Abnormal Response.
But the modification of which I have spoken does not stop short of more abolition of responsive power, but sometimes proceeds further, and actually reverses the sign of response—the excited wire becoming cuproid. This abnormal effect is sometimes found even in fresh unannealed wires, when feeble vibrations (of amplitude of 5° or less) may give rise to a negative response, but vibration of stronger intensity gives rise to the usual positive response. At other times the molecular modification is more pronounced, and there is a persistent reversal of response.
But even in such cases long-continued vibration transforms the abnormal negative to the normal positive. I give below photographic records which exhibit this. In fig. 8, α, the transformation took place during continued vibration. To detect the point of transformation, I experimented with a platinum cell which exhibited the abnormal effect, and took a long series of records of responses to uniform vibrations acting at intervals of a minute. In the record (fig. 8, β) I have been able to catch the point or rather points of transition.
Fig. 8.—(α) Abnormal negative (downward) response (a) converted into normal positive (upward) response (c) after continued vibration (b)) (tin).
(β) Shows points of transition from the abnormal negative to the normal positive (platinum).
Thus we may distinguish the following typical cases. Beginning with the case of extreme molecular modification, we have (1) a condition which gives rise to negative response; after continued vibration the negative becomes less negative, and ultimately becomes converted into positive: (2) an irresponsive or neutral condition; vibration or annealing transforms it into positive: (3) a sluggish, feebly positive, becoming more and more positive after continued vibration: (4) a
