PEIRCE. — BEHAVIOR OF THE CORE OF AN ELECTROMAGNET. 135 



CURRENT. 



2.3 amperes, the induced current curve was R. The sum of the areas 

 under the curves Q and B was 74.3 square centimeters. The curve P 

 shows the current record in the secondary 

 circuit when the primary circuit was sud- 

 denly closed with no resistance in the rheo- 

 stat : the area under this oscillogram was 

 74.6 square centimeters. All the currents 

 were reverse currents. Most of the area 

 determinations of this paper were made 

 with a Coradi " Grand planimetre roulant 

 et a sphere." 



Figure 30 shows a careful reproduction 

 of the record of an oscillograph in the 

 primary circuit of the arrangement just 

 described. These curves were taken on 

 the same day as those of the last figure. 

 In this case the flux change due to the 

 current which gave the curve T was 

 to the sum of the flux changes caused 

 by the partial currents as 1130 to 1126. 

 These numbers do not show any real dif- 

 ference between the corresponding physi- 

 cal quantities, but point to difficulties of 

 measurement. 



The Effect of the Magnetic Charac- 

 teristics of the Core upon the Man- 

 ner of Growth of a Current in the 

 Coil of a Large Electromagnet. 



If under the application of a constant 

 electromotive force to the coil circuit of 

 an electromagnet a current grows grad- 

 ually in the coil to its full value, the 

 magnetic flux in the core at any moment 

 depends, as we have seen, not only upon 8 

 the instantaneous strength of the current, 

 but also upon the magnetic state of the *" ■ 

 core at the beginning. Moreover, if the 

 core is solid, it is clear that the magne- 

 tizing field to which the interior of the iron mass is exposed may be 

 quite different at any instant from what it would be if eddy currents 

 were nonexistent. If, however, the core is built up of such thin sheets 



r* 



FlGCRE 30. 



