i9°5] McCLELLAN— USE OF OSCILLOGRAPH. 175 



granting that the loops have been calibrated so that current values 

 may be measured by them. It is evident that if the multiplying 

 power of the shunt for direct currents is known, i t can be obtained 

 from z\ without serious error. Also since s is non-inductive, the 

 angle (i/ 3 ) can be known from a plate taken similarly to Fig. 8. 

 Then the angle (/,/,) can be calculated, and subtracted from the 

 angle (i\i.,) leaving the angle (/>",). Having the latter angle, with 

 i t and /.,, (/>" 3 ) can be calculated, and added to (/>',), and (Ef), 

 which is known as before, thus giving Ei 3 , which is the desired 

 angle. 



The writer has not worked the latter discussion out for two 

 reasons. First, the errors of measurement on a photographic plate 



U 



Fig. io. 



would not permit of any accurate results since in any case the 

 angles are small. Second, in the large majority of cases, the mul- 

 tiplying power of the shunt is so large, that the currents /, and i 

 are in the same phase, so far as could be measured. Also the re- 

 sistance in the 2 circuit so large that E and i are in the same 

 phase. Therefore the angle desired can be obtained exactly as 8 

 was in the preceding discussion, with the introduction of the multi- 

 plying power of the shunt. The use of ammeters in some of the 

 circuits would greatly facilitate matters in many cases. 



The above discussion shows that, with the oscillograph, the phase 

 angle can be calculated. In no case can it be obtained by a simple 

 measurement on a single plate. Owing to the thickness of the lines 

 traced by the moving spot, measurements cannot be made closer 

 than a quarter of a millimeter, so that a long curve must be obtained 

 if any accuracy is to be attained, especially with small differences 

 of phase. While the double oscillograph could not be recom- 

 mended in any way as a phase meter, yet it does permit an ap- 



