42 



Electrical Oscillations in Coupled Circuits. 



These curves appear to be due to the presence of the octave *, 

 with varying intensity, along with the fundamental tone. 

 Thus, in the lower note of fig. 9, the amplitude of the octave 

 is approximately equal to that of the fundamental, while in 

 iig. 10 the amplitude of the fundamental is about six times 

 that of the octave. With given condensers in the circuits 

 the relative intensity of the octave in the lower note can be 

 varied by altering the length of the arc. 



In Table V. are given the frequencies of the arc notes, 

 along with the frequencies n x and n 2 calculated from the 

 inductances and capacities, for the four combinations de- 

 scribed in section (3). The arc frequencies were determined 

 from one photograph only in each case, and must not be 

 regarded as constant. The lower note in Case I. was rarely 

 heard, and the corresponding curve was not photographed. 



Table V. 



Capacities 

 in microfarads. 



Singing arc. 



Calculated frequencies. 



Primary. 



Secondary. 



Lower note. 



Higher note. 



i %• 



n 2 . 



9-55 



9-55 



11-87 



11-87 



•001063 



•000875 

 •001063 



•000875 



542 



470 

 445 



691 

 780 

 723 

 745 



542-2 

 582-8 

 5270 

 560-3 



882-7 

 905-0 

 814-7 

 844-4 



Under the circumstances of these experiments, therefore, 

 the musical arc gives, if the product of self-inductance and 

 capacity is not very different in the primary and secondary 

 circuits, two notes whose frequencies are generally con- 

 siderably lower than the values calculated for the system 

 from the inductances and capacities by (4) : in addition the 

 octave of the lower note is prominent. 



It should be remembered, however, that in the calculated 

 frequencies no account is taken of the resistance of the arc. 



If the secondary condenser is removed (so that C 2 is very 

 small) the arc gives one note only, the wave-curve being of 

 the low-note type. With d = 9'55 mfd. the arc frequency 

 determined from one photograph was 659 ; breaking a 

 current in the primary of this system (the arc being re- 

 moved) gives a simple damped oscillation of frequency 755*5. 



* The presence of harmonics in the high-frequency graphite arc has 

 been detected by L. W. Austin (Electrician, Aug. 2, 1907). 



