Page:Collected Physical Papers.djvu/217

Rh chemical activity of the substance, for the electromotive variation in the relatively inactive tin is greater than that of zinc. The electrolyte used in the following experiments is common tap-water, but similar effects are also obtained with distilled water.

It was said that the acted wire, usually speaking, becomes zincoid. This is not universally the case, for there are substances which become cuproid under mechanical stimulation. I have previously said that electric radiation produces opposite effects on different substances; silver is often found to show an effect (increase of resistance) opposite to that of generality of metals. It is very curious that silver is also often found to exhibit an opposite electromotive effect under mechanical stimulation, that is to say, the acted wire becomes C.

As long as the wire is not overstrained there is always a recovery. Observe the character of recovery in the curve for Zn when the twisting was stopped. It will be noticed that the recovery is very rapid at first, but slow in the later part, and that the recovery is complete.

In the case of electric radiation or light, the impulses are of a vibrational nature, unlike the uni-directioned mechanical twists used in the above experiments. To make the two sets of phenomena comparable, we should have the mechanical disturbance of a vibrational nature also. I therefore next tried to see what the effect would be by reversing the direction of the twist, and found that the induced electromotive force is independent of the direction of twist, that is to say the electromotive