338

INVENTIONS OF NIKOLA TESLA.

the terminals of the secondary s of an ordinary transformer, theprimary p of the latter being connected to an alternating distri-bution circuit or generator g of low or moderate frequency.The terminals of the secondary s are attached to a condenser cwhich discharges through an air gap d d which may be placedin series or shunt to the coil c x . When the conditions areproperly chosen the disc d rotates with considerable effort and theiron core i does not get very perceptibly hot. With currents froma high-frequency alternator, on the contrary, the core gets rapidlyhot and the disc rotates with a much smaller effort. To performthe experiment properly it should be first ascertained that thedisc d is not set in rotation when the discharge is not occurringat d d. It is preferable to use a large iron core and a condenserof large capacity so as to bring the superimposed quicker oscil-lation to a very low pitch or to do away with it entirely. Byobserving certain elementary rules I have also found it practi-cable to operate ordinary series or shunt direct-current motorswith such disruptive discharges, and this can be done with orwithout a return wire.

IMPEDANCE PHENOMENA.

Among the various current phenomena observed, perhaps themost interesting are those of impedance presented by conductorsto currents varying at a rapid rate. In my first paper before theAmerican Institute of Electrical Engineers, I have described afew striking observations of this kind. Thus I showed that whensuch currents or sudden discharges are passed through a thickmetal bar there may be points on the bar only a few inches apart,which have a sufficient potential difference between them tomaintain at bright incandescence an ordinary filament lamp. Ihave also described the curious behavior of rarefied gas surround-ing a conductor, due to such sudden rushes of current. Thesephenomena have since been more carefully studied and one ortwo novel experiments of this kind are deemed of sufficient in-terest to be described here.

Referring to Fig. 183a, b and b x are very stout copper barsconnected at their lower ends to plates c and c 1; respectively, of acondenser, the opposite plates of the latter being connected to theterminals of the secondary s of a high-tension transformer, theprimary r of which is supplied with alternating currents from anordinary low-frequency dynamo g or distribution circuit. The