Oscillatory Discharges. 33 



After connecting the points C and D with the electrodes 

 of a spark-gap and with the poles of a Ruhmkorff coil, there 

 could be sent through the differential exciter currents with a 

 frequency of the same order of magnitude as those of the 

 sparks we have photographed. 



Then it was tested whether the contact points A and B 

 between each self-induction and the corresponding condenser 

 were at the same potential. For this purpose we found most 

 convenient the detector suggested by Nernst, made up of a 

 vacuum-tube without electrodes, on whose terminals two 

 strips of tinfoil connected with A and B respectively had 

 been wound. 



As is known, the luminosity of the tube will be minimum 

 when the condition 



-L'iv--1 == -L^2^2 



is satisfied. 



The accuracy of this method depends upon the precision 

 with which this minimum is determined, as any one of the four 

 quantities L 1? L 2 , C 1? C 2 undergoes a small variation. This 

 precision is greatest when the degree of exhaustion in the tube 

 is the one corresponding to the first appearance of cathode 

 rays. 



Various numbers of spires of the spiral were successively 

 used until the detector showed a minimum of luminosity. 

 The self-induction L 2 of the spiral could be considered as 

 proportional to the number n of spires used : denoting by k 

 the coefficient of proportionality, the above-mentioned con- 

 dition of minimum was represented by 



L,C 1 = ^?2 C2. 



The wire with known self-induction was next replaced 

 by the spiral whose self-induction x had to be determined, 

 and the number of spires was again varied, until for some 

 number n the minimum with the detector was arrived at. 



The minimum condition became 



Those two determinations gave the self-induction to be 

 found 



n j 



tf= — hi 



for high-frequency currents. Our experimental conditions 

 allowed of such a precision in determining the minimum fehat 

 the numbers n and ?r , ranging as a rule between 70 and 350, 

 were ascertained to less than a unit. 

 Phil. Mag. S. (). Vol. 5. No. 25. Jan. 1903. D 



