POL YPIIA SE CURRENTS.

47

If tlie regulator be in its normal position, or that in which itsmagnetic circuit is most nearly closed, it delivers its maximuminduced current, the phases of which so correspond with those ofthe primary current that the motor will run as though both heldand armature were excited by the main current.

To vary the speed of the motor to any rate between the mini-mum and maximum rates, the core e and coils f are turned ineither direction to an extent which produces the desired result,for in its normal position the convolutions of coil f embrace themaximum number of lines of force, all of which act with thesame effect upon the coil; hence it will deliver its maximumcurrent; but by turning the coil f out of its position of maximumeffect the number of lines of force embraced by it is diminished.The inductive effect is therefore impaired, and the current de-livered by coil f will continue to diminish in proportion to theangle at which the coil f is turned until, after passing through

Fie. 36.

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an angle of ninety degrees, the convolutions of the coil will beat right angles to those of coils c c, and the inductive effect, re-duced to a minimum.

Incidentally to certain constructions, other causes may influ-ence the variation in the strength of the induced currents. Forexample, in the present case it will be observed that by the firstmovement of coil f a certain portion of its convolutions are carriedbeyond the line of the direct influence of the lines of force, andthat the magnetic path or circuit for the lines is impaired; hencethe inductive effect would be reduced.. Next, that after movingthrough a certain angle, which is obviously determined by therelative dimensions of the bobbin or coil f, diagonally oppositeportions of the coil will be simultaneously included in the field,but in such positions that the lines which produce a current-impulse in one portion of the coil in a certain direction will pro-