,530 Dr. A. 0. Rankine and Dr. F. B. Young on the 



sounds were clearly heard in the telephones corresponding 

 to the musical u clink" of the rod when struck. These 

 sounds, however, died out as the coil was rotated to either 

 position P or position R. The disturbances were thus clearly 

 due to an oscillating electric current induced in the cable by 

 magnetic changes produced in the rod ; such a current would 

 produce a magnetic field around the cable whose lines would 

 be concentric with the cable and would have no parallel or 

 radial component. 



If the circuit was broken the sounds in the telephone dis- 

 appeared entirely, as would be expected. 



(b) Coil near Rod. 



When the coil was held near the rod the vibrations were 

 audible in the telephones as before. The sounds were not, 

 however, cut out by the rotation of the coil ; they were in fact 

 sometimes greater in intensity for position P or R than for 

 position C Definite differences of quality were' perceptible 

 as the coil rotated, though the fundamental tone remained 

 unaltered. 



If the circuit was broken the sounds in the telephone- 

 receivers persisted, though with certain changes of intensity 

 and quality. 



(c) Observations with two Search- Coils. 



Two similar search-coils were connected in series with the 

 -amplifier. 



(i.) These were placed near different parts of the cable in 

 position C. By rotating one of these it was possible 

 to balance the e.m.f.'s induced in the two coils so that 

 silence was produced. 



(ii.) Attempts were made to balance one coil near the 

 cable against the other placed near the rod. Only a 

 slight reduction in the intensity of the sound could, 

 however, be produced, indicating that the e.m.f.'s 

 induced in the two coils were not in phase. 



s(iii.) The two coils were next placed near different parts of 

 the rod, both in position C. Since rotation of either 

 coil would have introduced some component of the 

 magnetic field other than the concentric, an attempt 

 was made to balance the induced e.m.f.'s by turning 

 the coils into opposition and then moving each in 

 turn, without rotation, further from the rod. No 

 signs of even partial neutralization were, however, 

 perceived. Hence the magnetic oscillation at two 

 different parts of the rod were out of phase. 



