342 THE RESISTANCE AND ELECTROMOTIVE FORCES OF THE ELECTRIC ARC 



these frequencies, even supposing the other arms of the bridge quite free from self- 

 inchiction and capacity. This explains the fact that only a minimum in the sound is 

 obtainable, and not absolute silence. 



The conclusion to be drawn from this experiment is that in any case where the 

 P.D. due to the polarisation of the electrodes cannot be made very small compared 

 with the ohmic drop along the liquid whose resistance is being measured, and where 

 the errors due to the polarisation cannot be eliminated by taking two or more tests, 

 then it must not be assumed without proof that the use, of alternating currents at 

 ordinary frequencies of a few hundred periods per second eliminates the possibility of 

 errors due to polarisation. For in the case of sulphuric acid used above, the 

 polarisation can vary as rapidly as the resistance of the cored arc. 



