640 Mr. Nikola Tesla [Feb. 4, 



high frequency streamer, namely, it is hot. The heat is easily per- 

 ceptible with frequencies of about 10,000. even if the potential is 

 not excessively high. The heating effect is, of course, due to the 

 molecular impacts and collisions. Could the frequency and potential 

 be pushed far enough, then a brush could be produced resembling 

 in every particular a flame and giving light and heat, yet without a 

 chemical process taking place. 



The hot brush, when properly produced, resembles a jet of burn- 

 ing gas escaping under great pressure, and it emits an extraordinary 

 strong smell of ozone. The great ozonising action is ascribed to 

 the fact that the agitation of the molecules of the air is more 

 violent in such a brush than in the ordinary streamer of a static 

 machine. 



But the most powerful brush discharges were produced by em- 

 ploying currents of much higher frequencies than it was possible to 

 obtain by means of the alternators. These currents were obtained 

 by disruptively discharging a condenser and setting up oscillations. 

 In this manner currents of a frequency of several hundred thousand 

 were obtained. 



Currents of this kind produce striking effects. At these fre- 

 quencies, the impedance of a copper bar is so great that a potential 

 difference of several hundred volts can be maintained between two 

 points of a short and thick bar, and it is possible to keep an ordinary 

 incandescent lamp burning at full candle power by attaching the 

 terminals of the lamp to two points of the bar no more than a few 

 inches apart. When the frequency is extremely high, nodes are 

 found to exist on such a bar, and it is easy to locate them by means 

 of a lamp. 



By converting the high tension discharges of a low frequency 

 coil in this manner, it was found practicable to keep a few lamps 

 burning on the ordinary circuit in the laboratory, and by bringing 

 the undulation to a low pitch, it was possible to [operate small 

 motors. 



This plan likewise allows of converting high tension discharges 

 of one direction in low tension unidirectional currents, by adjusting 

 the circuit so that there are no oscillations. In passing the oscil- 

 lating discharges through the jirimary of a specially constructed coil, 

 it is easy to obtain enormous potential differences with only few 

 turns of the secondary. 



Great difficulties were at the beginning experienced in producing 

 a successful 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 heavily 

 covered with gutta-percha and wound in oil, or the air was pumped 

 out by means of a Sprenj^el pumj). 



The general arrangement was the following : — An ordinary 

 induction coil, operated from a low frequency alternator, was used to 

 charge Leyden jars. Tlie jars were made to discharge over a single 



