22 



Prof. W. G. Adams on the Forms of 



circles which touch one another at the point where the current enters 

 the sheet (fig. 4). 



If, in an indefinite sheet (Plate 2. fig. 3), one of the battery-electrodes 

 be separated into four parts and attached to the tinfoil at the four 

 corners of a square, and if the other battery-electrode be attached at the 

 centre of the square, then the current at the centre will be four times 

 the current at each corner of the square ; and the forms of the equipo- 

 tential curves will be the same as when there are only two, unlike equal 

 electrodes in a sheet limited in two directions by straight lines meeting 

 at the centre and parallel to the sides of the square, the three elec- 

 trical images in the limited sheet being in the same positions as three of 

 the electrodes in the unlimited sheet. 



This is a particular case of the last, when an electrode and its image 

 lie at the ends of a diameter of the circle, and are equally distant from 

 the point at which the current enters the sheet (fig. 5). 



Pig. 5. 



The case with one positive electrode at the centre and four negative 

 electrodes at the corners of a square in an unlimited sheet may also be 

 regarded as equivalent to two sets of electrodes, each set consisting of 

 one positive electrode at the corner of a square and two negative elec- 

 trodes at equal distances along the two edges measured from that corner 

 when the sheet is cut along these two edges. 



The curves are also the same as in a sheet limited by two edges at 

 right angles to one another, when one electrode is at the corner and 

 the other on the diagonal of the square sheet, the electrodes being at the 

 same distance as in the two previous cases. 



The curves in Plate 2. fig. 4 are drawn on such a sheet with one posi- 

 tive electrode at A and a negative electrode at E, at a distance of 3 inches 

 from A, the whole sheet of tinfoil being 18 inches square. 



It may also be regarded as a particular case of two sets of electrodes 

 in an unlimited sheet, where there are three electrodes in each set at 

 equal distances along the same straight line, the current entering at the 

 middle one and flowing out at the other two electrodes. Since the circle 



