PEIRCE. — MANNER OP GROWTH OF A CURRENT. 



531 



The Manner of Growth of a Current in the Coil of an 

 Electromagnet which has a Solid Core. 



We may now consider some oscillograph records which show the 

 manner in which under given circumstances a current will grow in the 

 coil of the magnet represented by Figure 1. It is evident from what 

 precedes that when other conditions are determined, the magnetic state 

 of the core at the time when the coil circuit is closed will generally 

 influence the result greatly. By sending through the coil a long series 

 of steady currents of gradually decreasing intensity alternately in one 

 direction and the other, one may reduce very low the residual magnetism 

 in the iron even when the gap is closed. 



Figure 13 shows building-up curves from a nearly neutral core, under 

 a voltage of about 84, when the air gap was closed, for currents of six 

 different intensities from 1.2 amperes to 6.5 amperes. 



Figure 14. 



Figure 14 shows curves obtained with a voltage of about 80 under 

 two different conditions of the core. After the iron had been pretty 

 well demagnetized, the growth of the current when the coil circuit was 

 suddenly closed followed the law indicated by the upper curve : if, when 

 the current had become steady, the circuit was broken and, after fifteen 

 or twenty seconds, closed with the direction of the current reversed, the 

 march of the current followed the lower curve. The width of the gap 

 was 1.6 mm. in this experiment. To study the influence of the width 

 of the air gap upon the shape of the building-up curve of the current in 

 the coil circuit I used first a storage battery of relatively high voltage 



