174 



McCLELLAN— USE OF OSCILLOGRAPH. 



[April 



A 4 and l^, wave-lengths obtained from Figs. 7 and 8 respectively. 



/^ and l^, phase displacement, obtained from Figs. 7 and 8 

 respectively r obtained from ratio of amplitudes in Fig. 7. 



During the taking of each plate the value of the frequency must 

 be observed. 



R = resistance of the standard of inductance. We then have the 

 following : 



= /36o, 



9 = ; 3 6 °- 

 V 



By substituting <p' and r' in (3) we get 6, By substituting <s, d 

 and r in (2) we get «. The true value of a is given by the relation 



tan" 



Values for a as obtained from five different sets of plates are 

 given. A calculation on the first plate showed that was prac- 

 tically equal to <p' , so that (3) was not used. 



R = 9 . 



377 



It is evident, that in the simplest application of the oscillograph, 

 a mere inspection of the plate is not sufficient to obtain the true 

 difference of phase. The general case is much more complex. 

 This is represented by the diagram of connections in Fig. 10, and 

 the vector diagram in Fig. 11. It is necessary to introduce a series 

 non-inductive resistence in circuit with 2 , and a shunt on O v in 

 order to bring the current to a proper size. The letters have the 

 same significance as before, and in addition s is the resistance of the 

 shunt, R' is the series resistance, i, is the total current, and i, is 

 the current in the shunt. As before, the angle {Et z ) is the quan- 

 tity desired. Now a plate obtained with the connections ar- 

 ranged as in Fig. 10, would give us /,, i\, and the angle (*,*',), 





