328 



M. I. Pupin — Electrical Oscillations of 



fork. The tuning is done in a few seconds, without any diffi- 

 culty, by simply stretching the vibrator gradually by means of 

 the lever and micrometer screw and watching for the beats. 

 The stretching does not interfere in the slightest with the 

 vibrations of the vibrator. 



The secondary current is, of course, an alternating current 

 having the same frequency as the vibrator. But it is by no 

 means a simple harmonic current. On the contrary, it is a 

 very complex harmonic, its complexity depending on the fun- 

 damental frequency, on the ohmic resistances, and especially on 

 the self-induction and electrostatic capacity of the primary and 

 secondary circuits. A telephone placed in shunt with a part 

 of the secondary circuit shows that without the condensers 

 sparking is rather strong, producing that peculiar rattling noise 

 which is full of those exceedingly high notes for which the 

 telephone is especially sensitive. These high notes are due, as 

 is well known, to rapid electrical oscillations which accompany 

 the sparks. If the condensers are put in as indicated in fig. 4, 



Fig- 4. 



then the telephone shows that it is simply a question of ca- 

 pacity whether this or that overtone is particularly prominent. 

 These overtones mean, of course, that in addition to the alter- 

 nating current of the fundamental frequency there are also in 

 the secondary circuit higher harmonic currents. In fact, the 



