OERSTED'S THEORY. 241 



It has, however, been shown that soft iron, under 

 certain circumstances, may be made to retain a large 

 amount of magnetic force.* 



If a horse-shoe shaped bar of soft iron is rendered 

 magnetic V; the circulation of an electric current around 

 it, while its two ends are united by an armature of soft 

 iron, so that it is capable of supporting many hundred 

 pounds weight ; and we then, by breaking the circuit, 

 stop the current, taking care the armature is kept in 

 contact, the iron will not lose its magnetic property, 

 but will retain this power for many years. If the con- 

 necting piece of iron, the armature, is removed, the bar 

 immediately loses all its magnetism, and will not support 

 even the armature itself. This fact appears to confirm 

 the idea that magnetism is due to the retention of 

 electricity, and that steel possesses the property of 

 equalizing the opposing forces, or of binding this 

 principle to itself like an atmosphere. 



The influence of heat on magnetism is so remarkable 

 a proof of the dependence of this power upon molecular 

 arrangement, that it must not escape our notice. To 

 select but one of many experiments by Mr. Barlow, it 

 was found that in a bar of malleable iron, in which, 

 when cold, the magnetic effect was -f 30 0', all polarity 

 ceased at a white heat, that it was scarcely appreciable 

 at a red heat, but that at a blood-red heat it was equal 

 to + 41 O'.t 



The more closely we examine the peculiarities of the 

 magnetic power, and particularly as they are presented 

 to us in its terrestrial action, the more surprising will 

 its influence appear to be. We have discovered a 

 * On the Magnetic power of Soft Iron : by Mr. Watkins. 

 Plrlosophical Transactions, 1833. 



f Cavallo, On Magnetism. Cavallo was the first who noticed 

 the influence of heat on Magnetism. Consult On the anomalous 

 Magnetic Action of Hot Iron between the white and blood-red heat : 

 by Peter Barlow, Esq. Philosophical Transactions, 1822, p. 124. 

 Treatise on Magnetism : by Barlow. Encyclopaedia Metropolitana, 



R 



