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 zine and 
the other half copper, clamped in . 
the middle, so that a disturbance a ee 
produced at oneend may not reach Normal Current = <—— 
the other; the two ends are con-  Fie.51.—Current or Response 
nected to a galvanometer through 70™4"?S TH Sumunatep Exp 
non-polarisable electrodes. The tease Stared Te 
diminished (-85—-009) V. 
current through the electrolyte when Zn stimulated: action cur- 
(non-polarisable electrodes and in- SR ae em oui 
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 zine 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 zine 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 zine 
wire, a deflection of 33 dns. was obtained, in a direction which 

