OBTAINING DIRECT FROM ALTERNATING CURRENTS. 417

An alternating and a direct current have been combined so thatthe waves of one direction or sign were partially or wholly over-come by the direct current; but by this plan only one set of al-ternations are utilized, whereas by the system just described theentire current is rendered available. By obvious applications ofthis discovery Mr. Tesla is enabled to produce a self-exciting al-ternating dynamo, or to operate direct current meters on alter-nating-current circuits or to run various devices—such as arc lamps—by direct currents in the same circuit with incandescent lampsor other devices operated by alternating currents.

It will be observed that if an intermittent counter or opposingforce be developed in the branches of the circuit and of higherelectromotive force than that of the generator, an alternatingcurrent will result in each branch, with the waves of one signpreponderating, while a constantly or uniformly acting oppo-sition in the branches of higher electromotive force than thegenerator would produce a pulsating current, which conditionswould be, under some circumstances, the equivalent of those de-scribed.