McCLELLAN— USE OF OSCILLOGRAPH. 



173 



ator, so that its speed could be maintained constant, was connected 

 through a lamp resistance, a variable standard of inductance, and 

 the loop O v in series. The other loop was connected across the 

 inductance. The resistance of the standard of inductance was 

 9.89 ohms in all positions. The angle of lag for any given posi- 

 tion was therefore easily calculated. Moreover, as the resistance 

 of an oscillograph loop with its fuse, is also about ten ohms, quite 

 a difference between a and <p could be expected. Now we have to 

 determine r, <p, and 8, in order to determine a. The procedure 

 was as follows. With the inductance set to some definite value, 

 Z, a plate was taken. Such a plate is shown by Fig. 7. With 



Fig. 9. 



the standard set to zero another plate was taken. This is shown 

 in Fig. 8. Now to obtain the ratio r, we have to measure the 

 ratio of the amplitudes of the two waves. As these waves are 

 obtained from two different loops, it will be necessary to obtain 

 the ratio of the galvanometer constants of the two loops. A third 

 plate was taken with the two loops connected in series, and one 

 current passing through both. For accuracy in measurement, the 

 loops were connected oppositely, so that an apparent phase differ- 

 ence of 180 degrees results. This is shown in Fig. 9. The fol- 

 lowing measurements are then made. C = the ratio of galvanom- 

 eter constants of the two obtained from ratio of amplitudes in 

 Fig. 9. 

 r= iji 2 obtained from ratio of amplitudes in Fig. 7. 



