IV. — MISCELLANEOUS, 



Art. LIX. — Magnetization of Iron by High-frequency Dis- 

 charges. 



By E. Butherford, M.A. 



[Read before the Philosophical Institute of Canterbury, 7th November, 



1894.] 



Plates XLVIII. and XLIX. 



I. Magnetization of Iron by Leyden-jar Discharges. 



The subject of the magnetization of iron in very rapidly- 

 varying fields has been touched upon more or less fully by 

 several different scientists, notably Dr. Lodge, Professor J. J. 

 Thomson, Hertz, and a few others. In Dr. Lodge's 

 " Modern Views of Electricity " we find the following: "But 

 in the case of a discharge of a leyden-jar iron is of no 

 advantage. The current oscillates so quickly that any iron 

 introduced into the circuit, however subdivided into thin 

 wires it may be, is protected from magnetism by inverse 

 currents induced in its outer skin, and accordingly does not 

 get magnetized, and, so far from increasing the inductance of 

 the discharge circuit, it positively diminishes it by the reac- 

 tion effect of these induced currents ; it acts, in fact, much as 

 a mass of copper might be expected to do." 



In Fleming's " Alternate Current Transformer," vol. i., 

 p. 398, there is a description of Dr. Lodge's experiments on the 

 effect of iron in rapidly- varying fields : " With respect to the 

 apparent superiority of iron, it would naturally be supposed 

 that, since the magnetic permeability of iron bestows upon it 

 greater inductance, it would form a less suitable conductor for 

 discharging with great suddenness electrical energy. Owing to 

 the fact that the current only penetrates into the skin of the 

 conductor there is but little of the mass of the iron magnetized, 

 even if these instantaneous discharges are capable of mag- 

 netizing iron . . . the electro-motive impulses, or sudden 

 rushes of electricity, do not magnetize the iron, and hence do 

 not find in it greater self-inductance than they would find in a 

 non-magnetic but otherwise similar conductor." 

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