198 



Prof. D. E. Hughes. 



[May 10, 



Similar but stronger effects were observed on soft iron wires. A 

 neutral iron wire, 3 millims. diameter and 40 centims. in length, was 

 held vertically, to represent a lightning-rod, the enormous spark or 

 charge from the condenser, charged by the 3,360 cells, striking its 

 ripper portion. This rod became invariably magnetised by the earth's 

 directive influence, its upper portion being in all cases south and its 

 lower north. The magnetism, however, was comparatively feeble, and 

 only equal to that obtained on the same wire by mechanical vibrations 

 caused by repeated blows on the upper portion of the wire with a 

 wooden mallet. From these experiments we draw the conclusion that 

 every lightning-conductor must be magnetised, but that if it is without 

 spirality the magnetism can never be greater than that due to the 

 directive influence of terrestrial magnetism. 



If we could destroy or change the inherent polarity of iron, we 

 should expect to find traces of it in wires which had been submitted 

 to such an enormous electric current, but the wires thus acted upon 

 remain similar in every respect to ordinary iron wires, their polarity for 

 a given force and their neutrality being similar in nature and degree ; 

 consequently the inherent magnetic polarity has not been changed or 

 destroyed. 



Neutrality. 



The induction balance is affected by three distinct arrangements of 

 molecular structure in iron and steel, by means of which we have 

 apparent external neutrality. 



^Yy. 6 



In fig. 6, at A, we have neutrality by the mutual attraction of each 

 pair of molecules, being the shortest path in which they could satisfy 

 their mutual attractions. At B we have the case of superposed mag- 

 netism of equal external value, rendering the wire or rod apparently 

 neutral, although a lower series of molecules are rotated in the oppo- 

 site direction from the upper series, giving to the rod opposite and 

 equal polarities. At C we have the molecules arranged in a circular 

 chain around the axis of a wire or rod through which an electric 

 current has passed. At D we have the evident polarity induced by 

 the earth's directive influence when a soft iron rod is held in the 



