122 PROCEEDINGS OP THE AMERICAN ACADEMY 



But neglecting the magnetic property of the iron, its calculated re- 

 sistance to alternating currents of this periodicity was R' = 2.78 

 ohms. This is obviously inadequate, and would point to the conclu- 

 sion that the oscillation is not, as sometimes stated, too rapid to admit 

 of the magnetic action of the iron. 



If we substitute this value H' = 30 in the equation 



we have for the resulting value of the magnetic permeability jx = 230. 

 This lies between the limits yu, = 103 and /x = 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 fx 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 Ley- 

 den jar discharges through iron wires, the magnetic property of the 

 iron has time very materially to modify the character of the spark. 



We give an example of the measurement of the half-oscillation 

 which was the only one visible on the photograph of the discharge 

 over iron wires, all the others having been dampened or extinguished 

 by the iron, in compari>on 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 eight. 



The total duration of the discharge on iron wires was only three 

 millionths of a second, while that on similar copper wire was three 

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

 as the annealed iron wires. 



Comparative Leiigths of First Half-oscillation in Millimeters. 



Fine Iron Wire. Fine Copper Wire. 



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.21 .20 



.19 .20 



.21 .19 



