Circular and Longitudinal Magnetizations. 247 



nished when the current is flowing along the wire. This 

 means a diminution in susceptibility. Here also may be 

 mentioned the fact that the first effect of putting on the cur- 

 rent when the wire is strongly magnetized is a diminution of 

 longitudinal magnetic intensity. 



Secondly, when the linear current is flowing, the average 

 magnetic intensity over a whole cycle no longer corresponds 

 to the condition of zero polarity, as in the normal case when 

 no linear current is flowing. For the one current, the mag- 

 netic intensity oscillates, so to speak, about a large positive 

 polarity ; and for the current in the reverse direction it oscil- 

 lates about a nearly equal negative polarity. If we reckon 

 polarity in the usual way as a directed quantity measured 

 from the south pole to the north, then the direction of the 

 linear current is in the same direction as the average polarity 

 which it sustains, when the wire is subjected to an absolutely 

 symmetrical cycle of magnetizing force on each side of zero. 



Thirdly, the curves b and c are no longer symmetrical on 

 the side of the zero-line of magnetic force. The closed curve 

 b is more pointed at its positive end than at its negative end ; 

 the curve c, on the other hand, is more pointed at its negative 

 end than at its positive. If we turn the figure upside down, 

 the general appearance remains the same as before. Thus the 

 effect of the linear current is such as very distinctly to modify 

 the form of the ascending and descending branches. The 

 descending branch of b is very, similar to the ascending branch 

 of c ; and the ascending branch of b is very similar to the 

 descending branch of c. We may connect this peculiarity 

 with the peculiarities already described in these words : — 



A current passing along an iron wire, which is being mag- 

 netized, diminishes the apparent susceptibility of the wire ; 

 but this effect is more pronounced when the wire is acquiring 

 a longitudinal polarity in the opposite direction to that in 

 which the linear current is flowing. Hence, during any cyclic 

 operation, the wire tends to acquire an average polarity in the 

 same direction as that in which the current flows. 



These effects are more pronounced the stronger the linear 

 current is as compared with the magnetizing field. In a 

 moderate cyclic field the effect of the linear current may be 

 so strong as to prevent the wire ever acquiring other than one 

 kind of polarity. For example, this effect was produced in a 

 field + 4 with a current of nearly 2 amperes. For the linear 

 current in one direction the b curve never dipped below the 

 zero-intensity line, and for the current in the other direction 

 the curve c never rose above it. 



On the other hand, in stronger mao-netizing fields, from 10 



