HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 125

which the impedance of a coil was not affected by the presenceof a core consisting of a bundle of very thin well annealed andvarnished iron wires.

Experiments with a telephone, a conductor in a strong mag-netic field, or with a condenser or arc, seem to afford certainproof that sonuds far above the usually accepted limit of hearingwould he perceived if produced with sufficient power. The arcproduced by these currents possesses several interesting features.Usually it emits a note the pitch of which corresponds to twicethe frequency of the current, but if the frequency be sufficientlyhigh it becomes noiseless, the limit of audition being determinedprincipally by the linear dimensions of the arc. A curious fea-ture of the arc is its persistency, which is due partly to the in-ability of the gaseous column to cool and increase considerablyin resistance, as is the case with low frequencies, and partly tothe tendency of such a high frequency machine to maintain aconstant current.

In connection with these machines the condense)' affords a par-ticularly interesting study. Striking effects are produced bvproper adjustments of capacity and self-induction. It is easy toraise the electromotive force of the machine to many times theoriginal value by simply adjusting the capacity of a condense)'connected in the induced circuit. If the condenser be at somedistance from the machine, the difference of potential on theterminals of the latter may he only a small fraction of that onthe condenser.

But the most interesting experiences are gained who) the ten-sion of the currents from the machine is raised by means of aninduction coil. In consequence of the enormous rate of changeobtainable in the primary current, much higher potential differ-ences are obtained than with coils operated in the usual ways,and, owing to the high frequency, the secondary discharge pos-sesses many striking peculiarities. Both the electrodes behavegenerally alike, though it appears from some observations thatone current impulse preponderates over the other, as beforementioned.

The physiological effects of the high tension discharge arefound to be so small that the shock of the coil can he supportedwithout any inconvenience, except perhaps a small burn producedby the discharge upon approaching the hand to one of the ter-minals. The decidedly smaller physiological effects of these cur-