Low Frequency and their Resonance. 



329 



telephone shows plainly that sometimes these upper harmonics 

 are apparently much stronger than the fundamental current. 

 The method of reducing the complex harmonic current ob- 

 tained by the means just described forms the next part of this 

 paper. 



B. On the method of weeding out harmonics by electrical resonance. 

 If a coil, A, (fig. 5) is connected with a condenser B 



Fig. 5 



and an impulse starts an electrical disturbance in this sys- 

 tem, then electrical oscillations will result from this disturb- 

 ance. Electrical equilibrium is restored again after the elec- 

 trokinetic energy produced by the impulse is partly radiated 

 off and partly transformed into heat by the ohmic resistance of 

 the circuit. Not to mention losses due to magnetic and dielec- 

 tric hysteresis and to convection currents consisting of dust 

 particles charged by contact with the systems. In Hertzian 

 oscillations and in Tesla frequencies the period depends on the 

 self-induction and the capacity of the system only, as is well 

 known. But even in systems of large self-induction and large 

 capacity, where d priori we can expect a long period of oscil- 

 lation, this period can be easily shown to be independent of 

 the ohmic resistance of the system in the majority of cases. 

 An analytical discussion of this matter, as well as of other 

 matters relating to resonance of slow oscillations is reserved 

 for a future paper. Suffice it for the present to refer to these 

 things, only in so far as they bear upon the subject of this paper. 

 The period of the system represented in fig. 5 is given (pro- 

 vided certain well-known conditions are fulfilled) by 



'-—4/ 



LC 



where T is the period in seconds, L the coefficient of self- 

 induction in Henrys, and C the capacity in microfarads. I 

 shall refer to this period as the " natural period" of the sys- 

 tem. By varying the capacity or the self-induction of the 

 circuit we vary its natural period. I call this variation the 

 tuning of the electrical circuit. 



