2 Frof. W. G. Adams on the Forms of 



The lines of flow diverge from the electrodes or points where the 

 current enters and leaves the liquid, and lie closer and closer together 

 as they lie nearer to the shortest line of flow joining the electrodes. 



The whole of the conductor, whether it be a disk or a liquid, may be 

 regarded as being made up of tubes of flow, or of bundles of lines of 

 flow, each tube ending in conical points filling up the same solid angle at 

 the electrodes, and conveying a given quantity of electricity from one 

 battery-electrode to the other. 



These tubes increase in diameter at points further and further from 

 the electrodes ; and the strength of current at a given point (i. e. the 

 quantity of current flowing through a perpendicular section of unit area) 

 will be inversely as the cross section of the tube of flow passing through 

 that point. In passing from one electrode to the other along any line of 

 flow there will be a gradual fall of potential, and the lines of flow will 

 be cut at right angles by surfaces in which the potential is the same for 

 every point of the same surface. 



On attaching two wires to a galvanometer, and placing their free ends 

 on the same equip otential surface, no current will flow through the 

 galvanometer. 



If, then, two electrodes in connexion with the two poles of a battery 

 be fixed in contact with two points of a disk of tinfoil, or with two 

 points in a conducting liquid, and two other electrodes be attached to 

 a delicate galvanometer, by keeping one of these fixed and tracing 

 with the other we may determine the forms of equipotential curves or 

 surfaces in the disk of tinfoil or in the liquid by joining all the positions 

 of the tracing-pole which give no current through the galvanometer. 



It will be convenient to call the electrodes which are connected with 

 the battery the battery-electrodes, and those connected with the galvano- 

 meter the galvanometer-electrodes. By means of the tracing-electrode 

 points of the same potential as the fixed galvanometer-electrode may be 

 marked on the tinfoil ; and the curve joining them will be an equipo- 

 tential curve. 



Experimental Work. 



About five years ago, at the suggestion of Mr. J. T. Bottomley, the 

 tracing out of equipotential curves on sheets of tinfoil was first set as an 

 exercise for our more advanced students in the Physical Laboratory. I 

 have been assisted in the experimental work contained in this paper by 

 Messrs. Jacob, Cochrane, Day, and Harrison, students in the Physical 

 Laboratory of King's College. 



To trace the curves, one electrode of a Thomson's reflecting galvano- 

 meter was attached to a small screw or pin, fixed in contact with or 

 passing through the tinfoil disk ; and the other galvanometer-electrode 

 was attached to a small tube of the same size as the screw, with the end 

 of which contact could be made at any point of the disk. In the centre 



