ELECTRICAL MEASUREMENTS 319 



0=0, as is an angle whose tangent is , and (7 = nearly. In the 

 case of equal deflection D = D' and therefore 

 VD=(R'-R) (R+r} 



If capacity had been used in the place of self-inductance the formula 

 would be 



If self-inductance and capacity were used in series 



The application of this formula to the measurement of self-induc- 

 tance gave results that agreed to within the accuracy with which the 

 period of the alternations could be determined. That is, the results 

 agreed to within about 1 per cent. In the determination of L the 

 resistance in circuit R was varied from the least possible resistance as 

 determined by the coils up to 1000 ohms and more, and the self- 

 inductance was determined under these various conditions. These 

 results agreed among themselves, and were apparently independent of 

 the resistance in circuit with it. In the application of this method to 

 the determination of capacity, however, great trouble was encountered, 

 as the capacity apparently varied both with the resistance in circuit 

 with it and with the period. This variation was regular for each period, 

 the value derived depending on the resistance in circuit. This irregu- 

 larity of derived value of the capacity led to the investigation and 

 development of Maxwell's formula on the effect of absorption, a neces- 

 sary characteristic of heterogeneous substances. 



When the formula was deduced, as may be seen in the article already 

 referred to, the absorption comes in as an added resistance, the resist- 

 ance being constant for a given period. By an inspection of the results 

 this was found to be the case. The finding of the resistance due to 

 absorption in this method is one of approximation, but the values 

 deduced compare very favorably with those determined by direct meas- 

 urement, as will be seen later when various results are collected. In 

 the actual experiments the condensers used were two paraffined paper 

 condensers of about 2 and 3 microfarads. The currents used had 

 different periods, as seen in the table following, where n = 133, 53-3, 

 31 -9 and 14. 



The process was to place in the condenser circuit a resistance R, and 



