Electrical Oscillations on Iron Wires. 511 



we have for the resulting value of the magnetic permeability 



fi = 230. 



This lies between the limits //, = 103 and ^=1110, found by 

 taking the number of oscillations one and a half and one half 

 respectively for the case of the iron wire. 



It should be noticed that this estimate of fi necessitates 

 assuming that T and L remain the same within broad limits. 

 Measurements of the single oscillation on the negatives show 

 that this is near enough the case. Part of the more rapid 

 decay of the oscillation in the iron may be well ascribed to the 

 dissipation of energy by hysteresis. While we cannot place 

 much reliance upon an estimate of its value in such a case — 

 its percentage effect probably increasing rapidly with the 

 decay of the spark — it is not difficult to show that its influence 

 may be very great. 



There still remains the fact, not generally recognized, that 

 in Leyden-jar discharges through iron wires the magnetic 

 property of the iron has time very materially to modify the 

 character of the spark. 



I give an example of the measurement of the half oscil- 

 lation, which was the only one visible on the photograph of 

 the discharge over iron wires, all the others having been 

 damped or extinguished by the iron, in comparison with 

 the measurement of the similar half oscillation on copper 

 wires of the same diameter as the iron wires. The number of 

 oscillations on the copper wires was from eight to ten. The 

 total duration of the discharge on iron wires was only three 

 miliionths of a second, while that on similar copper wires was 

 three hundred-thousandths of a second. A steel wire gave the 

 same results as the annealed iron w T ires. 



Fine Iron Wire. 



1 

 Length of first | 

 half oscillation 

 in millimetres. 



Large Iron Wire. 



Length of first 

 half oscillation 

 in millimetres. 



•23 

 •21 

 •19 



•21 



•20 

 •20 

 •19 



•19 



Fine Copper 

 Wire. 



•19 

 •20 

 •20 



•19 



Large Copper 

 Wire. 



•17 



•18 

 •20 



•18 



