RESPONSE IN METALS 83 



still by torsional vibration, a transitory ' current of 

 action ' will be found to flow in the wire from B to A, 

 from the unstimulated to the stimulated, and in the 

 galvanometer from the stimulated to the unstimulated. 

 Stimulation of B will give rise to a current in an opposite 

 direction. 



Experiment to exhibit the balancing effect. If the 

 wire has been carefully annealed, the molecular condi- 

 tion of its different portions is found to be approximately 

 the same. If such a wire be held at the ' balancing 



(c) 



FIG. 50. ELECTRIC KESPONSE IN METALS 



(a) Method of block ; (b) Equal and opposite responses when the ends A and 

 B are stimulated; the dotted portions of the curves show recovery; 

 (c) Balancing effect when both the ends are stimulated simultaneously. 



point ' (which is at or near the middle) by the clamp, 

 and a quick vibration, say, of 90 be given to A, an up- 

 ward deflection will be produced ; if a vibration of 90 

 be given to B, there will be an equal downward deflec- 

 tion. If now both the ends A and B are vibrated simul- 

 taneously, the responsive E.M. variation at the two ends 

 will continuously balance each other and the galvano- 

 meter spot will remain quiescent (fig. 50, A, B, R). This 

 balance will be still maintained when the block is 

 removed and the wire is vibrated as a whole. It is to 

 be remembered that with the length of wire constant, 



G 2 



