412 Dr. J. Hopkinson and Messrs. E. Wilson and F. Lydall. 



purpose of introducing an electrode into the fluid between the plates. 

 This electrode consists of a platinum wire sealed into a glass tube 

 which was capable of being placed in any desired position between 

 the plates. The solution was, as before, of water 100 parts and 

 H 2 S0 4 5 parts by volume. 



The arrangement of connections was similar to that shown in fig. 1, 

 but, instead of observing the potential between the two platinum 

 plates, observations were taken of the values of E.M.F. between one 

 plate and the exploring electrode. 



Table II gives particulars of the experiments tried, and two sets of 

 results are shown in figs. 6 and 7, in each of which, from observa- 

 tions of the values of E.M.F. between the exploring electrode and the 

 platinum plate at different times in a period, a Curve A : was plotted, 

 giving potential in terms of time. This Curve AI is peculiar, in that 

 the ordinates at corresponding points in the two half periods are 

 not equal to one another, as is the case in Curve A, which gives the 

 potentials across the two plates. 



Table II. 



The Curve AI gives, at any epoch, the potential taken up in the 

 evolution of gas at the surface of the plate, plus the potential due to 

 the current in overcoming the resistance of the electrolyte itself. To 

 separate these quantities experiments were made upon the resistance 

 of the electrolyte for varying frequencies and currents. To this end 

 the plates were placed about 2 in. apart in the fluid, and two exploring 

 electrodes, as already described, were placed within the fluid in. a 

 straight line drawn perpendicularly between the faces of the plates, 

 the distance between the electrodes being 4*3 cm. Some difficulty 

 was experienced, owing to the gases being given off at the plates more 

 rapidly in some cases than in others. We, however, estimate that 

 the resistance of a layer of the electrolyte, of a thickness equal to the . 

 distance between the electrode and plate, and of area equal to the 

 area of plate submerged, in figs. 6 and 7, was approximately 0*0056 

 ohm. 



In fig. 6 the Curve A 2 is the result of correcting Curve AI for 



