8 



Prof. W. G. Adams on the Forms of 



Coordinates of 

 tracing- 

 electrode. 

 50, 30 

 50,40 

 50, 50 

 50, 60 

 50, 70 

 50, 80 

 50, 90 

 50, 100 

 50, 110 

 50, 120 

 50, 130 

 50, 140 

 50, 150 



Mean 

 deflection. 



76 



66 



61 



55 



50 



44 



36 



30 



24 



18 



13-5 

 7 

 2-5 



Diff. 



10 

 5 

 6 

 5 

 6 



6 



6 



6 



4-5 



6-5 



4-5 



Coordinates of 



Mean 



tracing- 



r 1 pfif^r*f"irv 



electrode. 



U.t'lJ.OOLU-' 



50, 150 



2-5 



50, 160 



- 6 



50, 170 



-11-5 



50, 180 



-16 



50, 190 



-22 



50, 200 



-28 



50, 210 



-34 



50, 220 



-40 



50, 230 



-47 



50, 240 



-52 



50, 250 



-60 



50, 260 



-68 



50, 270 



-74 



50, 30 



74 



50, 50 



60 



50, 150 



2 



Diff. 



8-5 



5-5 



4-5 



6 



6 



6 



6 



7 



5 



The column of differences gives the differences of potential between 

 the equipotential surfaces passing through the successive positions of 

 the tracing-electrode. These positions are points at equal distances of 

 10 millims. apart, along a horizontal straight line parallel to the sides of 

 the box at a distance of 50 millims. from the axis. 



The difference between the mean and each of the two deflections to 

 right and left may be taken to be the current due to polarization. This 

 was very small, the deflections being 6 at the beginning, 6*5 at the middle, 

 and 10 at the end of the experiments. 



Toward the end of the experiments, at (250, 50) there was an increase 

 of 2 in the deflections because the current was kept on for five minutes. 

 From these results it appears that with momentary currents and reversing 

 at each observation, the variation in the polarization current, even in 

 dilute sulphuric acid, may be kept very small. The sudden change in 

 the polarization at (50, 250) reduced the deflection of the tangent-gal- 

 vanometer from 46° to 41°. 



The value of the deflection recorded is the mean of two or more 

 deflections in each direction, but these were very generally the same. 



To reduce, if possible, the effect of polarization, I employed sulphate of 

 copper and gutta-percha-covered copper wire 3-6 millims in diameter, 

 with 4 millims. projecting beyond the covering for the battery-electrodes. 

 In the galvanometer-electrodes, which were of the same covered wire, 

 there were 2 millims. of wire projecting beyond the covering ; all the 

 electrodes were immersed to a depth of 75 millims. The battery-electrodes 

 were placed at distances of 10 millims. from the ends of the box, so 

 that they were 284 millims. apart. 



The fixed galvanometer-electrode was placed at (152, 50); then on 

 varying the position of the other electrode, it is found that for all posi- 

 tions in a plane parallel to the ends of the box, and dividing it into two 



