452 Dr. Gr. Grore on the Influence of Proximity 



sequence of the much greater total electric conduction- 

 resistance. The amounts of deflexion were recorded at 

 regular intervals of time, usually 2, 5, 10, 15, 30, and 

 60 minutes. 



Causes of Variation of the Current. 



Four chief causes operate to move the needles : — 1st 

 variation of the voltaic action ; 2nd, approach or recession of 

 the influencing substance ; 3rd, change of temperature; and 

 4th, diurnal variation of terrestrial and atmospheric mag- 

 netism. Of these the first and second were the most 

 powerful. The use of cadmium electro tes might diminish the 

 tirst one. 



Experiments. 



Several experiments, including a total of 28 observations, 

 were made during two days, to ascertain the effect of the 

 usual to-and-fro movements of the tubes alone in the absence 

 of the lead bars, the circuit being as usual left open all 

 night. The motion had a very nearly uniform effect of 



making when in one direction ■* the " A " electrodes 



positive, and when in the opposite direction ** the " B " 



ones positive ; but in each case the electrical effect was 

 opposite to that produced by the presence of the lead. 



Similar experiments, including 4 6 observations, were then 

 made during four days, with the lead bars present, the circuit 

 being again left open all night. After due corrections had 

 been made for the effects of motion of the tubes in the 

 absence of the lead, the influence of presence of lead upon 

 the " A " electrodes was still found to render them electro- 

 positive, and upon the " B " ones to render them also electro- 

 positive, and therefore to produce, or tend to produce, opposite 

 currents with the two sets of electrodes, as in the experiments 

 with the two previous apparatus. The disturbance caused 

 by motion was subsequently eliminated by preventing the 

 presence and formation of bubbles upon the electrodes. 



The results of numerous additional experiments fully proved 

 that the effect of the proximity of the lead was either to 

 diminish or reverse the deflexions produced by the move- 

 ments of the tubes alone. The opposite effect produced by 

 the presence of the lead to that produced by its absence was 

 not due to polarization, because the latter should have been 

 the same in both cases. Polarization was in all cases of the 

 research too minute to perceptibly affect the results. 



After having fixed to the apparatus buffers of very elastic 

 india-rubber, to diminish the sudden stoppage of motion, 

 several series of experiments were made ; in one series of 

 81 observations the lead bars were present, and in another of 



