116 PROCEEDINGS OF THE AMERICAN ACADEMY 



there is but little of the mass of the iron magnetized. Even if these 

 instantaneous discharges are capable of magnetizing iron, . . . the 

 electromotive impulses or sudden rushes of electricity do not mag- 

 netize the iron, and hence do not find in it any greater self-inductive 

 opposition than they would find in a non-magnetic but otherwise simi- 

 lar conductor. Dr. Lodge's further researches seem to show that 

 there is a real advantasre in using iron for lightniiiij conductors over 

 copper, and that its greater specific resistance and higher fusing point 

 enables an iron rod or tape to get rid safely of an amount of electric 

 energy stored up in the dielective which would not be the case if it 

 were copper." * 



Fleming describes in full Dr. Lodge's experiments to prove the 

 non-magnetizability of iron by sudden discharges : — 



" In the experiments on alternative path, as described by Dr. 

 Lodge, the main result is very briefly summed up by saying that, 

 when a sudden discharge had to pass through a conductor, it was 

 found that iron and copper acted about equally well, and indeed iron 

 sometimes exhibited a little superiority, and that the thickness of the 

 conductor and its ordinary conductivity mattered very little indeed. 

 ... In the case of enormously rapid oscillations the value of the 

 impulsive impedance varies in simple proportion to the frequency of 

 the oscillations, and depends on the form and size of the circuit, but 

 not at all on its specific resistance, magnetic permeability, or diame- 

 ter. . . . For discharges of a million per second and ujiwards, such as 

 occur in jar discharges and perhaps in lightning, the impedance of all 

 reasonably conducting circuits is the same, and independent of con- 

 ductivity and permeability, and hardly affected by enormous changes 

 in diameter." f 



Turning now to the observations of Hertz, we find it stated that the 

 material, the resistance, and the diameter of the wire of the microm- 

 eter circuit employed by him, have very little influence on the result. 

 The rate of propagation of an electrical disturbance along a con- 

 ductor depends mainly on its capacity and coelHcient of self-induction, 

 and only to a small extent on its resistance. Hertz concludes that, 

 owing to the great rapidity of the alternations, the magnetism of the 

 iron is unable to follow them, and therefore has no effect on the self- 

 induction. When a portion of the micrometer circuit employed by 

 Hertz was surrounded by an iron tube, or replaced by an iron wire, 

 no perceptible effect was obtained, and thus the result was apparently 



* Fleming, Inrluction of Electric Currents, p. 398. t Ibid., p. 411. 



