Magnetic Effects of Vibration in Iron Mods. 531 



The oscillating magnetic field around the rod was obviously 

 far less simple in character than that round the cable. 



Observations of various modes of Vibration. 



The following observations relate to particular modes of 

 vibration produced as described above. In each case the 

 frequency of the note transmitted directly through the air 

 was determined by means of a sonometer and standard 

 tuning-fork. This was compared with the frequency given 

 by calculation, a rough verification of the mode of vibration 

 being thus obtained. 



(a) Torsional Vibration. 



The note heard from the bar was 950^/sec. (calculated 

 frequency about 880^/sec), and the same note was detected 

 in the receivers. 



Near the rod on closed circuit the concentric, parallel and 

 radial components could all be detected, their relative inten- 

 sities varying at different points along the bar. Breaking 

 the circuit produced no marked change in the field around 

 the rod except in the case of the concentric component. In 

 this case a marked diminution was observed near the end of 

 the rod, but very little near the clamped centre. The obser- 

 vation suggests that the concentric component near the end 

 was largely secondary and due to the current produced in 

 the circuit ; whilst that near the centre was directly associated 

 with the magnetic state of the rod. 



(b) Longitudinal Vibrations. 



The note heard directly from the rod had a frequency of 

 1400^/sec. (calculated frequency about 1400-^/sec), and the 

 same note was detected in the receivers. 



The variation in the strengths of the radial and parallel 

 components at various parts of the rod suggested the existence 

 of a field such as is commonly associated with a rod longitu- 

 dinally magnetized. Thus at D the radial component was 

 stronger than the parallel component, whilst at E the parallel 

 component was the stronger though it was weaker than the 

 radial component at D. The effects observed when the coil 

 was threaded on the bar were consistent with this view; the 

 longitudinal note was clearly heard and was loudest when 

 the coil was near the centre of the bar. 



(c) Lateral Vibration. 



By striking the rod at suitable points it was possible to 

 emphasize various overtones which were identified by means 



