MAGNETISM. 151 



of iron arrived at a state of magnetic equilibrium, temporary 

 torsion diminishes the magnetism, and that the untwisting or 

 return to its primitive, state restores the original degree of 

 magnetisation. 



M. Guillemin observed that a bar slightly curved by its 

 own weight is straightened by being magnetised. Mr. Page 

 and Mr. Marrion discovered that a sound is emitted when 

 iron or steel is rapidly magnetised or demagnetised ; and Mr. 

 Joule found that a bar of iron is slightly elongated by mag- 

 netisation. 



Again, with regard to diamagnetic bodies, M. Matteucci 

 found that the mechanical compression of glass altered the 

 rotatory power upon a ray of polarised light which it trans- 

 mitted. He further considered that a change took place in 

 the temper of portions of glass which he submitted to the in- 

 fluence of powerful magnets. 



The same arguments which have been submitted to 

 the reader as to the other affections of matter being modes 

 of molecular motion, are therefore equally applicable to mag- 

 netism. 



