and Magnetic Permeability. 183 



the wire. The mean value, found by integrating this expres- 

 sion over the cross-section of the wire, is : 

 H mean = ^73a = 2/3H max . 



The following values were obtained by Klemencic* for the 

 susceptibility of iron wire to a steady circular magnetizing 

 force. The last column gives the permeability as calculated 

 from his results : 



i( Amperes) 



-timax. 



-tiixiean 



k 



/" 



•12 



•23 



•15 



14-3 



180 



•23 



•43 



•29 



16-7 



210 



•46 



•87 



•58 



20-2 



255 



•85 



1-62 



1*08 



28-7 



362 



1-26 



2-40 



1-60 



46-8 



590 



1-45 



2-77 



1-85 



61-2 



771 



2-39 



4-56 



3*04 



103-5 



1304 



3*62 



6*90 



4-60 



112-9 



1423 



These values of the permeability are thus seen not to differ 

 very much from the average values of the permeability with 

 longitudinal magnetization. 



From the results of our experiment and the above table, it 

 would seem that the oscillatory currents we employed were 

 equivalent in their magnetizing effects upon the iron wire to 

 •steady currents varying in strength from about 0*8 to 1*4 

 amperes. We can easily get an approximate idea of what the 

 maximum current strength was as follows. The images meas- 

 ured on the photographic plates were in every case the images 

 of the first half-oscillation. Neglecting the damping during 

 this first half-oscillation, which is small, the maximum current 

 is given by the following expression : 



I E 



mas ' a/R' 2 + 4ttVL' 2 



E is the potential to which the condenser was charged. The 

 e.m.f. of each cell was very approximately 2 volts, giving as 

 the total e.m.f., 



E = 20,000 X 10 8 



We can thus form the following table, making use of the 

 maximum current strengths thus obtained, and the maximum 

 magnetic field strengths : 



Imax. (Amperes) 



Frequency. 



■tj-rnax. 



Permeability 



140 



605 



53 



327 



282 



1280 



106 



443 



742 



3300 



278 



711 



* Wied. Annalen, lvi, p. 585. 



