portion of the curve is a repetition of the curve No. 6, and how the substance arrives at the second fatigued state b′. To observe the
Fig. 8.—Curve showing the Effect of Heat and Mechanical Vibration on a fatigued Iron-filings Receiver.
effect of mechanical disturbance a gentle tap was given to the receiver, and at once there was produced an increase of resistance due to the transformation of B into A, the receiver regaining its sensitiveness by the transformation. The action of radiation was continued, and after a few reversals the substance once more arrived at the third fatigued state, b′′. The process described above could be repeated any number of times.
Effect of Heat and and Mechanical Disturbance on a Negative Fatigued Substance.
Experiments similar to the above were carried out with an arsenic receiver. From the curve given below (fig. 9) it is seen that the reaction of the negative substance is in every respect opposite to that of a positive substance. It will be noticed that the same cause—i.e., heating or tapping—produces, as necessary consequences of the hypotheses previously stated, two opposite reactions in the two classes of substance. I have been able to verify this deduction by observations with nearly a dozen different substances, and have not, so far, come across any to contradict it. It thus appears that tapping restores the sensitiveness not by the separation of the electrically-welded particles (in which case tapping ought to have produced an increase of resist-
