1902.] accompanying Mechanical Disturbance in Metals. 285 



Abnormal Response. 



But the modification of which I have spoken does not stop short of 

 mere 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 un- 

 annealed 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, cc, 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, /?) I have been 

 .able to catch the point or rather points of transition. 



Fig. 8. — (a) Abnormal negative (downward) response (a) converted into normal- 

 positive (upward) response (c) after continued vibration (b) (tin). 

 (/3) Shows points of transition from the abnormal negative to the normal 



Thus we may distinguish the following typical cases. Beginning 

 with the case of extreme molecular modification, we have (1) a condi- 

 tion 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 



<a) (b) (O 



(CC) 



positive (platinum). 



