. The inventions : researches and writing of Nikola Tesla, with special reference to his work in polyphase currents and high potential lighting . OBTAINING DIRECT l^TtOM ALTERNATING CURRENT^. 413 set of secondaries be sliort-circuited, nearly all the current flowsthrough the corresponding primaries ; but the secondaries of theother branch being open-circuited, the self-induction in. theprimaries is highest, and hence little or no current ^vill passthrough that branch. If, as the current alternates, the second-aries of the two branches are alternately short-circuited, theresult will be that the
. The inventions : researches and writing of Nikola Tesla, with special reference to his work in polyphase currents and high potential lighting . OBTAINING DIRECT l^TtOM ALTERNATING CURRENT^. 413 set of secondaries be sliort-circuited, nearly all the current flowsthrough the corresponding primaries ; but the secondaries of theother branch being open-circuited, the self-induction in. theprimaries is highest, and hence little or no current ^vill passthrough that branch. If, as the current alternates, the second-aries of the two branches are alternately short-circuited, theresult will be that the currents of one sign pass over one branchand those of the op])osite sign over the other. The disadvan-tages of this arrangement, which would seem to result from theemployment of sliding contacts, are in reality very slight, inas-much as the electromotive force of the secondaries may be madeexceedingly low, so that sparking at the brushes is avoided. Fig. 223 is a diagram, partly in section, of another plan ofcarrying out the invention. The circuit b in this case is divided,as before, and each branch includes the coils of both tlie fields. Fig. 223. and revolving armatures of two induction devices. The arma-tures o p are preferably mounted on tJie same sliaft, and are ad-justed relatively to one another in such manner that w hen thrself-induction in one branch, as c, is maximum, in tlie other branchoit is minimum. Tlic armatures are rotated in synchronism withthe alternations from the source a. The winding or positionof the armature coils is such that a current in a givi-n dirtctionpassed through both armatures wouhl estai>lisli in one, poKs simi-lar to those in the adjacent poles of the tiehl, and in tlie titiier,poles unlike the adjacent Held poles, as indicated by // // .v .v intlie diagram. If the like poles are ])resentid, as shown in cir-cuit I), the eondilion is that ofaehtsed sicondary up(»n a j>rimarv,or the position of least indnetivi resistance; hence ii given
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