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INVENTIONS OF NIKOLA TESLA.

ber, glass, or any other insulating substance. This limits greatlythe output of the coil, but I will later show how I have been ableto overcome to a considerable extent this disadvantage in theordinary coil.

Besides the potential, the intensity of the streams depends onthe frequency; but if the coil be very large they show them-selves, no matter how low the frequencies used. For instance,in a very large coil of a resistance of 67,000 ohms, constructedby me some time ago, they appear with as low as 100 alternationsper second and less, the insulation of the secondary being J inchof ebonite. "When very intense they produce a noise similar tothat produced by the charging of a Holtz machine, but muchmore powerful, and they emit a strong smell of ozone. Thelower the frequency, the more apt they are to suddenly injurethe coil. With excessively high frequencies they may pass freely

Fie. 101

Fig. 102.

without producing any other effect than to heat the insulationslowly and uniformly.

The existence of these streams shows the importance of con-structing an expensive coil so as to permit of one’s seeingthrough the tube surrounding the primary, and the latter shouldbe easily exchangeable; or else the space between the primaryand secondary should be completely filled up with insulatingmaterial so as to exclude all air. The non-observance of thissimple rule in the construction of commercial coils is responsiblefor the destruction of many an expensive coil.

At the stage when the streaming discharge occurs, or withsomewhat higher frequencies, one may, by approaching the ter-minals quite nearly, and regulating properly the effect of capac-ity, produce a veritable spray of small silver-white sparks, or abunch of excessively thin silvery threads (Fig. 102) amidst apowerful brush—each spark or thread possibly corresponding