113 



Considerable range in sensibility for both coils is obtained by adjust- 

 ing them at different distances from the needle. Some idea of this rauge 

 may be obtained through inspection of the curve given in Fig. 3. 



This was taken vsith the coil S, having a constant E.M.P. of 69.8.S5 

 volts at its terminals. The abscissae represent the distances of the coil 

 from the needle; the ordinates, the corresponding value of the deflections 

 on the scale. 



Both coils w^ere calibrated at different distances from the needle with 

 the Thomson balances. Fig. 4 represents curves taken vpith the coil, M, 

 and shows no appreciable departure from the law of the squares. 



In order to facilitate taking the readings, compensating coils, M' and 

 /?', Fig. 5, were arranged in the circuit for M and S respectively, so that 

 the conditions within the conductor on which the observations were being 

 made remained the same when either M or S was cut out. This obviated 

 removing either coil when the reading due to the cuiTent in the other was 

 desired. 



In Fig. 5 is shown a diagram of the connections used in making an 

 observation for the angle of lag in a circuit which is here shown to be a 

 coil, J, on a split anchor ring. X and M are connected in series in the 

 secondary of a one-to-one transformer, in order to have no appreciable 

 impedance in the circuit, other than X. The electrical conditions in this 

 circiiit were then controlled by the resistance and choking coil in the 

 intermediate circuit. One commutator was arranged in the shunt circuit 

 to reverse the current inS, another to substitute the compensating coil 

 8' for S. 



One of the greatest diflficulties encountered in measurements of this 

 character is due to unsteadiness in the source. Particularly is this true 

 when all the readings can not be taken simultaneously. This may, 

 however, in a measure, be overcome by arranging an auxiliary voltmeter 

 similar to the E.M.F. coil, S, with its terminals connected across the ter- 

 minals of the secondary of the city transformer. The phasemeter readings 

 are then taken when the deflection due to their auxiliary coil is constant. 



With respect to accuracy the phasemeter as a current meter is per- 

 fectly similar to the galvanometer. 



