VIBRATION OF FERROMAGNETIC WIRES. 3 



"2. A sliort consideratioM of these results leads us to distino-uish 



o 



three kinds of tlie sound. The tirst is the combined effect of the 

 magnetic force and the electric currerit. The sounds noticed by Page, 

 Delezenne and de la Rive belong to this category ; they do not depend 

 upon the magnetic property of the substance, but on the mechanical 

 action produced by the magnetic force and current. 



The second kind of sounds accompanies the magnetization or 

 demagnetization of a magnetic substance at the make or break of 

 a magnetizing current. The sounds noticed by Marrian arid others 

 belong to this category. The cause of the sound is probably the change 

 of length by magnetization. When a magnetic substance is suddenly 

 magnetized or demagnetized, it elongates or contracts and attains its 

 linal length, after several oscillatory changes in length have occurred 

 in quick succession. This oscillation will produce a clinging note 

 at the moment of magnetization or demagnetization. This view is 

 favoured by the experiments of Marrian and Wertheim. But Matteucci 

 tound that the tension does not affect the pitcli of the sound ; if his 

 result were true, the vibration would be of more complex nature. 



The third kind of sounds is one accompanying magnetization by 

 an intermittent or alternate current of a definite frequency, or one 

 produced when the above mentioned current is passed directly through 

 the substance. The sound is probably produced by the continuous 

 series of vibration above referred to. The experiments of Beatson and 

 others will agree with this view. 



De la Rive and Wiedemann ascribe the cause of the phenomenon 

 to the molecular effect, but Wertheim and Bachmetjew to the 

 magnetic change of length. We also consider it highly probable that 

 the change of length is the cause producing the sound belonging to 

 the second and third kinds. The present experiment was undertaken 

 to get a clearer insight into the nature of the plienomenon. 



