IN YENTIONS OF NIKOLA TESLA.

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rotation of the pulley. Experiments were also carried on witliliquids of different insulating power with the view of reducingthe loss in the arc. When an insulating liquid is moderatelywarmed, the loss in the arc is diminished.

A point of some importance was noted in experiments withvarious discharges of this kind. It was found, for instance, thatwhereas the conditions maintained in these forms were favorablefor the production of a great spark length, the current so ob-tained was not best suited to the production of light effects. Ex-perience undoubtedly has shown, that for such purposes a har-monic rise and fall of the potential is preferable. Be it that asolid is rendered incandescent, or phosphorescent, or be it that en-ergy is transmitted by condenser coating through the glass, it isquite certain that a harmonically rising and falling potential pro-duces less destructive action, and that the vacuum is more per-manently maintained. This would be easily explained if it wereascertained that the process going on in an exhausted vessel is ofan electrolytic nature.

In the diagrammatical sketch, Fig. 165, which has been alreadyreferred to, the cases which are most likely to be met with inpractice are illustrated. One has at his disposal either direct oralternating currents from a supply station. It is convenient foran experimenter in an isolated laboratory to employ a machine o,such as illustrated, capable of giving both kinds of currents. Insuch case it is also preferable to use a machine with multiplecircuits, as in many experiments it is useful and convenient tohave at one’s disposal currents of different phases. In thesketch, d represents tlie direct and a the alternating circuit. ,Ineach of these, three branch circuits are shown, all of which areprovided with double line switches s s s s s s. Consider first thedirect current conversion; i a represents the simplest case. Ifthe e. m. f. of the generator is sufficient to break through a smallair space, at least when the latter is warmed or otherwise rend-ered poorly insulating, there is no difficulty in maintaining avibration with fair economy by judicious adjustment of thecapacity, self-induction and resistance of the circuit l containingthe devices 11 m. The magnet jst, s, can be in this case advan-tageously combined with the air space. The discharger d d withthe magnet may be placed either way, as indicated by the full orby the dotted lines. The circuit i a with the connections and de-vices is supposed to possess dimensions such as are suitable for