648 Messrs. K. Honda and S. Shimizu on the Vibration of 



maintained constantly oscillating by the electromagnet n 

 and s. If the string is set in vibration with a single node at R, 

 an alternate current is produced in the circuit C ; if only one 

 set of batteries is used, an intermittent current is produced 

 in tbe same circuit. The frequency of alternation or of inter- 

 ruption can easily be varied by the change of length and of 

 tension of the wire. Cx and C 2 are two condensers with 

 suitable capacity to diminish the sparks at the mercury 

 contacts Mi and M 2 . 



For the study of the longitudinal vibration of a ferromag- 

 netic wire under a varying field, we used Professor Nagaoka's 

 apparatus for the measurement of minute changes of length. 

 In the present experiment, the glass fibre in the slit of the 

 collimator was removed and the fine slit illuminated by a gas 

 flame was used instead. The image of the slit, after reflexion 

 by the revolving mirror and refraction through a converging 

 lens, was formed in the field of a micrometer ocular. If the 

 wire makes a rapid longitudinal vibration, its amplitude can 

 be measured by observing the broadening of the image of 

 the slit. 



The wire to be tested was 21 cm. long and 0*150 cm. thick. 

 The magnetizing coil was 30 cm. long and wound in 4 layers 

 on a wooden frame, and gave a field of 19*82 c.G.s. units due 

 to a current of one ampere. The coefficient of self-induction 

 of the whole circuit was 5*2 xlO 6 c.G.s. units and its re- 

 sistance 12*9X1, so that the time of relaxation was 0*000403 

 second. 



The results of experiments may be summarized as follows : — 



(a) Wires of non-magnetic metals give no sound by an 

 intermittent or alternate field of any frequency up to 

 200 per second. 



(b) A ferromagnetic wire emits an audible sound in an 



intermittent or alternate field. 



(c) The pitch of the sound is always the same as that of an 



intermittent or alternate current. 



(d) The amplitude of vibration is in general far greater than 

 the change of length produced by a steady field of such 

 strength that it is equal to the maximum value of the 

 intermittent or alternate field. 



The pitch of the sound was determined by tuning a mono- 

 chord to the period of the current and counting the number 

 of beats. From the results above mentioned, we may safely 

 conclude that the sound emitted by the ferromagnetics is due 

 to the magnetic change in length of the wire. One make or 

 break of the current forces the wire to accomplish a vibration, 

 and a succession of such series constitutes a sound, the pitch 



