Page:Collected Physical Papers.djvu/311

Fig. 75. Successive modifications of the "straight wire" ending in "cell form." (b) shows how the ends of A and B of the wire may be vibrated by ebonite clip-holders, H and H′. When A is excited, current of response in the wire, normally speaking, is from the unexcited B to the excited A. The stimulated wire becomes zincoid. Note that though the current of response is constant in direction, the galvanometer deflection in (d) will be opposite in direction to (b). In (e) is shown one of the two graduated circles by which the amplitude of vibration is measured.