98 



strength of field at 6,000 ampere turns is 

 142 English lines, and the observed 

 terminal pressure when running idle is 

 1,560 volts. This gives a coefficient of k 

 == 2.370. When working at the full out- 

 put of 30 amperes and 2,000 volts, the 

 mean electromotive force of self induction 

 is 1,250 volts, and the induced electromo- 

 tive force 2,400 volts. The loss of press- 

 ure through armature-resistance is in that 

 case 52 volts, or about 2.6 per cent, of 

 the terminal electromotive force. The 

 energy lost in exciting the field, which 

 requires 12,000 ampere turns, is 3.2 

 kilowatts, or 5.3 per cent, of the output. 

 This somewhat large percentage is due to 

 the employment of cast iron for the mag- 

 net-cores, and will, in the machine illus- 

 trated, which has cylindrical magnets of 

 wrought-iron, be reduced to about 3.6 

 per cent. The data, obtained by Mr. 

 Brown in testing this machine, suffice for 

 the determination of the coefficient of 

 self-induction by means of a diagram 

 similar to Fig. 7, which also gives the 

 angle of lag. Knowing the latter, it is 



