siIvSbee; and honaman: conductivity measurements 263 



the same phase as the alternating voltage applied to the speci- 

 men. The direct current through the specimen was measured 

 by a D. C. milliammeter connected in series with the specimen 

 and the dynamometer. With this arrangement, each pair of 

 instruments measured only its particular component of the re- 

 sultant current and voltage and was not affected by the pres- 

 ence of the other component. Figure 4 shows the variation with 

 time during the course of the experiments of the resistances as 

 computed from the two components of the current. In this ex- 

 periment the maximum value of the A. C. voltage was greater 

 than the D. C. voltage, so that the resultant voltage applied to the 

 specimen reversed in sign during each alternation. Other ex- 

 periments, in which the maximum alternating voltage was less 

 than the D. C. voltage, and the resultant voltage was conse- 

 quently unidirectional, showed substantially the same effects. 

 Throughout the experiments, the temperature was held as nearly 

 constant as possible, but a gradual drift of resistance will be 

 noticed, which can be accounted for by a slight change of tem- 

 perature. It appears from these results that the resistance of 

 the specimen is substantially the same for both the alternating 

 and direct currents for all states of polarization. Or, in other 

 words, the polarization produced by the direct current offers 

 resistance to the passage of the alternating current and the de- 

 polarization produced by the alternating current reduces the 

 resistance offered to the passage of the direct current. 



When alternating current alone was applied to a fresh speci- 

 men, the power factor of the circuit was found to be substantially 

 unity. If, however, the specimen had recently been polarized 

 by the application of direct current, the power factor was some- 

 what reduced; values as low as .9 having been observed. 



The data described above are quite insufficient for the devel- 

 opment of any complete theory of this "polarization," but it 

 would appear that the assumption of a counter E. M. F. is ruled 

 out by both the experiments of combined alternating and direct 

 current and by the difficulty of imagining a mechanism capable 

 of producing a counter E. M. F. of the order of several thousand 

 volts, which would be required to produce the observed decrease 



