. The London, Edinburgh and Dublin philosophical magazine and journal of science . element As is in rota-tion at a distance r round a magnetic pole of which the inten-sity is equal to that of the exterior of the magnet, and isconsequently 27r^M. 5. It is easy to explain in an elementary way why, whenthe element is outside of the external layer, the inductionbecomes so feeble in comparison with that produced when theelement is situated in the axis of the ring. Let the circle dpfmg (fig. 5)represent the horizontal plane inwhich one of the poles of the ver-tical magnet is situated, and let ussupp
. The London, Edinburgh and Dublin philosophical magazine and journal of science . element As is in rota-tion at a distance r round a magnetic pole of which the inten-sity is equal to that of the exterior of the magnet, and isconsequently 27r^M. 5. It is easy to explain in an elementary way why, whenthe element is outside of the external layer, the inductionbecomes so feeble in comparison with that produced when theelement is situated in the axis of the ring. Let the circle dpfmg (fig. 5)represent the horizontal plane inwhich one of the poles of the ver-tical magnet is situated, and let ussuppose that the element As at restis placed at the point a. The magnetis in rotation in the direction indi-cated by the arrow. An elementarymagnet at m moves then in the di-rection mk, and the angle which thisdirection of motion makes with theline of junction between m and a(the angle /3 of the formula 6) is aright angle. When the elementarymagnet reaches g the angle in ques-tion is acute, and it becomes zero atd, from which point a line drawn toa is a tangent to the circle. Sin 8. of Unipolar Induction. 419 consequently changes its sign at d, and it retains this changeof sign until it comes to/. It follows from this that the ele-mentary magnets upon the arc dpf produce an, induction ofopposite sense to those upon the arc fmgd. If these con-trary inductions become of equal value, no induction will beproduced in the element of circuit at rest As. It is moreoverclear that if the element As were situated at a vertical dis-tance H above or below the horizontal plane in question, theinduction would change its sign when the elementary magnetpassed the points d and/. If, on the contrary, the elementof the circuit is situated at the centre o of the circle, the in-ductions of all the elementary magnets would act in the samedirection, and the result would consequently be equal to theirarithmetical sum. 6. In the preceding explanation we have taken into consi-deration only the induction of t
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