and other Electrical Instruments. 



13 



Driving Flux. — The distribution of the somewhat compli- 

 cated alternating field was traced by the following method, 

 which also gave rough quantitative results. A telephone T 



Fi<r. 5. 



*±^r\ 



l&AO 



S 



(fig. 6) was arranged in a circuit with the search-coil F and 

 the low-resistance strip H K in such a way that the strip 

 could be switched out of circuit at will. One of the con- 

 nexions to HF was through a sliding contact, so that the 



Fiff. 6. 



resistance of the part in the telephone-circuit could be varied 

 from 0*05 ohm downwards. A current of 1 ampere was 

 maintained in the strip and was from the alternating circuit 

 which supplied the meter load. With the strip out of circuit 

 the search-coil was moved into various positions, and the dis- 

 tribution of the alternating flux observed by means of the 

 sound in the telephone. To measure the flux at any position 

 H K was set to such a value that the small P.D. introduced 

 by it into the telephone-circuit gave a sound of the same 

 loudness as that given when the search-coil was placed in the 

 flux. The absolute values given by this method came out 10 



