98 



St rienti ti< ■ Intell igence. 



determined, on which quantity they directly depended. Taking 

 into account absorption, capacity can be determined by the same 

 method witli about the same degree of accuracy. This method is 

 easy to Use, as it requires but one adjustment, JV. 



The methods for the comparison oi' the above quantities gave 

 much more accurate results, as they are independent of the period 

 of the current, the great cause of error in the measurement of the 

 quantities. When care Avas taken to guard against all inductive 

 and electrostatic action of the different parts of the apparatus on 

 each other, the results derived by the different methods tried 

 were remarkably good, notably the results obtained by the 

 method for the comparison of two self-inductances. The connec- 

 tions for this method are made in this manner : 



Let there be two coils of self-inductances, B t and //.. placed 

 together, and let the circuit pass through the coil /?,,. From the 

 main circuit, after it has passed through the coil B.,, the hanging 

 coil of the electrodynamometer, having in circuit a self-inductance, 

 X, and a resistance, B, is shunted around a small resistance, r. 

 The coil B 1 is placed in circuit with the fixed coils of the electro- 

 dynamometer and a resistance, B'\ 



The condition, then, for zero deflection when the current is 



flowing is 



L 

 B, 



B + r 

 ~R TV 



Using this method and taking B 1 as a standard equal to 1 Henry, 

 several coils were compared with B^ both singly and in series. 

 To show with what accuracy self-inductances of different amounts 

 can be compared, a few values are given for two periods. The 

 coils being compared with B x as a standard. 



^=40 



n = 1 33 



Coils. 



P x 



C 

 C + P, 



Results 



found 



by direct 



measurement. 



•5664 

 1-3050 

 1-8713 



Sums and 



differences 



of direct 



measurement. 



•5663 

 1-3049 

 1-8714 



Results 



found 



by direct 



measurem't. 



•5653 

 1-3034 



1-8682 



Sums and 



differences 



of direct 



measurem't. 



•5648 

 1-3029 



1-8677 



Sum 8 and 

 differences. 



(C + PJ-C^P, 



(C + PJ-P^O 



C + P, 



These are good cases of agreement, and show the accuracy of 

 the method for the comparison of self-inductance of different 

 amounts, when care is taken to eliminate heating and electrostatic 

 action of' the resistance and leads. 



It will be noticed that the value of the self-inductance for the 

 two periods is different ; this was due to the electrostatic action 

 of the turns of the coils on each other, and therefore could not be 

 avoided. 



When equal self-inductances are to be compared, the accuracy 



