1884.] 



On Magnetic Polarity and Neutrality. 



411 



This is seen in No. 2, which represents exactly what takes place in 

 No. 1 npon the cessation of the inducing influence. We notice that 

 the first portion of the exterior has rotated to south polarity, followed 

 by an intense north, but not of great density ; its reaction, being more 

 violent, rapidly rotates all the interior to a south polarity, gradually 

 weakening in intensity as the distance increases from the inducing 

 north polarity. The exterior, in fact, reacts upon its interior precisely 

 as before the inducing exterior magnet reacted upon the whole. In 

 No. 1 the south pole of the permanent magnet produced a continuous 

 curve of north the instant this ceased, the north of the exterior 

 produced an interior south, and if these are perfectly balanced, then 

 and then only will the bar become neutral. 



"When both sides of a bar are polarised at the same time, then we 

 have two similar curves to No. 2, as shown at No. 3, the diminishing 

 curves of internal opposing polarity overlapping each other ; the curve 

 represents those obtained on bars 2 centims. in thickness. If the 

 inducing force is great the penetration is greater and more intense, 

 reacting more violently, and the central depression of the opposing 

 waves is less pronounced. If we keep the previous force and diminish 

 the thickness of the bar, the two central waves cross each other, and 

 at last, as in No. 4, we have only one wave ; this occurs with bars of 

 but 3 millims. thickness. We notice here that from a want of 

 sufficient material in the centre of the iron, it is constrained to 

 force its central wave to a far higher degree, and that the exterior 

 now also commences to be reacted upon more violently. Evidently 

 the conditions are strained, and we shall see the result later. This 

 want of sufficient material to form the internal opposing wave of 

 polarity is shown when we reduce the thickness of the bar to 1 millim., 

 the width being 3 centims., and the length 30 or more, as in all pre- 

 vious cases. Here there are no traces of an internal curve, the 

 opposing polarity, as shown in No. 5, being entirely on the sur- 

 face. 



I have shown that we may clearly perceive this curve by dissolving 

 its exterior in dilute nitric acid, but as I employed vibrations to 

 reduce it to neutrality, this might give rise to objections on the score 

 of mechanical reactions. To meet this objection several strips of 

 magnetised steel of various forms, but all \ millim. in thickness, were 

 reduced almost to neutrality by simply heating them to a dull red 

 heat, allowing them to cool slowly. These gave remarkable results, 

 proving that the vibrations caused by heat are similar in results to 

 mechanical vibrations, and I found that in most cases their external 

 evident magnetism was increased 100 per cent, by an immersion of 

 fifteen minutes, and 600 per cent, in one hour. 



Interesting results can be obtained by this method, but if rapidity 

 of chemical action is desired we must first remove the scale or oxide 



