Ill Gil FREQUENCY AND HIGH POTENTIAL CURRENTS. 305

The rushes of current may be of the same direction under theconditions before assumed, but most generally there is an oscilla-tion superimposed upon the fundamental vibration of the current.When the conditions are so determined that there are no oscilla-tions, the current impulses are unidirectional and thus a means isprovided of transforming a continuous current of high tension,into a direct current of lower tension, which I think may findemployment in the arts.

This method of conversion is exceedingly interesting and Iwas much impressed by its beauty when I first conceived it. It isideal in certain respects. It involves the employment of no me-chanical devices of any kind, and it allows of obtaining currentsof any desired frequency from an ordinary circuit, direct or al-ternating. The frequency of the fundamental discharges depend-ing on the relative rates of supply and dissipation can be readilyvaried within wide limits, by simple adjustments of these quanti-ties, and the frequency of the superimposed vibration by thedetermination of the capacity, self-induction and resistance of thecircuit. The potential of the currents, again, may be raised ashigh as any insulation is capable of withstanding safely by com-bining capacity and self-induction or by induction in a secondary,which need have hut comparatively few turns.

As the conditions are often such that the intermittence or os-cillation does not readily establish itself, especially when a directcurrent source is employed, it is of advantage to associate an in-terrupter with the arc, as I have, some time ago, indicated theuse of an air-blast or magnet, or other such device readily athand. The magnet is employed with special advantage in theconversion of direct currents, as it is then very effective. If theprimary source is an alternate current generator, it is desirable,as I have stated on another occasion, that the frequency shouldbe low, and that the current forming the arc be large, in orderto render the magnet more effective.

A form of such discharger with a magnet which has beenfound convenient, and adopted after some trials, in the conversionof direct currents particularly, is illustrated in Fig. 166. n s arethe pole pieces of a very strong magnet which is excited by a coilc. The pole pieces are slotted for adjustment and can be fastenedin any position by screws s The discharge rods d d x , thinneddown on the ends in order to allow a closer approach of the mag-netic pole pieces, pass through the columns of brass b b^ and arefastened in position by screws s 2 s -z- Springs r and collars c c x