J. Trowbridge — Electrical Waves on Iron Wires. 307 



Art. XLIV. — Change of Period of Electrical Waves on Iron 

 Wires ; by John Trowbridge. 



In an investigation upon the damping of electrical waves on 

 iron wires'" I endeavored to detect a change of periodicity as well 

 as a damping of these waves. On account, however, of the 

 strong damping effect exerted by the magnetic nature of the con- 

 ductors, not a sufficient number of oscillations could be set up 

 in the conductors to enable one to make conclusive measure- 

 ments. With more powerful means of experimenting I re- 

 turned to the subject ; and I have detected a marked change 

 in the period of electrical waves which is produced by the 

 magnetic nature of the wire. At the same time Mr. Charles 

 E. St. John, working in the Jefferson Physical Laboratory, by 

 an entirely different method has shown a change in wave 

 length on iron wires even for the very rapid periods of the 

 Hertz vibrator. It will be remembered that Hertz believed 

 that iron wires behaved like copper wires when transmitting 

 very rapid electrical oscillations. Stefanf in a recent paper 

 gives an analysis of electrical oscillations in which he proves 

 that rapid electrical waves on iron wire circuits have the same 

 wave length as those on a copper circuit of the same geometrical 

 form — the electrostatic capacity of the two circuits being the 

 same. 



With reference, therefore, both to the theory of electrical 

 waves and to the theories of magnetism, it seemed important 

 to determine whether there is a lengthening of electrical waves 

 on iron wires. 



The method of investigation I employed was the same as 

 that which I have described in my paper on the damping of 

 electrical waves on iron wires. A Leyden jar was discharged 

 through the given wires and the resulting spark spread out by 

 a revolving mirror, was photographed. The apparatus was also 

 modified as I have described in my paper on electrical resonance 

 and electrical interference.^: 



It was important in this investigation to be able to compare 

 the times of oscillation on the iron circuits and the copper cir- 

 cuits, and it seemed best to employ some method of imprinting, 

 so to speak, the time of a standard circuit on each photograph, 

 beside the photograph of the spark produced on either the iron 

 circuit or the copper circuit; for if the speed of the mirror 

 changed this change could be readily detected by the measure- 



* Phil. Mag., Dec, 1891. 



f Ann. der Physik und Chemie, xli. 1890, p. 422. 



\ Phil. Mag., Aug., 1894. 



Am. Jour. Sci.— Third Series, Vol. XLVIII, No. 286.— October, 1S94. 

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