390 BELL SYSTEM TECHNICAL JOURNAL 



voltage waves, and if wound to have low impedance it is better suited 

 for recording current waves. The sensitivity, as usually expressed, in 

 millimeters deflection per milliampere of input, varies approximately 

 as the square root of the impedance of the winding. The ratio of 

 deflection to input is constant over a considerable range due to the 

 balanced structure of the motor element. 



As noted previously the oscillographs described are intended for 

 recording in a comparatively low frequency range. In the range given 

 there has been no difficulty in obtaining good records with a two-candle- 

 power flashlight lamp. This of course, is principally due to the large 

 size of the mirror on the vibrator. 



Samples or records made with the oscillographs described are shown 

 in Figs. 6, 8, 18, 19, 20 and 21. Those in Figs. 6, 8 and 18 have already 

 been mentioned. Fig. 19 shows eight continuous oscillograms and 

 Fig. 20 shows four polar oscillograms illustrating some of the possibili- 

 ties of these instruments. Fig. 21 is a response calibration at constant 

 frequency of a polar oscillograph. 



A number of field applications of oscillographs of both types have 

 been made with satisfactory results. In some cases where cooperative 

 studies were being made, the oscillographs have been used for recording 

 transient neutral currents in power systems as well as to record voltages 

 induced in telephone circuits by power system transients. Experience 

 with the oscillographs in these field installations has suggested a few 

 improvements of a mechanical nature and certain rearrangements of 

 parts to increase the convenience of operation. These changes are 

 now being embodied in a new design. It is hoped that it will be pos- 

 sible in a later paper to describe these features and to give the results 

 of field experience more fully than can be done at this time. 



