HIGH FUEQ UENGY AND HIGH POTENTIAL GUBEEN7K 127

duced resembling in every particular a flame and giving lightand heat, yet without a chemical process taking place.

The hot brush, when properly produced, resembles a jet ofburning gas escaping under great, pressure, and it emits an extra-ordinary strong smell of ozone. The great ozonizing action isascribed to the fact that the agitation of the molecules of the airis more violent in such a brush than in the ordinary streamer ofa static machine. But the most powerful brush discharges wereproduced by employing currents of much higher frequencies thanit was possible to obtain by means of the alternators. Thesecurrents were obtained by disruptively discharging a condenserand setting up oscillations. In this manner currents of a fre-quency of several hundred thousand were obtained.

Currents of this kind, Mr. Tesla pointed out, produce strikingeffects. At these frequencies, the impedance of a copper bar isso great that a potential difference of several hundred volts canbe maintained between two points of a short and thick bar, andit is possible to keep an ordinary incandescent lamp burning atfull candle power by attaching the terminals of the lamp to twopoints of the bar no more than a few inches apart. When thefrequency is extremely high, nodes are found to exist on such abar, and it is easy to locate them by means of a lamp.

By converting the high tension discharges of a low frequencycoil in this manner, it was found practicable to keep a few lampsburning on the ordinary circuit in the laboratory, and by bring-ing the undulation to a low pitch, it was possible to operate smallmotors.

This plan likewise allows of converting high tension dischargesof one direction into low tension unidirectional currents, by ad-justing the circuit so that there are no oscillations. In passingthe oscillating discharges through the primary of a speciallyconstructed coil, it is easy to obtain enormous potential differenceswith only few turns of the secondary.

Great difficulties were at first experienced in producing a suc-cessful coil on this plan. It was found necessary to keep all air,or gaseous matter in general, away from the charged surfaces,and oil immersion was resorted to. The wires used were heavilycovered with gutta-percha and wound in oil, or the air was pumpedout by means of a Sprengel pump. The general arrangementwas the following:—An ordinary induction coil, operated froma low frequency alternator, was used to charge Leyden jars. The