498 Transactions. — Miscellaneous. 



solenoid is to reduce the amplitude of the second half-oscilla- 

 tion considerably, for when the iron is removed and dis- 

 charges passed the deflection falls from 200 to 150, and 

 when the iron is in the solenoid from 200 to 162. 



We must now consider to what this effect is due. If the 

 iron increased the inductance of the circuit the effect would 

 be to increase the amplitude of the second half-oscillation 

 rather than decrease it. The iron cannot sensibly alter the 

 inductance of the circuit, for we observe that the effect of the 

 first half-oscillation is diminished very slightly — in this parti- 

 cular case from 200 to 100 to 200 to 103. 



The result must therefore be due to an absorption of 

 energy by the iron core, and a consequent increase of actual 

 resistance in the circuit. The absorption of energy repre- 

 sents an addition of real resistance to the circuit, and increases 

 the rate of dissipation of energy in the circuit. 



The energy absorbed by the conductor may then be readily 

 compared with the energy absorbed when a resistance of very 

 small inductance is placed in the circuit — e.g., a carbon pencil, 

 or a tube containing an electrolyte. 



The final deflection when the cylinder was in the solenoid 

 was carefully observed. The cylinder was removed, and a 

 short length of carbon rod of high resistance introduced into 

 the circuit until the added resistance caused the final deflec- 

 tion to be the same as when the metal cylinder was in the 

 solenoid. 



Since the damping is identical in the two cases, the added 

 resistance must absorb the same amount of energy as the 

 metal core. The absorption of energy in the metal core there- 

 fore increases the impedance of the circuit, and this increase 

 of impedance may be expressed in ohms. 



The resistance of the carbon rod or electrolyte was deter- 

 mined for steady currents, and, since the conductivity is small, 

 it will be found, by substitution in the equations given by Lord 

 Eayleigh, that its resistance is practically the same for steady 

 currents as for a frequency of 2,000,000 per second, which is 

 very approximately the frequency of the discharge. 



Proceeding in this way, the absorption of energy by various 

 conductors was compared. 



(1.) A test-tube was taken and filled with finely laminated 

 soft-iron wires 0-008in. in diameter. In order to insure 

 thoroughly good insulation from eddy-currents the test-tube 

 was filled up with petroleum. The absorption of energy in 

 this case increased the impedance of the circuit 10 - 25 ohms. 



(2.) A test-tube full of steel filings was next placed in the 

 solenoid. Increase of impedance, 9 ohms. 



(3.) A thin soft-iron cylinder, T9cm. in diameter, 14cm. 

 long. Increase of impedance, 3 - 9 ohms. 



