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AKNOWLEDGE of the total core loss and its components is of vital importance to design engineers who use ferromagnetic materials which are subject to magnetic flux changes in direction or magnitude. Generally this information is obtained from measurements made on strip samples in an Epstein frame, with the use of a wattmeter. In many cases, however, there would be certain advantages, such as increased sensitivity and greater frequency range, in making these loss measurements by a bridge method. For measurements at low inductions and high frequencies the bridge methods have been successfully used for several years.1,2 However, if the induction is increased over 10 to 12 kilogausses in nonoriented silicon steels or 16 to 18 kilogausses in oriented silicon steels, the distortion in the wave form of the exciting current is considerable, and it has been found that the results obtained with the bridge methods hitherto used differ from those obtained with the wattmeter. This difference increases rapidly with increases in induction. The bridge method always indicates larger power losses.