Capacity of Electrolytes. 347 



da 2 d& 



forces -j- = — -r = ~r 

 J dx A dy 



The force increases as we pass either way from the origin 

 along the axis of X, and decreases along the axis of Y. We 

 may replace any equipotential surface, as a g , by a conductor 

 bearing a charge equal to that of the line N, and then re- 

 moving N from the system the space within u Q is at a uniform 

 potential, and the field without is entirely unaltered. Hence, 

 instead of using two charged lines M, N to produce the 

 electric field, two circular cylinders of considerable diameter 

 are employed. A solid dielectric at any point on the axis of 

 Y will approach or recede from the origin according as its 

 specific inductive capacity is greater or less than that of the 

 medium surrounding it. When the liquid medium is slightly 

 conducting the case is not so simple ; for then surface charges 

 develop on the solid, and the lines of force, which are now 

 stream lines, go round the solid. The distribution of energy 

 is modified, and we cannot say at once that the ratio of the 

 specific inductive capacities is the sole criterion which de- 

 termines the direction of the resultant force on the solid. 



The Apparatus. 



In the experiment there were employed two pairs of elec- 

 trodes, Mi, Nj and M 2 , N 2 , shown in section in fig. 2. They 

 were of platinum, 0*9 centim. in diameter, 5*0 centim. long, 

 and their centres were 2*6 centim. apart. M x and M 2 were 

 joined to one pole of a battery furnishing any desired potential 

 up to 140 volts ; Nj and N 2 were joined to the other pole ; 

 and a rotating commutator served to give alternations of 50 

 to 100 per second. Two cylinders S x , S 2 of glass, mounted on 

 glass stems, were carried on the arms of a torsion balance, d 

 being the axis of rotation. The deflexion was measured by a 

 telescope and scale, and the force determined in absolute 

 measure. The cylinders of glass were subsequently replaced 

 by cylinders of paraffin, beeswax, and other dielectrics, and 

 carbon and brass among conductors. The force / on the 

 cylinders is perpendicular to the direction of the lines of 



electric force and is proportional to ~ — -? where H is the 



electric force. 



H = C 



A* + y 



2' 



