Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/471

 performed in a plane at right angles to the magnetic field. In order to determine the nature of these two principal oscillations, we observe that it is possible for the electron to describe a circular orbit in this plane, if the radius of the orbit be suitably chosen; for in a circular motion the forces and $$e[\mathbf{\dot r .K}]$$ would be directed towards the centre of the circle; and it would therefore be necessary only to adjust the radius so that these furnish the exact amount of centripetal force required. Such a motion, being periodic, would be a principal oscillation. Moreover, since the force $$e[\mathbf{\dot r .K}]$$ changes sign when the sense of the movement in the circle is reversed, it is evident that there are two such circular orbits, corresponding to the two senses in which the electron may circulate; these must, therefore, be no other than the two principal oscillations of frequencies. When the light received in the spectroscope is that which has been emitted in a direction at right angles to the external magnetic field, the circles are seen edgewise, and the light appears polarized in a plane parallel to the field; but when the light examined is that which has been emitted in a direction parallel to the external magnetic force, the radiations of frequencies are seen to be circularly polarized in opposite senses. All these theoretical .conclusions have been verified by observation.

It was found by Cornu and by C. G. W. König that the more refrangible component (i.e., the one whose period is shorter than that of the original radiation) has its circular vibration in the same sense as the current in the electromagnet. From this. it may be inferred that the vibration must be due to a resinously charged electron; for let the magnetizing current and the electron be supposed to circulate round the axis of z in the direction in which a right-handed screw must turn in order to progress along the positive direction of the axis of ; then the magnetic force is directed positively along the axis of, and, in order that the force on the electron may be directed