PEIRCE. — BEHAVIOR OF THE CORE OF AN ELECTROMAGNET. 155 



pure time-lag 12 of magnetization, like that observed by Ewing and Lord 

 Rayleigh, large enough in the case of a very large core to affect some- 

 what the forms of the current curves ; in fact, I have spent a very long 

 time and have made many measurements upon a great number of oscil- 

 lograph records in order to see whether any such lag could be shown ; 

 but after all allowances have been made for the effects of eddy currents, 

 nothing tangible, if anything at all, remains, for such moderate excita- 

 tions as I have used with closed, finely divided cores. 



Figure 49. 



The full line represents the actual form of a reverse current curve in the coil 

 of a certain transformer the core of which is laminated; the curve sketched out 

 by dashes represents the theoretical form as obtained from the statical hysteresis 

 diagram. The dotted curve represents on an arbitrary scale the areas between 

 the real curve and the asymptote ; the flux change being nearly proportional to 

 the time. 



If to a circuit — without iron and unaffected by any neighboring 

 currents — which has a fixed inductance L, and resistance r, be applied 

 a fixed electromotive force, E, the current-time curve will follow the 

 equation 



E rt 



and the current will attain the intensity I = E/(r + fi) at the time ^ 

 such that 



12 G. Wiedemann, Galvanismus, 3, 738. Ewing, Magnetic Induction, § 84. 

 Gumlich und Schmidt, Electrotechnische Zeitschrift, 21, 1900. Eiicker, In- 

 augural Dissertation, Halle- Wittenberg, 1905. 



