STEADILY ALTERNATING CURRENT ON A LONG LINE. 333 



O^ records the initial current waves entering the line for the first 

 few cycles after the switch 5 is closed. The voltage-recording 

 oscillograph 0^ records simultaneously the wave form of the im- 

 pressed e.m.f. The distant or receiving end B, is freed in Fig. 3, 

 except that it is connected to ground through the high non-inductive 

 resistance, ordinarily of 9900 ohms, in order to permit of operating 

 the voltage-recording oscillograph 0^'. All three oscillographs are 

 set into operation simultaneously, on closing the phase-selecting 

 switch S, during about 8 cycles from the 60 /-' generator G, or for 

 a duration of about %5 second ; and all three are recorded on the 

 same photographic film 8.25 cm. (3^ inches) wide. In this manner, 

 the voltage at each end of the line, and the current at the entering 

 end, are recorded immediately after closing the line switch S. 



Alternating-Current Generator. — The a.-c. generator G, Fig. 3, 

 was a 6-pole lo-k.v.a. alternator of the Lauffen type, designed by 

 Prof. C. A. Adams, for the delivery of a nearly pure sine-wave 

 e.m.f. At the time these tests were made, no other load was con- 

 nected to the machine. It was driven by a directly coupled d.-c. 

 iio-volt motor, of approximately 10 kw. continuous rating, rotating 

 at approximately 1200 r.p.m. The current in the d.-c. motor field 

 magnet was adjusted in the testing room, so as to maintain constant 

 frequency. The frequency was measured in the testing room by 

 mounting a stroboscopic disk on the shaft of the small synchronous 

 motor, and observing this revolving disk, illuminated by a fixed 

 incandescent lamp, through shts in the prongs of a stroboscopies 

 fork on a telescope. Unless in such measurement, the frequency is 

 held constant, the results are of little value. 



Oscillograph. — The oscillograph had three vibrators, in an elec- 

 tromagnetic field common to all. The instrument was designed and 

 constructed by Mr. H. G. Crane, at Harvard University. The 

 bifilar vibrators had a working length of 12.5 mm., and were damped 

 in castor oil. As the currents observed were of low frequency, the 

 correction factors for frequency of the vibrators^ are insignificant at 

 60'— ', and are omitted. 



'^ Bibliography 7. 

 s Bibliography 39. 



