The paper contains an account of experiments carried out by the authors to analyse some of the various factors concerned in the behaviour of induction watt-hour meters, with particular reference to the changes in accuracy produced by different frequencies.The subject is dealt with under the following headings:—Experimental determination of the changes in accuracy of induction watt-hour meters with changes in frequency.The causes of the changes, namely braking effect of the voltage flux, and reactance of the disc.Separation of the two effects, and determination of their relative magnitudes.Determination of the time-constants of the discs.Explanation of the torques produced in induction meters.Determination of some of the other phase errors in the meters.Conclusions.