ticle is termed an "electron." This hypothesis, made long before Zeeman made his discovery, was found necessary to account for the facts of electrolysis. For the decomposition of an electrolyte by an electric current is most simply explained upon the hypothesis that it contains positively and negatively charged particles, and that the positively charged atoms go toward the negative pole, and the negatively charged toward the positive pole. They then give up their electricity, and this giving up of electricity constitutes an electric current. Hence this assumption, which is useful in explaining the Zeeman effect, is nothing new. It is known, also, that the vibrations of these particles, or of their electric charges, produce the disturbance in the ether which is propagated in the form of light waves; and that the period of any light wave corresponds to the period of vibration of the electric charge which produces it.
The most general form of path of such a vibrating electric charge would be an ellipse. Now, an elliptical vibration can always be resolved into a circular vibration and a plane one, so that any polarized ray may be resolved into a plane polarized ray and a circularly polarized ray. So all we need to consider are plane and circularly polarized rays. But we may suppose that a plane vibration is due to two oscillations in a circle, one going in a direction opposite to that of the hands of a watch, and the other in their direction. Hence, we need consider only circular vibrations. Now, if the electric charge is moving in a circle, it can be shown that when the plane of the circle is at right angles to the direction between the two poles of the magnet, the effect of the field would be to accelerate the motion when the rotation is, say, counter-clockwise, but to retard it when it is clockwise.
It was shown above that the position of a spectral line in the spectrum depends on the period of the light which produces it. Hence the position of the line will be altered
