466

INVENTIONS OF NIKOLA TESLA.

manner of pulleys, and are connected together by flexible con-ducting bands or belts.

The machine is built in such manner that the direction ofmagnetism or order of the poles in one field of force is oppositeto that in the other, so that rotation of the discs in the same di-rection develops a current in one from centre to circumferenceand in the other from circumference to centre. Contacts appliedtherefore to the shafts upon which the discs are mounted formthe terminals of a circuit the electro-motive force in which is thesum of the electro-motive forces of the two dises.

It will be obvious that if the direction of magnetism in both

Fig. 390.

Fig. 391.

fields be the same, the same result as above will be obtained bydriving the discs in opposite directions and crossing the connect-ing belts. In this way the difficulty of securing and maintaininggood contact with the peripheries of the discs is avoided and acheap and durable machine made which is useful for many pur-poses—such as for an exciter for alternating current generators,for a motor, and for any other purpose for which dynamo ma-chines are used.

Fig. 290 is a side view, partly in section, of this machine.Fig. 291 is a vertical section of the same at right angles to theshafts.