PEIRCE. — BEHAVIOR OF THE CORE OF AN ELECTROMAGNET. 147 



the same magnetic journeys of the cores, but I could not detect any 

 differences which did not lie far within the small uncertainty which 

 the viscosity of the oil in the oscillograph may be supposed to cause. 

 It does not seem worth while to print a long series of numbers to 

 illustrate this kind of comparison though the labor was great. 



If, then, the core of an electromagnet is made of iron wire not more 

 than one tenth of a millimeter in diameter and carefully varnished, it 

 seems to be true within the limits of accuracy of my measurements 

 and for the comparatively moderate excitations used, that if the core 



FlGDKE 41. 



Theoretical forms of direct and reverse current curves for a coil of 1394 turns 

 belonging to the magnet Q, when the resistance of the circuit is 15 ohms and the 

 applied voltage is 19.5. 



is in a given magnetic state at the start, the change of the flux of 

 magnetic induction caused by a current which grows from zero with- 

 out decreasing to a given final intensity, is quite independent of the 

 manner of growth of this current. It may grow continuously or by 

 steps, and if eddy currents are not appreciable, the condition of the 

 core at the end is the same. According to this, one would get exactly 

 the same hysteresis diagram from an accurately drawn current curve 

 of the form V (Figure 4) corresponding to any change of current in the 

 exciting coil as from the corresponding U diagram or from any slow 

 step-by-step ballistic method. Nothing of the nature of time lag, if it 

 exists at all, affects the growth of the induction in the iron appreci- 

 ably. Even in the case of an ordinary transformer, where the effects 



