4 Prof. W. G. Adams on the Forms of 



From / to g 50 



„ ytoA 80 



It will be seen that the fall of potential from 1c to d is greater than 

 the fall of potential from d to h. This may arise from a difference in 

 the resistances of the contacts with the two battery-electrodes. 



The radii of the circles are 28, 56, 290, 82, 28, and 12 millims., be- 

 ginning from the point k ; and the distances between them, measured 

 along the line joining the electrodes, are 20, 13, 15, 19, 15, 10, and 

 12 millims. 



The distances 13, 15, 19, 15, 10 correspond to equal differences of 

 potential ; and hence the resistances of the portions of the disk between 

 these consecutive equipotential curves are equal to one another. In 

 this case there was considerable resistance between the binding-screw 

 and the tinfoil disk at the point of contact ; but this does not alter the 

 forms of the equipotential curves. 



Case 3. Plate 2. fig. 3 represents a large sheet of tinfoil 18 inches 

 square, with one electrode in the centre, by which the current enters the 

 sheet, and four similar electrodes at four corners of a square, each being 3 

 inches from the central electrode, by which the currents leave the sheet. 

 The electrodes were needles, with shoulders of brass 3 millims. in diameter 

 soldered on them. The four negative electrodes may be united together 

 beneath the board on which the tinfoil is placed, by strips of copper 

 screwed to the electrodes by a small nut on each needle. On the 

 needles which pass through the tinfoil are shoulders which come down 

 tight on the tinfoil so as to make good contact. For these curves two 

 cells of Grove were used ; and the difference of potential between two 

 successive curves causes a deflection of 50 divisions of the scale. The 

 resistances of the portions of this disk between successive equipotential 

 curves are equal to one another. 



Case 4. The curves in Plate 2. fig. 4, lying within the octant BAH, 

 are equipotential curves, when one positive electrode A is at the corner 

 of a square sheet of tinfoil of which AH and AM are the edges, and one 

 negative electrode at B, at a distance of 3 inches from A, the line AB 

 bisecting the angle between the two edges. The curves between the 

 lines AB and AM have not been drawn in the figure. 



The potential at any point in this sheet is that due to the electrodes, 

 together with the three images of each formed by the rectangular edges ; 

 and hence the curves should be the same as in the previous case. On 

 comparing the curves it will be seen that that is the case. 



The curves, with two exceptions, are drawn at distances corresponding 

 to equal differences of potential ; so that, omitting the interpolated 

 curves, the resistances of the portions of the sheet between two consecu- 

 tive equipotential curves are equal to one another. 



This figure also represents the equipotential curves for a square 

 sheet BAB p of which AB and AB X are the edges, with one positive 



