Low Frequency and their Resonance. 



511 



resistance of nearly 40 ohms. The secondary consisted of 120 

 turns No. 11 JB. & S. W. G. wire. The iron core e was a 

 cylinder of well packed fine iron wire. The diameter of this 

 cylinder was 5 cm and its length 40 cm . High voltage was 

 measured by a Thomson electrostatic voltmeter, small volt- 

 age by a Thomson multicellular voltmeter or a Weston alter- 

 nating current voltmeter. It is, however, not advisable to use 

 this last instrument in resonance work when the voltage ex- 

 ceeds 50 volts. An inertia coil a' b\ fig. 3 was connected in 

 series with the secondary of the induction coil and also with an 

 adjustable Marshall condenser of 1'9 microfarads, the smallest 

 subdivision being 0*05 M.F. The inertia coil consisted of 

 about 1000 turns of coarse copper wire, about No. 16, so that 

 its resistance was only a few ohms. A removable iron wire 

 bundle could be inserted into this coil, so as to study the effect 

 of iron upon resonance. 



The first series of experiments was done without iron in the 

 inertia coil. The speed of the alternator was maintained at 

 28 L0 revolutions per minute or nearly 375 complete periods 

 per second. The capacity was gradually varied from to 1 "(5 

 microfarads when the maximum point of the voltage of the 

 condenser was reached. The values are tabulated in table 1, 

 curve fig. 4 (unfortunately very indistinct in the reproduction), 

 was plotted from this table, by taking the capacities in 

 10" 7 Farads for abscissae and the corresponding difference of 

 potential in volts in the condenser for ordinates. 





Table I. 





Condenser 



Corre 



sponding value of the 



capacity in 

 10" 1 Farads. 



difference of potential of the 

 condenser in volts. 



•o 





40-5 



0-5 





43' 



1*0 





46- 



1-5 





51- 



2-0 





56-5 



2'5 





53- 



3-0 





51-5 



3-5 





52- 



40 





53- 



5-0 





57-5 



6-0 





63'c 



7-0 





70-5 



8-0 





77* 



9-0 





89- 



10-0 





103- 



11-0 





lis- 



12-0 





140- 



15-0 





750- 



16-0 





1090- 



