Ferromagnetic Wires in a Magnetizing Field. 647 



the sound is probably the change in length by magnetization . 

 When a magnetic substance is suddenly magnetized or 

 demagnetized it elongates or contracts, and attains its initial 

 length, after several oscillatory changes in length have 

 occurred in quick succession. This oscillation will produce a 

 clinking note at the moment of magnetization or demag- 

 netization. This view is favoured by the experiments of 

 Marrian and Wertheim. But Matteucci found that the tension 

 does not affect the pitch of the sound ; if his result were 

 true, the vibration would be of more complex nature. 



The third kind of sounds is one accompanying magnetiza- 

 tion 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 caused by the continuous series of vibrations above 

 referred to. The experiments of Beatson and others will 

 agree with this view. 



De la Rive and Wiedemann ascribe the phenomenon to 

 the molecular effect, but Wertheim and Bachmetjew to the 

 magnetic change in length. We also consider it highly 

 probable that the change of length is the cause producing the 

 sound belonging to the second and third categories. The 

 present experiment was undertaken to get a clearer insight 

 into the nature of the phenomenon. 



In all previous experiments, the range of the frequency of 

 an intermittent or alternate current was very limited ; but in 

 our case, a string alternator * was introduced for continuously 

 varying the period of the current. The arrangement is 

 shown in fig. 1. A copper wire is horizontally stretched; 



one of the ends is fixed to a support S, while the other 

 passing over the pulley P is attached to a weight Q. The 

 wire is electrically insulated at the centre R, so that the 

 current through the two mercury cups ra x and m 2 flows in 

 the circuit C. The battery currents pass through the two 

 mercury contacts M 2 and M 2 . The vibration of the string is 



* K. Honda and S. Shimizu, Amer. Journ. Sci. vol. x. p. 64 (1900) j 

 Phys. Zeitsch. 2 Jahrgang, vol. xxv. p. 371 (1901). 



