RESPONSE IN METALS 85 



zincoid, i.e. the current through the electrolyte (non-polaris- 

 able electrodes with interposed galvanometer) is from A to B, 

 and through the wire, from the less stimulated B to the more 

 stimulated A. Conversely, when B is stimulated, the action 

 current flows round the circuit in an opposite direction. This 

 positive is the most usual form of response, but there are cases 

 where the response is negative. 



In order to show that normally speaking a stimulated wire 

 becomes zincoid, and also to show once more the anomalies 

 into which we may fall by adopting no more definite termino- 

 logy than that of negative varia- 

 tion, I have devised the following 

 experiment (fig. 51). Let us take 

 a bar, one half of which is zinc and 

 the other half copper, clamped in 

 the middle, so that a disturbance ^^^^^^ ^^ 

 produced at one end may not reach vormai Current < 



the other; the two ends are COn- FIG. 51. CURRENT OF KESPONSE 



nected to a galvanometer through TOWARDS THE STIM ATED END 



. . . , , " Hence when Cu stimulated: ac- 



non-polansable electrodes. The tion current -, normal E.M.F. 



,-, i ,-, , i , diminished ('85 -'009) V. 



Current through the electrolyte When Zn stimulated : action cur- 



(non-polarisable electrodes and in- M<F ' 



+is) v 

 terposed galvanometer) will then 



flow from left to right. We must remember that metals 

 under stimulation generally become, in an electrical sense, 

 more zinc-like. On vibrating the copper end (inasmuch 

 as copper would then become more zinc-like) the differ- 

 ence of potential between zinc and copper ought to be 

 diminished, and the current flowing in the circuit would 

 therefore be lessened. But vibration of the zinc end ought to 

 increase the potential difference, and there ought to be then 

 an increase of current during stimulation of zinc. 



In the particular experiment of fig. 51, the E.M.F. between 

 the zinc and copper ends was found to be *85 volt. This 

 was balanced by a potentiometer arrangement, so that the 

 galvanometer spot came to zero. On vibrating the zinc 

 wire, a deflection of 33 dns. was obtained, in a direction which 



