72

INVENTIONS OF NIKOLA TESLA.

heretofore employed a practical difference of magnetic phasemay readily be secured.

Fig. 58 is a view of a motor, partly in section, with a dia-gram illustrating the invention. Fig. 59 is a similar view of amodification of the same.

In Fig. 58, which exhibits the simplest form of the invention,a a is the field-magnet of a motor, having, say, eight poles orinwardly-projecting cores b and c. The cores b form one set ofmagnets and are energized by coils d. The cores c, formingthe other set are energized by coils e, and the coils areconnected, preferably, in series with one another, in two de-rived or branched circuits, f g, respectively, from a suitablesource of current. Each coil e is surrounded by a magneticshield h, which is preferably composed of an annealed, insulated,

Fro. 59.

Fro. 58.

or oxidized iron wire wrapped or wound on the coils in the man-ner indicated so as to form a closed magnetic circuit around thecoils and between the same and the magnetic cores c. Be-tween the pole pieces or cores b c is mounted the armature k,which, as is usual in this type of machines, is wound with coilsr, closed upon themselves. The operation resulting from thisdisposition is as follows: If a current impulse be directedthrough the two circuits of the motor, it will quickly energizethe cores b, but not so the cores c, for the reason that inpassing through the coils e there is encountered the influenceof the closed magnetic circuits formed by the shields h. Thefirst effect is to retard effectively the current impulse in circuitg, while at the same time the proportion of current which doespass does not magnetize the cores c, which are shielded or