PEIRCE. — BEHAVIOR OF THE CORE OF AN ELECTROMAGNET. 159 



point (P) on the time axis — by PDXU. The upper part of the curve 

 was in no way distinguishable from the corresponding portion of the U 

 diagram. Mr. John Coulson and I have taken many records of this 

 kind and have not been able to detect any difference between the 

 upper parts of the different kinds of curves. The second part of the 

 U diagram starts off at exactly the same angle with the horizontal that 

 the other curve has when the line KG is crossed. The area OKDHO 

 when divided by the length OK should be the same as the area PSTDP 

 divided by the length 0.1. 



If eddy currents are present, the upper portions of a U diagram and 

 of a V diagram do not entirely agree. Figure 53 represents diagrams 



SECONDS. 



Figure 53. 



Growth from an originally neutral core of a current in a transformer with 

 a laminated core. The effects of eddy currents are here noticeable. 



for the magnet Q which has a laminated core, although eddy currents 

 are not entirely shut out. If the upper part of the U diagram (GBQ) 

 be shifted to the left, it will be found to agree with the curve PCO from 

 P to C, but beyond C the two are quite different, as the dotted line 

 indicates. When the V current, the growth' of which is represented 

 by the line OOP, has reached the strength OA, the induction flux 

 through the core is only a small fraction of the flux when a steady 

 current of final strength OA is established in the coil in the manner 

 represented by OKG. The existence of eddy currents is indicated 

 clearly by the fact that the first portion of the curve GBQ is nearly 

 vertical. These diagrams were obtained when the core had been well 

 demagnetized. Figure 54 shows similar diagrams for direct curves 

 (dotted) and for reverse curves (full). 



