332 2L I. Pupin — Electrical Oscillations of 



tions will permit. It is not difficult at all to construct a coil 

 whose L=5 and R = 5, in which case E^over 12000 volts. 



In a circuit of this kind the amplitude of the fundamental 

 harmonic would be at least 2000 times as large as that of any 

 of the upper harmonics. In other words, we should have a 

 simple harmonic current in the circuit. In such a circuit the 

 condenser has very small capacity and can be replaced by 

 vacuum bulbs partially coated with tinfoil on the outside and 

 electrical discharges could be produced in them by this enor- 

 mous rise in potential. Hence the interest attached to this 

 method of tuning. I expect to take up this interesting sub- 

 ject in another communication as soon as time will permit. 



Case II — Method of Tuning for the purpose of supplying a 

 Wheatstone Bridge with a simple Harmonic Current of con- 

 stant frequency. 



In this case the method of tuning is governed somewhat by 

 the well known conditions under which the flow in a Wheat- 

 stone bridge system will have the highest sensitiveness. These 

 conditions exclude the possibility of using self-inductions 

 which are very much larger than those in the principal 

 branches of the bridge. Two kinds of apparatus can he em- 

 ployed. The first and in a great many respects the most con- 

 venient kind of apparatus is the interrupter described above. 

 In this case the most difficult, but at the same time the most 

 interesting part of the tuning consists in establishing resonance 

 between the circuits ADGC, BCHE (fig. 4) and the vibrator. 

 It is done in the following way : 



The vibrator is first tuned up to any frequency we wish, 

 say, 256, in the manner described above, all the iron having 

 been previously removed from the coils and a high resistance 

 inserted between F and C so as to reduce sparking at the dip- 

 pers. The iron cores are then gradually pushed in and the 

 capacity of the condensers Gr and H varied until the sparking 

 is reduced to a minimum. This process is continued until the 

 iron core of the principal coil AB is entirely in the coil. The 

 final touches to this part of the tuning are given by means of 

 shifting the iron cores of the small auxiliary coils D and E. 

 By watching the sparks in the cups a and c the point of maxi- 

 mum resonance can be determined with great accuracy. For 

 at this point the sparks are scarcely visible. If there is any 

 defect in this adjustment it shows up immediately when the 

 current is increased, by gradually diminishing and finally re- 

 moving the resistance which, as a matter of precaution, was 

 inserted in the circuit between F and C. The voltage of the 

 generator F does not (within reasonable limit) seem to cause a 



