one side be either thicker or of a higher specificinductive capacity. A Crookes electric radiometer is also spunaround when connected to one of the terminals of the coil, butonly at very high exhaustion or at ordinary pressures.

There is still another and more striking peculiarity of such ahigh frequency streamer, namely, it is hot. The heat is easilyperceptible with frequencies of about 10,000, even if the poten-tial is not excessively high. The heating effect is, of course, dueto the molecular impacts and collisions. Could the frequencyand potential he pushed far enough, then a brush could be pro-