500 Transactions. — Miscellaneous. 



iron cylinder of the same dimensions does, or one-thirtieth of 

 the energy of a carbon rod of the same dimensions. It could 

 always be told whether any considerable amount of energy 

 was being absorbed in the solenoid by the peculiar deadened, 

 sound of the spark. A copper cylinder did not deaden the 

 sound like an iron or carbon cylinder. The same sound was 

 caused by adding a carbon rod in series with the circuit, so 

 as to increase the resistance of the circuit. 



VI. Eesistances of Ikon Wires foe High-frequency 



Discharges. 



Since iron has been shown to retain its magnetic proper- 

 ties in fields which are reversed a hundred million times per 

 second, it was expected that the resistance of iron wires 

 would be much greater for frequencies of several million per 

 second than for steady fields, on account of the concentration 

 of the current on the surface-skin of the conductor. 



The resistances of conductors for these very rapid alterna- 

 tions have not yet been able to be determined, and so any 

 method of attacking the difficulty is of interest. The method 

 of experiment was practically the same as that used to deter- 

 mine the absorption of energy in conductors. 



Plate XLIX., Fig. 14. 



About 4 metres of iron wire were taken, and arranged in 

 a rectangular discharge circuit. The other wire connections 

 were copper conductors of the same diameter as the iron. 

 The fall of deflection in the "detector" was observed for a 

 series of discharges first in one direction and then in the 

 other. The iron wire was then removed, and a copper wire 

 of the same radius and length substituted. This insured that 

 the self-inductance of the circuit was practically unaltered. 

 A short carbon resistance was then added in the circuit until 

 the fall of deflection with the copper wire and the carbon 

 resistance was exactly the same as the fall of deflection in the 

 case of the iron wire. Where this is the case, the resistance 

 of the iron is equal to resistance of copper wire of equal 

 length together with the carbon resistance. 



Example of the Method of Determination. 



When iron wire is m circuit, deflection falls — (1) From 

 200 to 103 for one direction ; (2) from 200 to 176* in opposite 

 direction. 



When the iron wire was removed, and a copper one sub- 

 stituted, the fall of deflection was— (1) From 200 to 101 

 for one direction ; (2) from 200 to 162 for opposite direc- 

 tion. 



