CHAP. VIII. FARADAY'S EXPERIMENTS. in
the poles of a battery and immersed in the solution. It was supposed that the oppositely charged constituents of the nearest salt molecules were attracted by the electrodes — for instance, in a solution of potassium chloride the chlorine was attracted by the positive pole and the potassium by the negative pole.
It was assumed that the electrical, decomposing force was only active near the poles, and that it decreased greatly with increasing distance from the poles, just as was assumed in the case of all forces which were regarded as actions at a distance.
Faraday, who strongly opposed the conception of action at a distance, showed in the following simple way that the electrical (electromotive) force is the same at all points of a paral- lel-sided trough through which a current is passing. By means of the wires C and D the poles of the battery B are connected with two poles immersed in a salt solution contained in the trough T. While
the current is passing through the solution two strips of platinum, P and A, which are kept at a fixed distance apart, are dipped into the solution. These strips are connected by the wires r and s. with a galvanometer, G, The galva- nometer shows a deflection indicating that a current is passing in the direction from P to Pi through G, and this current may be regarded as a branch of the main current passing through the trough T, It is found that the galvanometer-needle shows the same deflection at whatever point between the poles the strips P and Pi are placed, so long as a line joining these is parallel with the sides of the trough. This proves that the electromotive force between P and Pi, which causes the current through G, is the same at all points, and independent of the distance from the poles. Theoretically the experiment is simplest when the solution used is one of zinc sulphate, and the 4- and — electrodes as well as P and Pi consist of amalgamated zinc, because,
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