492 Mr. T. S. Moore on the 



difference between the values obtained for the internal resist- 

 ance will measure the divergence of the cell from reversibility. 

 The results were calculated from formulae which are easily 

 deduced. 



Let D =E.M.F. of experimental cell on open circuit. 



D 1 = ., ., .. when running through 



resistance R ohms. 

 D 2 = „ „ .. when reversed through 



R ohms. 

 B = ,, ., the accumulators. 



Current from cell through R — -, where r is internal 



resistance of cell. + r 



.*. E.M.F. between poles of cell = ^— x R = D X ; 



••• -^xB («) 



Or, if we regard the internal resistance as known, we have 



D *=Sr, w 



Now the reverse current through cell and resistance R ohms 

 = Tj , if the cell is reversible; 



/. External E .M.F. = R x ^^ I 



.-. E.M.F. between poles=B- R{ ^ ~ D) =D 2 ; 



D 2 -D 



R (c) 



B-D 2 



Or, if we regard the internal resistance as known, 



,-B + BD ,,. 



D2= ->+ir {d) 



For the experiments a Croinpton potentiometer was used, 

 the arrangement of which is shown in fig. 2, together 

 with the arrangement of the experimental cell and the 

 resistance-box. 



The accumulators L are connected with the circuit ABDEFG, 

 and by means of the rheostat F and by balancing a Clark 



