GENERAL ACCOUNT OF MAGNETIC ACTIONS 183 



ultimately reverse it, we find that the magnetisation will in general 

 decrease in different ways according to the position of the point P, 



FIG. 130. 



Fig. 131, on the curve representing the condition arrived at before 

 decrease. If P is in the straight initial part O A, the magnetisation 

 will decrease in proportion to the decrease in the magnetising 

 force. But if P is on the upper part of the curve when we begin 



FIG. 131. 



to diminish the magnetising force, the magnetisation for a given 

 current on the return journey is greater than it was on the outgoing 

 journey, and the magnetisation curve P M now lies above O A P. 

 The magnetic condition tends then to persist, and this tendency 

 for a preceding magnetic condition to persist is termed magnetic 

 hysteresis, a term introduced by Ewing. If the current is brought 

 down to zero so that there is no magnetising force, there is still 



