. The inventions : researches and writing of Nikola Tesla, with special reference to his work in polyphase currents and high potential lighting . y with w liich such a machine may bi made toexcite itself is striking, but this may be «lue—besides to the ab-sence of armature reaction—to the perfect smoothness of the cur-rcTit and luni-existence of self-induction. UNIPOLAR GENERATORS. 469 If tlie poles do not cover the disc completely on both sides,then, of course, unless the disc ])e pro])erly subdivided, themachine will be very inefficient. Again, in this case there arepoints worthv of notice.
. The inventions : researches and writing of Nikola Tesla, with special reference to his work in polyphase currents and high potential lighting . y with w liich such a machine may bi made toexcite itself is striking, but this may be «lue—besides to the ab-sence of armature reaction—to the perfect smoothness of the cur-rcTit and luni-existence of self-induction. UNIPOLAR GENERATORS. 469 If tlie poles do not cover the disc completely on both sides,then, of course, unless the disc ])e pro])erly subdivided, themachine will be very inefficient. Again, in this case there arepoints worthv of notice. If the disc be rotated and the fieldcurrent interrupted, tlie current through the armature will con-tinue to fl(jw and the field magnets will lose their strengtli com-paratively slowly. The reason for this will at once appear whenwe consider the direction of the currents set up in the disc. Referring to the diagram Fig. 292, d represents the disc withthe sliding contacts b b on the shaft and periphery, n and srepresent tlie two poles of a magnet. If the jiole x be above, asindicated in the diagram, the disc being supposed to be in the. Fig. 293. plane of the ])a[>er, niid rotating in the directinn of the arrow d,the curient set up in the disc will flow from the centre to thel)eripherv, as indicated \)\ the arrow a. Since the magnetic ac-tion is more or less confined to tlie s[)ace between the poks n s,the other portions of tlie disc may be consideretl inactivt. Thecurrent set up will therefore not wholly pass through thei-Mernalinrcnit k, but will close thiHtugh the disc itself, and generally, ifthe disposition be in any way similar to the one illustratiorti<tn of the current genirated will not appi-ar i-vternally, as the circuit v is pi-aetically shd bv the dotted 470 INVENTIONS OF NIKOLA TKSLA. lines and arrows /// and // ; and tlie direction of the energizingfield current being indicated l)y tlie arrows a b c d, an inspection of
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