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LXI. Damping pf Electrical Oscillations on Iron Wires. 

 By John Trowbridge*. 



IT has generally been assumed by those who have studied 

 the subject of very rapid oscillations of Electricity, such 

 as occur in Leyden-jar discharges, that the magnetic character 

 cf the conductor has very little influence upon the character 

 of the discharge. Thus, in a note to an article on Electrical 

 Waves (Annalen der Physik unci Chemie, vol. cviii. 1859, 

 p. 499), W. Feddersen states that electrical oscillations may 

 suffer a slight weakening on iron ; but this diminution is very 

 slight, and results from the resistance of iron being greater 

 than that of other metals f. 



In Dr. Lodge's treatise on Modern Views of Electricity 

 (ed. 1889) we find the following : — 



" But in the case of the discharge of a ueyden jar iron is of 

 no advantage. The current oscillates so quickly that any iron 

 introduced into its 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 mag- 

 netized ; and so far from increasing the inductance of the 

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

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

 mass of copper might be expected to do" (p. 365). 



Fleming writes as follows : — 



" 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 

 electric energy. Owing to the fact that the current only 

 penetrates just into the skin of the conductor, there is but 

 little of the mass of the iron magnetized. Even if these instan- 

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

 electromotive impulses or sudden rushes of electricity do not 

 magnetize the iron, and hence do not find in it any greater 

 self-inductive opposition than they would find in a non- 

 magnetic but otherwise similar conductor. Dr. Lodge's further 

 researches seem to show that there is a real advantage in using 

 iron for lightning-conductors over copper, and that its greater 

 specific resistance and higher fusing-point enable an iron rod 

 or tape to get rid safely of an amount of electric energy 



* Frum an advance proof communicated by the Author. 



t " JBeim Eisen konnte in Folge der Magnetisirungen eine Abweichung 

 heivortreten ; indess zeigt der Versuch, dass dieselbe keinenfalls bedeutend 

 ist, iibrigens in dem Sinne erfolgen miisste, als wenn die Elektricitat beim 

 Eisen ein grosseres Hinderniss faiide, wie bei den ubrigen Metallen." 



